ALBERT

Beschreibung: Abstract Repeated measures experiments can be conducted to empirically estimate the uncertainty of a streamgauging method, such as the widespread moving‐boat acoustic Doppler current profilers (ADCP) approach. Previous ADCP repeated measures experiments, a.k.a. inter‐laboratory comparisons, provided a credible range of uncertainty estimates reflecting the quality of the site conditions. However, the method, which is a one‐way analysis of variance (ANOVA), only addresses the uncertainty of one lumped factor that combines several distinct factors: instrument, operator, procedure and cross‐section effects. To decompose the uncertainty of ADCP streamflow measurements due to cross‐section selection and team effects, a large repeated measures experiment has been conducted in the Taurion River (France). The experiment design was crossed and balanced, with two sets of 24 teams circulated over two sets of 12 cross‐sections. A constant flow rate was released from a dam, located immediately upstream of the experimental site. Prior to the statistical analysis, a data quality review was performed using the U.S. Geological Survey (USGS) QRev software to clean the dataset from avoidable errors and to homogenize the discharge computations. A two‐way ANOVA was applied to quantify the cross‐section effect, the team effect and their interaction, which was found to dominate the pure cross‐section effect. It was then possible to predict the average uncertainty of multiple‐transect ADCP discharge measurements, depending on the number of teams, cross‐sections and repeated transects included in the discharge average. The method opens interesting avenues for documenting difficult‐to‐estimate uncertainty sources of streamgauging techniques in other measuring conditions, especially the most adverse ones.

Beschreibung: Abstract Snow albedo is a dominant control on snowmelt in many parts of the world. An empirical albedo decay equation, developed over 60 years ago, is still used in snowmelt models. Several empirical snow albedo models developed since show wide spread in results. Remotely sensed snow albedos have been used in a few studies, but validations are scarce because of the difficulty in making accurate in situ measurements. Reconstruction of snow water equivalent (SWE), where the snowpack is built in reverse, is especially sensitive to albedo. We present two new contributions: (1) an updated albedo model where grain size and light absorbing particle (LAP) content are solved for simultaneously; (2) multiyear comparisons of remotely sensed and in situ albedo measurements from three high‐altitude sites in the western U.S. Our remotely sensed albedos show 4 to 6% RMSE and negligible bias. In comparison, empirical albedo decay models, which require extensive in situ measurements, show RMSE values of 7 to 17% with biases of ‐6 to ‐14%. We examine the sensitivity of SWE reconstructions to albedo error at two sites. With no simulated error in albedo, reconstructed SWE had MAE values of 7 to 13% and 5‐6% bias. The accuracy actually improved with some simulated added error, likely because of a fundamental bias in the reconstruction approach. Conversely, the best age‐based decay model showed an 18‐20% MAE and bias in reconstructed SWE. We conclude that remotely sensed albedos where available are superior to age‐based approaches in all aspects except simplicity.

Beschreibung: Abstract Describing the space‐time variability of hydrologic extremes in relation to climate is important for scientific and operational purposes. Many studies demonstrated the role of large‐scale modes of climate variability such as the El Nino Southern Oscillation (ENSO) or the North Atlantic Oscillation (NAO), amongst many others. Climate indices have hence frequently been used as predictors in probabilistic models describing hydrologic extremes. However, standard climate indices such as ENSO/NAO are poor predictors in some regions. Consequently, this paper describes an innovative method to avoid relying on standard climate indices, based on the following idea: the relevant climate indices are effectively unknown (they are hidden), and they should therefore be estimated directly from hydrologic data. In statistical terms, this corresponds to a Bayesian hierarchical model describing extreme occurrences, with hidden climate indices treated as latent variables. This approach is illustrated using three case studies. A synthetic case study first shows that identifying hidden climate indices from occurrence data alone is feasible. A second case study using flood occurrences at 42 East‐Australian sites confirms that the model correctly identifies their ENSO‐related climate driver. The third case study is based on 207 sites in France, where standard climate indices poorly predict flood occurrence. The hidden climate indices model yields a reliable description of flood occurrences, in particular their clustering in space and their large interannual variability. Moreover, some hidden climate indices are linked with specific patterns in atmospheric variables, making them interpretable in terms of climate variability and opening the way for predictive applications.

Beschreibung: Abstract Phaeodaria, which comprise one group of large, single‐celled eukaryotic zooplankton, have been largely ignored by past marine biological studies because Phaeodaria and their delicate skeletons are liable to collapse. As a result, collection and quantification of specimens are difficult, and seasonal changes of phaeodarian abundance have not been thoroughly studied. The transport of biogenic elements by sinking phaeodarians has been estimated for only a few representative species. Sinking particles 〉1 mm in size and swimmers have traditionally been excluded when estimating sinking particle fluxes. The focus of this study is the large number of phaeodarians among the 〉1 mm sinking particles collected in the western North Pacific from June 2014 to July 2015. Careful sorting by microscopic examination and chemical analyses revealed that phaeodarians accounted for up to about 10% of the organic carbon in all sinking particles and accounted for a mean of 33% of the organic carbon in the 〉1 mm sinking particles. The high standing stocks of phaeodarians at depths of 150–1000 m in the mesopelagic twilight zone suggested that particles sinking from the euphotic zone as aggregates and fecal pellets can be efficiently ex to the deep sea by the ballasting effect of large phaeodarian particles rich in organic carbon.

Beschreibung: Hydrological Processes, Volume 33, Issue 19, Page 2499-2501, 15 September 2019.

Beschreibung: Abstract Monitoring and estimation of snow depth in alpine catchments is needed for a proper assessment of management alternatives for water supply in these water resources systems. The distribution of snowpack thickness is usually approached by using field data that come from snow samples collected at a given number of locations that constitute the monitoring network. Optimal design of this network is required to obtain the best possible estimates. Assuming that there is an existing monitoring network, its optimization may imply the selection of an optimal network as a subset of the existing one (if there are not funds to maintain them) or enlarging the existing network by one or more stations (optimal augmentation problem). We propose an optimization procedure that minimizes the total variance in the estimate of snowpack thickness. The novelty of this work is to treat, for the first time, the problem of snow observation network optimization for an entire mountain range rather than for small catchments as done in previous studies. Taking into account the reduced data available, which is a common problem in many mountain ranges, the importance of a proper design of these observation networks is even larger. Snowpack thickness is estimated by combining regression models to approach the effect of the explanatory variables and kriging techniques to consider the influence of the stakes location. We solve the optimization problems under different hypotheses, studying the impacts of augmentation and reduction, both, one by one and in pairs. We also analyse the sensitivity of results to non‐snow measurements deduced from satellite information. Finally, we design a new optimal network by combining the reduction and augmentation methods. The methodology has been applied to the Sierra Nevada mountain range (southern Spain), where very limited resources are employed to monitor snowfall and where an optimal snow network design could prove critical. An optimal snow observation network is defined by relocating some observation points. It would reduce the estimation variance by around 600 cm2 (15%).

Beschreibung: Abstract Climate‐driven sea ice loss has led to changes in the timing of key biological events in the Arctic, however the consequences and rate of these changes remain largely unknown. Polar bears (Ursus maritimus) undergo seasonal changes in energy stores in relation to foraging opportunities and habitat conditions. Declining sea ice has been linked to reduced body condition in some subpopulations, however, the specific timing and duration of the feeding period when bears acquire most of their energy stores and its relationship to timing of ice break‐up is poorly understood. We used community‐based sampling to investigate seasonality in body condition (energy stores) of polar bears in Nunavut, Canada, and examined the influence of sea ice variables. We used adipose tissue lipid content as an index of body condition for 1206 polar bears harvested from 2010‐ 2017 across five subpopulations with varying seasonal ice conditions: Baffin Bay (October‐ August), Davis Strait and Foxe Basin (year‐round), Gulf of Boothia and Lancaster Sound (August‐ May). Similar seasonal patterns were found in body condition across subpopulations with bears at their nadir of condition in the spring, followed by fat accumulation past break‐up date and subsequent peak body condition in autumn, indicating that bears are actively foraging in late spring and early summer. Late season feeding implies that even minor advances in the timing of break‐up may have detrimental effects on foraging opportunities, body condition, and subsequent reproduction and survival. The magnitude of seasonal changes in body condition varied across the study area, presumably driven by local environmental conditions. Our results demonstrate how community‐based monitoring of polar bears can reveal population‐level responses to climate warming in advance of detectable demographic change. Our data on the seasonal timing of polar bear foraging and energy storage should inform predictive models of the effects of climate‐mediated sea ice loss.

Beschreibung: Abstract Mangrove forests play an important role in climate change adaptation and mitigation by maintaining coastline elevations relative to sea level rise, protecting coastal infrastructure from storm damage and storing substantial quantities of carbon (C) in live and detrital pools. Determining the efficacy of mangroves in achieving climate goals can be complicated by difficulty in quantifying C inputs (i.e., differentiating newer inputs from younger trees from older residual C pools), and mitigation assessments rarely consider potential offsets to CO2 storage by methane (CH4) production in mangrove sediments. The establishment of non‐native Rhizophora mangle along Hawaiian coastlines over the last century offers an opportunity to examine the role mangroves play in climate mitigation and adaptation both globally and locally as novel ecosystems. We quantified total ecosystem C storage, sedimentation, accretion, sediment organic C burial and CH4 emissions from ~70 year old R. mangle stands and adjacent uninvaded mudflats. Ecosystem C stocks of mangrove stands exceeded mudflats by 434 ± 33 Mg C ha‐1, and mangrove establishment increased average coastal accretion by 460%. Sediment organic C burial increased 10‐fold (to 4.5 Mg C ha‐1 yr‐1), double the global mean for old growth mangrove forests, suggesting that C accumulation from younger trees may occur faster than previously thought, with implications for mangrove restoration. Simulations indicate that increased CH4 emissions from sediments offset ecosystem CO2 storage by only 2‐4%, equivalent to 30‐60 Mg CO2‐eq ha‐1 over mangrove lifetime (100‐year sustained global warming potential). Results highlight the importance of mangroves as novel systems that can rapidly accumulate C, have a net positive atmospheric greenhouse gas removal effect, and support shoreline accretion rates that outpace current sea level rise. Sequestration potential of novel mangrove forests should be taken into account when considering their removal or management, especially in the context of climate mitigation goals.

Beschreibung: The predictability of the atmosphere at short and long time scales, associated with the coupling to the ocean, is explored in a new version of the Modular Arbitrary‐Order Ocean‐Atmosphere Model (MAOOAM). This version features a new ocean basin geometry with periodic boundary conditions in the zonal direction. The analysis presented in this paper considers a low‐order version of the model with 40 dynamical variables. First the increase of surface friction (and the associated heat flux) with the ocean can either induce chaos when the aspect ratio between the meridional and zonal directions of the domain of integration is small, or suppress chaos when it is large. This reflects the potentially counter‐intuitive role that the ocean can play in the coupled dynamics. Second, and perhaps more importantly, the emergence of long‐term predictability within the atmosphere for specific values of the friction coefficient occurs through intermittent excursions in the vicinity of a (long‐period) unstable periodic solution. Once close to this solution the system is predictable for long times, i.e. a few years. The intermittent transition close to this orbit is, however, erratic and probably hard to predict. This new route to long‐term predictability contrasts with the one found in the closed ocean‐basin low‐order version of MAOOAM, in which the chaotic solution is permanently wandering in the vicinity of an unstable periodic orbit for specific values of the friction coefficient. The model solution is thus at any time influenced by the unstable periodic orbit and inherits from its long‐term predictability.

Beschreibung: Abstract The effects of root systems on soil detachment by overland flow are closely related to vegetation types. The objective of this study was to quantify the effects of two gramineous roots (Paspalum mandiocanum with shallow roots and Pennisetum giganteum with deep roots) on soil detachment capacity, rill erodibility and critical shear stress on alluvial fans of benggang in southeast China. A 4 m long and 0.12 m wide flume was used. Slope steepness ranged from 9% to 27%, and unit flow discharge ranged from 1.39×10‐3 to 4.19×10‐3 m2 s‐1. The mean detachment capacities of Paspalum mandiocanum and Pennisetum giganteum lands were 18% and 38% lower than that of bare land, respectively, and the effects of root on reducing soil detachment were mainly reflected in the 0‐5 cm soil layer. The most important factors in characterizing soil detachment capacity were root length density and soil cohesion, and soil detachment capacity of the two grass lands could be estimated using flow shear stress, soil cohesion, and root length density (NSE=0.90). With the increase in soil depth, rill erodibility increased, while shear stress decreased. The mean rill erodibilities of Paspalum mandiocanum and Pennisetum giganteum lands were 81% and 61% as much as that of bare land, respectively. Additionally, rill erodibilities of the two grass lands could be estimated as an exponential function by root length density and soil cohesion (NSE=0.88). The mean critical shear stress of Paspalum mandiocanum and Pennisetum giganteum lands were 1.29 and 1.39 times that of bare land, respectively, and it could be estimated with a linear function by root length density (NSE=0.76). This study demonstrated that planting of the two grasses Paspalum mandiocanum and Pennisetum giganteum could effectively reduce soil detachment and enhance soil resistance to erosion on alluvial fans, with the deep roots of Pennisetum giganteum being more effective than the shallow roots of Paspalum mandiocanum. The results are helpful for understanding the influencing mechanism of root systems on soil detachment process.

Beschreibung: Abstract Erosion of volcanic islands ultimately creates shallow banks and guyots, but the ways erosion proceeds to create them over time and how coastline retreat rate relates to wave conditions, rock mass strength and other factors are unclear. The Capelinhos volcano was formed in 1957/58 during a Surtseyan and partly effusive eruption that added a ~2.5 km2 tephra and lava promontory to the western end of Faial Island (Azores, central North Atlantic). Subsequent coastal and submarine erosion has reduced the subaerial area of the promontory and created a submarine platform. This study uses historical information, photos and marine geophysical data collected around the promontory to characterize how the submarine platform developed following the eruption. Historical coastline positions are supplemented with coastlines interpreted from 2004 and 2014 Google Earth images in order to work out the progression of coastline retreat rate and retreat distance for lava‐ and tephra‐dominated cliffs. Data from swath mapping sonars are used to characterise the submarine geometry of the resulting platform (position of the platform edge, gradient and morphology of the platform surface). Photographs collected during SCUBA and ROV dives on the submarine platform reveal a rugged surface now covered with boulders. The results show that coastal retreat rates decreased rapidly with time after the eruption and approximately follow an inverse power law relationship with coastal retreat distance. We develop a finite‐difference model for wave attenuation over dipping surfaces to predict how increasing wave attenuation contributed to this trend. The model is verified by reproducing the wave height variation over dipping rock platforms in the UK (platform gradient 1.2° to 1.8°) and Ireland (1.8°). Applying the model to the dipping platform around Capelinhos, using a diversity of cliffs resistance predicted from known lithologies, we are able to predict erosion rate trends for some sectors of the edifice. We also explore wider implications of these results, such as how erosion creates shallow banks and guyots in reef‐less mid‐oceanic archipelagos like the Azores.

Beschreibung: Abstract Exceptional flood events with a return period of about 50 years can be destructive to step‐pool channel segments. However, field investigations and flume experiments have not examined the hydraulic and morphological feedbacks of step‐pool morphology during unsteady hydrographs of exceptional flood events. We performed a series of flume experiments with a manually constructed step model, perturbed with three hydrographs that varied in the rate of water supply change. The bed texture, topography, flow regimes, surface flow field and water depth were characterized and measured as the flow rate was increased during the experiments. A distinct pool feature emerged downstream of the manually constructed step when the flow rate exceeded the threshold scaled to the peaks of ordinary flood events in well‐graded mountain streams. The pool feature was modified in several different ways with flow rate increase. The bed surface steadily coarsened, micro‐bedforms developed and became more pronounced, the bed topography became more spatially complex based on analysis using the Hurst exponent, and last, pool depth steadily increased. Pool modification was also linked to the flow regime: the impinging jet regime led to grain size segmentation in the pool while the jump regime contributed to decelerating flow velocity. The steeper rising limb of hydrograph led to a less developed pool feature, with smaller sized micro‐bedforms in the pool bottom to outlet, and higher discharge threshold for distinct coarsening and scouring in the pool. The estimated energy dissipation within the step‐pool unit decreased as a power function from low to high flow, quantified as the ratio hc/HS, where hc is the critical water depth and HS is scour depth. Our results highlight the interaction between morphology, hydraulics, and energy dissipation of step‐pool unit and the crucial role of hydrograph shape on the interaction during flow increase.

Beschreibung: Abstract Aim To define the major biogeographical regions and transition zones for freshwater fish species. Taxon Strictly freshwater species of actinopterygian fish (i.e. excluding marine and amphidromous fish families). Methods We based our bioregionalization on a global database of freshwater fish species occurrences in drainage basins, which, after filtering, includes 11,295 species in 2,581 basins. On the basis of this dataset, we generated a bipartite (basin‐species) network upon which we applied a hierarchical clustering algorithm (the Map Equation) to detect regions. We tested the robustness of regions with a sensitivity analysis. We identified transition zones between major regions with the participation coefficient, indicating the degree to which a basin has species from multiple regions. Results Our bioregionalization scheme showed two major supercontinental regions (Old World and New World, 50% species of the world and 99.96% endemics each). Nested within these two supercontinental regions lie six major regions (Nearctic, Neotropical, Palearctic, Ethiopian, Sino‐Oriental and Australian) with extremely high degrees of endemism (above 96% except for the Palearctic). Transition zones between regions were of limited extent compared to other groups of organisms. We identified numerous subregions with high diversity and endemism in tropical areas (e.g. Neotropical), and a few large subregions with low diversity and endemism at high latitudes (e.g. Palearctic). Main conclusions Our results suggest that regions of freshwater fish species were shaped by events of vicariance and geodispersal which were similar to other groups, but with freshwater‐specific processes of isolation that led to extremely high degrees of endemism (far exceeding endemism rates of other continental vertebrates), specific boundary locations and limited extents of transition zones. The identified bioregions and transition zones of freshwater fish species reflect the strong isolation of freshwater fish faunas for the past 10–20 million years. The extremely high endemism and diversity of freshwater fish fauna raises many questions about the biogeographical consequences of current introductions and extinctions.

Beschreibung: Abstract Photosynthetic biochemical limitation parameters (i.e., Vcmax, Jmax and Jmax:Vcmax ratio) are sensitive to temperature and water availability, but whether these parameters in cold climate species at biome ecotones are positively or negatively influenced by projected changes in global temperature and water availability remains uncertain. Prior exploration of this question has largely involved greenhouse based short‐term manipulative studies with mixed results in terms of direction and magnitude of responses. To address this question in a more realistic context, we examined the effects of increased temperature and rainfall reduction on the biochemical limitations of photosynthesis using a long‐term chamber‐less manipulative experiment located in northern Minnesota, USA. Nine tree species from the boreal‐temperate ecotone were grown in natural neighborhoods under ambient and elevated (+3.4°C) growing season temperatures and ambient or reduced (≈40% of rainfall removed) summer rainfall. Apparent rubisco carboxylation and RuBP regeneration standardized to 25°C (Vcmax25°C and Jmax25°C, respectively) were estimated based on ACi curves measured in situ over three growing seasons. Our primary objective was to test whether species would downregulate Vcmax25°C and Jmax25°C in response to warming and reduced rainfall, with such responses expected to be greatest in species with the coldest and most humid native ranges, respectively. These hypotheses were not supported, as there were no overall main treatment effects on Vcmax25°C or Jmax25°C (P〉0.14). However, Jmax:Vcmax ratio decreased significantly with warming (P=0.0178), whereas interactions between warming and rainfall reduction on the Jmax25°C to Vcmax25°C ratio were not significant. The insensitivity of photosynthetic parameters to warming contrasts with many prior studies done under larger temperature differentials and often fixed daytime temperatures. In sum, plants growing in relatively realistic conditions under naturally varying temperatures and soil moisture levels were remarkably insensitive in terms of their Jmax25°C and Vcmax25°C when grown at elevated temperatures, reduced rainfall, or both combined.

Beschreibung: Abstract Extreme climate events (ECEs) such as severe droughts, heat waves and late spring frosts are rare but exert a paramount role in shaping tree species distributions. The frequency of such ECEs is expected to increase with climate warming, threatening the sustainability of temperate forests. Here, we analyzed 2844 tree‐ring width series of five dominant European tree species from 104 Swiss sites ranging from 400 to 2200 m a.s.l. for the period 1930–2016. We found that (i) the broadleaved oak and beech are sensitive to late frosts that strongly reduce current year growth; however, tree growth is highly resilient and fully recovers within two years; (ii) radial growth of the conifers larch and spruce is strongly and enduringly reduced by spring droughts—these species are the least resistant and resilient to droughts; (iii) oak, silver fir, and to a lower extent beech, show higher resistance and resilience to spring droughts and seem therefore better adapted to the future climate. Our results allow a robust comparison of the tree growth responses to drought and spring frost across large climatic gradients and provide striking evidence that the growth of some of the most abundant and economically important European tree species will be increasingly limited by climate warming. These results could serve for supporting species selection to maintain the sustainability of forest ecosystem services under the expected increase in ECEs.

Beschreibung: Abstract Due to extremely high rates of evaporation and low precipitation in the Persian Gulf, discharges from desalination plants (DPs) can lead to ecological stresses by increasing water temperatures, salinities, and heavy metal concentrations, as well as decreasing dissolved oxygen levels. We discuss the potential ecological impacts of DPs on marine organisms and propose mitigating measures to reduce the problems induced by DPs discharges. The daily capacity of DPs in the Persian Gulf exceeds 11 million m3 d‐1, which is approximately half of global daily fresh‐water production; multi‐stage flash distillation (MSF) is the dominant desalinization process. Results from field and laboratory studies indicate that there are potentially serious and chronic threats to marine communities following exposure to DPs discharges, especially within the zoobenthos, echinodermata, seagrasses, and coral reefs. DP discharges can lead to decreases in sensitive species, plankton abundance, hard substrate epifauna, and growth rates of seagrasses. However, the broad applicability of any one of these impacts is currently hard to scale because of the limited number of studies that have been conducted to assess the ecological impacts of DP discharge on Persian Gulf organisms. Even so, available data suggest that appropriately sited, designed, and operated DPs combined with current developments in impingement and entrainment reduction technology can mitigate many of negative environmental impacts of DPs.

Beschreibung: Spatially autocorrelated weather and climate may cause population co‐fluctuations over large distances. We show that increasingly frequent rain‐on‐snow (ROS) and icing events in winter synchronize the annual dynamics of Svalbard reindeer populations, while, paradoxically, spatial variation in ROS trends and density‐dependent weather effects cause diverging local population trajectories in the long run. Such decoupling of population dynamics increases species viability under a rapidly warming high‐Arctic climate. Abstract The ‘Moran effect’ predicts that dynamics of populations of a species are synchronized over similar distances as their environmental drivers. Strong population synchrony reduces species viability, but spatial heterogeneity in density dependence, the environment, or its ecological responses may decouple dynamics in space, preventing extinctions. How such heterogeneity buffers impacts of global change on large‐scale population dynamics is not well studied. Here, we show that spatially autocorrelated fluctuations in annual winter weather synchronize wild reindeer dynamics across high‐Arctic Svalbard, while, paradoxically, spatial variation in winter climate trends contribute to diverging local population trajectories. Warmer summers have improved the carrying capacity and apparently led to increased total reindeer abundance. However, fluctuations in population size seem mainly driven by negative effects of stochastic winter rain‐on‐snow (ROS) events causing icing, with strongest effects at high densities. Count data for 10 reindeer populations 8–324 km apart suggested that density‐dependent ROS effects contributed to synchrony in population dynamics, mainly through spatially autocorrelated mortality. By comparing one coastal and one ‘continental’ reindeer population over four decades, we show that locally contrasting abundance trends can arise from spatial differences in climate change and responses to weather. The coastal population experienced a larger increase in ROS, and a stronger density‐dependent ROS effect on population growth rates, than the continental population. In contrast, the latter experienced stronger summer warming and showed the strongest positive response to summer temperatures. Accordingly, contrasting net effects of a recent climate regime shift—with increased ROS and harsher winters, yet higher summer temperatures and improved carrying capacity—led to negative and positive abundance trends in the coastal and continental population respectively. Thus, synchronized population fluctuations by climatic drivers can be buffered by spatial heterogeneity in the same drivers, as well as in the ecological responses, averaging out climate change effects at larger spatial scales.

Beschreibung: Abstract Observations of the vertical and temporal structure of the nocturnal boundary layer before and after a transition from the weakly to the very stable regime have been presented in part 1. Here, similar transitions are investigated using a 1‐D second order closure numerical model, with an energy budget solved at the surface. The transition is driven by a decreasing mean wind at the top of the domain, and simulations with different cloud covers and surface thermal properties are considered. The time of the transition depends on the wind speed at the top of the domain and on the” coupling strength” between the surface and the atmosphere, which is affected by the cloud cover and surface thermal properties. The vertical profiles and temporal evolutions of the terms of the budgets of turbulent kinetic energy (TKE), heat flux and temperature variance are presented. Of these, only TKE budget presents the same dominant terms in both regimes. Absolute heat flux in the model is proportional to the cube of the wind speed in the very stable regime. This article is protected by copyright. All rights reserved.

Beschreibung: Little is known about compensatory processes shaping regional differences in organismal vulnerability. We examined large‐scale spatial variations in biomineralization under heterogeneous environmental gradients across a 30° latitudinal range in critical foundation species, the blue mussels Mytilus edulis and M. trossulus. Salinity was the best predictor of within‐region differences in mussel shell deposition, mineral and organic composition. We identified biomineralization plasticity as a potential compensatory mechanism conferring Mytilus species a protective capacity for quantitative and qualitative trade‐offs in shell deposition as a response to regional alterations of abiotic and biotic conditions in future environments. Abstract Although geographical patterns of species' sensitivity to environmental changes are defined by interacting multiple stressors, little is known about compensatory processes shaping regional differences in organismal vulnerability. Here, we examine large‐scale spatial variations in biomineralization under heterogeneous environmental gradients of temperature, salinity and food availability across a 30° latitudinal range (3,334 km), to test whether plasticity in calcareous shell production and composition, from juveniles to large adults, mediates geographical patterns of resilience to climate change in critical foundation species, the mussels Mytilus edulis and M. trossulus. We find shell calcification decreased towards high latitude, with mussels producing thinner shells with a higher organic content in polar than temperate regions. Salinity was the best predictor of within‐region differences in mussel shell deposition, mineral and organic composition. In polar, subpolar, and Baltic low‐salinity environments, mussels produced thin shells with a thicker external organic layer (periostracum), and an increased proportion of calcite (prismatic layer, as opposed to aragonite) and organic matrix, providing potentially higher resistance against dissolution in more corrosive waters. Conversely, in temperate, higher salinity regimes, thicker, more calcified shells with a higher aragonite (nacreous layer) proportion were deposited, which suggests enhanced protection under increased predation pressure. Interacting effects of salinity and food availability on mussel shell composition predict the deposition of a thicker periostracum and organic‐enriched prismatic layer under forecasted future environmental conditions, suggesting a capacity for increased protection of high‐latitude populations from ocean acidification. These findings support biomineralization plasticity as a potentially advantageous compensatory mechanism conferring Mytilus species a protective capacity for quantitative and qualitative trade‐offs in shell deposition as a response to regional alterations of abiotic and biotic conditions in future environments. Our work illustrates that compensatory mechanisms, driving plastic responses to the spatial structure of multiple stressors, can define geographical patterns of unanticipated species resilience to global environmental change.

Beschreibung: Abstract Aim Current species distributions are shaped by present and past biotic and abiotic factors. Here, we assessed whether abiotic factors (habitat availability) in combination with past connectivity and a biotic factor (body mass) can explain the unique distribution pattern of Southeast Asian mammals, which are separated by the enigmatic biogeographic transition zone, the Isthmus of Kra (IoK), for which no strong geophysical barrier exists. Location Southeast Asia. Taxon Mammals. Methods We projected habitat suitability for 125 mammal species using climate data for the present period and for two historic periods: mid‐Holocene (6 ka) and last glacial maximum (LGM 21 ka). Next, we employed a phylogenetic linear model to assess how present species distributions were affected by the suitability of areas in these different periods, habitat connectivity during LGM and species body mass. Results Our results show that cooler climate during LGM provided suitable habitat south of IoK for species presently distributed north of IoK (in mainland Indochina). However, the potentially suitable habitat for these Indochinese species did not stretch very far southwards onto the exposed Sunda Shelf. Instead, we found that the emerged landmasses connecting Borneo and Sumatra provided suitable habitat for forest dependent Sundaic species. We show that for species whose current distribution ranges are mainly located in Indochina, the area of the distribution range that is located south of IoK is explained by the suitability of habitat in the past and present in combination with the species body mass. Main conclusions We demonstrate that a strong geophysical barrier may not be necessary for maintaining a biogeographic transition zone for mammals, but that instead a combination of abiotic and biotic factors may suffice.

Beschreibung: Abstract Aim To review the histories of the Colorado River and North American monsoon system to ascertain their effects on the genetic divergence of desert‐adapted animals. Location Lower Colorado River region, including Mojave and Sonoran deserts, United States. Methods We synthesized recent geological literature to summarize initiation phases of lower Colorado River evolution, their discrepancies, and potential for post‐vicariance dispersal of animals across the river. We simulated data under geological models and performed a meta‐analysis of published and unpublished genetic data including population diversity metrics, relatedness and historical migration rates to assess alternative divergence hypotheses. Results The two models for arrival of the Colorado River into the Gulf of California impose east‐west divergence ages of 5.3 and 4.8 Ma, respectively. We found quantifiable river‐associated differentiation in the lower Colorado River region in reptiles, arachnids and mammals relative to flying insects. However, topological statistics, historical migration rates and cross‐river extralimital populations suggest that the river should be considered a leaky barrier that filters, rather than prevents, gene flow. Most markers violated neutrality tests. Differential adaptation to monsoon‐based precipitation differences may contribute to divergence between Mojave and Sonoran populations and should be tested. Main Conclusions Rivers are dynamic features that can both limit and facilitate gene flow through time, the impacts of which are mitigated by species‐specific life history and dispersal traits. The Southwest is a geo‐climatically complex region with the potential to produce pseudocongruent patterns of genetic divergence, offering a good setting to evaluate intermediate levels of geological‐biological (geobiological) complexity.

Beschreibung: Abstract The particle filter‐based data assimilation method is an effective tool to adjust model states based on observations. In this study, we proposed a modified particle filter‐based data assimilation method with a local weighting procedure (MPFDA‐LW) for a high‐precision two‐dimensional hydrodynamic model (HydroM2D) in dam‐break flood simulation. Moreover, a particle filter‐based data assimilation method with a global weighting procedure (PFDA‐GW) for the HydroM2D model was also investigated. The MPFDA‐LW and the PFDA‐GW for the HydroM2D model, respectively, adopted spatially nonuniform and uniform Manning's roughness coefficients. The MPFDA‐LW considering spatial‐temporal variability of Manning's roughness coefficient could significantly improve the performances of the HydroM2D model in simulating water stages at all gauges simultaneously, whereas the PFDA‐GW considering temporal variability of Manning's roughness coefficient could only slightly improve the performances of the HydroM2D model in simulating water stages at a few gauges. The MPFDA‐LW is more suitable for improving the performance of 2‐D hydrodynamic models in flood inundation simulation than the PFDA‐GW.

Beschreibung: Abstract The physics of disconnection between interrelated surface and groundwater has evolved considerably in recent years, especially since conjunctive use of water resources is increasingly dependent on groundwater resilience, but methods to measure disconnection on a river basin scale are lacking especially for managed‐ephemeral and irrigated‐agricultural systems. Multiyear drought limited surface water along Rincon Valley within the Elephant Butte Irrigation District (EBID) in the arid, Lower Rio Grande Basin of south‐central New Mexico, USA, and effects were compounded by continued extraction of groundwater to meet crop requirements. Average year‐end water table elevations in recent years have been below the average elevation of the riverbed, indicating potential disconnection between the river and the aquifer even when the river flows during the irrigation season. This study analyzed data from EBID groundwater monitoring wells adjacent to the river, infiltration determined from river flows, and riverbed measurements along the Rincon Valley reach to determine net annual seepage discharge to the aquifer and annual average pressure head below the river. Annual assessment from 2010 to 2017 confirmed that the drought shifted the system from connection to transition and then to disconnection. Nonlinear regression was used to quantify this shift to disconnection and back, enabled determination of several disconnection process metrics, and was also used to confirm that nonlinear disconnection behavior was reversible without significant hysteresis. The method developed herein confirms that the total head difference transition threshold can be determined from river/riparian monitoring sites over reach to basin scales.

Beschreibung: Abstract Dissolution trapping is one of the primary mechanisms of carbon dioxide (CO2) storage in a geological formation. In this study, a numerical model was used to examine the impacts of single and multiple fractures on the transport of dissolved CO2 plumes in various geological settings. The effects of the fracture angle, fracture‐matrix permeability ratio, fracture intersection, and matrix heterogeneity on density‐driven CO2 convection were systematically investigated. The fractures were found to play time‐varying roles in both homogeneous and heterogeneous media by serving as preferential pathways for both CO2‐rich plumes (fingers) and CO2‐free water. The competition between the enhancement of convective mixing and the inhibition of finger growth by the upward flow of freshwater generated a complex flow system. The interaction between the strong upward flow of freshwater through the fractures and the falling CO2‐rich fingers through the porous matrix induced a positive feedback, resulting in accelerated domain‐scale circulation and CO2 dissolution. While the CO2‐rich fingers grew relatively evenly at the top boundary in the homogeneous media, they selectively developed through the high permeable zones in the heterogeneous media. Compared with homogeneous media, the heterogeneous media preserving fractures particularly generated a more dynamic fracture‐matrix mass transfer, resulting in more rapid CO2 dissolution. The findings of this study were extended to examine the effects of fracture connectivity on the enhancement of CO2 transport and dissolution on a field scale.

Beschreibung: Abstract Continuous data assimilation (CDA) is successfully implemented for the first time for efficient dynamical downscaling of a global atmospheric reanalysis. A comparison of the performance of CDA with the standard grid and spectral nudging techniques for representing long‐ and short‐scale features in the downscaled fields using the Weather Research and Forecast (WRF) model is further presented and analyzed. The WRF model is configured at 0.25° × 0.25° horizontal resolution and is driven by 2.5° × 2.5° initial and boundary conditions from NCEP/NCAR reanalysis fields. Downscaling experiments are performed over a one‐month period in January, 2016. The similarity metric is used to evaluate the performance of the downscaling methods for large (2000 km) and small (300 km) scales. Similarity results are compared for the outputs of the WRF model with different downscaling techniques, NCEP/NCAR reanalysis, and NCEP Final Analysis (FNL, available at 0.25° × 0.25° horizontal resolution). Both spectral nudging and CDA describe better the small‐scale features compared to grid nudging. The choice of the wave number is critical in spectral nudging; increasing the number of retained frequencies generally produced better small‐scale features, but only up to a certain threshold after which its solution gradually became closer to grid nudging. CDA maintains the balance of the large‐ and small‐scale features similar to that of the best simulation achieved by the best spectral nudging configuration, without the need of a spectral decomposition. The different downscaled atmospheric variables, including rainfall distribution, with CDA is most consistent with the observations. The Brier skill score values further indicate that the added value of CDA is distributed over the entire model domain. The overall results clearly suggest that CDA provides an efficient new approach for dynamical downscaling by maintaining better balance between the global model and the downscaled fields. This article is protected by copyright. All rights reserved.

Beschreibung: Earth Surface Processes and Landforms, Volume 44, Issue 9, Page 1876-1878, July 2019.

Beschreibung: No abstract is available for this article. © 2019 John Wiley & Sons, Ltd.

Beschreibung: Abstract Discharge from multiple wastewater treatment plants (WWTPs) distributed in urbanized river basins contributes to impairments of river water‐quality and aquatic ecosystem integrity, with size and location of WWTPs determined by population distribution within a river basin. Here we used geo‐referenced data for WWTPs in Germany to investigate the spatial organization of three attributes of interest in this study: population, population equivalents (the aggregated population served by each WWTP), and the number/sizes of WWTPs. To this end, we selected as case studies three large urbanized river basins (Weser, Elbe, and Rhine), home to about 70% of the population in Germany. We employed fractal river networks as structural platforms to examine the spatial patterns from two perspectives: spatial hierarchy (stream order) and patterns along longitudinal flow paths (width function). Moreover, we proposed three dimensionless scaling indices to quantify (1) human settlement preferences by stream order, (2) non‐sanitary flow contribution to total wastewater treated at WWTPs, and (3) degree of centralization in WWTPs locations. Across the three river basins, we found scale‐invariant distributions for each of the three attributes with stream order, quantified using extended Horton scaling ratios. We found a weak downstream clustering of population in the three basins. Variations in population equivalent clustering among different class‐sizes of WWTPs reflected the size, number, and locations of urban agglomerations in these river basins. We discussed the applicability of this approach to other large urbanized basins to analyze spatial organization of population and WWTPs.

Beschreibung: Abstract Stream channel morphology forms the template upon which hydraulic aspects of aquatic habitat are created, yet spatial and temporal variability in habitat imposed by changing morphology is not well understood. This paper presents a conceptual model linking sediment supply patterns to spatial and temporal variability in channel form and aquatic habitat. To evaluate this model, change over time in three habitat variables is quantified using a 2D hydrodynamic modeling approach. A 45‐year record of topographic data from Carnation Creek, a catchment in coastal British Columbia, is used for the flow modeling. Using the Nays2DH modeling platform, water depths and velocities are simulated in eight channel segments located at different positions relative to locations of historical colluvial input using seven flow levels ranging from 3% to 400% of mean annual discharge (0.02 to 3.31 m3s‐1). Results indicate that habitat availability changes through time as a result of sediment supply‐driven changes to channel morphology and wood loads, but patterns in habitat vary as a function of dominant channel segment morphology. Spatial and temporal variability in morphology also influences the relationship between habitat availability and river discharge, leading to non‐stationary habitat‐discharge rating curves. When habitat areas are predicted by applying these curves to daily flow series spanning annual dry seasons, over 50% of the variance in cumulative seasonal habitat area can be explained by year‐to‐year changes in channel morphology and wood loading, indicating that changing morphology is an important factor for driving temporal habitat variability. This variance is related to the morphological variability of a channel segment, which in turn is associated with the segment position relative to zones of colluvial input. Collectively, these results suggest that variability in habitat is impacted by channel morphology, and can be evaluated partly on the basis of a channel's sediment supply regime.

Beschreibung: Abstract This study analyses the mechanisms involved in the formation of a moist meso‐vortex associated with an extreme rain event that occurred in Burkina Faso on 1 September 2009, on the basis of high resolution convection‐permitting simulations. After an evaluation of the 6‐day simulation skill to capture the main characteristics of this event, budgets of heat, moisture and relative vorticity are calculated. Results allow to propose the following scenario for the occurrence of this extreme rain event, completing the large‐scale analysis of the same event performed in the companion paper Lafore et al. (2017): The arrival of a large‐scale wet spell is a key factor, creating a quite unusual wet environment over Sahel, resulting in weak rain evaporation. As over oceanic regions, it favours intense heating at low levels and thus strong mean ascent and convergence. The combination with the arrival of the trough of an African easterly wave provides a second key factor. The associated relative vorticity maximum on the southern flank of the African easterly jet core, is boosted by the strong low‐level convergence through the stretching term. The vortex deepening is favoured by the tilting and by eddies at upper‐levels. In turn the quasi‐balanced vortex circulation brings warm and moist air from the north, favouring the convection triggering to the west of the vortex in the down‐shear direction, in agreement with Raymond and Jiang (1990) theory for long‐lived meso‐scale convective systems. This scenario exhibits a positive feedback that could explain its extreme character. This article is protected by copyright. All rights reserved.

Beschreibung: ABSTRACT Reconstructions of the timing and frequency of past eruptions are important to assess the propensity for future volcanic activity, yet in volcanic areas such as the East African Rift only piecemeal eruption histories exist. Understanding the volcanic history of scoria‐cone fields, where eruptions are often infrequent and deposits strongly weathered, is particularly challenging. Here we reconstruct a history of volcanism from scoria cones situated along the eastern shoulders of the Kenya–Tanzania Rift, using a sequence of tephra (volcanic ash) layers preserved in the ~250‐ka sediment record of Lake Chala near Mount Kilimanjaro. Seven visible and two non‐visible (crypto‐) tephra layers in the Lake Chala sequence are attributed to activity from the Mt Kilimanjaro (northern Tanzania) and the Chyulu Hills (southern Kenya) volcanic fields, on the basis of their glass chemistry, textural characteristics and known eruption chronology. The Lake Chala record of eruptions from scoria cones in the Chyulu Hills volcanic field confirms geological and historical evidence of its recent activity, and provides first‐order age estimates for seven previously unknown eruptions. Long and well‐resolved sedimentary records such as that of Lake Chala have significant potential for resolving regional eruption chronologies spanning hundreds of thousands of years.

Beschreibung: Abstract The aim of this study was to investigate how the spatial distribution of grass influenced runoff and erosion from a hillslope with loess and cinnamon soils in the rocky area of Northern China. We set up a trial to test the two soils with different treatments, including bare soil (BS), grass strips on the upper (UGS) and lower (DGS) parts of the slope, grass cover over the entire slope (GS), and a grass carpet on the lower part of the slope (GC), under simulated rainfall conditions. The results showed that the runoff coefficients for the loess and cinnamon soils decreased by between 4% and 20% and by between 2% and 37%, respectively, when covered with grass. Grass spatial distribution had little effect on the runoff, but more effect on erosion than vegetation coverage degree. The most effective location of grass cover for decreasing hillslope erosion was at the foot, and the high efficiency was mainly due to controlling of rill formation and sediment deposition. The soil loss from GS, DGS, and GC on the loess and cinnamon soils was between 77% and 93% less and 55% and 80% less, respectively, compared to the loss from BS. However, the soil characteristics had little effect on soil erosion for well‐vegetated slopes. The results highlight the importance of vegetation re‐establishment at the foot of hillslope in controlling soil erosion.

Beschreibung: Abstract Secondary circulation in river confluences results in a spatial and temporal variation of fluid motion and a relatively high level of morphodynamic change. Acoustic Doppler current profiler (aDcp) vessel‐mounted flow measurements are now commonly used to quantify such circulation in shallow water fluvial environments. It is well established that such quantification using vessel‐mounted aDcps requires repeated survey of the same cross‐section. However, less attention has been given to how to process these data. Most aDcp data processing techniques make the assumption of homogeneity between the measured radial components of velocity. As acoustic beams diverge with distance from the aDcp probe, the volume of the flow that must be assumed to be homogeneous between the beams increases. In the presence of secondary circulation cells, and where there are strong rates of shear in the flow, the homogeneity assumption may not apply, especially deeper in the water column and close to the bed. To reduce dependence on this assumption, we apply a newly‐established method to aDcp data obtained for two medium‐sized (~60‐80 m wide) gravel‐bed river confluences and compare the results with those from more conventional data processing approaches. The comparsion confirms that in the presence of strong shear our method produces different results to more conventional approaches. In the absence of a third set of fully independent data, we cannot demonstrate conclusively which method is best, but our method involves less averaging and so in the presence of strong shear is likely to be more reliable. We conclude that it is wise to apply both our method and more conventional methods to identify where data analysis might be impacted upon by strong shear and where inferences of secondary circulation may need to be made more cautiously.

Beschreibung: This paper derives unified equations of A. Arakawa and C.S. Konor (2009) rigorously formulated in a suitable mass‐based sigma‐coordinate and develops an efficient semi‐implicit integration scheme. The unified equations accurately capture the non‐hydrostatic small‐scale effects and retain the hydrostatic compressibility of the flow at large scales. As with the classical quasi‐hydrostatic equations, the underlying approximations filter vertically‐propagating acoustic waves. In contrast to the quasi‐hydrostatic equations though, the filtering property of the unified equations imposes that the wind field satisfies a divergence constraint similar to anelastic and pseudo‐incompressible (small‐scale limit) soundproof systems. An efficient semi‐implicit integration scheme for the unified equation system is achieved by combining a constant‐coefficient linear partitioning approach with an iterative implicit treatment of the non‐linear residuals arising from the soundproof divergence constraint. The resulting linear implicit problem to be solved at each iteration may be reduced to a single Helmholtz equation with horizontally‐homogeneous coefficients, which is akin to the one typically solved in the semi‐implicit integration of the quasi‐hydrostatic equations. The stability and accuracy of the developed semi‐implicit scheme for the unified equations in the mass‐based coordinate is numerically assessed by means of standard vertical plane test cases in linear and nonlinear atmospheric flow regimes. Moreover, in order to ascertain the convergence of the iterative semi‐implicit scheme, the test cases also include a large‐scale three‐dimensional configuration that resembles the stiffness typically encountered in global atmospheric models. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract Rain‐on‐snow (RoS) events have caused severe floods in mountainous catchments in the recent past. Challenges in forecasting such events are uncertainties in meteorological input variables, the accurate estimation of snow cover and deficits in process understanding during runoff formation. Here, we evaluate the potential of the European Centre for Medium‐Range Weather Forecasts Integrated Forecasting System (ECMWF IFS) to forecast RoS disposition (i.e. minimum rainfall amounts, initial snow cover and meltwater contribution) several days ahead. We thereby evaluate forecasts of rain and snowfall with disdrometer observations and show that ensemble‐based forecasts have larger potential than the high‐resolution forecast of ECMWF IFS. Then, we use ECMWF IFS weather forecasts as input to a conceptual hydrological model, which is calibrated using estimates of snow‐covered area (SCA), snow water equivalent (SWE) as well as discharge observations. We show that the forecast skill of this model chain is reasonably high with respect to SCA and SWE, even several days ahead. However, a number of RoS events are missed in the forecast, mainly due to an underestimation of rainfall amounts. These misses can be reduced by lowering the rainfall amount threshold for the forecast as compared to the analysis, being accompanied by only a moderate increase in false alarm rates. In contrast, the forecast of RoS disposition is found to be less sensitive to thresholds of initial snow cover and meltwater contribution. We conclude that valuable disposition warnings for RoS events can be issued several days ahead, and we illustrate this idea with a case study.

Beschreibung: The North Atlantic Ocean is a region of intense uptake of atmospheric CO2. To assess how this CO2 sink has evolved over recent decades, various approaches have been used to estimate basin‐wide uptake from the irregularly sampled in‐situ CO2 observations. Until now, the lack of robust uncertainties associated with observation‐based gap‐filling methods required to produce these estimates has limited the capacity to validate climate model simulated surface ocean CO2 concentrations. After robustly quantifying basin‐wide and annually‐varying interpolation uncertainties using both observational and model data, we show that the North Atlantic surface ocean fugacity of CO2 (fCO2−ocean) increased at a significantly slower rate than that simulated by the latest generation of Earth System Models during the period 1992‐2014. We further show, with initialised model simulations, that the inability of these models to capture the observed trend in surface fCO2−ocean is primarily due to biases in the models' ocean biogeochemistry. Our results imply that current projections may underestimate the contribution of the North Atlantic to mitigating increasing future atmospheric CO2 concentrations.

Beschreibung: Holocene sedimentation patterns and environmental development in Aarhus Bay, Denmark, were reconstructed based on proxy analyses of two sediment cores (M1 and M5). Together, the two cores offer an opportunity to examine the history of the area during the past c. 10 000 years. The investigation consisted of acoustic mapping and multi‐proxy analyses of the sediment cores including macrofossils, sediment physical properties, sediment accumulation rates, grain size, and X‐ray fluorescence elemental counts. Radiocarbon dating of the two sediment successions revealed that they cover the periods c. 10 000–3700 cal. a BP (M1) and c. 4400 cal. a BP to the present (M5). The data from the M1 site indicate the presence of a near‐shore lake environment between c. 10 000 and 9000 cal. a BP. The first intrusion of marine water into the area is dated to c. 9000 cal. a BP. In the following c. 1300 years, brackish‐water conditions prevailed in the area characterized by a mixture of taxa from marine, limnic and terrestrial habitats, reflecting a shallow estuarine environment. Around 7700 cal. a BP full marine conditions were established, accompanied by a marked increase in sedimentation rates. The changes to full marine conditions and higher sedimentation rates are probably due to a significant sea‐level rise leading to flooding of former land areas and intensified erosion. A subsequent distinct decrease in sedimentation rates around 6350 cal. a BP is presumably linked to a previously documented sea‐level drop about this time. Continuous sedimentation ceased around 3700 cal. a BP in the central part of the bay, most probably due to a major sea‐level lowering involving widespread erosion. In the eastern and deeper part of the bay, sedimentation continued until today. Fully marine conditions prevailed there for at least the last 4400 years.

Beschreibung: Abstract The water quality and ecosystem health of river corridors depend on the biogeochemical processes occurring in the hyporheic zones (HZs) of the beds and banks of rivers. HZs in riverbeds often form because of bedforms. Despite widespread and persistent variation in river flow, how the discharge‐ and grainsize‐dependent geometry of bedforms and how bedform migration collectively and systematically affects hyporheic exchange flux, solute transport and biogeochemical reaction rates are unknown. We investigated these linked processes through morphodynamically‐consistent multiphysics numerical simulation experiments. Several realistic ripple geometries based on bedform stability criteria using mean river flow velocity and median sediment grainsize were designed. Ripple migration rates were estimated based primarily on the river velocity. The ripple geometries and migration rates were used to drive hyporheic flow and reactive transport models which quantified HZ nitrogen transformation. Results from fixed bedform simulations were compared with matching migrating bedform scenarios. We found that the turnover exchange due to ripple migration has a large impact on reactant supply and reaction rates. The nitrate removal efficiency increased asymptotically with Damköhler number for both mobile and immobile ripples, but the immobile ripple always had a higher nitrate removal efficiency. Since moving ripples remove less nitrogen, and may even be net nitrifying at times, consideration for bedform morphodynamics may therefore lead to reduction of model‐based estimates of denitrification. The connection between nitrate removal efficiency and Damköhler number can be integrated into frameworks for quantifying transient, network‐scale, HZ nitrate dynamics.

Beschreibung: Abstract Global urbanization trends impose major alterations on surface waters. This includes impacts on ecosystem functioning that can involve feedbacks on climate through changes in rates of greenhouse gas emissions. The combination of high nutrient supply and shallow depth typical of urban freshwaters is particularly conducive to high rates of methane (CH4) production and emission, suggesting a potentially important role in the global CH4 cycle. However, there is a lack of comprehensive flux data from diverse urban water bodies, of information on the underlying drivers, and of estimates for whole cities. Based on measurements over four seasons in a total of 32 water bodies in the city of Berlin, Germany, we calculate the total CH4 emission from various types of surface waters of a large city in temperate climate at 2.6 ± 1.7 Gg CH4 yr‐1.The average total emission was 219 ± 490 mg CH4 m‐2 d‐1. Water‐chemical variables were surprisingly poor predictors of total CH4 emissions, and proxies of productivity and oxygen conditions had low explanatory power as well, suggesting a complex combination of factors governing CH4 fluxes from urban surface waters. However, small water bodies (area 〈1 ha) typically located in urban green spaces were identified as emission hotspots. These results help constrain assessments of CH4 emissions from freshwaters in the world's growing cities, facilitating extrapolation of urban emissions to large areas, including at the global scale. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract Human activities have increasingly strong impacts on the sediment dynamics of watersheds, directly, for example through water abstraction and sediment extraction, but also indirectly through climate change. This study aims at disentangling these impacts on natural sediment fluxes for the Borgne river, located in the Alps of South‐West Switzerland, using two approaches: First, an assessment of contemporary sediment sources and their relative contribution to the sediment delivered to the catchment outlet is undertaken by geochemical fingerprinting and a mixing model. Second, a spatially distributed conceptual model of suspended sediment production and transfer is used to quantify the contribution of different portions of the catchment to the total sediment yield. The model describes the influence of hydroclimatic variables (rainfall, snowmelt, and ice melt), water diversions and reservoir trapping on the sediment yield accounting for the erodibility of the different land covers present in the catchment. The analysis of different scenarios based on this conceptual model aids the interpretation of the fingerprinting results and the identification of the most important factors controlling sediment fluxes. Although the conceptual model overestimates the contribution of the downstream source area and underestimates the contribution of the upstream source area, the results allow us to qualitatively assess the impacts of different drivers influencing the sediment yield at the catchment scale. The results suggest: (1) high sediment yield from the uppermost part of the catchment due to sediment delivery by glacial ice melt; (2) delayed sediment transfer from areas impacted by water abstraction; and (3) reduced sediment contribution from areas upstream of a major hydropower reservoir that intercepts and traps sediment. Although process (1) and processes (2) and (3) serve to counter one another, our study emphasizes that the relative impacts of Anthropocene climate change and human impacts on sediment delivery may be disentangled through multi‐proxy approaches.

Beschreibung: Abstract The INCOMPASS field campaign combines airborne and ground measurements of the 2016 Indian monsoon, towards the ultimate goal of better predicting monsoon rainfall. The monsoon supplies the majority of water in South Asia, but forecasting from days to the season ahead is limited by large, rapidly developing errors in model parametrizations. The lack of detailed observations prevents thorough understanding of the monsoon circulation and its interaction with the land surface: a process governed by boundary‐layer and convective‐cloud dynamics. INCOMPASS used the UK Facility for Airborne Atmospheric Measurements (FAAM) BAe‐146 aircraft for the first project of this scale in India, to accrue almost 100 hours of observations in June and July 2016. Flights from Lucknow in the northern plains sampled the dramatic contrast in surface and boundary layer structures between dry desert air in the west and the humid environment over the northern Bay of Bengal. These flights were repeated in pre‐monsoon and monsoon conditions. Flights from a second base at Bengaluru in southern India measured atmospheric contrasts from the Arabian Sea, over the Western Ghats mountains, to the rain shadow of southeast India and the south Bay of Bengal. Flight planning was aided by forecasts from bespoke 4km convection‐permitting limited‐area models at the Met Office and India's NCMRWF. On the ground, INCOMPASS installed eddy‐covariance flux towers on a range of surface types, to provide detailed measurements of surface fluxes and their modulation by diurnal and seasonal cycles. These data will be used to better quantify the impacts of the atmosphere on the land surface, and vice versa. INCOMPASS also installed ground instrumentation supersites at Kanpur and Bhubaneswar. Here we motivate and describe the INCOMPASS field campaign. We use examples from two flights to illustrate contrasts in atmospheric structure, in particular the retreating mid‐level dry intrusion during the monsoon onset. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract This study addresses the evaluation of flow resistance in natural gravel‐bed rivers. Through a new dataset collected on 136 reaches of 78 gravel‐bed rivers (Calabrian fiumare) in southern Italy, different conventional flow resistance equations to predict mean flow velocity in gravel‐bed rivers were tested in their original form. These equations have shown considerable disagreement with observed data, especially in river reaches characterized by high bed load conditions and for the domains of intermediate‐ and large‐scale roughness. This disagreement produced in almost all the cases an underestimation of the flow resistance, which can be corrected by introducing the Froude number and a particular form of the Shields sediment mobility parameter into the Manning, Chezy, and Darcy‐Weisbach equations. Through analyses carried out both on the whole dataset and on its sub‐sets, we propose a semiempirical approach with which, on the one hand the tractive forces exerted by the flow on the bed are taken into account by considering the ratio between the sediment mobility parameter and its critical value, and on the other hand water surface distortions are evaluated using the Froude number. This approach has been further validated using a literature‐based dataset showing, even in this case, excellent performances. Finally, the literature‐based dataset allowed to improve the performances of the proposed approach in the field of large‐scale roughness. Efficiency tests indicate that the new equations can better reproduce the flow velocity in river reach where conventional flow resistance equations are not able to explain the entire dissipative process.

Beschreibung: Abstract The spatiotemporal distribution of pore water in the vadose zone can have a critical control on many processes in the near‐surface Earth, such as the onset of landslides, crop yield, groundwater recharge, and runoff generation. Electrical geophysics has been widely used to monitor the moisture content (θ) distribution in the vadose zone at field sites, and often resistivity (ρ) or conductivity (σ) is converted to moisture contents through petrophysical relationships (e.g., Archie's law). Though both the petrophysical relationships (i.e., choices of appropriate model and parameterization) and the derived moisture content are known to be subject to uncertainty, they are commonly treated as exact and error‐free. This study examines the impact of uncertain petrophysical relationships on the moisture content estimates derived from electrical geophysics. We show from a collection of data from multiple core samples that significant variability in the θ(ρ) relationship can exist. Using rules of error propagation, we demonstrate the combined effect of inversion and uncertain petrophysical parameterization on moisture content estimates and derive their uncertainty bounds. Through investigation of a water injection experiment, we observe that the petrophysical uncertainty yields a large range of estimated total moisture volume within the water plume. The estimates of changes in water volume, however, generally agree within (large) uncertainty bounds. Our results caution against solely relying on electrical geophysics to estimate moisture content in the field. The uncertainty propagation approach is transferrable to other field studies of moisture content estimation.

Beschreibung: Abstract Water vapor adsorption/desorption isotherms are measured on five shales from Illinois basin by dynamic vapor sorption method. The experimental adsorption data are modeled by the Guggenheim, Anderson, and De Boer model and the Freundlich model over the entire range of measured relative humidity (Rh) values (0–0.95). Modeling results show that shale hydration is controlled by surface chemistry at low Rh through a strong intermolecular bonding, while is mainly influenced by the pore structure at high Rh (〉0.9) through capillary condensation. This is consistent with the progressive decrease of isosteric heat of adsorption with water content, obtained by the Clausius‐Clapeyron equation. Exceptionally, for the one shale containing 8.6% montmorillonite, mesopore condensation only accounts for 33% of the measured water adsorption even at Rh ~0.95 due to the limited external pores and the important role of clay swelling. The specific surface area defined by Guggenheim, Anderson, and De Boer analysis as available for water adsorption is larger than that available for low‐pressure N2 adsorption due to the complex surface chemistry. The one shale rich in expansive montmorillonite and with a large interlayer capacity for water but inaccessible to N2 molecules conditions this result. Among the other four shales, one with high kerogen content behaves the highest water adsorption, possibly due to the high content of oxygen‐containing functional groups and the potentially high pore volume of kerogen. These findings contribute to a better understanding of water storage and transport behavior in shales and impact behavior relevant to structures and reservoirs founded in such media.

Beschreibung: Ensemble weather forecasts often under‐represent uncertainty, leading to over‐confidence in their predictions. Multi‐model forecasts combining several individual ensembles have been shown to display greater skill than single‐ensemble forecasts in predicting temperatures, but tend to retain some bias in their joint predictions. Established postprocessing techniques are able to correct bias and calibration issues in univariate forecasts, but are generally not designed to handle multivariate forecasts (of several variables or at several locations, say). We propose a flexible multivariate Bayesian postprocessing framework, based on a directed acyclic graph representing the relationships between the ensembles and the observed weather. The posterior forecast is inferred from available ensemble forecasts and an estimate of the shared discrepancy, obtained from a collection of past forecast‐observation pairs. We also propose a novel approach to selecting an appropriate training set for estimation of the required correction, using synoptic‐scale analogues to obtain a regime‐dependent estimate of the adjustment. The proposed technique is applied to forecasts of surface temperature over the UK during the winter period from 2007‐2013. Although the resulting parametric multivariate‐normal probabilistic forecasts are marginally less sharp than those of the leading competitor, they capture the spatial structure of the observations better than a correlation structure based on either the ensembles or climatology alone, and are robust to changes in the variables and spatial domain of the forecast, at a greatly reduced computational cost. This article is protected by copyright. All rights reserved.

Beschreibung: ABSTRACT We present here the results of the first‐ever Quaternary entomological research in China. The Halashazi Wetland, located in the southern Altai Mountain region in the northernmost part of Xinjiang Province, yielded Holocene insect fossils (mostly beetles) from two peat profiles. In total, 55 Coleoptera taxa were found, including 37 identified species. A new species, Helophorus sinoglacialis, was identified. The fauna is strongly northern Holarctic in character. The interval from 10 424 to 9705 cal a BP was probably a cold and wet period, and the study site was above the treeline. From 9665 to 9500 cal a BP it was probably warmer and drier, and treeline moved to higher elevations. Following a depositional hiatus, mid‐Holocene (5400–4400 cal a BP) insect assemblages represent cold conditions with the site above the treeline. The exception was a brief warming around 5450 cal a BP, when bark beetle evidence suggests that the treeline moved to a higher elevation. Of the 37 identified beetle species from the Halashazi site, 34 (92%) have modern records in Siberia. The Altai Mountains probably served as a dispersal corridor between the Siberian arctic and alpine regions of northern China.

Beschreibung: Abstract We present results from a global inverse marine nitrogen (N) cycle model that include nitrate (NO3−) and nitrite (NO2−) concentrations and their N isotopic compositions as constraints on N cycle process rates in marine oxygen deficient zones (ODZs). NO2− is an important intermediate in the N cycle, particularly in ODZs where it is a substrate in the N loss processes, denitrification, and anammox. Similar to earlier work, our model yields a total water column N loss rate of 61 ± 10 Tg N/year. However, by including NO2− and its N isotopic composition, we are able to assess the relative contributions of denitrification and anammox to N loss and examine some of the potential drivers of that balance. We find that anammox contributes 60% of global water column N loss, dominating N loss along the edges of ODZs, while denitrification is more important in the anoxic ODZ cores. The decoupling of anammox and denitrification is supported by NO2− oxidation, which co‐occurs with NO3− reduction and anammox in ODZs. High rates of NO2− oxidation (up to 400 nM/day), which are tightly coupled to heterotrophic NO3− reduction, are required to match NO3− and NO2− concentration and isotope observations in marine ODZs. Lowering the rate of NO2− oxidation in ODZs by adjusting O2‐sensitive parameters results in higher rates of water column N loss, highlighting the role of NO2− oxidation in maintaining the marine fixed N inventory.

Beschreibung: Long‐term data characterizing the oceans’ biological carbon pump are essential for understanding impacts of climate variability on marine ecosystems. The ‘Bakun upwelling intensification hypothesis’ suggests intensified coastal upwelling due to a greater land‐sea temperature gradient influenced by global warming. We present long time‐series of bathypelagic (ca. 1200‐3600m) particle fluxes from a coastal (CBeu: 2003‐2016] and an offshore (CBmeso: 1988‐2016) sediment trap setting located in the Canary Current upwelling. Organic carbon (Corg) and biogenic opal (BSi, diatoms) fluxes were two‐ to three‐fold higher at the coastal upwelling site compared to the offshore site, respectively, and showed higher seasonality with flux maxima in spring. A relationship between winter and spring BSi fluxes to the North Atlantic Oscillation (NAO) index was best expressed at the offshore site CBmeso. Lithogenic (dust) fluxes regularly peaked in winter when frequent low‐altitude dust storms and deposition occurred, decreasing offshore by about three‐fold. We obtained a high temporal match of short‐term peaks of BSi and dust fluxes in winter‐spring at the inner site CBeu. We found synchronous flux variations at both sites and an anomalous year 2005, characterized by high BSi and Corg fluxes under a low NAO. Corg and BSi fluxes revealed a decreasing trend from 2006 to 2016 at the coastal site CBeu, pointing to coastal upwelling relaxation during the last two decades. The permanent offshore upwelling zone of the deflected Canary Current represented by the flux record of CBmeso showed no signs of increasing upwelling as well which contradicts the Bakun hypothesis.

Beschreibung: Abstract Copper (Cu) is an unusual micronutrient as it can limit primary production, but can also become toxic for growth and cellular functioning under high concentrations. Cu also displays an atypical linear profile, which will modulate its availability to marine microbes across the ocean. Multiple chemical forms of Cu coexist in seawater as dissolved species and understanding the main processes shaping the Cu biogeochemical cycling is hampered by key knowledge gaps. For instance, the drivers of its specific linear profile in seawater are unknown and the bioavailable form of Cu for marine phytoplankton is debated. Here, we developed a global 3D biogeochemical model of oceanic Cu within the NEMO/PISCES global model, which represents the global distribution of dissolved copper well. Using our model, we find that reversible scavenging of Cu by organic particles drives the dissolved Cu vertical profile and its distribution in the deep ocean. The low modeled inorganic copper (Cu') in the surface ocean means that Cu' cannot maintain phytoplankton cellular copper requirements within observed ranges. The global budget of oceanic Cu from our model suggests that its residence time may be shorter than previously estimated, and provides a global perspective on Cu cycling and the main drivers of Cu biogeochemistry in different regions. Cu scavenging within particle microenvironments and uptake by denitrifying bacteria could be a significant component of Cu cycling in oxygen minimum zones.

Beschreibung: Abstract One of the main problems of hydrologic/hydrodynamic routing models is defining the right set of parameters, especially on inaccessible and/or large basins. Remote Sensing techniques provide measurements of the basin topography, drainage system and channel width, however current methods for estimating riverbed elevation are not as accurate. This paper presents methods of altimetry data assimilation for estimating effective bathymetry of a hydrodynamic model. We tested past altimetry observations from satellites ENVISAT, ICESAT and JASON 2 and synthetic altimetry data from satellites ICESAT 2, JASON 3, SARAL and SWOT to assess future/present mission's potential. The data assimilation (DA) methods used were Direct Insertion, Linear Interpolation, the SCE‐UA optimization algorithm and an adapted Kalman Filter developed with hydraulically based variance and covariance introduced in this paper. The past satellite altimetry data assimilation was evaluated comparing simulated and observed water surface elevation (WSE) while the synthetic altimetry DA were assessed through a direct comparison with a “true” bathymetry. The SCE‐UA and hydraulically based Kalman Filter methods presented the best performances, reducing WSE error in 65% in past altimetry data experiment and reducing biased bathymetry error in 75% in the synthetic experiment, however the latter method is much less computationally expensive. Regarding satellites, it was observed that the performance is related to the satellite inter‐track distance, as higher number of observation sites allows more accurate bed elevation estimation.

Beschreibung: We compared the spatio‐temporal dynamics of species and trait structure in North Sea fish communities over 33 years. Both species and trait structure changed significantly over time; however, communities in the southern and northern North Sea diverged towards different species, becoming taxonomically more dissimilar over time, yet they converged towards the same traits regardless of species differences. In particular, communities shifted towards smaller, faster growing species with higher thermal preferences and pelagic water column position. Our findings suggest that global environmental change, notably climate warming, will lead to convergence towards traits more adapted for novel environments regardless of species composition. Abstract Describing the spatial and temporal dynamics of communities is essential for understanding the impacts of global environmental change on biodiversity and ecosystem functioning. Trait‐based approaches can provide better insight than species‐based (i.e. taxonomic) approaches into community assembly and ecosystem functioning, but comparing species and trait dynamics may reveal important patterns for understanding community responses to environmental change. Here, we used a 33‐year database of fish monitoring to compare the spatio‐temporal dynamics of taxonomic and trait structure in North Sea fish communities. We found that the majority of variation in both taxonomic and trait structure was explained by a pronounced spatial gradient, with distinct communities in the southern and northern North Sea related to depth, sea surface temperature, salinity and bed shear stress. Both taxonomic and trait structure changed significantly over time; however taxonomically, communities in the south and north diverged towards different species, becoming more dissimilar over time, yet they converged towards the same traits regardless of species differences. In particular, communities shifted towards smaller, faster growing species with higher thermal preferences and pelagic water column position. Although taxonomic structure changed over time, its spatial distribution remained relatively stable, whereas in trait structure, the southern zone of the North Sea shifted northward and expanded, leading to homogenization. Our findings suggest that global environmental change, notably climate warming, will lead to convergence towards traits more adapted for novel environments regardless of species composition.

Beschreibung: Abstract In 2017, the Birmingham Institute of Forest Research (BIFoR) began to conduct Free Air Carbon Dioxide Enrichment (FACE) within a mature broadleaf deciduous forest situated in the United Kingdom. BIFoR FACE employs large scale infrastructure, in the form of lattice towers, forming ‘arrays' which encircle a forest plot of ~30 m diameter. BIFoR FACE consists of three treatment arrays to elevate local CO2 concentrations (e[CO2]) by +150 μmol mol‐1. In practice, acceptable operational enrichment (ambient [CO2] + e[CO2]) is ± 20% of the set‐point 1‐minute average target. There are a further three arrays that replicate the infrastructure and deliver ambient air as paired controls for the treatment arrays. For the first growing season with e[CO2] (April to November 2017), [CO2] measurements in treatment and control arrays show that the target concentration was successfully delivered, i.e.: +147 ± 21 μmol mol‐1 (mean ± SD) or 98 ± 14% of set‐point enrichment target. e[CO2] treatment was accomplished for 97.7% of the scheduled operation time, with the remaining time lost due to engineering faults (0.6% of the time), CO2 supply issues (0.6%), or adverse weather conditions (1.1%). CO2 demand in the facility was driven predominantly by wind speed and the formation of the deciduous canopy. Deviations greater than 10% from the ambient baseline CO2 occurred 〈 1% of the time in control arrays. Incidences of cross‐contamination 〉 80 μmol mol‐1 (i.e., 〉 53% of the treatment increment) into control arrays accounted for 〈 0.1% of the enrichment period. The median [CO2] values in reconstructed 3‐dimensional [CO2] fields show enrichment somewhat lower than the target but still well above ambient. The data presented here provide confidence in the facility setup and can be used to guide future next‐generation forest FACE facilities built into tall and complex forest stands. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract Cropping is responsible for substantial emissions of greenhouse gasses (GHGs) worldwide through the use of fertilizers and through expansion of agricultural land and associated carbon losses. Especially in sub‐Saharan Africa (SSA) GHG emissions from these processes might increase steeply in coming decades, due to tripling demand for food until 2050 to match the steep population growth. This study assesses the impact of achieving cereal self‐sufficiency by the year 2050 for ten SSA countries on GHG emissions related to different scenarios of increasing cereal production, ranging from intensifying production to agricultural area expansion. We also assessed different nutrient management variants in the intensification. Our analysis revealed that irrespective of intensification or extensification, GHG emissions of the ten countries jointly are at least 50% higher in 2050 than in 2015. Intensification will come, depending on the nutrient use efficiency (N‐AE) achieved, with large increases in nutrient inputs and associated GHG emissions. However, matching food demand through conversion of forest and grasslands to cereal area likely results in much higher GHG emissions. Moreover, many countries lack enough suitable land for cereal expansion to match food demand. In addition, we analysed the uncertainty in our GHG estimates and found that it is caused primarily by uncertainty in the IPCC Tier 1 coefficient for direct N2O emissions, and by the N‐AE value. In conclusion, intensification scenarios are clearly superior to expansion scenarios in terms of climate change mitigation, but only if current N‐AE is increased to levels commonly achieved in e.g. the United States, and which have been demonstrated to be feasible in some locations in SSA. As such, intensifying cereal production with good agronomy and nutrient management is essential to moderate inevitable increases in GHG emissions. Sustainably increasing crop production in SSA is therefore a daunting challenge in the coming decades. This article is protected by copyright. All rights reserved.

Beschreibung: Global Change Biology, Volume 25, Issue 9, Page i-ii, September 2019.

Beschreibung: Abstract Gravitational sinking of photosynthetically fixed particulate organic carbon (POC) constitutes a key component of the biological carbon pump. The fraction of POC leaving the surface ocean depends on POC sinking velocity (SV) and remineralization rate (Cremin), both of which depend on plankton community structure. However, the key drivers in plankton communities controlling SV and Cremin are poorly constrained. In fall 2014, we conducted a 6‐week mesocosm experiment in the subtropical NE Atlantic Ocean to study the influence of plankton community structure on SV and Cremin. Oligotrophic conditions prevailed for the first 3 weeks, until nutrient‐rich deep water injected into all mesocosms stimulated diatom blooms. SV declined steadily over the course of the experiment due to decreasing CaCO3 ballast and—according to an optical proxy proposed herein—due to increasing aggregate porosity mostly during an aggregation event after the diatom bloom. Furthermore, SV was positively correlated with the contribution of picophytoplankton to the total phytoplankton biomass. Cremin was highest during a Synechococcus bloom under oligotrophic conditions and in some mesocosms during the diatom bloom after the deep water addition, while it was particularly low during harmful algal blooms. The temporal changes were considerably larger in Cremin (max. fifteenfold) than in SV (max. threefold). Accordingly, estimated POC transfer efficiency to 1,000 m was mainly dependent on how the plankton community structure affected Cremin. Our approach revealed key players and interactions in the plankton food web influencing POC export efficiency thereby improving our mechanistic understanding of the biological carbon pump.

Beschreibung: Abstract Marine nitrogen fixation contributes to the budget of biologically available N and thus fuels phytoplankton productivity and carbon cycle through biological pump. Modern N fixation rates are proved to be constrained by oceanographic condition and nutrient supply to the surface waters. However, the paleoceanographic reconstruction of N fixation and its regulation mechanism remain highly uncertain in many regions. Here we present records of N fixation changes in the South China Sea over the past 250,000 years reconstructed by compound‐specific nitrogen isotopes of individual amino acids. The δ15N of source amino acids (δ15NSrc), reflecting the δ15N of the substrate nitrate originating from the subsurface water, is distinctly lower during interglacial periods, indicating intensified N fixation during interglacials. The δ15NSrc of the South China Sea covaries with the thermal gradient between surface and subsurface waters, implying a tight link between the upper water structure and N fixation. It could be hypothesized that stronger mixing during interglacials enhances the supply of excess phosphorous from the subsurface waters and thus encourages the growth of diazotrophs. Furthermore, records of bulk sediment δ15N with relatively high time resolution show dominant precession cycle, probably related to the nutrient supply from subsurface water driven by summer monsoon and associated upper water structure changes. Similar mechanism controlling N fixation is also effective in regions with enough iron supply and low concentrations of nitrogen and phosphorous, like the North Atlantic, supporting that upper water structure can dominate N fixation rates by regulating nutrient stoichiometry supplied to the surface waters.

Beschreibung: We examine coastal cliff ground motion due to individual wave impacts using a seismometer and video data to directly link the wave forcing and cliff response. The maximum peak ground shaking did not necessarily coincide with periods of maximum significant wave height. Instead, the type of wave impact controlled peak shaking magnitude, with breaking wave impacts generating the highest shaking velocities. Abstract Coastal cliff erosion is caused by a combination of marine forcing and sub‐aerial processes, but linking cliff erosion to the environmental drivers remains challenging. One key component of these drivers is energy transfer from wave–cliff interaction. The aim of this study is to directly observe cliff ground motion in response to wave impacts at an individual wave scale. Measurements are described from two coastal cliff sites: a 45‐minute pilot study in southern California, USA and a 30‐day deployment in Taranaki, New Zealand. Seismometers, pressure sensors and video are used to compare cliff‐top ground motions with water depth, significant wave height (Hs) and wave impact types to examine cliff ground motion response. Analyses of the dataset demonstrate that individual impact events can be discriminated as discrete events in the seismic signal. Hourly mean ground motion increases with incident Hs, but the largest hourly peak ground motions occurred across a broad range of incident Hs (0.9–3.7 m), including during relatively calm conditions. Mean hourly metrics therefore smooth the short‐term dynamics of wave–cliff interaction; hence, to fully assess wave impact energy transfer to cliffs, it is important also to consider peak ground motion. Video analyses showed that the dominant control on peak ground motion magnitude was wave impact type rather than incident Hs. Wave–cliff impacts where breaking occurs directly onto the cliff face consistently produced greater ground motion compared to broken or unbroken wave impacts: breaking, broken and unbroken impacts averaged peak ground motion of 287, 59 and 38 μm s−1, respectively. The results illustrate a novel link between wave impact forcing and cliff ground motion response using individual wave field measurements, and highlight the influence of wave impact type on peak energy transfer to coastal cliffs. © 2019 John Wiley & Sons, Ltd.

Beschreibung: Abstract Aim Alexander von Humboldt observed that plant communities on different continents but under similar climatic conditions shared few common species but often contained representatives of the same genera or higher taxonomic groups. To test if this observation can be extended to substrate type, we explored whether a phylogenetic signature could be seen among floras growing on ultramafic substrates that present challenging edaphic conditions for plant growth and are well‐known for their distinctive vegetation. Location Cuba, Madagascar, New Caledonia. Taxon Angiosperms. Methods We compared the floras of Cuba, Madagascar and New Caledonia to test whether the same plant families were under‐ or over‐represented on the ultramafic substrates of the three islands. Results Pairwise comparisons showed that plant orders and families tended to have the same behaviour on the three islands, i.e. ultramafic substrates filtered (in favour of or against) the same plant groups in the three biogeographical distinct areas. The COM clade (comprising Celastrales, Oxalidales and Malpighiales) appears to be over‐represented on ultramafic substrates in all three islands and contains over half of the world's known nickel hyperaccumulators. Main conclusions Our analyses provide support for Humboldt's observation by showing that ecological sorting can favour the same plant lineages in similar environments in different biogeographical regions.

Beschreibung: Seasonal variations in u*t and PM10 fluxes for different landform types in northern China. Abstract Representation of dust sources remains a key challenge in quantifying the dust cycle and its environmental and climatic impacts. Direct measurements of dust fluxes from different landform types are useful in understanding the nature of dust emission and characterizing the dynamics of soil erodibility. In this study we used the PI‐SWERL® instrument over a seasonal cycle to quantify the potential for PM10 (particles with diameter ≤10 μm) emission from several typical landform types across the Tengger Desert and Mu Us Sandy Land, northern China. Our results indicate that sparse grasslands and coppice dunes showed relatively high emission potentials, with emitted fluxes ranging from 10−1 to 101 mg m−2 s−1. These values were up to five times those emitted from sand dunes, and one to two orders of magnitude greater than the emissions from dry lake beds, stone pavements and dense grasslands. Generally, PM10 emission fluxes were seen to peak in the spring months, with significant reductions in summer and autumn (by up to 95%), and in winter (by up to 98%). Variations in soil moisture were likely a primary controlling factor responsible for this seasonality in PM10 emission. Our data provide a relative quantification of differences in dust emission potential from several key landform types. Such data allow for the evaluation of current dust source schemes proposed by prior researchers. Moreover, our data will allow improvements in properly characterizing the erodibility of dust source regions and hence refine the parameterization of dust emission in climate models. © 2019 John Wiley & Sons, Ltd.

Beschreibung: Abstract Sustainably feeding the growing population amid a changing climate and dwindling resources is a grand challenge facing mankind. Decades‐long advancement in crop breeding has progressively elevated yield potential, markedly enhancing global food production capacity. However, relevant impact on reactive N (Nr) emissions associated with crop variety improvement has not been explicitly described. Here, we report multi‐tiered evidence that newer and select maize, wheat, and rice varieties developed in China have the capacity to substantially lower Nr losses while producing more grain. First, we pooled studies featuring side‐by‐side comparison of different varieties, totaling 269 paired observations, to demonstrate that collectively, relatively newer varieties of maize, wheat, and rice had less Nr emissions (9.6‐23.5%) while yielding more grains (7.3‐11.2%) compared to older varieties under wide‐ranging conditions. Next, we built an extended database (142 field studies with 833 observations) and comprehensively evaluated the Nr‐loss reduction potential of newer varieties (2000 and after) vs. older ones (1985‐1999). We found that newer varieties had Nr emission factors (EF, N loss as a percentage of N applied after correcting for background emissions) 18.2 to 75.7% less for N2O, 18.3 to 75.7% less for NO3−, and ‐8.5 to 22.8% less for NH3, while producing more grains (16.0‐24.4%). Individual varieties differed markedly in yield‐emission scores. A nationwide farmer survey (2.47 million responses) indicated tremendous opportunities for a new way of management intervention. Coupling variety selection with sound N and other agronomic management can help lower N footprint while producing more grain. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract Resilience of soil moisture regimes (SMRs) describes the stability of a particular SMR and its ability to withstand disturbances. This study analyzes the resilience of SMRs with quantifiable ecological (ECO‐) and engineering (ENG‐) metrics for a stochastic dynamic soil moisture system. The SMR is defined by the stationary state, described by a stationary probability distribution function (pdf), of the soil moisture dynamical system, and further classified into arid, semi‐arid, semi‐wet and wet classes. Applying the stationary pdf of soil moisture dynamics derived by Rodriguez‐Iturbe et al. [1999] and Laio et al. [2001a], the ENG‐ and ECO‐ resilience metrics of the various SMRs are quantified. We show that the recovery rate of soil moisture is a convex function of the expected soil moisture at the stationary state — the recovery rate reaches a minimum value at some intermediate soil moisture status. We also show that the maximum acceptable changes in the infiltration condition indicate the capacity of a system to avoid possible regime shifts. SMR shifts are characterized by phenomena of stagnation and hysteresis, which suggest two distinct thresholds for SMR shifts and their reversion. In particular, the semi‐wet SMR that is favorable to agriculture requires stricter infiltration conditions than other SMRs. This resilience analysis provides better understanding of how natural hydrological conditions control soil moisture, which helps provide guidance on maintaining SMRs suitable for agricultural activities and desertification prevention.

Beschreibung: Abstract A fundamental understanding of the fluid movement and dynamic partitioning process at fracture intersections is important to accurately predict water infiltration and contaminant transport in networks of fractures. We present an experimental study on the flow‐splitting behavior at a T‐shaped intersection. Different combinations of apertures of the vertical (bv) and horizontal (bh) fractures are considered. Experimental results confirm that the gravity‐driven flow in the vertical fracture transitions from droplet to rivulet mode as the flow rate increases. We quantify the flow dynamics through the intersection and especially focus on the partitioning efficiency (η) defined as the percentage of flow partitioned into the horizontal fracture. We identify three regimes of flow partitioning at the intersection for the case of bv 〈 bh: total partitioning (η → 1), splitting or partial bypass (0 〈 η 〈 1), and total bypass (η → 0). The total bypass regime is associated with the rivulet mode with a flow rate higher than ~1.5 ml/min. We find a simple relationship between η and the flow rate Q for droplet flow, η = min(1, ChQ−1), where Ch is a threshold flow rate below which droplets almost completely imbibe into the horizontal fracture, leading to η → 1. A force balance analysis links Ch to a critical droplet length for the transition from complete partitioning to path splitting. The obtained relationship is further supported by numerical simulations of droplet flow through intersections. The results and analysis from this study may provide insights and physical constraints on construction of reduced order unsaturated flow models based on simplified discrete fracture networks.

Beschreibung: The manuscript analyses links between flood spatial arrangement and soil water balance in a plain watershed, and, with that purpose, landscape metrics are calculated in maps obtain by remote sensed data in different hydrological scenarios. In contrast with previous works that investigate connectivity, we applied landscape metrics focusing on flooding pattern, their spatial and temporal variability, and their relationship with soil water balance. In addition, the analysis of patterns allows highlighting the internal heterogeneity that plain landscapes usually exhibit. Abstract In areas with very mild relief, water drains in a disordered way due to the lack of a developed drainage network, as it occurs in extremely flat sedimentary regions like the Argentine Pampas. The study analysed the flood spatial arrangements in 2014 by calculating landscape metrics and relating them to soil water balance. The study area is located at Del Azul creek lower basin (Pampa Ecoregion, Argentina). Daily soil water balances were obtained, and seven landscape metrics were calculated in 15 windows in five LandSat images, all along 2014, to explore the relationship between hydrological scenarios and spatial pattern summarized with principal component analysis. Water excess concentrated in winter (June and August); deficits were in late spring and summer (January and November), whereas the beginning of autumn (March) was an intermediate situation. Principal component 1 (44.7%) reflected area and shape metrics and correlated positively with water table level; principal component 2 (32.3%) summarized aggregation ones and was negatively associated with accumulated water excesses or deficits in previous 30 days and useful reserve. Both exhibited possible threshold‐driven behaviour. Internal heterogeneity between NW and SE zones within the study area coincided with the existence of ancient alluvial fans. The results highlight the peculiarities of the flood spatial patterns in regions with very mild relief, where landforms usually determine water flows.

Beschreibung: Abstract The major and trace element concentrations of volcanic glass shards from visible tephra layers in the SG93 and SG06 cores from Lake Suigetsu, central Japan, were determined by femtosecond laser ablation–inductively coupled plasma–mass spectrometry. The glass‐shard analyses, together with the petrographic properties of the tephra samples, allow the Suigetsu tephra layers to be broadly classified into tephras derived from calderas on Kyushu Island, and from Daisen and Sambe volcanoes in the Chugoku district of southwest Japan. The layers correlated with tephras from Kuju caldera and Daisen volcano, and with the younger Sambe tephras, have adakitic elemental features. A Suigetsu tephra sample correlated with the Sambe−Kisuki tephra based on petrographic properties has an elemental pattern similar to that of the Toya tephra from Hokkaido Island, northeast Japan. This match implies that tephras from northeast Japan, as well as Kyushu–Chugoku tephras, are possible correlatives of the Suigetsu tephra layers. Both petrographic properties and major–trace element data of volcanic glass shards are essential for robust tephra correlations, and hierarchical cluster analysis proved additionally useful in statistically evaluating relationships among the tephras.

Beschreibung: Seasonal predictions of wintertime climate in the Northern Hemisphere mid‐latitudes, while showing clear correlation skill, suffer from anomalously low signal‐to‐noise ratio. The low signal‐to‐noise ratio means that forecasts need to be made with large ensemble sizes and require significant post‐processing to correct the forecast distribution. In this study, a recently introduced statistical model of seasonal climate predictability is adapted so that it can be used to examine the signal‐to‐noise ratio in two versions of the ECMWF seasonal forecast system. Three novel features of the low signal‐to‐noise ratio are revealed. The low signal‐to‐noise ratio is present only for forecasts initialised on November 1st and not for forecasts initialised on December 1st. The low signal‐to‐noise ratio is predominantly a feature of the lower and middle troposphere and is not present in the stratosphere. The low signal‐to‐noise ratio is linked to low signal amplitude of the forecast systems in early winter. Future studies attempting to examine the signal‐to‐noise ratio should focus on the extent to which this early winter variability is predictable. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract This paper evaluates the prospects for increasing the horizontal resolution of the Aeolus horizontal line‐of‐sight (HLOS) wind profiles at the expense of their accuracy. The evaluation is performed by combining a 10‐day atmosphere simulation by the ECMWF model at T3999 horizontal resolution with the CALIPSO observations of atmospheric composition as inputs to the Aeolus simulator. The validation shows that the ECMWF model represents the location and the vertical structure of the observed cloud systems well. At the nominal accumulation length of L≈90 km (from the Aeolus measurement scale of ∼3 km), the Mie‐cloudy retrieval provides 1‐4 times fewer observations than Rayleigh‐clear but the Mie‐cloudy HLOS winds have the highest quality with estimated error standard deviation of about 1 m s−1 in the troposphere and no bias. The experiments with reduced L reveal that neither the observation error standard deviation nor bias of the Mie‐cloudy winds are significantly affected when the accumulation length L varies in the range between 100 and 10 km. At the same time, the number of observations significantly increases as L reduces. This suggests that mesoscale NWP may profit from the Aeolus Mie‐cloudy HLOS profiles with the accumulation lengths as small as 10 km. This article is protected by copyright. All rights reserved.

Beschreibung: Journal of Quaternary Science, Volume 34, Issue 4-5, Page i-iii, May-June 2019.

Beschreibung: Abstract Aim To assess habitat filtering and dispersal limitation in spore plant community assembly using bryophytes on recently emerged land uplift islands as study system. Location Gulf of Bothnia, northern Europe. Taxa Bryophytes, including the spore plant phyla Bryophyta (mosses) and Marchantiophyta (liverworts). Methods The species compositions of 20 coastal land uplift islands differing in age, area, connectivity and habitat composition were recorded in the field. In addition, we compiled a list of the regional species pool (446 species) and gathered data on species traits related to habitat affiliations (substrate, light, moisture, and pH) and dispersal capacity (regional abundance, spore size, sporophyte frequency, sexual system, vegetative propagules). For the 420 species with available trait data, we used multivariate generalized linear models to compare trait effects on species occurrence probabilities on the islands. Results Occurrence probabilities depended strongly on habitat affiliations. In addition, occurrence probabilities were lower for predominantly asexual species than for sexual species and for regionally rare than for regionally abundant species. Having specialized asexual propagules increased occurrence probabilities, but compensated only partly for the reductions in asexual species. No effect of the size of sexually produced spores was detected. Comparison of trait effects across island size and connectivity gradients revealed (a) reduced habitat filtering on larger islands and (b) decreasing negative effects of being predominantly asexual with increasing island connectivity. Conclusions Both habitat filtering and dispersal capacities affect the community assembly of spore plants on land uplift islands. Asexual mosses and liverworts show landscape scale (≤10 km) dispersal limitation. The weak or absent relationships between island connectivity and the effects of dispersal traits suggest that colonization is regulated mainly by habitat availability and the abundance of each species in a “regional spore rain” from which colonists are recruited.

Beschreibung: Abstract Streamflow simulation of the headwater catchment of the Yellow River basin (HCYRB) in China is important for water resources management of the Yellow River basin. A statistical‐dynamical model, combining regular vine copulas with an optimization method for structure estimation, is presented with an application for simulating the monthly streamflow with local climate drivers at HCYRB. Local climate drivers for streamflow in every month are analyzed using rank‐based correlation. Precipitation, evaporation, and temperature generally show strong associations with streamflow. Winter streamflows relate to total precipitation of the wet season, and total evaporation of Oct and Nov, while unfrozen‐month streamflows are correlated with evaporation and precipitation of current and previous one months in the wet season. Both canonical vine and D‐vine copulas are applied to develop different conditional quantile functions for streamflows in different months with their dynamical covariates. The covariates are selected from historical streamflows and climate drivers with appropriate lags using partial correlations. The optimal vine trees are selected using the sequential maximum spanning tree algorithm with the weight based on both dependence and goodness of fit. The model demonstrates higher skill than existing vine‐based models and the seasonal autoregressive integrated moving average model. The enhanced skill of the hybrid statistical‐dynamical model comes from an improved capability of capturing nonlinear correlation and tail dependence of streamflow and climate drivers with the optimization of vine structure selection. The model provides an effective advance to enhance water resources planning and management for HCYRB and the whole basin.

Beschreibung: ABSTRACT The chronologies of few Neolithic sites in the lower reaches of the Min River of China have been well investigated for the middle to late Holocene. In this study, the Hengyu Neolithic site in Fujian Province, South China, which has significant archaeological remains, was dated using blue‐stimulated optically stimulated luminescence (OSL) and accelerator mass spectrometry radiocarbon (AMS14C) techniques. The results, comprising nine OSL and three AMS 14C ages through the Neolithic sequence, provide new evidence towards understanding the relationship between environmental evolution and human activities in the middle to late Holocene in the Fuzhou Basin and coastal areas of South China. The ages of the site deposits vary from 6.83 to 1.67 ka and can be divided into two main phases: the Keqiutou–Tanshishan culture period and the Bronze culture period. In contrast, the persistent periods of ancient human activities at the Hengyu site seem to correspond to regional sea‐level changes and the East Asian winter monsoon as a secondary factor, which can affect human activities through sea‐level impacts. The warm and high sea level conditions provided a liveable environment for the ancient humans of Fujian and even South China. The ages of two building column bases are linked to the early stage of the Han dynasty, suggesting a potentially favourable habitation environment; that is, ancient humans occupied and settled this area for the long term within this time period, which is consistent with sea‐level changes and palynology records.

Beschreibung: Abstract This work introduces water–air two‐phase flow into integrated surface–subsurface flow by simulating rainfall infiltration and run‐off production on a soil slope with the finite element method. The numerical model is formulated by partial differential equations for hydrostatic shallow flow and water–air two‐phase flow in the shallow subsurface. Finite element computing formats and solution strategies are presented to obtain a numerical solution for the coupled model. An unsaturated seepage flow process is first simulated by water–air two‐phase flow under the atmospheric pressure boundary condition to obtain the rainfall infiltration rate. Then, the rainfall infiltration rate is used as an input parameter to solve the surface run‐off equations and determine the value of the surface run‐off depth. In the next iteration, the pressure boundary condition of unsaturated seepage flow is adjusted by the surface run‐off depth. The coupling process is achieved by updating the rainfall infiltration rate and surface run‐off depth sequentially until the convergence criteria are reached in a time step. A well‐conducted surface run‐off experiment and traditional surface–subsurface model are used to validate the new model. Comparisons with the traditional surface–subsurface model show that the initiation time of surface run‐off calculated by the proposed model is earlier and that the water depth is larger, thus providing values that are closer to the experimental results.

Beschreibung: Abstract Indirect effects of climate change are often mediated by trophic interactions and consequences for individual species depend on how they are tied into the local food web. Here we show how the response of demographic rates of an arctic bird of prey to fluctuations in small rodent abundance changed when small rodent community composition and dynamics changed, possibly under the effect of climate warming. We observed the breeding biology of rough‐legged buzzards (Buteo lagopus) at the Erkuta Tundra Monitoring Site in southern Yamal, low arctic Russia, for 19 years (1999 – 2017). At the same time, data on small rodent abundance were collected and information on buzzard diet was obtained from pellet dissection. The small rodent community experienced a shift from high amplitude cycles to dampened fluctuations paralleled with a change in species composition towards less lemmings and more voles. Buzzards clearly preferred lemmings as prey. Breeding density of buzzards was positively related to small rodent abundance, but the shift in small rodent community lead to lower numbers relative to small rodent abundance. At the same time, after the change in small rodent community, the average number of fledglings was higher relative to small rodent abundance than earlier. These results suggest that the buzzard population adapted to a certain degree to the changes in the major resource, although at the same time density declined. The documented flexibility in the short‐term response of demographic rates to changes in structure and dynamics of key food web components make it difficult to predict how complex food webs will be transformed in a warmer Arctic. The degree of plasticity of functional responses is indeed likely to vary between species and between regions, depending also on the local food web context. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract We model mudstone permeability during consolidation and grain rotation, and during fluid injection by simulating porous media flow using the lattice Boltzmann method. We define the mudstone structure using clay platelet thickness, aspect ratio, orientation, and pore widths. Over the representative range of clay platelet lengths (0.1–3 μm), aspect ratios (length/thickness = 20–50), and porosities (ϕ = 0.07–0.80) our permeability results match mudstone datasets well. Homogenous kaolinite and smectite models document a log linear decline in vertical permeability from 8.31 × 10−15–6.84 × 10−17 m2 at ϕ = 0.76–0.80 to 6.33 × 10−19–1.30 × 10−23 m2 at ϕ = 0.14–0.16, showing good correlation with experimental data (R2 = 0.42 and 0.56).We employ our methodology to predict the permeability of two natural mudstone samples composed of smectite, illite, and chlorite grains. Over ϕ = 0.32–0.58, the permeability trends of two models replicating the mineralogical composition of the natural mudstone samples match experimental datasets well (R2 = 0.78 and 0.74). We extend our methodology to evaluate how vertical permeability might evolve during microfracture network growth or macrofracture propagation upon fluid injection in compacted mudstone. Fluid injection results in a permeability increase from 1.02 × 10−20 m2 at ϕ = 0.07 to 2.07 × 10−16 m2 at ϕ = 0.29 for growth of a microfracture network, and from 1.02 × 10−20 m2 at ϕ = 0.07 to 1.23 × 10−16 m2 at ϕ = 0.32 for macrofracture propagation. Our results suggest that a distributed microfracture network results in greater permeability during fluid injection in compacted mudstones (ϕ = 0.07–0.32) in comparison to a wide macrofracture. Our modeling approach provides a simple means to estimate permeability during burial and compaction or fluid injection based on knowledge of porosity and mineralogy.

Beschreibung: Abstract Phase five of the Coupled Model Intercomparison Project (CMIP5) enabled a range of decadal modelling experiments where climate models were initialised with observations and allowed to evolve freely for 10‐30 years. However, climate models struggle to realistically simulate rainfall and the skill of rainfall prediction in decadal experiments is poor. Here, we examine how predictions of sea surface temperature anomaly (SSTA) indices from CMIP5 decadal experiments can provide skilful rainfall forecasts at interannual timescales for Australia. Forecasts of commonly used SSTA indices relevant to Australian seasonal rainfall are derived from decadal hindcasts of six different climate models and corrected for model drift. The corrected indices are then combined to form a multi‐model ensemble. The resultant forecasts are used as predictors in a statistical rainfall model developed in this study. As SSTA forecasts lose skill with increasing lead time, a new methodology for predicting interannual rainfall is proposed. We allow our statistical prediction model to evolve with lead time while accounting for the loss of skill in SSTA forecasts instead of using one statistical model for all lead times. Results in this pilot study across two of the largest climate zones in Australia show that SSTA outputs from the decadal experiments provide enhanced skill in rainfall prediction over using the conventional model (based purely on lagged observed indices) up to a maximum of three years ahead. This methodology could be used more broadly for other regions around the world where rainfall variability is known to have strong links to ocean temperatures.

Beschreibung: Abstract Probabilistic modelling of streamflow in ephemeral catchments, where streamflow is frequently zero or negligible, is a major scientific and operational challenge. This paper evaluates the benefits of an explicit treatment of zero flows in the residual error models used for hydrological model calibration and prediction. In this approach, the lower bound of zero for streamflow is implemented using a censoring approach. The explicit approach is compared to a simpler pragmatic approach, which imposes the zero streamflow bound in prediction but not in calibration. Following a theoretical exposition, empirical comparisons are reported using a daily rainfall‐runoff model (GR4J), four residual error schemes (based on log, log‐sinh and Box‐Cox (BC) transformations with λ = 0.2 and 0.5), 74 Australian catchments with diverse hydroclimatology, and five performance metrics (reliability, precision, bias, proportion of zero flow days and CRPS skill score). The key findings are: (1) in “mid‐ephemeral” catchments (5‐50% zero flows) the explicit approach improves predictive performance, especially reliability, through better characterization of residual errors; (2) BC0.2 and BC0.5 schemes are Pareto optimal in mid‐ephemeral catchments (when the explicit approach is used): BC0.2 achieves better reliability and is recommended for probabilistic prediction, whereas BC0.5 attains lower volumetric bias; (3) in “low‐ephemeral” catchments (〈5% zero flows) the pragmatic approach is sufficient; (4) in “high‐ephemeral” catchments (〉50% zero flows) theoretical limitations result in poor performance of these particular explicit and pragmatic approaches, and further development is needed. The findings provide guidance on improving probabilistic streamflow predictions in ephemeral catchments.

Beschreibung: Scaling issues in snow hydrology persist due to limitations in instrumentation and inability to measure physical properties and processes at spatiotemporal scales required for analysis. Snow depth and water equivalent (SWE) across scale estimated using time‐lapse photos, transects, and model grids (Canadian Meteorological Centre depth, GlobSnow SWE) were found to represent different physical processes and have substantially different statistical moments. Findings have implications for understanding limitations of distributing snowpack measurements, data assimilation, and validation of remotely sensed estimates. Abstract This study investigates scaling issues by evaluating snow processes and quantifying bias in snowpack properties across scale in a northern Great Lakes–St. Lawrence forest. Snow depth and density were measured along transects stratified by land cover over the 2015/2016 and 2016/2017 winters. Daily snow depth was measured using a time‐lapse (TL) camera at each transect. Semivariogram analysis of the transect data was conducted, and no autocorrelation was found, indicating little spatial structure along the transects. Pairwise differences in snow depth and snow water equivalent (SWE) between land covers were calculated and compared across scales. Differences in snowpack between forested sites at the TL points corresponded to differences in canopy cover, but this relationship was not evident at the transect scale, indicating a difference in observed process across scale. TL and transect estimates had substantial bias, but consistency in error was observed, which indicates that scaling coefficients may be derived to improve point scale estimates. TL and transect measurements were upscaled to estimate grid scale means. Upscaled estimates were compared and found to be consistent, indicating that appropriately stratified point scale measurements can be used to approximate a grid scale mean when transect data are not available. These findings are important in remote regions such as the study area, where frequent transect data may be difficult to obtain. TL, transect, and upscaled means were compared with modelled depth and SWE. Model comparisons with TL and transect data indicated that bias was dependent on land cover, measurement scale, and seasonality. Modelled means compared well with upscaled estimates, but model SWE was underestimated during spring melt. These findings highlight the importance of understanding the spatial representativeness of in situ measurements and the processes those measurements represent when validating gridded snow products or assimilating data into models.

Beschreibung: ABSTRACT Madagascar is a complex ‘biodiversity hotspot’ with a rapidly dwindling biota. The Late Quaternary subfossil record includes many extinct species whose loss is attributed to natural climate change and human impacts. Investigation of the chronology of these events is challenging because few localities document pre‐Holocene communities not impacted by humans. Caves with extinct lemurs of large body size comprise some of Madagascar's richest subfossil sites, but provide only a limited window into the island's past. Open highland sites may have fewer primates, but may better document other megafauna, and allow the analysis of the role of the Central Highlands as refugia and as corridors for the dispersal of vertebrates before and after human arrival. Here we present a new subfossil site, Tsaramody (Sambaina basin, Central Madagascar), a high‐altitude wetland area that preserves a diverse late glacial and postglacial vertebrate community. Tsaramody bears testimony to fluctuations in the highland flora during the transition from glacial to postglacial conditions, and the composition of a highland vertebrate community before humans arrived. We compare its biota to those of other sites to begin to document the decline and disappearance of megafauna from some of Madagascar's open ecosystems – wetlands dominated by hippopotamuses and crocodylians.

Beschreibung: To reveal the relative contribution of labile carbon (LC) limitation and soil microbial community responses in attenuating the effect that extended warming has on soil heterotrophic respiration (Rh), soil samples from Tibetan grasslands were exposed to an initial incubation (Experiment 1). Subsequently, soils were sterilized then inoculated with parent soil microbes to assess the LC limitation effects (Experiment 2) or soil microbes from the incubations were used to inoculate sterilized parent soils to assess the microbial community effects (Experiment 3). Both LC limitation and microbial community responses led to significant declines in Rh by 37% and 30%, respectively. Abstract Changes in labile carbon (LC) pools and microbial communities are the primary factors controlling soil heterotrophic respiration (Rh) in warming experiments. Warming is expected to initially increase Rh but studies show this increase may not be continuous or sustained. Specifically, LC and soil microbiome have been shown to contribute to the effect of extended warming on Rh. However, their relative contribution is unclear and this gap in knowledge causes considerable uncertainty in the prediction of carbon cycle feedbacks to climate change. In this study, we used a two‐step incubation approach to reveal the relative contribution of LC limitation and soil microbial community responses in attenuating the effect that extended warming has on Rh. Soil samples from three Tibetan ecosystems—an alpine meadow (AM), alpine steppe (AS), and desert steppe (DS)—were exposed to a temperature gradient of 5–25°C. After an initial incubation period, soils were processed in one of two methods: (a) soils were sterilized then inoculated with parent soil microbes to assess the LC limitation effects, while controlling for microbial community responses; or (b) soil microbes from the incubations were used to inoculate sterilized parent soils to assess the microbial community effects, while controlling for LC limitation. We found both LC limitation and microbial community responses led to significant declines in Rh by 37% and 30%, respectively, but their relative contributions were ecosystem specific. LC limitation alone caused a greater Rh decrease for DS soils than AMs or ASs. Our study demonstrates that soil carbon loss due to Rh in Tibetan alpine soils—especially in copiotrophic soils—will be weakened by microbial community responses under short‐term warming.

Beschreibung: ABSTRACT Ring‐width dendrochronology, based on matching patterns of ring width variability, works best when trees are growing under significant environmental (climatic) stress. In the UK, and elsewhere in the temperate mid‐latitudes, trees generally experience low stress, so dating is more difficult and often fails. Oxygen isotopes in tree rings passively record changes in the isotopic ratios of summer precipitation, so they carry a strong common signal, which offers potential for cross‐dating. A master chronology covering the period 1200–2000 ce was constructed using the oxygen isotope ratios of the latewood cellulose of oak samples from central England. Two independent chronologies, developed to verify the isotopic signal, were combined (n = 10 trees) and the method was evaluated by dating timbers of known age and historical timbers that could not be dated by ring‐width dendrochronology, from both within and beyond the central England region. The agreement between samples and the master chronology is exceptionally strong, allowing the dating of timbers with far fewer rings than is normally the case for ring‐width dendrochronology. Tree‐ring oxygen isotope values are more suited to correlation analysis than tree‐ring widths, so it is possible to provide t‐values that conform to Student's t‐distribution and can be converted into probabilities of error. A protocol for assigning dates using ‘stable‐isotope dendrochronology’ is proposed, which has the potential to revolutionize the dating of wooden structures and artefacts, allowing the dating of short and invariant ring sequences from young, fast‐grown trees. Such samples are commonplace throughout the historical building and archaeological records and were, until now, considered impossible to date.

Beschreibung: Abstract Soil carbon transformation and sequestration have received significant interest in recent years due to a growing need for quantifying its role in mitigating climate change. Even though our understanding of the nature of soil organic matter has recently been substantially revised, fundamental uncertainty remains about the quantitative importance of microbial necromass as part of persistent organic matter. Addressing this uncertainty has been hampered by the absence of quantitative assessments whether microbial matter makes up the majority of the persistent carbon in soil. Direct quantification of microbial necromass in soil is very challenging because of overlapping molecular signature with non‐microbial organic carbon. Here we use a comprehensive analysis of existing biomarker amino sugar data published between 1996‐2018, combined with novel appropriation using ecological systems approach, elemental carbon‐nitrogen stoichiometry, and biomarker scaling, to demonstrate a suit of strategies for quantifying the contribution of microbe‐derived carbon to the topsoil organic carbon reservoir in global temperate agricultural, grassland, and forest ecosystems. We show that microbial necromass can make up more than half of soil organic carbon. Hence, we suggest next‐generation field management requires promoting microbial biomass formation and necromass preservation to maintain healthy soils, ecosystems, and climate. Our analyses have important implications for improving current climate and carbon models, and helping develop management practices and policies. This article is protected by copyright. All rights reserved.

Beschreibung: The timing of reproduction is a critical component of how free‐living organisms respond to ongoing climate change, especially in the Arctic, which is disproportionally impacted by climate warming. Arctic seabirds respond to climate change by moving the start of their reproduction earlier, coincident with an advancing onset of spring, but their response is dependent on the ocean basin and foraging strategy. Surface‐feeding species advanced their reproduction in the last 35 years while diving species showed remarkably stable breeding timing. The earlier reproduction for Arctic surface‐feeding birds was significant in the Pacific only, where the spring advancement was most pronounced. Abstract The timing of annual events such as reproduction is a critical component of how free‐living organisms respond to ongoing climate change. This may be especially true in the Arctic, which is disproportionally impacted by climate warming. Here, we show that Arctic seabirds responded to climate change by moving the start of their reproduction earlier, coincident with an advancing onset of spring and that their response is phylogenetically and spatially structured. The phylogenetic signal is likely driven by seabird foraging behavior. Surface‐feeding species advanced their reproduction in the last 35 years while diving species showed remarkably stable breeding timing. The earlier reproduction for Arctic surface‐feeding birds was significant in the Pacific only, where spring advancement was most pronounced. In both the Atlantic and Pacific, seabirds with a long breeding season showed a greater response to the advancement of spring than seabirds with a short breeding season. Our results emphasize that spatial variation, phylogeny, and life history are important considerations in seabird phenological response to climate change and highlight the key role played by the species’ foraging behavior.

Beschreibung: In this study, we found that the advancing leaf‐out was accompanied by a shortening length of temperature‐relevant period (TRP) in six dominant tree species mainly located in central Europe during 1951–2016. We tested different hypotheses, and found that the advanced leaf‐out and unchanged start of TRP might be explained by sufficient chilling and faster accumulation of the required heat due to climatic warming, which overcompensated for the retarding effect of shortening daylength on bud development. These results implicate that phenology modules in global land surface models might be reliable assuming a fixed TRP starting date at least for temperate central Europe. Abstract Temperature during a particular period prior to spring leaf‐out, the temperature‐relevant period (TRP), is a strong determinant of the leaf‐out date in temperate‐zone trees. Climatic warming has substantially advanced leaf‐out dates in temperate biomes worldwide, but its effect on the beginning and length of the TRP has not yet been explored, despite its direct relevance for phenology modeling. Using 1,551 species–site combinations of long‐term (1951–2016) in situ observations on six tree species (namely, Aesculus hippocastanum, Alnus glutinosa, Betula pendula, Fagus sylvatica, Fraxinus excelsior, and Quercus robur) in central Europe, we found that the advancing leaf‐out was accompanied by a shortening of the TRP. On average across all species and sites, the length of the TRP significantly decreased by 23% (p 〈 .05), from 60 ± 4 days during 1951–1965 to 47 ± 4 days during 2002–2016. Importantly, the average start date of the TRP did not vary significantly over the study period (March 2–5, DOY = 61–64), which could be explained by sufficient chilling over the study period in the regions considered. The advanced leaf‐out date with unchanged beginning of the TRP can be explained by the faster accumulation of the required heat due to climatic warming, which overcompensated for the retarding effect of shortening daylength on bud development. This study shows that climate warming has not yet affected the mean TRP starting date in the study region, implying that phenology modules in global land surface models might be reliable assuming a fixed TRP starting date at least for the temperate central Europe. Field warming experiments do, however, remain necessary to test to what extent the length of TRP will continue to shorten and whether the starting date will remain stable under future climate conditions.

Beschreibung: Abstract Microbially induced carbonate precipitation (MICP) is a promising technique that could be used for soil stabilization, for permeability control in porous and fractured media, for sealing leaky hydrocarbon wells, and for immobilizing contaminants. Many further field trials are required before optimum treatment strategies can be established. These field trials will be costly and time consuming to \carry out and are currently a barrier to transitioning MICP from a lab‐scale process to a practical field‐scale deployable technology. To narrow down the range of potential treatment options into a manageable number, we present a field‐scale reactive transport model of MICP that captures the key processes of bacteria transport and attachment, urea hydrolysis, tractable CaCO3 precipitation, and modification to the porous media in terms of porosity and permeability. The model, named biogroutFoam, is implemented in OpenFOAM, and results are presented for MICP treatment in a planar fracture, three‐dimensional sand media at pore scale, and at continuum scale for an array of nine injection/abstraction wells. Results indicate that it is necessary to model bacterial attachment, that bacterial attachment should be a function of fluid velocity, and that phased injection strategies may lead to the most uniform precipitation in a porous media.

Beschreibung: Abstract Background Studies that attempt to measure shifts in species distributions often consider a single species in isolation. However, understanding changes in spatial overlap between predators and their prey might provide deeper insight into how species redistribution affects food web dynamics. Predator–prey overlap metrics Here, we review a suite of 10 metrics [range overlap, area overlap, the local index of collocation (Pianka's O), Hurlbert's index, biomass‐weighted overlap, asymmetrical alpha, Schoener's D, Bhattacharyya's coefficient, the global index of collocation and the AB ratio] that describe how two species overlap in space, using concepts such as binary co‐occurrence, encounter rates, spatial niche similarity, spatial independence, geographical similarity and trophic transfer. We describe the specific ecological insights that can be gained using each overlap metric, in order to determine which is most appropriate for describing spatial predator–prey interactions for different applications. Simulation and case study We use simulated predator and prey distributions to demonstrate how the 10 metrics respond to variation in three types of predator–prey interactions: changing spatial overlap between predator and prey, changing predator population size and changing patterns of predator aggregation in response to prey density. We also apply these overlap metrics to a case study of a predatory fish (arrowtooth flounder, Atheresthes stomias) and its prey (juvenile walleye pollock, Gadus chalcogrammus) in the Eastern Bering Sea, AK, USA. We show how the metrics can be applied to understand spatial and temporal variation in the overlap of species distributions in this rapidly changing Arctic ecosystem. Conclusions Using both simulated and empirical data, we provide a roadmap for ecologists and other practitioners to select overlap metrics to describe particular aspects of spatial predator–prey interactions. We outline a range of research and management applications for which each metric may be suited.

Beschreibung: No abstract is available for this article.

Beschreibung: Abstract Aim Establishments of non‐native forest pests (insects and pathogens) continue to increase worldwide with growing numbers of introductions and changes in invasion pathways. Quantifying spatio‐temporal patterns in establishment locations and subsequent invasion dynamics can provide insight into the underlying mechanisms driving invasions and assist biosecurity agencies with prioritizing areas for proactive surveillance and management. Location United States of America. Time period 1794–2018. Major taxa studied Insecta, plant pathogens. Methods Using locations of first discovery and county‐level occurrence data for 101 non‐native pests across the contiguous USA, we (a) quantified spatial patterns in discovery points and county‐level species richness with spatial point process models and spatial hotspot analyses, respectively, and (b) identified potential proxies for propagule pressure (e.g., human population density) associated with these observed patterns. Results Discovery points were highly aggregated in space and located in areas with high densities of ports and roads. Although concentrated in the north‐eastern USA, discovery points also occurred farther west and became less aggregated as time progressed. Invasion hotspots were more common in the north‐east. Geographic patterns of discovery points and hotspots varied substantially among pest origins (i.e., global region of pests’ native ranges) and pest feeding guilds. Significant variation in invasion richness was attributed to the patterns of first discovery locations. Data and shapefiles comprising analyses are provided. Main conclusions Use of spatial point pattern analyses provided a quantitative characterization of the central role of human activities in establishment of non‐native pests. Moreover, the decreased aggregation of discovery points through time suggests that invasion pathways to certain areas in the USA have either been created or intensified by human activities. Overall, our results suggest that spatio‐temporal variability in the intensity of invasion pathways has resulted in marked geographic patterns of establishment and contributed to current macroscale patterns of pest invasion in the USA.

Beschreibung: ABSTRACT This paper reviews some of the main advances in our understanding of human evolution over the last 1 million years, presenting a holistic overview of a field defined by interdisciplinary approaches to studying the origins of our species. We begin by briefly summarizing the climatic context across the Old World for the last 1 million years before directly addressing the fossil and archaeological records. The main themes in this work explore (i) recent discoveries in the fossil record over the last 15 years, such as Homo naledi and Homo floresiensis; (ii) the implications of palaeogenetics for understanding the evolutionary history of, and relationships between, Neanderthals, Denisovans and Homo sapiens; (iii) the interplay between physiology and metabolic demand, landscape use, and behavioural adaptations in the evolution of morphological and behavioural innovation; and (iv) recent advances in archaeological understanding for the behavioural record, in particular that of the Neanderthals. This paper seeks to provide a broad‐scale, holistic perspective of our current understanding of human evolution for the last 1 Ma, providing a reference point for researchers that can be built upon as new discoveries continue to develop the landscapes of human evolution.

Beschreibung: Abstract Among the numerous environmental factors affecting plant communities in alpine ecosystems, the influence of geomorphic processes and landforms has been minimally investigated. Subjected to persistent climate warming, it is vital to understand how these factors affect vegetation properties. Here, we studied 72 vegetation plots across three sites located in the Western Swiss Alps, characterized by high geomorphological variability and plant diversity. For each plot, vascular plant species were inventoried and ground surface temperature, soil moisture, topographic variables, earth surface processes (ESPs) and landform morphodynamics were assessed. The relationships between plant communities and environmental variables were analysed using non‐metric multi‐dimensional scaling (NMDS) and multivariate regression techniques (generalized linear model, GLM, and generalized additive model, GAM). Landform morphodynamics, growing degree days (sum of degree days above 5 °C) and mean ground surface temperature were the most important explanatory variables of plant community composition. Furthermore, the regression models for species cover and species richness were significantly improved by adding a morphodynamics variable. This study provides complementary support that landform morphodynamics is a key factor, combined with growing degree days, to explain alpine plant distribution and community composition.

Beschreibung: Abstract Aim Species distribution models (SDMs) are widely used to study geographic distributions of taxa in response to natural and anthropogenic environmental conditions. For a community, common approaches include fitting individual SDMs (iSDMs) to all taxa or directly modelling community properties such as richness. However, the parameters of iSDMs are difficult to identify for rare taxa, and community properties do not reveal taxon‐specific responses. Individual models can be combined into a hierarchical multispecies distribution model (mSDM) that constrains taxon‐specific parameters according to overarching community parameters, or a joint model (jSDM) in which interdependencies between taxa are jointly inferred. We compare how individual, hierarchical multispecies and joint SDMs differ in quality of fit, explanatory power and predictive performance, and analyse how these properties depend on the prevalence of taxa. Taxa Presence–absence observations of 245 benthic macroinvertebrate taxa identified at a mixed taxonomic resolution. Location Four hundred and ninety‐two sites in rivers throughout Switzerland. Methods Individual, hierarchical and joint hierarchical generalized linear models (GLM) were developed for all taxa. Parameters were estimated using maximum likelihood estimation or Bayesian inference with Hamiltonian Markov chain Monte Carlo simulations. Predictive performance was assessed with cross‐validation. In addition, the predicted family and species richness of the models was compared with a GLM for richness. Results Individual models show a slightly higher quality of fit largely due to overfitting for rare taxa. The mSDM achieves a similar quality of fit and explanatory power, mitigates overfitting for rare taxa and considerably improves predictive performance over the whole community. The joint models further improve the quality of fit, but decrease predictive performance and increase predictive uncertainty. Main conclusions We show that even a relatively simple mSDM combines many of the analytical capabilities of iSDMs and improves predictive performance. Increasingly complex mSDMs and jSDMs provide additional analytical possibilities, but depending on the data and research questions, different levels of complexity may be appropriate.

Beschreibung: Abstract Aim This study aims to quantify the patterns in compositional turnover of native and exotic ants on small islands in two oceans, and to explore whether such patterns are driven by similar environmental, geographical and potentially biotic variables. Location Pacific and Atlantic islands. Time period Present. Major taxa studied Ants. Methods We applied Multi‐Site Generalised Dissimilarity Modelling (MS‐GDM), which relates zeta diversity, the number of species shared by a given number of islands, to differences in environmental, geographical and biotic drivers. The use of zeta diversity enabled us to differentiate the contribution of rare species (shared by few islands) from those of widespread ones (shared by multiple islands) to compositional turnover. For completion, we also related species richness of insular ants per island with the same set of explanatory variables using Generalised Additive Models (GAM). Results Pacific and Atlantic islands have similar patterns of ant species turnover and richness, albeit partly driven by different drivers. Native and exotic species turnover are mostly explained by the same set of variables in the Pacific (annual precipitation and distance to the nearest island), but not in the Atlantic (annual precipitation is a good predictor of native species turnover, but none of the variables considered in our study explained exotic species turnover). No signal of biotic interactions was detected at the insular community level. Main conclusions Successful invasion strategies may depend on a combination of factors specific to the region in question. In the Pacific, milder environments and the absence of natives on certain islands enable exotic ants to select the same types of environment as native ants. In the harsher Atlantic Ocean, however, native ant species are likely to be well adapted to local environmental conditions, making it harder for exotics to become established. Exotic ant species, therefore, potentially rely on other attributes to establish, such as a combination of tolerance to a wide range of environmental conditions and human‐mediated colonization.

Beschreibung: Abstract A Bayesian model that uses the spatial dependence induced by the river network topology, and the leading principal components of regional tree‐ring chronologies for paleo‐streamflow reconstruction is presented. In any river basin, a convergent, dendritic network of tributaries comes together to form the main stem of a river. Consequently, it is natural to think of a spatial Markov process that recognizes this topological structure to develop a spatially consistent basin‐scale streamflow reconstruction model that uses the information in streamflow and tree‐ring chronology data to inform the reconstructed flows, while maintaining the space‐time correlation structure of flows that is critical for water resource assessments and management. Given historical data from multiple streamflow gauges along a river, their tributaries in a watershed, and regional tree‐ring chronologies, the model is fit and used to simultaneously reconstruct the full network of paleo‐streamflow at all gauges in the basin progressing upstream to downstream along the river. Our application to eighteen streamflow gauges in the Upper Missouri River Basin shows that the mean adjusted‐R2 for the basin is approximately 0.5 with good overall cross‐validated skill as measured by five different skill metrics. The spatial network structure produced a substantial reduction in the uncertainty associated with paleo‐streamflow as one proceeds downstream in the network aggregating information from upstream gauges and tree‐ring chronologies. Uncertainty was reduced by more than 50% at six gauges, between 6 and 50% at one gauge, and by less than 5% at the remaining eleven gauges when compared with the traditional PCR reconstruction model.

Beschreibung: Abstract Extreme precipitation events (EPEs) are meteorological phenomena of major concern for society. They can have different characteristics depending on the physical mechanisms responsible for their generation, which in turn depend on the large and mesoscale conditions. This work provides a systematic classification of EPEs over Northern‐Central Italy, one of the regions in Europe with the highest frequency of these events. The EPE statistics have been deduced using the new high‐resolution precipitation dataset ArCIS (Climatological Archive for Central Northern Italy), that gathers together a very high number of daily, quality controlled and homogenized, observations from different networks of 11 Italian regions. Gridded precipitation is aggregated over Italian operational warning‐area units (WA). EPEs are defined as events in which daily average precipitation in at least one of the 94 WAs exceeds the 99th percentile with respect to the climate reference 1979‐2015. A list of 887 events is compiled, significantly enlarging the database compared to any previous study of EPEs. EPEs are separated in three different dynamical classes: Cat1, events mainly attributable to frontal/orographic uplift; Cat2, events due to frontal uplift with (equilibrium) deep convection embedded; Cat3, events mainly generated by non‐equilibrium deep convection. A preliminary version of this classification is based on fixed thresholds of environmental parameters, but the final version is obtained using a more robust machine learning unsupervised K‐means clustering and random forest algorithm. All events are characterized by anomalously high‐integrated water vapour transport (IVT). This confirms IVT as an important large‐scale predictor, especially for Cat2 events, which is shown to be the most important category in terms of impacts and EPE area extension. Large IVT values are caused by upper‐level waves associated with remotely triggered Rossby Wave Packets, as shown for two example Cat2 events. This article is protected by copyright. All rights reserved.

Beschreibung: Abstract Forest canopies present irregular surfaces that alter both the quantity and spatiotemporal variability of precipitation inputs. The drop size distribution (DSD) of rainfall varies with rainfall event characteristics and is altered substantially by the forest stand properties. Yet, the influence of two major European tree species, European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) H. Karst), on throughfall DSD is largely unknown. In order to assess the impact of these two species with differing canopy structures on throughfall DSD, two optical disdrometers, one above and one below the canopy of each European beech and Norway spruce, measured DSD of both incident rainfall and throughfall over two months at a 10 second resolution. Fractions of different throughfall categories were analysed for single precipitation events of different intensities. While penetrating the canopies, clear shifts in drop size and temporal distributions of incoming rainfall were observed. Beech and spruce, however, had different DSD, behaved differently in their effect on diameter volume percentiles as well as width of drop spectrum. The maximum drop sizes under beech were higher than under spruce. The mean ± standard deviation of the median volume drops size (D50) over all rain events was 2.7 ± 0.28 mm for beech and 0.80 ± 0.04 mm for spruce, respectively. In general, there was a high DSD variability within events indicating varying amounts of the different throughfall fractions. These findings help to better understand the effects of different tree species on rainfall partitioning processes and small scale variations in subcanopy rainfall inputs, thereby demonstrating the need for further research in high resolution spatial and temporal properties of rainfall and throughfall.

Beschreibung: ABSTRACT The Eifel Laminated Sediment Archive (ELSA), which comprises several cores from maar lakes, includes numerous tephra layers spanning the last 140 000 years. The sediment cores are dated by 14C and thermoluminescence as well as tuned to Greenland stadial–interstadial successions. Within the last glacial cycle, the Eifel Volcanic Fields are source to several widespread tephra layers, namely the Laacher See, Eltville, Rambach and Rocourt Tephra. However, a corresponding source volcano was so far only identified for the Laacher See Tephra. In this study we use glass and clinopyroxene geochemistry to link the remaining tephra layers to possible eruption centers within the West and East Eifel Volcanic Fields: while we demonstrate that the Eltville Tephra originated from an earlier eruption of the Laacher See Volcano at 24 300 a bp from within the East Eifel Volcanic Field, the Rambach and Rocourt Tephras are sourced from the West Eifel Volcanic Field and erupted from Wartgesberg at 27 900 a bp and Pulvermaar at 75 000 a bp, respectively. Phases of volcanic activity peaked at 10 000–30 000 and 60 000–80 000 a bp and were thus erupted around the temperature minima of the last glacial cycle. The longest phase of dormancy between individual vents was around 30 000 years long, within the last interglacial.

Beschreibung: Globally, freshwater megafauna populations declined by 88% from 1970 to 2012, with the highest declines in the Indomalaya and Palearctic realms (−99% and −97%, respectively). Among taxonomic groups, mega‐fishes exhibited the greatest global decline (−94%). In addition to population declines, major range contractions of freshwater megafauna have been observed, which is more pronounced in Europe than in the United States. Abstract Freshwater ecosystems are among the most diverse and dynamic ecosystems on Earth. At the same time, they are among the most threatened ecosystems but remain underrepresented in biodiversity research and conservation efforts. The rate of decline of vertebrate populations is much higher in freshwaters than in terrestrial or marine realms. Freshwater megafauna (i.e., freshwater animals that can reach a body mass ≥30 kg) are intrinsically prone to extinction due to their large body size, complex habitat requirements and slow life‐history strategies such as long life span and late maturity. However, population trends and distribution changes of freshwater megafauna, at continental or global scales, remain unclear. In the present study, we compiled population data of 126 freshwater megafauna species globally from the Living Planet Database and available literature, and distribution data of 44 species inhabiting Europe and the United States from literature and databases of the International Union for Conservation of Nature and NatureServe. We quantified changes in population abundance and distribution range of freshwater megafauna species. Globally, freshwater megafauna populations declined by 88% from 1970 to 2012, with the highest declines in the Indomalaya and Palearctic realms (−99% and −97%, respectively). Among taxonomic groups, mega‐fishes exhibited the greatest global decline (−94%). In addition, freshwater megafauna experienced major range contractions. For example, distribution ranges of 42% of all freshwater megafauna species in Europe contracted by more than 40% of historical areas. We highlight the various sources of uncertainty in tracking changes in populations and distributions of freshwater megafauna, such as the lack of monitoring data and taxonomic and spatial biases. The detected trends emphasize the critical plight of freshwater megafauna globally and highlight the broader need for concerted, targeted and timely conservation of freshwater biodiversity.

Beschreibung: This paper presents an assessment of the usage of Arctic atmospheric observations in the Numerical Weather Prediction (NWP) system of the European Centre for Medium‐Range Weather Forecasts, and of their impact on the quality of short to medium range forecasts. The Arctic has low coverage of conventional data north of 70° N but one of the highest coverages of satellite sounding data on the globe. The impact of Arctic observations on forecast skill was assessed by performing Observing System Experiments (OSEs) in which different observation types were removed from the full observing system. This assessment was complemented by an analysis of Forecast Sensitivity to Observation Impact diagnostics. To our knowledge it is the first time that comprehensive numerical experimentation has been carried out to explore the role of different Arctic observations in a state‐of‐the‐art global operational NWP system. All Arctic observations were found to have a positive impact on forecast skill in the Arctic region with the largest tropospheric impacts on both short and medium range forecasts due to microwave sounding, conventional and infrared sounding observations. Results indicate the high importance of microwave sounding data and conventional data, which are found to be the key observing systems in the summer and winter seasons respectively. These observations were found to have a positive and statistically significant impact on forecasts not only in the Arctic but also in the mid‐latitude regions at longer lead times. Differences between the seasons are most likely due to problems assimilating microwave sounding observations over snow and sea‐ice leading to a reduced impact in winter, but there is also a suggestion of an increased importance of conventional data in winter, and other factors may also play a role. This article is protected by copyright. All rights reserved.

Beschreibung: Despite our growing understanding of the impacts of invasive plants on ecosystem structure and function, important gaps remain, including whether resident native and exotic species respond differently to plant invasion. We found that invasive plants reduced the abundance of native, but not exotic, animals, though this varied by animal phyla, with invasive plants reducing the abundance of native annelids and chordates, but not mollusks or arthropods. We provide an important first insight into how native and exotic species respond differently to plant invasion, the consequences of which may facilitate cascading trophic disruptions further exacerbating the impacts of invasive plants. Abstract Despite our growing understanding of the impacts of invasive plants on ecosystem structure and function, important gaps remain, including whether native and exotic species respond differently to plant invasion. This would elucidate basic ecological interactions and inform management. We performed a meta‐analytic review of the effects of invasive plants on native and exotic resident animals. We found that invasive plants reduced the abundance of native, but not exotic, animals. This varied by animal phyla, with invasive plants reducing the abundance of native annelids and chordates, but not mollusks or arthropods. We found dissimilar impacts among “wet” and “dry” ecosystems, but not among animal trophic levels. Additionally, the impact of invasive plants increased over time, but this did not vary with animal nativity. Our review found that no studies considered resident nativity differences, and most did not identify animals to species. We call for more rigorous studies of invaded community impacts across taxa, and most importantly, explicit consideration of resident biogeographic origin. We provide an important first insight into how native and exotic species respond differently to invasion, the consequences of which may facilitate cascading trophic disruptions further exacerbating global change consequences to ecosystem structure and function.

Beschreibung: Abstract The interleaving of impermeable and permeable surfaces along a runoff flow path controls the hillslope hydrograph, the spatial pattern of infiltration, and the distribution of flow velocities in landscapes dominated by overland flow. Predictions of the relationship between the pattern of (im)permeable surfaces and hydrological outcomes tend to fall into two categories: (i) generalized metrics of landscape pattern, often referred to as connectivity metrics, and (ii) direct simulation of specific hillslopes. Unfortunately, the success of using connectivity metrics for prediction is mixed, while direct simulation approaches are computationally expensive and hard to generalize. Here we present a new approach for prediction based on emulation of a coupled Saint Venant equation‐Richards equation model with random forest regression. The emulation model predicts infiltration and peak flow velocities for every location on a hillslope with an arbitrary spatial pattern of impermeable and permeable surfaces but fixed soil, slope, and storm properties. It provides excellent fidelity to the physically based model predictions and is generalizable to novel spatial patterns. The spatial pattern features that explain most of the hydrological variability are not stable across different soils, slopes, and storms, potentially explaining some of the difficulties associated with direct use of spatial metrics for predicting landscape function. Although the current emulator relies on strong assumptions, including smooth topography, binary permeability fields, and only a small collection of soils, slope, and storm scenarios, it offers a promising way forward for applications in dryland and urban settings and in supporting the development of potential connectivity indices.

Beschreibung: Abstract Ongoing intensification of the hydrological cycle is altering rainfall regimes by increasing the frequency of extreme wet and dry years and the size of individual rainfall events. Despite longstanding recognition of the importance of precipitation amount and variability for most terrestrial ecosystem processes, we lack understanding of their interactive effects on ecosystem functioning. We quantified this interaction in native grassland by experimentally eliminating temporal variability in growing season rainfall over a wide range of precipitation amounts, from extreme wet to dry conditions. We contrasted the rain use efficiency (RUE) of aboveground net primary productivity (ANPP) under conditions of experimentally reduced vs. naturally high rainfall variability using a 32‐yr precipitation‐ANPP dataset from the same site as our experiment. We found that increased growing season rainfall variability can reduce RUE and thus ecosystem functioning by as much as 42% during dry years, but that such impacts weaken as years become wetter. During low precipitation years, RUE is lowest when rainfall event sizes are relatively large, and when a larger proportion of total rainfall is derived from large events. Thus, a shift towards precipitation regimes dominated by fewer but larger rainfall events, already documented over much of the globe, can be expected to reduce the functioning of mesic ecosystems primarily during drought, when ecosystem processes are already compromised by low water availability. This article is protected by copyright. All rights reserved.