ALBERT

Description: Abstract Groundwater transit time is an essential hydrologic metric for groundwater resources management. However, especially in tropical environments studies on the transit time distribution (TTD) of groundwater infiltration and its corresponding mean transit time (mTT) have been extremely limited due to data sparsity. In this study, we primarily use stable isotopes to examine the TTDs and their mTTs of both vertical and horizontal infiltration at a riverbank infiltration area in the Vietnamese Mekong Delta (VMD), representative of the tropical climate in Asian Monsoon regions. Precipitation, river water, groundwater, and local ponding surface water were sampled for three to nine years and analyzed for stable isotopes (δ18O and δ2H), providing a unique data set of stable isotope records for a tropical region. We quantified the contribution that the two sources contributed to the local shallow groundwater by a novel concept of two‐component lumped parameter models (LPMs) that are solved using δ18O records. The study illustrates that two‐component LPMs, in conjunction with hydrological and isotopic measurements, are able to identify subsurface flow conditions and water mixing at riverbank infiltration systems. However, the predictive skill and the reliability of the models decrease for locations farther from the river, where recharge by precipitation dominates, and a low‐permeable aquitard layer above the highly permeable aquifer is present. This specific setting impairs the identifiability of model parameters. For river infiltration short mTTs (〈40 weeks) were determined for sites closer to the river (〈200 m), whereas for the precipitation infiltration the mTTs were longer (〉80 weeks) and independent of the distance to the river. The results not only enhance the understanding of the groundwater recharge dynamics in the VMD but also suggest that the highly complex mechanisms of surface‐groundwater interaction can be conceptualized by exploiting two‐component LPMs in general. The model concept could thus be a powerful tool for better understanding both the hydrological functioning of mixing processes and the movement of different water components in riverbank infiltration systems.

Description: Abstract Artificial lighting at night (ALAN) is a global phenomenon that can be detrimental to organisms at individual and population levels, yet potential consequences for communities and ecosystem functions are less resolved. Riparian systems may be particularly vulnerable to ALAN. We investigated the impacts of ALAN on invertebrate community composition and food web characteristics for linked aquatic‐terrestrial ecosystems. We focused on food chain length (FCL), a central property of ecological communities that can influence their structure, function, and stability; and the contribution of aquatically derived energy (i.e., nutritional subsidies originating from stream periphyton). We collected terrestrial arthropods and emergent aquatic insects from a suite of stream and wetland sites in Columbus, Ohio, USA. Stable isotopes of carbon (13C) and nitrogen (15N) were used to infer FCL and contribution of aquatically derived energy. We found that moderate‐to‐high levels of ALAN altered invertebrate community composition, favoring primarily predators and detritivores. Impacts of ALAN, however, were very taxon specific as illustrated, for example, by the negative impact of ALAN on the abundance of orb‐web spiders belonging to the families Tetragnathidae and Araneidae: key invertebrate riparian predators. Most notably, we observed decreases in both invertebrate FCL and reliance on aquatically derived energy under ALAN (although aquatic energetic contributions appeared to increase again at higher levels of ALAN), in addition to shifts in the timing of reciprocal nutritional subsidies. Our study demonstrates that ALAN can alter the flows of energy between aquatic and terrestrial systems, thereby representing an environmental perturbation that can cross ecosystem boundaries. Given projections for global increases in ALAN, both in terms of coverage and intensity, these results have broad implications for stream ecosystem structure and function.

Description: Abstract Rising temperatures and more frequent and severe droughts are driving increases in tree mortality in forests around the globe. However, in many cases, the likely trajectories of forest recovery following drought‐related mortality are poorly understood. In many fire‐suppressed western U.S. forests, management is applied to reverse densification and restore natural forest structure and composition, but it is unclear how such management affects post‐mortality recovery. We addressed these uncertainties by examining forest stands that experienced mortality during the severe drought of 2012‐2016 in California, USA. We surveyed post‐drought vegetation along a gradient of overstory mortality severity in paired treated (mechanically thinned or prescribed‐burned) and untreated areas in the Sierra Nevada. Treatment substantially reduced tree density, particularly in smaller tree size classes, and these effects persisted through severe drought‐related overstory mortality. However, even in treated areas with severe mortality (〉 67% basal area mortality), the combined density of residual (surviving) trees (mean 44 trees ha‐1) and saplings (mean 189 saplings ha‐1) frequently (86% of plots) fell within or exceeded the natural range of variation (NRV) of tree density, suggesting little need for reforestation intervention to increase density. Residual tree densities in untreated high‐mortality plots were significantly higher (mean 192 trees ha‐1 and 506 saplings ha‐1), and 96% of these plots met or exceeded the NRV. Treatment disproportionately removed shade‐tolerant conifer species, while mortality in the drought event was concentrated in pines (Pinus ponderosa and P. lambertiana); as a consequence, the residual trees, saplings, and seedlings in treated areas, particularly those that had experienced moderate or high drought‐related mortality, were more heavily dominated by broadleaf (“hardwood”) trees (particularly Quercus kelloggii and Q. chrysolepis). In contrast, residual trees and regeneration in untreated stands were heavily dominated by shade‐tolerant conifer species (Abies concolor and Calocedrus decurrens), suggesting a need for future treatment. Because increased dominance of hardwoods brings benefits for plant and animal diversity and stand resilience, the ecological advantages of mechanical thinning and prescribed‐fire treatments may, depending on the management perspective, extend even to stands that ultimately experience high drought‐related mortality following treatment.

Description: Abstract Patterns of feeding interactions between species are thought to influence the stability of communities and the flux of nutrients and energy through ecosystems. However, surprisingly few well‐resolved food webs allow us to evaluate factors that influence the architecture of species interactions. We constructed a meta‐food web consisting of 714 invertebrate species collected over nine years of suction and pitfall sampling campaigns in the Jena Experiment, a long‐term grassland biodiversity experiment located in Jena, Germany. In this paper, we summarize information on the 51,496 potential trophic links, which were established using information on diet specificity and species traits that typically constrain feeding interactions (trophic group, body size, and vertical stratification). The list of species identities, traits, and link‐derivation rules will be useful not only for tests of plant diversity effects on food web structure within the Jena Experiment, but also for considering consistent construction of food webs from empirical data, and for comparisons of network structure across ecosystems. No copyright or proprietary restrictions are associated with the use of this data set other than citation of this Data Paper. This article is protected by copyright. All rights reserved.

Description: Abstract For benthic marine invertebrates, recruitment strongly influences the composition and abundance of resulting communities. We present the results of a long‐term (1999–2017) colonization experiment at the Long‐Term Ecological Research observatory HAUSGARTEN in the Fram Strait (Arctic Ocean, 79°N, 04°E, 2500 m water depth). Recruitment panels were constructed from plastic and brick and deployed attached to a metal frame in 1999. The experiment was monitored using a remotely operated vehicle in 2003 and 2011 and recovered in 2017. Recruitment was very low, with only foraminiferans being visible after 4 yr (2003) and one metazoan species, the hydroid Halisiphonia arctica, being visible on the panels after 12 yr (2011). After 18 yr underwater, panels were colonized by 13 metazoan species as well as calcareous and agglutinating foraminiferans. Recruitment was higher on brick panels than on plastic, but while some species were more common on panels at higher altitude (H. arctica and the crinoid Bathycrinus carpenterii), others were more common on panels closer to the seafloor (serpulid polychaetes) or on panels in line with the predominant bottom current (small round white sponges). The most common species recruiting to our panels can be described as opportunistic. Meanwhile, large hexactinellid sponges that are common in natural communities did not recruit to our panels. These results suggest that community assembly in the Arctic deep sea takes much longer than the two decades spanned by this study.

Description: Abstract Ship‐tracks appear as long winding linear features in satellite images and are produced by aerosols from ship exhausts changing low cloud properties. They are one of the best examples of aerosol‐cloud interaction experiments. However, manually finding ship‐tracks from satellite data on a large‐scale is prohibitively costly while a large number of samples are required. Here we train a deep neural network to automate finding ship‐tracks. The neural network model generalizes well as it not only finds ship‐tracks labeled by human experts, but also detects those that are occasionally missed by humans. It finds more ship‐tracks than all previous studies combined and produces a map of ship‐track distributions off the California coast that matches well with known shipping traffic. Our technique will enable studying aerosol effects on low clouds using ship‐tracks on a large‐scale, which will potentially narrow the uncertainty of the aerosol‐cloud interactions.

Description: Abstract The paper presents oxygen and hydrogen isotopes of 284 precipitation event samples systematically collected in Irkutsk, in the Baikal region (southeast Siberia), between June 2011 and April 2017. This is the first high‐resolution dataset of stable isotopes of precipitation from this poorly studied region of continental Asia, which has a high potential for isotope‐based paleoclimate research. The dataset revealed distinct seasonal variations: relatively high δ18O (up to –4‰) and δD (up to –40‰) values characterise summer air masses, while lighter isotope composition (–41‰ for δ18O and –322‰ for δD) is characteristic of winter precipitation. Our results show that air temperature mainly affects the isotope composition of precipitation, while no significant correlations were obtained for precipitation amount and relative humidity. A new temperature dependence was established for weighted mean monthly precipitation: +0.50‰/°C (r2 = 0.83; p 〈 0.01; n = 55) for δ18O and +3.8‰/°C (r2 = 0.83, p 〈 0.01; n = 55) for δD. Secondary fractionation processes (e.g. contribution of recycled moisture) were identified mainly in summer from low d excess. Backward trajectories assessed with the HYSPLIT model indicate that precipitation with the lowest mean δ18O and δD values reaches Irkutsk in winter related to moisture transport from the Arctic. Precipitation originating from the west/southwest with the heaviest mean isotope composition reaches Irkutsk in summer, thus representing moisture transport across Eurasia. Generally, moisture transport from the west i.e. the Atlantic Ocean predominates throughout the year. A comparison of our new isotope dataset with simulation results using the ECHAM5‐wiso climate model reveals a good agreement of variations in δ18O (r2 = 0.87; p 〈 0.01; n = 55) and air temperature (r2 = 0.99; p 〈 0.01; n = 71). However, the ECHAM5‐wiso model fails to capture observed variations in d excess (r2 = 0.14; p 〈 0.01; n = 55). This disagreement can be partly explained by a model deficit of capturing regional hydrological processes associated with secondary moisture supply in summer.

Description: Abstract The importance of macrobenthos in benthic‐pelagic coupling and early diagenesis of organic carbon has long been recognized but has not been quantified at a regional scale. By using the southern North Sea as an exemplary area we present a modeling attempt to quantify the budget of total organic carbon (TOC) reworked by macrobenthos in seafloor surface sediments. Vertical profiles in sediments collected in the field indicate a significant but nonlinear correlation between TOC and macrobenthic biomass. A mechanistic model is used to resolve the bidirectional interaction between TOC and macrobenthos. A novelty of this model is that bioturbation is resolved dynamically depending on variations in local food resource and macrobenthic biomass. The model is coupled to 3‐D hydrodynamic‐biogeochemical simulations to hindcast the mutual dependence between sedimentary TOC and macrobenthos from 1948 to 2015. Agreement with field data reveals a satisfactory model performance. Our simulations show that the preservation of TOC in the North Sea sediments is determined not only by pelagic conditions (hydrodynamic regime and primary production) but also by the vertical distribution of TOC, bioturbation intensity, and the vertical positioning of macrobenthos. Macrobenthos annually ingest 20–35% and in addition vertically diffuse 11–22% of the total budget of TOC in the uppermost 30‐cm sediments in the southern North Sea. This result indicates a central role of benthic animals in modulating the organic carbon cycling at the sediment‐water interface of continental margins.

Description: Grain‐textured PMN‐PT ceramics were produced by templated grain growth and the symmetry of the textured samples was evaluated by pole figure analysis. Shown in the following figure parts are: (A) templated grain growth model, (B) micrograph of textured PMN‐PT, (C) 3D pole figure showing twofold symmetry and (D) 3D pole figure showing 2m orthotropic symmetry for a unique domain‐engineered condition. Inset shows 2D pole figures. Abstract We have performed studies of the orientation distribution in 〈001〉C textured, 0.03(Na1/2Bi1/2)TiO3 ‐ 0.97[0.715Pb(Mg1/3Nb2/3)TiO3 ‐ 0.285PbTiO3] (0.03NBT‐0.97[PMN‐28.5PT]) ceramics by a pole figure method, comparing the results to those for PMN‐PT single crystal and polycrystal samples. The pole figures about the (001) zone are found to have monoclinic, Ma, phase for textured ceramics in the annealed condition and were similar to those for electrically poled single crystals. However, electrical poling of the textured ceramics resulted in a doublet splitting of the orientation distribution about the direction that defined the original grain texturing. Studies of pole figures about other high‐symmetry zones also revealed the development of some degree of preferred orientation along the in‐plane directions after poling. Our findings demonstrate that E‐field induced phase transformation and domain textures superimpose with that of preferred grain orientations, giving rise to a unique texture symmetry for PMN‐PT. The texture symmetry changes are driven by minimization of the elastic strain energy, and have an important effect upon the piezoelectric properties.