ALBERT

Description: New, commensurate members of the fluorite-related Bi 3 Nb 1− x Ta x O 7 family were synthesized and their crystal structures, microstructures, and microwave (MW) dielectric properties were characterized. The incorporation of Ta into the tetragonal Bi 3 Nb 1− x Ta x O 7 solid solution was found to gradually affect the density and the MW dielectric properties. The materials sintered at 870°C exhibited relative permittivities in the range k ′ = 86–72, Q  ×  f values from 793 to 1189 GHz and a positive temperature coefficient of resonant frequency from 88 to 12 ppm/K. The formation of the members of the fluorite-related solid solution along the Bi 3 Nb 1− x Ta x O 7 composition depends on a phase transition, and thus their properties are compared within the compositional range. The correlations between their MW dielectric properties, compositions, crystal structures, and processing parameters were discussed in detail. Optimization of MW properties can be achieved by utilizing the ability of the Bi 3 Nb 1− x Ta x O 7 solid solution that it undergoes a phase transformation from cubic to tetragonal structure which are both characterized by unique properties, under certain synthesis conditions.

Description: Transparent novel glass-ceramics containing Sr 2 YbF 7 :Er 3+ nanocrystals were successfully fabricated by melt-quenching technique. Their structural and up-conversion luminescent properties were systemically investigated by XRD, HRTEM, and a series of spectroscopy methods. The temperature-dependent up-conversion spectra prove that 2 H 11/2 and 4 S 3/2 levels of Er 3+ are thermally coupled energy levels (TCEL). Consequently, the 2 H 11/2 4 I 15/2 and 4 S 3/2 4 I 15/2 emissions of Er 3+ in Sr 2 YbF 7 :Er 3+ glass-ceramics can be used as optical thermometry based on fluorescence intensity ratio (FIR) technique. Combined with low phonon energy and high thermal stability, Er 3+ ions in Sr 2 YbF 7 glass-ceramics present broad operating temperature range (300–500 K), large energy gap of TCEL (786 cm −1 ) and high theoretical maximum value of relative sensitivity (62.14 × 10 −4  K −1 at 560 K), which suggests that Sr 2 YbF 7 :Er 3+ glass-ceramics may be excellent candidates for optical temperature sensors.

Description: We investigate how the choice of injection mode impacts transport properties in kilometer-scale three-dimensional discrete fracture networks (DFN). The choice of injection mode, resident or flux-weighted, is designed to mimic different physical phenomena. It has been hypothesized that solute plumes injected under resident conditions evolve to behave similarly to solutes injected under flux-weighted conditions. Previously, computational limitations have prohibited the large scale simulations required to investigate this hypothesis. We investigate this hypothesis by using a high performance DFN suite, dfnWorks , to simulate flow in kilometer-scale three-dimensional DFNs based on fractured granite at the Forsmark site in Sweden, and adopt a Lagrangian approach to simulate transport therein. Results show that after traveling through a pre-equilibrium region both injection methods exhibit linear scaling of the first moment of travel time and power law scaling of the breakthrough curve with similar exponents, slightly larger than two. The physical mechanisms behind this evolution appear to be the combination of in-network channeling of mass into larger fractures, which offer reduced resistance to flow, and in-fracture channeling, which results from the topology of the DFN. This article is protected by copyright. All rights reserved.

Description: Hydrologic ensemble forecasts driven by atmospheric ensemble prediction systems need statistical post-processing in order to account for systematic errors in terms of both location and spread. Runoff is an inherently multivariate process with typical events lasting from hours in case of floods to weeks or even months in case of droughts. This calls for multivariate post-processing techniques that yield well calibrated forecasts in univariate terms and ensure a realistic temporal dependence structure at the same time. To this end, the univariate ensemble model output statistics (EMOS) post-processing method is combined with two different copula approaches that ensure multivariate calibration throughout the entire forecast horizon. The domain of this study covers three sub-catchments of the river Rhine that represent different sizes and hydrological regimes: the Upper Rhine up to the gauge Maxau, the river Moselle up to the gauge Trier, and the river Lahn up to the gauge Kalkofen. In this study the two approaches to model the temporal dependence structure are ensemble copula coupling (ECC), which preserves the dependence structure of the raw ensemble, and a Gaussian copula approach (GCA), which estimates the temporal correlations from training observations. The results indicate that both methods are suitable for modelling the temporal dependencies of probabilistic hydrologic forecasts. This article is protected by copyright. All rights reserved.

Description: A three-dimensional mathematical model that describes transport of contaminant in a horizontal aquifer with simultaneous diffusion into a fractured clay formation is proposed. A group of semi-analytical solutions is derived based on specific initial and boundary conditions as well as various source functions. The analytical model solutions are evaluated by numerical Laplace inverse transformation and analytical Fourier inverse transformation. The model solutions can be used to study the fate and transport in a three-dimensional spatial domain in which a non-aqueous phase liquid exists as a pool atop a fractured low permeability clay layer. The non-aqueous phase liquid gradually dissolves into the groundwater flowing past the pool, while simultaneously diffusing into the fractured clay formation below the aquifer. Mass transfer of the contaminant into the clay formation is demonstrated to be significantly enhanced by the existence of the fractures, even though the volume of fractures is relatively small compared to the volume of the clay matrix. The model solution is a useful tool in assessing contaminant attenuation processes in a confined aquifer underlain by a fractured clay formation. This article is protected by copyright. All rights reserved.

Description: The present work investigates pollutant removal and the transformation of nitrogen from sewage wastewater using a pilot-scale multi-stage bio-vermifilter system. Over a study period of 48 weeks, the pollutant removal performance of the system was measured and the effects of hydraulic loading rate (HLR) and dry–wet ratio (D/W) were estimated. The relationship between oxygen transfer rate and load of oxygen necessity was calculated and analysed for system optimisation. The method for diluting the isotope δ 15 N-NO 3 − was applied to study nitrogen transfer. Moreover, statistical correlations were analysed to determine the crucial factors which influence nitrogen transfer efficiency. The system removes pollutants efficiently; specifically, the average removal efficiencies are 94.2 % for chemical oxygen demand (COD), 93.3 % for NH 4 + -N, and 58.2 % for total nitrogen (T-N). Lowering HLR and D/W can enhance nitrogen removal. Nitrogen speciation and transformation were examined under an optimised condition with an HLR of 0.36 m day −1 and a D/W of 3. The results of isotope δ 15 N-NO 3 − dilution showed that NO 3 − -N was mainly produced in trickling bio-filter and vermibio-filter (VBF) I. By contrast, NO 3 − -N was mainly reduced in VBF II. Under stable operating conditions and environmental factors, COD/T-N was verified as the crucial factor in nitrogen removal.

Description: Extraction of oil and natural gas (hydrocarbons) from shale is increasing rapidly in North America, with documented impacts to native species and ecosystems. With shale oil and gas resources on nearly every continent, this development is set to become a major driver of global land-use change. It is increasingly critical to quantify spatial habitat loss driven by this development to implement effective mitigation strategies and develop habitat offsets. Habitat selection is a fundamental ecological process, influencing both individual fitness and population-level distribution on the landscape. Examinations of habitat selection provide a natural means for understanding spatial impacts. We examined the impact of natural gas development on habitat selection patterns of mule deer on their winter range in Colorado. We fit resource selection functions in a Bayesian hierarchical framework, with habitat availability defined using a movement-based modeling approach. Energy development drove considerable alterations to deer habitat selection patterns, with the most substantial impacts manifested as avoidance of well pads with active drilling to a distance of at least 800 m. Deer displayed more nuanced responses to other infrastructure, avoiding pads with active production and roads to a greater degree during the day than night. In aggregate, these responses equate to alteration of behavior by human development in over 50% of the critical winter range in our study area during the day and over 25% at night. Compared to other regions, the topographic and vegetative diversity in the study area appear to provide refugia that allow deer to behaviorally mediate some of the impacts of development. This study, and the methods we employed, provides a template for quantifying spatial take by industrial activities in natural areas and the results offer guidance for policy makers, mangers, and industry when attempting to mitigate habitat loss due to energy development.

Description: Although long-distance migratory songbirds are widely believed to be at risk from warming temperature trends, species capable of attempting more than one brood in a breeding season could benefit from extended breeding seasons in warmer springs. To evaluate local and global factors affecting population dynamics of the black-throated blue warbler ( Setophaga caerulescens ), a double-brooded long-distance migrant, we used Pradel models to analyze 25 years of mark-recapture data collected in New Hampshire, USA. We assessed the effects of spring temperature (local weather) and the El Niño Southern Oscillation index (a global climate cycle), as well as predator abundance, insect biomass, and local conspecific density on population growth in the subsequent year. Local and global climatic conditions affected warbler populations in different ways. We found that warbler population growth was lower following El Niño years (which have been linked to poor survival in the wintering grounds and low fledging weights in the breeding grounds) than La Niña years. At a local scale, populations increased following years with warm springs and abundant late-season food, but were unaffected by spring temperature following years when food was scarce. These results indicate that the warming temperature trends might have a positive effect on recruitment and population growth of black-throated blue warblers if food abundance is sustained in breeding areas. In contrast, potential intensification of future El Niño events could negatively impact vital rates and populations of this species. This article is protected by copyright. All rights reserved.

Description: Ecotones are transition zones that form, in forests, where distinct forest types meet across a climatic gradient. In mountains, ecotones are compressed and act as potential harbingers of species shifts that accompany climate change. As the climate warms in New England, USA, high elevation boreal forests are expected to recede upslope, with northern hardwood species moving up behind. Yet recent empirical studies present conflicting findings on this dynamic, reporting both rapid upward ecotonal shifts and concurrent increases in boreal species within the region. These discrepancies may result from the limited spatial extent of observations. We developed a method to model and map the montane forest ecotone using Landsat imagery to observe change at scales not possible for plot-based studies, covering mountain peaks over 39,000 km 2 . Our results show that ecotones shifted downward or stayed stable on most mountains between 1991 and 2010, but also shifted upward in some cases (13-15% slopes). On average, upper ecotone boundaries moved down -1.5 m·yr −1 in the Green Mountains, VT, and -1.3 m·yr −1 in the White Mountains, NH. These changes agree with re-measured forest inventory data from Hubbard Brook Experimental Forest, NH and suggest that processes of boreal forest recovery from prior red spruce decline, or human landuse and disturbance, may swamp out any signal of climate-mediated migration in this ecosystem. This approach represents a powerful framework for evaluating similar ecotonal dynamics in other mountainous regions of the globe. This article is protected by copyright. All rights reserved.

Description: In order to adequately monitor biodiversity trends through time and their responses to natural or anthropogenic impacts, researchers require long time series that are often unavailable. This general lack of datasets that are several decades or longer makes establishing a background or baseline of diversity metrics difficult – especially when attempting to understand species composition changes against a backdrop of climate and ecological variability. Here we present an analysis of a community of juvenile nearshore fishes based on nearly 8 decades of highly standardized Norwegian survey records. Using multivariate statistical techniques, we: a) characterize the change in taxonomic community composition through time, b) determine whether there has been an increase in warm water affinity species relative to their cold water affinity counterparts, and c) characterize the temporal change in the species’ functional trait assemblage. Our results strongly indicate a shift towards a novel fish assemblage between the late 1990s and 2000s. The context of changes within the most recent two decades are in stark contrast to those during the 60s and 70s, but similar to those during the previous warm period during the 30s and 40s. This novel assemblage is tightly linked to the warming temperatures in the region portrayed by the increased presence of warm water species and a higher incidence of pelagic, planktivorous species. The results indicate a clear influence of ocean temperature on the region's juvenile fish community that points to climate mediated effects on the species assemblages of an important fish nursery area. This article is protected by copyright. All rights reserved.

Description: This work focuses on the implementation of a Shallow Water-Exner model for compound natural channels with complex geometry and movable bed within the finite volume framework. The model is devised for compound channels modeling: cross-section overbanks are treated with fixed bed conditions, while the main channel is left free to modify its morphology. A capacitive approach is used for bedload transport modeling, in which the solid flow rates are estimated with bedload transport formulas. The model equations pose some numerical issues in the case of natural channels, where bedload transport may occur for both subcritical and supercritical flows and geometry varies in space. An explicit path-conservative scheme, designed to overcome all these issues, is presented in the paper. The scheme solves liquid and solid phases dynamics in a coupled manner, in order to correctly model near critical currents/channel interactions and is well-balanced, that is able to properly reproduce steady states. The Roe and Osher Riemann solvers are implemented, so as to take into account the spatial geometry variations of natural channels. The scheme reaches up to 2 nd order accuracy. Validation is performed with fixed and movable bed test cases whose analytical solution is known, and with flume experimental data. An application of the model to a real case study is also shown. This article is protected by copyright. All rights reserved.

Description: In this paper we use a physical modelling approach to explore the effect of lateral confinement on gravel bed river planform style, bed morphology, and sediment transport processes. A set of 27 runs was performed in a large flume (25 m long, 2.9 m wide), with constant longitudinal slope (0.01) and uniform grain size (1 mm), changing the water discharge (1.5 to 2.5 l/s) and the channel width (0.15 m to 1.5 m) to model a wide range of channel configurations, from narrow, straight, embanked channels to wide braided networks. The outcomes of each run were characterized by a detailed digital elevation model describing channel morphology, a map of dry areas and areas actively transporting sediment within the channel, and continuous monitoring of the amount of sediment transported through the flume outlet. Analysis reveals strong relationships between unit stream power and parameters describing the channel morphology. In particular, a smooth transition is observed between narrow channels with an almost rectangular cross section profile (with sediment transport occurring across the entire channel width) and complex braided networks where only a limited proportion (30%) of the bed is active. This transition is captured by descriptors of the bed elevation frequency distribution, e.g. standard deviation, skewness and kurtosis. These summary statistics represent potentially useful indicators of bed morphology that are compared with other commonly used summary indicators such as the braiding index and the type and number of bars. This article is protected by copyright. All rights reserved.

Description: Accurate information on the interactions between water and silica is critical to the understanding of its properties including mechanical strength under stress and long-term chemical durability of silica and silicate glasses. In this study, interactions between water and nanoporous amorphous silica models were investigated using density functional theory (DFT) based ab initio molecular dynamics (AIMD) simulations which accurately describe bond breakage and formation as well as chemical reactions. AIMD simulations up to 30 ps were performed for systems containing water and nanoporous silica with a wide range of porosities (31%–67%). Partial removal of defects, such as two-membered rings, was observed during the AIMD runs whereas more reactive coordination defects were removed during the initial geometry optimization. The limited two-membered ring removal can be attributed to restricted water-defect movement or the increased stability of rings located on concave surfaces. Two-membered ring removal mechanisms included the formation of an overcoordinated silicon (Si 5 ) intermediate defect from the dynamic simulations. Si 5 defects continued to develop throughout the simulations, indicating a thermodynamic drive for two-membered ring removal which is kinetically limited. Changes in the electronic structures, such as atomic charges, and bond length-bond angle correlation functions were monitored during the hydroxylation process.

Description: Amorphous calcium polyphosphate (ACPP), an inorganic polymer ceramic, has shown promise as a drug delivery matrix following a repeat gelling protocol. This study described a simple method of preparing ACPP hydrogel in the presence of an excess volume of water. The increased water availability accelerates water molecule ingress and microstructural transformation of ACPP hydrogels. The impact of some experimental settings (soaking time, temperature, stirring, and ACPP particle size) on the physiochemical and rheological natures of ACPP hydrogel were investigated and from which possible hydrogel formation mechanisms were inferred. We believe that the formation of ACPP hydrogel is through the mechanisms of intermolecular ionic interaction and entanglement of polyphosphate chains. The potential application of ACPP hydrogel as a ceramic matrix for sustained drug release warrants further investigation.

Description: Melting gels are hybrid gels that have the ability to soften and flow at around 100°C for some combinations of mono- and di-substituted alkoxysiloxanes, where substitutions are either all aromatic or all aliphatic. In this study, melting gels were prepared using phenyltriethoxysilane (PhTES) and dimethyldiethoxysilane (DMDES), meaning both an aromatic and aliphatic substitution. Differential scanning calorimetry was performed to identify glass-transition temperatures, and thermal gravimetric analysis coupled with differential thermal analysis (TGA-DTA) was performed to measure weight loss. The glass-transition temperatures ( T g ) ranged from −61°C to +5.6°C, which are between the values in the methyl only system, where all T g values are less than 0°C, and those values in the phenyl only system, where T g values are greater than 0°C. The T g decreased with an increase in the DMDES fraction. Below 450°C, the gels lost little weight, but around 600°C there was a drop in weight. This temperature is lower than the temperature for gels prepared with only aromatic substitutions, but higher than that for gels prepared with only aliphatic substitutions. Final heat treatment was carried out at 150°C for the gel with 80%PhTES-20%DMDES (in mol%), and the consolidation temperature increased with increasing DMDES content to 205°C for the gel with 50%PhTES-50%DMDES. After this heat treatment, the melting gels no longer soften.

Description: Direct integration of nanostructures into macroscopic substrates is very important for their practical applications. In this work, we report a simple method that can be introduced for the Sn-catalyzed growth of alumina nanowires on ceramic substrates such as porous disk, monolith, and foam. Our study focuses on the role of the Sn catalysts in the formation mechanisms governing nanowire growth. Using the proposed approach, hair- or grass-like tufts of 20 nm diameter nanowires grow on the surface of the ~3 μm diameter Sn particles, in a tip growth mechanism. The nanowires of α-phased polycrystalline structure grow and are packed via a complex process involving batch-by-batch, branching, and amalgamation growth. The detailed observations reveal that the Sn catalyst is key to tailoring the growth patterns of the nanowires. In addition, cathodoluminescence studies highlight the potential optical applications of the alumina nanowires.

Description: Flash sintering is a nonlinear phenomenon characterized by a sharp increase in the conductivity of the sample and concomitant rapid densification under an electric field in low temperatures in a matter of seconds. Since it is a transient phenomenon, the power dissipation on the sample is not uniform during the process. Thus, a transient analysis is needed to estimate the temperature of the sample during flash sintering due to Joule heating. In this work, the Finite Element Method on a coupled electrothermal nonlinear analysis was used in order to obtain the specimen temperature of 8YSZ after 5 s of flashing. The results agree with the experimental data obtained by the flashing of dense samples and with previous literature.

Description: Temperature-dependent in-situ Raman spectroscopy is used to investigate the phase transformation of zinc metastannate (ZnSnO 3 ) to zinc orthostannate (Zn 2 SnO 4 ) induced upon annealing in the ambient. ZnSnO 3 microcubes (MCs) were synthesized at room temperature using a simple aqueous synthesis process, followed by characterization using electron microscopy, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). Annealing of the ZnSnO 3 MCs was carried out up to 1000°C, while recording the Raman spectra in-situ at regular intervals. Phase transformation from metastannate to orthostannate was found to begin around 500°C with an activation energy of ~0.965 eV followed by the recrystallization into the inverse spinel orthostannate phase at ~750°C. Results from this study provide detailed understanding of the phase transformation behavior of perovskite ZnSnO 3 to inverse spinel Zn 2 SnO 4 upon thermal annealing.

Description: High Arctic landscapes are expansive and changing rapidly. However our understanding of their functional responses and potential to mitigate or enhance anthropogenic climate change is limited by few measurements. We collected eddy covariance measurements to quantify the net ecosystem exchange (NEE) of CO 2 with polar semidesert and meadow wetland landscapes at the highest-latitude location measured to date (82°N). We coupled these rare data with ground and satellite vegetation production measurements (Normalized Difference Vegetation Index; NDVI) to evaluate the effectiveness of upscaling local to regional NEE. During the growing season, the dry polar semidesert landscape was a near zero sink of atmospheric CO 2 (NEE: -0.3±13.5 g C m −2 ). A nearby meadow wetland accumulated over 300 times more carbon (NEE: -79.3±20.0 g C m −2 ) than the polar semidesert landscape, and was similar to meadow wetland NEE at much more southerly latitudes. Polar semidesert NEE was most influenced by moisture, with wetter surface soils resulting in greater soil respiration and CO 2 emissions. At the meadow wetland, soil heating enhanced plant growth, which in turn increased CO 2 uptake. Our upscaling assessment found that polar semidesert NDVI measured on site was low (mean: 0.120-0.157) and similar to satellite measurements (mean: 0.155-0.163). However, weak plant growth resulted in poor satellite NDVI-NEE relationships and created challenges for remotely-detecting changes in the cycling of carbon on the polar semidesert landscape. The meadow wetland appeared more suitable to assess plant production and NEE via remote-sensing, however high Arctic wetland extent is constrained by topography to small areas that may be difficult to resolve with large satellite pixels. We predict that until summer precipitation and humidity increases substantially, climate-related changes of dry high Arctic landscapes may be restricted by poor soil moisture retention, and therefore have some inertia against short-term changes in NEE. This article is protected by copyright. All rights reserved.

Description: We believe that there are too many models in hydrology and we should ask ourselves the question, if we are currently wasting time and effort in developing another model again instead of focusing on the development of a community hydrological model. In other fields this kind of models have been quite successful, but due to several reasons, no single community model has been developed in the field of hydrology yet. The concept, strength and weakness of a community model was discussed at the Chapman Conference on Catchment Spatial Behaviour and Complex Organisation held in Luxembourg in September 2014. This discussion as well as out own opinions about the potential of a community models, or at least the necessary discussion to establish one are debated in this commentary. This article is protected by copyright. All rights reserved.

Description: Here, we demonstrate the relationship between glass network topological structure and the chemical state of embedded lanthanide ions. It is revealed that a more dispersed state of lanthanide ions is shown in more constrained 3D rigid network, which delivers valuable information toward homogeneous doping in glasses from the perspective of glass topological structure. The results are believed to be of great significances in the development of advanced optoelectronic devices like high-power laser, efficient fiber amplifier, smaller integrated photonic circuit, etc.

Description: The mechanofusion process, a dry particle coating route, has been successfully applied to coat micrometric SiC particles with submicrometric Ni filaments. In a first step, the mechanofusion parameters were optimized to form a continuous Ni coating onto SiC particles. In a second step, the Ni-coated SiC particles were sintered by hot isostatic pressing. The temperature and pressure cycles were determined to ensure a good densification of the material. Such a densification process leads to the formation of a δ-Ni 2 Si bilayer at the SiC/Ni interface; the inner δ-Ni 2 Si layer in contact with SiC being more rich in carbon than the one in contact with the matrix. From X-ray diffraction, wavelength-dispersive X-ray spectrometry and scanning electron microscopy characterizations, a mechanism is proposed to explain the microstructure of the end-product.

Description: Soil surface sealing is a widespread natural process occurring frequently in bare soil areas between vegetation patches. The low hydraulic conductivity that characterizes the seal layer reduces both infiltration and evaporation fluxes from the soil, and thus has the potential to affect local vegetation water uptake (VWU). This effect is investigated here using experimental data, 2D physically based modelling and a long-term climatic dataset from three dry sites presenting a climatic gradient in the Negev Desert, Israel. The Feddes VWU parameters for the dominant shrub at the study site ( Sarcopoterium spinosum ) were acquired using lysimeter experiments. The results indicate that during the season surface sealing could either increase or decrease VWU depending on initial soil water content, rainfall intensity, and the duration of the subsequent drying intervals. These factors have a marked effect on inter-annual variability of the seal layer effect on VWU, which on average was found to be 26% higher under sealed conditions than in the case of unsealed soil surfaces. The seal layer was found to reduce the period where the vegetation was under water stress by 31% compared with unsealed conditions. This effect was more pronounced for seasons with total rainfall depth higher than 10 cm/y, and was affected by interseasonal climatic variability. These results shed light on the importance of surface sealing in dry environments and its contribution to the resilience of woody vegetation. This article is protected by copyright. All rights reserved.

Description: Urban areas are expanding rapidly in tropical regions, with potential to alter ecosystem dynamics. In particular, exotic grasses and atmospheric nitrogen (N) deposition simultaneously affect urbanized landscapes, with unknown effects on properties like soil carbon (C) storage. We hypothesized that: (H1.) Soil nitrate (NO 3 - ) is elevated nearer to the urban core, reflecting N deposition gradients. (H2.) Exotic grasslands have drier soils, elevated NO 3 - , and decreased soil C relative to secondary forests, with higher N promoting decomposer activity. (H3.) Exotic grasslands have greater seasonality in soil NO 3 - versus secondary forests, due to higher sensitivity of grassland soil moisture to rainfall. We predicted that NO 3 - would be related to dissolved organic C (DOC) production via changes in decomposer activity. We measured six paired grassland/secondary-forest sites along a tropical urban-to-rural gradient during three dominant seasons (hurricane, dry, and early wet). We found that: (1.) Soil NO 3 - was generally elevated near the urban core, with particularly clear spatial trends for grasslands. (2.) Exotic grasslands had lower soil C than secondary forests, which was related to elevated decomposer enzyme activities and soil respiration. Unexpectedly, soil NO 3 - was negatively related to enzyme activities, and was higher in forests than grasslands. (3.) Grasslands had greater soil NO 3 - seasonality versus forests, but this was not strongly linked to shifts in soil moisture or DOC. Our results suggest that exotic grasses in tropical regions are likely to drastically reduce soil C storage, but that N deposition may have an opposite effect via suppression of enzyme activities. However, soil NO 3 - accumulation here was higher in urban forests than grasslands, potentially due to an interplay of aboveground N interception and soil processes. Net urban effects on C storage across tropical landscapes will likely vary depending on rates of N deposition, the mosaic of land covers, and responses by local decomposer communities. This article is protected by copyright. All rights reserved.

Description: Soils are subject to varying degrees of direct or indirect human disturbance, constituting a major global change driver. Factoring out natural from direct and indirect human influence is not always straightforward, but some human activities have clear impacts. These include land use change, land management, and land degradation (erosion, compaction, sealing and salinization). The intensity of land use also exerts a great impact on soils, and soils are also subject to indirect impacts arising from human activity, such as acid deposition (sulphur and nitrogen) and heavy metal pollution. In this critical review, we report the state-of-the-art understanding of these global change pressures on soils, identify knowledge gaps and research challenges, and highlight actions and policies to minimise adverse environmental impacts arising from these global change drivers. Soils are central to considerations of what constitutes sustainable intensification. Therefore, ensuring that vulnerable and high environmental value soils are considered when protecting important habitats and ecosystems, will help to reduce the pressure on land from global change drivers. To ensure that soils are protected as part of wider environmental efforts, a global soil resilience programme should be considered, to monitor, recover or sustain soil fertility and function, and to enhance the ecosystem services provided by soils. Soils cannot, and should not, be considered in isolation of the ecosystems that they underpin and vice versa. The role of soils in supporting ecosystems and natural capital needs greater recognition. The lasting legacy of the International Year of Soils in 2015 should be to put soils at the centre of policy supporting environmental protection and sustainable development. This article is protected by copyright. All rights reserved.

Description: The response of soil organic carbon (SOC) pools to globally rising surface temperature crucially determines the feedback between climate change and the global carbon cycle. However, there is a lack of studies investigating the temperature sensitivity of decomposition for decadally cycling SOC which is the main component of total soil carbon stock and the most relevant to global change. We tackled this issue by using two decadally 13 C-labeled soils and a much improved measuring system in a long-term incubation experiment. Results indicated that the temperature sensitivity of decomposition for decadally-cycling SOC (〉 23 years in one soil and 〉 55 years in the other soil) was significantly greater than that for faster-cycling SOC (〈 23 or 55 years) or for the entire SOC stock. Moreover, decadally-cycling SOC contributed substantially (35-59%) to the total CO 2 loss during the 360-day incubation. Overall, these results indicate that the decomposition of decadally-cycling SOC is highly sensitive to temperature change, which will likely make this large SOC stock vulnerable to loss by global warming in the 21 st century and beyond. This article is protected by copyright. All rights reserved.

Description: Female salmonids bury and lay their eggs in streambeds by digging a pit, which is then covered with sediment from a second pit. The spawning process alters streambed topography, winnows fine sediment, and mixes sediment in the active layer. The resulting egg nests (redds) contain coarser and looser sediments than those of unspawned streambed areas, and display a dune-like shape with an amplitude and length that vary with fish size, substrate conditions, and flow conditions. Redds increase local bed surface roughness (〈10 −1 channel width, W ), but may reduce the size of macro-bedforms by eroding reach scale topography (10 ° -10 1 W ). Research has suggested that spawning may increase flow resistance due to redd form drag, resulting in lower grain shear stress and less particle mobility. Spawning however also prevents streambed armoring through surface and subsurface material mixing, potentially increasing particle mobility. Here, we use 2-dimensional hydraulic modeling with detailed pre- and post-spawning bathymetries and field observations to test the effect of small spawning salmonids on sediment transport. Our results show that topographical roughness added by small-bodied salmon redds has negligible effects on shear stress at the reach-unit scale, and limited effects at the local scale. Conversely, our results indicate sediment mixing reduces armoring and enhances sediment mobility, which increases potential bed load transport by subsequent floods. River restoration in fish-bearing streams should take into consideration the effects of redd excavation on channel stability. This is particularly important for streams that historically supported salmonids, and at present are the focus of habitat restoration actions. This article is protected by copyright. All rights reserved.