ALBERT

Description: ABSTRACT A reactive transport modeling framework is presented that allows simultaneous assessment of groundwater flow, water quality evolution including δ 13 C, and 14 C activity or “age”. Through application of this framework, simulated 14 C activities can be directly compared with measured 14 C activities. This bypasses the need for interpretation of a 14 C age prior to flow simulation through factoring out processes other than radioactive decay, which typically involves simplifying assumptions regarding spatial and temporal variability in reactions, flow, and mixing. The utility of the approach is demonstrated for an aquifer system with spatially variable carbonate mineral distribution, multiple organic carbon sources, and transient boundary conditions for 14 C activity in the recharge water. In this case the simulated 14 C age was shown to be relatively insensitive to isotopic fractionation during DOC oxidation and variations in assumed DOC degradation behaviour. We demonstrate that the model allows quantitative testing of hypotheses regarding controls on groundwater age and water quality evolution for all three carbon isotopes. The approach also facilitates incorporation of multiple environmental tracers and combination with parameter optimization techniques. This article is protected by copyright. All rights reserved.

Description: Water scarcity is likely to increase in the coming years, making improvements in irrigation efficiency increasingly important. An emerging technology that promises to increase irrigation efficiency substantially is a wireless irrigation sensor network that uploads sensor data into irrigation management software, creating an integrated system that allows real-time monitoring and control of moisture status that has been shown in experimental settings to reduce irrigation costs, lower plant loss rates, shorten production times, decrease pesticide application, and increase yield, quality, and profit. We use an original survey to investigate likely initial acceptance, ceiling adoption rates, and profitability of this new sensor network technology in the nursery and greenhouse industry. We find that adoption rates for a base system and demand for expansion components are decreasing in price, as expected. The price elasticity of the probability of adoption suggests that sensor networks are likely to diffuse at a rate somewhat greater than that of drip irrigation. Adoption rates for a base system and demand for expansion components are increasing in specialization in ornamental production: Growers earning greater shares of revenue from greenhouse and nursery operations are willing to pay more for a base system and are willing to purchase larger numbers of expansion components at any given price. We estimate that growers who are willing to purchase a sensor network expect investment in this technology to generate significant profit, consistent with findings from experimental studies. This article is protected by copyright. All rights reserved.

Description: Herein, we report on the crystal structures of Nb 2 AlC and TiNbAlC—actual composition (Ti 0.45 ,Nb 0.55 ) 2 AlC—compounds determined from Rietveld analysis of neutron diffraction patterns in the 300–1173 K temperature range. The average linear thermal expansion coefficients of a Nb 2 AlC sample in the a and c directions are, respectively, 7.9(5) × 10 −6 and 7.7(5) × 10 −6  K −1 on one neutron diffractometer and 7.3(3) × 10 −6 and 7.0(2) × 10 −6  K −1 on a second diffractometer. The respective values for the (Ti 0.45 ,Nb 0.55 ) 2 AlC composition—only tested on one diffractometer—are 8.5(3) × 10 −6 and 7.5(5) × 10 −6  K −1 . These values are relatively low compared to other MAX phases. Like other MAX phases, however, the atomic displacement parameters (APDs) show that the Al atoms vibrate with higher amplitudes than the Ti and C atoms, and more along the basal planes than normal to them. When the predictions of the APDs obtained from density functional theory are compared to the experimental results, good quantitative agreement is found for the Al atoms. In case of the Nb and C atoms, the agreement was more qualitative.

Description: In this study, lithium disilicate (LS 2 ) glass samples with different particle sizes ranging from less than 105 to 850 μm were prepared. These specimens were inserted in a Pt-Rh DSC crucible and heated to 850°C at different rates (ϕ = 0.5–30 K/min) to identify their crystallization peaks. The activation energies for the overall crystallization ( E ) and the Avrami coefficient ( n ) were evaluated using different nonisothermal models. Specifically, n was evaluated using the Augis–Benett model and the Ozawa method, and E was evaluated using the Kissinger and Ligero methods. As expected, the coarse particles mainly crystallized in the volume, while surface crystallization was predominant in the samples with particle sizes of less than 350 μm. This result was confirmed through SEM analysis of the double stage heat-treated samples. In contrast with previous studies, our results demonstrated that the activation energy decreased as the particle size increased. In addition, no clear correlation between the peak intensity (δ T p ) and the particle size was observed.

Description: This technical note presents a useful methodology for studying how the variance of hydraulic and/or reactive attributes of an aquifer are linked to the multi-scaled and hierarchical sedimentary architecture of the aquifer. A new recursive equation is derived which quantitatively describes how the variance is related to sedimentary facies defined at all scales across an entire stratal hierarchy. As compared to prior published equations that emphasize differences in means among facies populations within a hierarchical level, it emphasizes differences across levels. Because of the hierarchical relationships among the terms of the equation, we find it to be useful for conducting a holistic analysis of the relative contributions to the variance arising from all facies types defined across all scales. The methodology is demonstrated using appropriate field data, and is shown to be useful in defining parsimonious classification systems.

Description: ABSTRACT A primary concern for geologic carbon storage is the potential for leakage of stored carbon dioxide (CO 2 ) into the shallow subsurface where it could degrade the quality of groundwater and surface water. In order to predict and mitigate the potentially negative impacts of CO 2 leakage, it is important to understand the physical processes that CO 2 will undergo as it moves through naturally heterogeneous porous media formations. Previous studies have shown that heterogeneity can enhance the evolution of gas phase CO 2 in some cases, but the conditions under which this occurs have not yet been quantitatively defined, nor tested through laboratory experiments. This study quantitatively investigates the effects of geologic heterogeneity on the process of gas phase CO 2 evolution in shallow aquifers through an extensive set of experiments conducted in a column that was packed with layers of various test sands. Soil moisture sensors were utilized to observe the formation of gas phase near the porous media interfaces. Results indicate that the conditions under which heterogeneity controls gas phase evolution can be successfully predicted through analysis of simple parameters, including the dissolved CO 2 concentration in the flowing water, the distance between the heterogeneity and the leakage location, and some fundamental properties of the porous media. Results also show that interfaces where a less permeable material overlies a more permeable material affect gas phase evolution more significantly than interfaces with the opposite layering.

Description: Fluvial sediment loads are frequently calculated with rating curves fit to measured sediment transport rates. Rating curves are often treated as statistical representations in which the fitted parameters have little or no physical meaning. Such models, however, may produce large errors when extrapolation is needed, and they provide no insight into the sediment transport process. It is shown that log-linear least squares, the usual method for fitting rating curves, does not generally produce physically meaningful parameter values. In addition, it cannot accommodate data that include zero-transport samples. Alternative fitting methods based non-linear least squares and on maximum likelihood parameter estimation are described and evaluated. The maximum likelihood approach is shown to fit synthetic data better than linear or non-linear least squares, and to perform well with data that include zero-transport samples. In contrast, non-linear least squares methods produce large errors in the parameter estimates when zero-transport samples are present or when the variance structure of the data is incorrectly specified. Analyses with fractional bedload data from a mountain stream suggest that bedload transport rates are gamma distributed, that the arrivals of bedload particles in a sampler conform to a Poisson distribution, and that the variance of non-zero samples can be expressed as a power function of the mean. Preliminary physical interpretations of variations in the rating curve parameters fit to fractional bedload data with the maximum likelihood method are proposed, and their relation to some previous interpretations of rating curve parameters are briefly discussed. This article is protected by copyright. All rights reserved.

Description: In this letter, 2-μm Pb 0.97 La 0.02 (Zr 0.75 Sn 0.18 Ti 0.07 )O 3 antiferroelectric thick film with tetragonal structure was prepared. The effects of operating electric field, temperature, and frequency on the thermal–electrical energy harvesting capacity of the film were studied by using the Olsen cycle. The results demonstrated that giant energy harvesting effect could be realized in the antiferroelectric thick film. The maximum harvestable energy density per cycle of the film was about 7.8 J/cm 3 at 1 kHz, which was the largest reported value to date. The corresponding energy harvesting efficiency was 0.53%. Moreover, the film had a low leakage current density (about 7.3 × 10 −7 and 3.9 × 10 −5  A/cm 2 at 25 and 200°C, respectively), which was favorable for its application in the devices of the thermal–electrical energy harvesting.

Description: Discharged energy properties of PbO–SrO–Na 2 O–Nb 2 O 5 –SiO 2 glass-ceramics with crystallization time from 1 to 1000 min were investigated by measuring their hysteresis loops (described as quasi-static measuring method) and pulse-discharge current-time curves (described as dynamic measuring method). The results show the same trend for both measuring methods: With the increment of crystallization time, the discharged energy density increases gradually, while the energy efficiency decreases. The highest energy efficiencies were obtained in the sample with crystallization time of 1 min, which are 96.3% and 82.4%, corresponding quasi-static and dynamic measurement, respectively. The reduction of energy efficiency with crystallization time is attributed to combined effect of ferroelectric polarization and interfacial polarization, and part of the corresponding energy could not release in the pulse-discharge process.

Description: New lead-free perovskite solid solution ceramics of (1  − x )( Bi 1/2 Na 1/2 ) TiO 3 – x Ba ( Ni 1/2 Nb 1/2 ) O 3 [(1− x )BNT– x BNN, x  =   0.02–0.06) were prepared and their dielectric, ferroelectric, piezoelectric, and electromechanical properties were investigated as a function of the BNN content. The X-ray diffraction results indicated that the addition of BNN has induced a morphotropic phase transformation from rhombohedral to pseudocubic symmetry approximately at x  =   0.045, accompanying an evolution of dielectric relaxor behavior as characterized by enhanced dielectric diffuseness and frequency dispersion. In the proximity of the ferroelectric rhombohedral and pseudocubic phase coexistence zone, the x  =   0.045 ceramics exhibited optimal piezoelectric and electromechanical coupling properties of d 33 ~121 pC/N and k p ~0.27 owing to decreased energy barriers for polarization switching. However, further addition of BNN could cause a decrease in freezing temperatures of polar nanoregions till the coexistence of nonergodic and ergodic relaxor phases occurred near room temperature, especially for the x  =   0.05 sample which has negligible negative strains and thus show the maximum electrostrain of 0.3% under an external electric field of 7 kV/mm, but almost vanished piezoelectric properties. This was attributed to the fact that the induced long-range ferroelectric order could reversibly switch back to its original ergodic state upon removal of external electric fields.

Description: Light transmission in polycrystalline magnesium fluoride was studied as a function of the mean grain size at different wavelengths. The mean grain size was varied by annealing hot-pressed billets in argon atmosphere at temperatures ranging from 600°C to 800°C for 1 h. The grain-size and grain-orientation distributions were characterized by electron back scatter diffraction. The scattering coefficients were calculated from the in-line transmittance measured at various wavelengths. The scattering coefficient of polycrystalline magnesium fluoride increased linearly with the mean grain size and inversely with the square of the wavelength of light. It is shown that these trends are consistent with theoretical models based on both a limiting form of the Raleigh–Gans–Debye (RGD) theory of particle scattering and light retardation theories that take refractive index variations along the light path. Quantitative predictions of the theories are, however, subject to uncertainly due to the restrictive assumptions made in the theories and difficulties in representing the microstructure in the theoretical models. In particular, grain-size distribution has a significant influence on the scattering coefficient calculated using particle scattering models.

Description: Determining the absolute chronology of ceramic artifacts has significant implications for archeological and historical research. Wilson, Hall et al . recently suggested a new technique for direct absolute dating of archeological ceramics based on a moisture-induced chemical reaction, called rehydroxylation (RHX) dating. RHX dating proceeds by measuring the mass of chemically combined water in the ceramics in the form of OH hydroxyls, and the mass gain rate at the Effective Lifetime Temperature (ELT) that the ceramics experienced over its lifetime. To date, ELT determinations have been based on estimates of the ceramic's lifetime temperature history; taking into account weather and climate data and the depth at which the artifact was found. The uncertainty in determining the ELT can be a major component of the overall dating uncertainty. Here, we propose an alternative method which relies minimally on weather and climate data, and provides more precise determinations of the ELT and the ceramic age . The proposed method (SAS: Same Age Samples) involves a minimum of four measurements of the RHX mass gain rate constant for two ceramic samples of the same age at two temperatures. We show via simulations that the proposed SAS method can determine the ELT with a precision of 0.2 K which is comparable to the best ELT determination based on lifetime temperature history, and also comparable to available microbalance temperature resolutions of around 0.1 K. The corresponding percent age error is then 1.4%, or 43 yr for a 3000-yr-old ceramic. The proposed SAS method should be tested with ceramic samples of different ages, whose ELT are well-known.

Description: Glasses in the Na 2 O–CaO–SrO–ZnO–SiO 2 system have previously been investigated for suitability as a reagent in Al-free glass polyalkenoate cements (GPCs). These materials have many properties that offer potential in orthopedics. However, their applicability has been limited, to date, because of their poor strength. This study was undertaken with the aim of increasing the mechanical properties of a series of these Zn-based GPC glasses by doping with nitrogen to give overall compositions of: 10Na 2 O–10CaO–20SrO–20ZnO–(40−3 x )SiO 2 – x Si 3 N 4 ( x is the no. of moles of Si 3 N 4 ). The density, glass-transition temperature, hardness, and elastic modulus of each glass were found to increase fairly linearly with nitrogen content. Indentation fracture resistance also increases with nitrogen content according to a power law relationship. These increases are consistent with the incorporation of N into the glass structure in threefold coordination with silicon resulting in extra cross-linking of the glass network. This was confirmed using 29 Si MAS-NMR which showed that an increasing number of Q 2 units and some Q 3 units with extra bridging anions are formed as nitrogen content increases at the expense of Q 1 units. A small proportion of Zn ions are found to be in tetrahedral coordination in the base oxide glass and the proportion of these increases with the presence of nitrogen.

Description: This paper presents the results of a comprehensive model-based analysis of a uranyl [U(VI)] tracer test conducted at the U.S. DOE Hanford 300 Area (300A) IFRC. Despite the highly complex field conditions the numerical three-dimensional multi-component reactive transport model was able to capture most of the spatiotemporal variations of the observed U(VI) concentrations. A multi-model analysis was performed to interrogate the relative importance of various processes and factors for controlling field-scale reactive transport during the uranyl tracer test. The results indicate that multi-rate sorption/desorption, surface complexation reactions, and initial concentrations were the most important processes and factors controlling U(VI) migration. On the other hand, cation exchange reactions, the choice of the surface complexation model, and dual-domain mass transfer processes played less important roles under the prevailing field-test condition. Further analysis of the modeling results demonstrates that these findings are conditioned to the relatively stable groundwater chemistry and the selected length of the field experimental duration (16 days). The model analysis also revealed the crucial role of the intraborehole flow that occurred within the long-screened monitoring wells and thus affected both field measurements and simulated U(VI) concentrations as a combined effect of aquifer heterogeneity and dynamic flow conditions. This study provides the first highly data-constrained uranium transport simulations under highly dynamic flow conditions. It illustrates the value of reactive transport modeling for elucidating the relative importance of individual processes in controlling uranium transport under specific field-scale conditions.

Description: The dynamics of drying processes from porous media are critically influenced by the intensity of an adjacent free flow and by processes at the interface between free flow and the porous medium. In this paper, the influence of hydraulic properties of a porous medium and of the interaction between fluids and porous medium on the drying dynamics during the capillary-flow dominated stage-1 and transition to the diffusion-dominated stage-2 are studied using a coupled free-flow - porous-medium flow model on the REV scale. We present a detailed model concept that considers mass balance equations, an energy balance equation and the coupling to the adjacent free flow. Key microscale processes are identified and incorporated in the macroscale description of the evaporation process. Own experimental results are used to illustrate main features of the modeling framework. We demonstrate that the use of a homogeneous distribution of soil parameters without consideration of pore-scale induced nonlinearities in the numerical simulations results in a rather constant drying rate in stage-1, which was not observed for the high evaporative demand in the experiments. To account for the dependency of the drying rate on the surface moisture content, special conditions based on the work of Haghighi et al. [2013] and Schlünder [1988] are analyzed for their applicability on the REV scale. Typical features of a drying process, such as different stages of the drying rate, could be reproduced.

Description: Making useful predictions in ungauged basins is an incredibly difficult task given the limitations of hydrologic models to represent physical processes appropriately across the heterogeneity within and among different catchments. Here, we introduce a new method for this challenge, Bayes empirical Bayes, that allows for the statistical pooling of information from multiple donor catchments and provides the ability to transfer parametric distributions rather than single parameter sets to the ungauged catchment. Further, the methodology provides an efficient framework with which to formally assess predictive uncertainty at the ungauged catchment. We investigated the utility of the methodology under both synthetic and real data conditions, and with respect to its sensitivity to the number and quality of the donor catchments used. This study highlighted the ability of the hierarchical Bayes empirical Bayes approach to produce expected outcomes in both the synthetic and real data applications. The method was found to be sensitive to the quality (hydrologic similarity) of the donor catchments used. Results were less sensitive to the number of donor catchments, but indicated that predictive uncertainty was best constrained with larger numbers of donor catchments (but still adequate with fewer donors)

Description: Autumn is a season of dynamic change in forest streams of the northeastern USA due to effects of leaf fall on both hydrology and biogeochemistry. Few studies have explored how interactions of biogeochemical transformations, various nitrogen sources, and catchment flowpaths affect stream nitrogen variation during autumn. To provide more information on this critical period, we studied 1) the timing, duration, and magnitude of changes to stream nitrate, dissolved organic nitrogen (DON), and ammonium concentrations; 2) changes in nitrate sources and cycling; and 3) source areas of the landscape that most influence stream nitrogen. We collected samples at higher temporal resolution for a longer duration than typical studies of stream nitrogen during autumn. This sampling scheme encompassed the patterns and extremes that occurred during baseflow and stormflow events of autumn. Baseflow nitrate concentrations decreased by an order of magnitude from 5.4 to 0.7 μmol L -1 during the week when most leaves fell from deciduous trees. Changes to rates of biogeochemical transformations during autumn baseflow explained the low nitrate concentrations; in-stream transformations retained up to 72% of the nitrate that entered a stream reach. A decrease of in-stream nitrification coupled with assimilatory nitrate uptake was a primary factor in the seasonal nitrate decline. The period of low nitrate concentrations ended with a storm event in which stream nitrate concentrations increased by 25 fold. In the ensuing weeks, stormflow nitrate concentrations progressively decreased over closely-spaced, yet similarly sized events. Most stormflow nitrate originated from nitrification in near-stream areas with occasional, large inputs of unprocessed atmospheric nitrate, which has rarely been reported for non-snowmelt events. A maximum input of 33% unprocessed atmospheric nitrate to the stream occurred during one event. The large inputs of unprocessed atmospheric nitrate show direct and rapid effects on forest streams that may be widespread, although undocumented, throughout nitrogen-polluted temperate forests. In contrast to a week-long nitrate decline during peak autumn litterfall, baseflow DON concentrations increased after leaf fall and remained high for two months. Dissolved organic nitrogen was hydrologically flushed to the stream from riparian soils during stormflow. In contrast to distinct seasonal changes in baseflow nitrate and DON concentrations, ammonium concentrations were typically at or below detection limit, similar to the rest of the year. Our findings reveal couplings among catchment flow paths, nutrient sources and transformations that control seasonal extremes of stream nitrogen in forested landscapes.

Description: During the recent years there has been an increasing interest in multivariate frequency analysis of hydrological variables, e.g. those describing extreme events like rainfall, floods or droughts. The multivariate analysis provides a better understanding of the phenomena under investigation and an additional insight about the interrelationships between the different variables (e.g. peak, volume and duration of the flood), exploiting the complete structure of the problem and making a full use of the available data. However, while the developments on multivariate analysis of hydrological data has produced a large body of literature, a clear assessment of the use of these methods in the design and risk assessment of hydraulic structures is still a matter of debate. In the present work we illustrate a general, structure-based framework for the design and/or risk assessment of hydraulic structures in a bivariate environment; we also compare it to recently proposed methods which are based on the assumption of hydrological design events (as is customary in the univariate context). For illustration purposes, both the structure-based and the design event-based approaches are applied to the design of an idealized structure, thus exploring the differences among the methods as function of the parameters involved. Our work highlights that the return period of structure failure in a multivariate environment strictly depends on the particular structure under design, and in most cases the design of an hydraulic structure cannot be based on a single, hydrological multivariate design event. This acts as a warning for practitioners against the use of design methods based on single hydrological events, as usually done in the context of univariate hydrology, thus neglecting the interplay between the structure and the hydrological loads acting on it.

Description: Proliferation of evapotranspiration (ET) products warrants comparison of these products. The study objective was to assess uncertainty in ET output from four land surface models (LSMs), Noah, Mosaic, VIC, and SAC in NLDAS-2, two remote sensing-based products, MODIS and AVHRR, and GRACE-inferred ET from a water budget with precipitation from PRISM, monitored runoff, and total water storage change (TWSC) from GRACE satellites. The three cornered hat method, which does not require a priori knowledge of the true ET value, was used to estimate ET uncertainties. In addition, TWSC or total water storage anomaly (TWSA) from GRACE was compared with water budget estimates of TWSC from a flux-based approach or TWSA from a storage-based approach. The analyses were conducted using data from three regions (humid – arid) in the South Central US as case studies. Uncertainties in ET are lowest in LSM ET (~5 mm/month), moderate in MODIS- or AVHRR-based ET (10 – 15 mm/month), and highest in GRACE-inferred ET (20 – 30 mm/month). There is a tradeoff between spatial resolution and uncertainty, with lower uncertainty in the coarser-resolution LSM ET (~14 km) relative to higher uncertainty in the finer-resolution (~ 1 ‒ 8 km) RS ET. Root-mean-square (RMS) of uncertainties in water budget estimates of TWSC is about half of RMS of uncertainties in GRACE-derived TWSC for each of the regions. Future ET estimation should consider a hybrid approach that integrates strengths of LSMs and satellite-based products to constrain uncertainties.

Description: It is well documented that deforestation results in an increase in landslide frequency due to the control that forest roots have on slope stability. The loss of forest vegetation leads to a reduction in soil cohesion and a decrease in the shear strength of the soil profile. As a result, the slope becomes more susceptible to landsliding and the return time of landslides decreases. When a landslide removes the soil profile, there may not be adequate time for seedlings to grow and enhance soil stability. In this study, we investigate whether bistable dynamics emerge from the interaction of forest vegetation with the formation and accumulation of colluvial deposits in soil-mantled landscapes. To that end, we develop deterministic and stochastic models of landslide occurrence with a dynamic vegetation component. Results show that bistability exists for the deterministic case for both steep and shallow hollows under event and supply limited conditions. However, for the stochastic case, the randomness of landslide occurrence largely changed the states of the system such that the system only exhibited one stable state, which was the fully vegetated condition. Examining different management practices under stochastic conditions showed that the system eventually recovered; however, management practices influenced the recovery time of the forest. Thus, different management practices could render the land in a state of low vegetation over economically significant time periods.

Description: Seepage flux from ephemeral streams can be an important component of the water balance in arid and semi-arid regions. An emerging technique for quantifying this flux involves the measurement and simulation of a flood wave as it moves along an initially dry channel. This study investigates the usefulness of including surface water and groundwater data to improve model calibration when using this technique. We trialed this approach using a controlled flow event along a 1387 m reach of artificial stream channel. Observations were then simulated using a numerical model that combines the diffusion wave approximation of the Saint-Vénant equations for streamflow routing, with Philips’ infiltration equation and the groundwater flow equation. Model estimates of seepage flux for the upstream segments of the study reach, where streambed hydraulic conductivities were approximately 10 1 m d -1 , were on the order of 10 -4 m 3 d -1 m -2 . In the downstream segments, streambed hydraulic conductivities were generally much lower but highly variable (~10 -3 – 10 -7 m d -1 ). The Latin Hypercube Monte Carlo sensitivity analysis showed that the flood front timing, surface water stage, groundwater heads and the predicted stream flow seepage were most influenced by specific yield. Furthermore, inclusion of groundwater data resulted in a higher estimate of total seepage estimates than if the flood front timing were used alone.

Description: Ecological Applications, Volume 24, Issue 1, Page 3, January 2014.

Description: Ecological Applications, Volume 24, Issue 1, Page 23-24, January 2014.

Description: Ecological Applications, Volume 24, Issue 1, Page 227-228, January 2014.

Description: Ecological Applications, Volume 24, Issue 1, Page 71-83, January 2014. Concerns about bycatch of protected species have become a dominant factor shaping fisheries management. However, efforts to mitigate bycatch are often hindered by a lack of data on the distributions of fishing effort and protected species. One approach to overcoming this problem has been to overlay the distribution of past fishing effort with known locations of protected species, often obtained through satellite telemetry and occurrence data, to identify potential bycatch hotspots. This approach, however, generates static bycatch risk maps, calling into question their ability to forecast into the future, particularly when dealing with spatiotemporally dynamic fisheries and highly migratory bycatch species. In this study, we use boosted regression trees to model the spatiotemporal distribution of fishing effort for two distinct fisheries in the North Pacific Ocean, the albacore (Thunnus alalunga) troll fishery and the California drift gillnet fishery that targets swordfish (Xiphias gladius). Our results suggest that it is possible to accurately predict fishing effort using

Description: We present a probabilistic sediment cascade model to simulate sediment transfer in a mountain basin (Illgraben, Switzerland) where sediment is produced by hillslope landslides and rockfalls and exported out of the basin by debris flows and floods. The model conceptualizes the fluvial system as a spatially lumped cascade of connected reservoirs representing hillslope and channel storages where sediment goes through cycles of storage and remobilization by surface runoff. The model includes all relevant hydrological processes that lead to runoff formation in an Alpine basin, such as precipitation, snow accumulation, snow melt, evapotranspiration, and soil water storage. Although the processes of sediment transfer and debris flow generation are described in a simplified manner, the model produces complex sediment discharge behavior which is driven by the availability of sediment and antecedent wetness conditions (system memory) as well as the triggering potential (climatic forcing). The observed probability distribution of debris flow volumes and their seasonality in 2000-2009 are reproduced. The stochasticity of hillslope sediment input is important for reproducing realistic sediment storage variability, although many details of the hillslope landslide triggering procedures are filtered out by the sediment transfer system. The model allows us to explicitly quantify the division into transport and supply-limited sediment discharge events. We show that debris flows may be generated for a wide range of rainfall intensities because of variable antecedent basin wetness and snowmelt contribution to runoff, which helps to understand the limitations of methods based on a single rainfall threshold for debris flow initiation in Alpine basins.

Description: This study presents a thermodynamic analysis to predict the type of initial, amorphous oxide overgrowth (i.e., am - Al 2 O 3 or am - SiO 2 ) on bare Al – Si alloy substrates. This analysis have taken into account the energies associated with both its interfaces (interface between the Al – Si alloy substrate and the thin oxide film and interface between the thin oxide film and vacuum) along with the bulk Gibbs free energy of oxide formation. This developed analysis is then applied for various parameters, such as, Si alloying element content at the substrate/oxide interface, the growth temperature, the oxide film thickness (up to 1 nm), and various low-index crystallographic surfaces of the substrate. It is found that am - SiO 2 overgrowth is thermodynamically preferred for a combination of lower oxide film thickness, lower growth temperature, and lower Si alloying content at the alloy/oxide interface. This is because of the overcompensation of the lower energies of both the interfaces over the bulk Gibbs free energy. Furthermore, it is found that for all cases, am - Al 2 O 3 forms a more stable interface with Al – Si alloy than am - SiO 2.

Description: Characterizing the complex geometries and the heterogeneity of the deposits in meandering river systems is a long-standing issue for the 3D modeling of alluvial formations. Such deposits are important sources of accessible groundwater in alluvial aquifers throughout the world and also play a major role as hydrocarbons reservoirs. In this paper we present a method to generate meandering river centerlines that are stochastic, geologically realistic, connected and conditioned to local observations or global geomorphological characteristics. The method is based on fast 1D multiple-point statistics in a transformed curvilinear domain: the succession in directions observed in a real world meandering river (the analog) is considered as statistical model for multiple-point statistics simulation. The integration of local data is accomplished by an inverse procedure ensuring that the channels pass through a given set of locations while conserving the high-order spatial characteristics of an analog. The methodology is applied on seven real world case studies. This work demonstrates the flexibility and the applicability of multiple-point statistics outside the standard paradigm that considers the simulation of a 2D or 3D variable with spatial coordinates.

Description: Large asymmetric bedforms commonly develop in rivers. The turbulence associated with flow separation that develops over their steep lee side is responsible for the form shear stress which can represent a substantial part of total shear stress in rivers. This paper uses the Delft3D modeling system to investigate the effects of bedform geometry and forcing conditions on flow separation length and associated turbulence, and bedform shear stress over angle-of-repose (30° lee side angle) bedforms. The model was validated with laboratory measurements that showed sufficient agreement to be used for a systematic analysis. The influence of flow velocity, bed roughness, relative height (bedform height / water depth) and aspect ratio (bedform height / length) on the variations of the normalized length of the flow separation zone, the extent of the wake region (where the turbulent kinetic energy (TKE) was more than 70% of the maximum TKE), the average TKE within the wake region and the form shear stress were investigated. Form shear stress was found not to scale with the size of the flow separation zone but to be related to the product of the normalized extent of the wake region (extent of the wake region / extent of water body above the bedform) and the average TKE within the wake region. The results add to understanding of the hydrodynamics of bedforms and may be used for the development of better parameterizations of small-scale processes for application in large-scale studies.

Description: We explore the bankfull width ( W bf ) vs. drainage area ( A da ) relationship across a range of climatic and geologic environments, and ask (1) is the relationship between ln ( W bf ) and ln ( A da ) best described by a linear function and (2) can a reliable relationship be developed for predicting W bf with A da as the only independent variable. The principal dataset for this study was compiled from regional curve studies and other reports that represent 1,018 sites (1 m ≤ W bf ≤ 110 m and 0.50 km 2 ≤ A da ≤ 22,000 km 2 ) in the continental U.S. Two additional datasets were used for validation. After dividing the data into small-, medium-, and large-size basins which, respectfully, correspond to A da 〈 4.95 km 2 , 4.95 km 2 ≤ A da 〈 337 km 2 , and A da ≥ 337 km 2 , regression lines from each dataset were compared using one-way analysis of covariance (ANCOVA). A second ANCOVA was performed to determine if mean annual precipitation ( P ) is an extraneous factor in the W bf vs. A da relationship. The ANCOVA results reveal that using A da alone does not yield a reliable W bf vs. A da relationship that is applicable across a wide range of environments and that P is a significant extraneous factor in the relationship. Considering data for very small basins ( A da ≤ 0.49 km 2 ) and very large basins ( A da ≥ 1.0×10 5 km 2 ) we conclude that a two-segment linear model is the most probable form of the ln ( W bf ) vs. ln ( A da ) relationship. This study provides useful information for building complex multivariate models for predicting W bf .

Description: Recent studies show that multimodel combinations improve hydroclimatic predictions by reducing model uncertainty. Given that climate forecasts are available from multiple climate models, which could be ingested with multiple watershed models, what is the best strategy to reduce the uncertainty in streamflow forecasts? To address this question, we consider three possible strategies: (1) reduce the input uncertainty first by combining climate models and then use the multimodel climate forecasts with multiple watershed models (MM-P) (2) ingest the individual climate forecasts (without multimodel combination) with various watershed models and then combine the streamflow predictions that arise from all possible combinations of climate and watershed models (MM-Q)(3) combine the streamflow forecasts obtained from multiple watershed models based on strategy (1) to develop a single streamflow prediction that reduces uncertainty in both climate forecasts and watershed models (MM-PQ) . For this purpose, we consider synthetic schemes that generate streamflow and climate forecasts, for comparing the performance of three strategies with the true streamflow generated by a given hydrologic model. Results from the synthetic study show that reducing input uncertainty first ( MM-P ) by combining climate forecasts results in reduced error in predicting the true streamflow compared to the error of multimodel streamflow forecasts obtained by combining streamflow forecasts from all-possible combination of individual climate model with various hydrologic models ( MM-Q ). Since the true hydrologic model structure is unknown, it is desirable to consider MM-PQ as an alternate choice that reduces both input uncertainty and hydrologic model uncertainty. Application on two watersheds in NC also indicates that reducing the input uncertainty first is critical before reducing the hydrologic model uncertainty.

Description: The understanding of reasons leading to non-uniqueness of soil erosion susceptibility is still inadequate, yet indispensable for establishing general relations between runoff volume and sediment yield. To obtain relevant insights, we performed a series of numerical simulations with a detailed hydrodynamic model using synthetic storms of varying intensity, duration, and lag time between events as representations of different hydrologic response conditions in a zero-order catchment. The design targeted to generate surface flow and ‘perturb’ soil substrate by a first rainfall event, creating a set of initial conditions in terms of flow and deposited sediment prior to the onset of a subsequent rainfall event. Due to the differential effect of (re)detachment and (re)entrainment processes on soil particles of varying sizes, the deposited sediment mass formed shielding layer. One of the essential results is that unless the initial condition of flow and sediment is identical, the same volume of runoff can generate different total sediment yields and their variation can reach up to ~200%. The effect is attributed to two major conflicting effects exerted by the deposited ‘initialization’ (soil antecedent condition) sediment mass: erosion enhancement, because of supply of highly erodible sediment, and erosion impediment, because of constrain on the availability of lighter particles by heavier sediment. Consistently with this inference, long-term simulations with continuous rainfall show that a peculiar feature of sediment yield series is the existence of maximum before the steady-state is reached. The two characteristic time scales, the time to peak and the time to steady-state, separate three characteristic periods that correspond to flow-limited, source-limited, and steady-state regimes. These time scales are log-linearly and negatively related to the spatially averaged Shields parameter: the smaller the rainfall input and the heavier a given particle is, the larger the two scales are. The results provide insights on how the existence of shield operates on erosion processes, possibly implying that accurate short-term predictions of geomorphic events from headwater areas may never become a tractable problem: the latter would require a detailed spatial characterization of particle size distribution prior to precipitation events.

Description: Ecological Applications, Volume 24, Issue 1, Page 4-14, January 2014. Although market-based incentives have helped resolve many environmental challenges, conservation markets still play a relatively minor role in wildlife management. Establishing property rights for environmental goods and allowing trade between resource extractors and resource conservationists may offer a path forward in conserving charismatic species like whales, wolves, turtles, and sharks. In this paper, we provide a conceptual model for implementing a conservation market for wildlife and evaluate how such a market could be applied to three case studies for whales (minke [Balaenoptera acutorostrata], bowhead [Balaena mysticetus], and gray [Eschrictius robustus]). We show that, if designed and operated properly, such a market could ensure persistence of imperiled populations, while simultaneously improving the welfare of resource harvesters.

Description: Ecological Applications, Volume 24, Issue 1, Page 15-23, January 2014. We critique a proposal to use catch shares to manage transboundary wildlife resources with potentially high non-extractive values, and we focus on the case of whales. Because whales are impure public goods, a policy that fails to capture all nonmarket benefits (due to free riding) could lead to a suboptimal outcome. Even if free riding were overcome, whale shares would face four implementation challenges. First, a whale share could legitimize the international trade in whale meat and expand the whale meat market. Second, a legal whale trade creates monitoring and enforcement challenges similar to those of organizations that manage highly migratory species such as tuna. Third, a whale share could create a new political economy of management that changes incentives and increases costs for nongovernmental organizations (NGOs) to achieve the current level of conservation. Fourth, a whale share program creates new logistical challenges for quota definition and allocation regardless of whether the market for whale products expands or contracts. Each of these issues, if left unaddressed, could result in lower overall welfare for society than under the status quo.

Description: Ecological Applications, Volume 24, Issue 1, Page 142-157, January 2014. Global wetland biodiversity loss continues unabated, driven by increased demand for freshwater. A key strategy for conservation management of freshwater systems is to maintain the quantity and quality of the natural water regimes, including the frequency and timing of flows. Formalizing an ecological model depicting the key ecological components and the underlying processes of cause and effect is required for successful conservation management. Models linking hydrology with ecological responses can prove to be an invaluable tool for robust decision-making of environmental flows. Here, we explored alternative water management strategies and identified maximal strategies for successful long-term management of colonial waterbirds in the Macquarie Marshes, Australia. We modeled fluctuations in breeding abundances of 10 colonial waterbird species over the past quarter century (1986–2010). Clear relationships existed between flows and breeding, both in frequencies and total abundances, with a strong linear relationship for flows 〉200 GL. Thresholds emerged for triggering breeding events in all 10 species, but these varied among species. Three species displayed a sharp threshold response between 100 GL and 250 GL. These had a breeding probability of 0.5 when flows were 〉180 GL and a 0.9 probability of breeding with flows 〉350 GL. The remaining species had a probability greater than 0.5 of breeding with flows 〉400 GL. Using developed models, we examined the effects of five environmental flow management strategies on the variability of flows and subsequent likelihood of breeding. Management to different target volumes of environmental flows affected overall and specific breeding probabilities. The likelihood of breeding for all 10 colonial waterbirds increased from a regulated historical mean (±SD) of 0.36 ± 0.09 to 0.53 ± 0.14, an improvement of 47.5% ± 18.7%. Management of complex ecosystems depends on good understanding of the responses of organisms to the main drivers of change. Considerable opportunity exists for implementing similar frameworks for other ecosystem attributes, following understanding of their responses to the flow regime, achieving a more complete model of the entire ecosystem.

Description: Ecological Applications, Volume 24, Issue 1, Page 84-93, January 2014. Information on landscape-scale patterns in species distributions and community types is vital for ecological science and effective conservation assessment and planning. However, detailed maps of plant community structure at landscape scales seldom exist due to the inability of field-based inventories to map a sufficient number of individuals over large areas. The Carnegie Airborne Observatory (CAO) collected hyperspectral and lidar data over Kruger National Park, South Africa, and these data were used to remotely identify 〉500 000 tree and shrub crowns over a 144-km2 landscape using stacked support vector machines. Maps of community compositional variation were produced by ordination and clustering, and the importance of hillslope-scale topo-edaphic variation in shaping community structure was evaluated with redundancy analysis. This remote species identification approach revealed spatially complex patterns in woody plant communities throughout the landscape that could not be directly observed using field-based methods alone. We estimated that topo-edaphic variables representing catenal sequences explained 21% of species compositional variation, while we also uncovered important community patterns that were unrelated to catenas, indicating a large role for other soil-related factors in shaping the savanna community. Our results demonstrate the ability of airborne species identification techniques to map biodiversity for the evaluation of ecological controls on community composition over large landscapes.

Description: Ecological Applications, Volume 0, Issue 0, Ahead of Print. Vegetation-type conversions between grasslands and shrublands have occurred worldwide in semi-arid regions over the last 150 years. Areas once covered by drought deciduous shrubs in Southern California (Coastal Sage Scrub) are converting to grasslands dominated by non-native species. Increasing fire frequency, drought, and nitrogen deposition have all been hypothesized as causes of this conversion, though there is little direct evidence. We constructed rain-out shelters in a Coastal Sage Scrub community following a wildfire, manipulated water and nitrogen input in a split plot design, and collected annual data on community composition for four years. While shrub cover increased through time in all plots during the post-fire succession, both drought and nitrogen significantly slowed recovery. Four years after the fire, average native shrub cover ranged from over 80% in water addition, ambient nitrogen plots to 20% in water reduction, nitrogen addition plots. European grass cover was high following the fire and remained high in the water reduction plots through the third spring after the fire before decreasing in the fourth year of the study. Adding nitrogen decreased the cover of native plants and increased the cover of Eurasian grasses, but also increased growth of crown-sprouting individuals of one shrub species. Our results suggest that extreme drought during post-fire succession may slow or alter succession, possibly facilitating vegetation-type conversion of Coastal Sage Scrub to grassland. Nitrogen addition slowed succession and, when combined with drought, significantly decreased native cover and increased grass cover. Fire, drought, and atmospheric N deposition are widespread aspects of environmental change that occur simultaneously in this system. Our results suggest these drivers of change may reinforce each other, leading to a continued decline of native shrubs and conversion to annual grassland.

Description: Ecological Applications, Volume 0, Issue 0, Ahead of Print. Accelerating climate change and other cumulative stressors create an urgent need to understand the influence of environmental variation and landscape features on the connectivity and vulnerability of freshwater species. Here, we introduce a novel modeling framework for aquatic systems that integrates spatially-explicit, individual-based, demographic and genetic (demogenetic) assessments with environmental variables. To show its potential utility, we simulated a hypothetical network of 19 migratory riverine populations (e.g., salmonids) using a riverscape connectivity and demogenetic model (CDFISH). We assessed how stream resistance to movement -- a function of water temperature, fluvial distance, and physical barriers -- might influence demogenetic connectivity and hence population vulnerability. We present demographic metrics (abundance, immigration, and change in abundance) and also genetic metrics (diversity, differentiation, and change in differentiation), and combine them into a single vulnerability index for identifying populations at risk of extirpation. We considered four realistic scenarios that illustrate the relative sensitivity of these metrics for early detection of reduced connectivity: (1) maximum resistance due to high water temperatures throughout the network, (2) minimum resistance due to low water temperatures throughout the network, (3) increased resistance at a tributary junction caused by a partial barrier, and (4) complete isolation of a tributary, leaving resident individuals only. We then apply this demogenetic framework using empirical data for a bull trout metapopulation in the upper Flathead River system, Canada and USA, to assess how current and predicted future stream warming may influence population vulnerability. Results suggest that warmer water temperatures and associated barriers to movement (e.g., low flows, de-watering) are predicted to fragment suitable habitat for migratory salmonids, resulting in the loss of genetic diversity and reduced sizes in certain vulnerable population. This demogenetic simulation framework, which is illustrated in a web-based interactive mapping prototype (http://ptolemy.dbs.umt.edu/pvm/), should be useful for evaluating population vulnerability in a wide variety of dendritic and fragmented riverscapes, helping to guide conservation and management efforts for freshwater species.

Description: Ecological Applications, Volume 0, Issue 0, Ahead of Print. Tree and shrub abundance has increased in many grasslands causing changes in ecosystem carbon and nitrogen pools that are related to patterns of woody plant distribution. However, with regard to spatial patterns of shrub proliferation, little is known about (i) how they are influenced by grazing or (ii) the extent to which they are influenced by intraspecific interactions. We addressed these questions by quantifying changes in the spatial distribution of Prosopis velutina (mesquite) shrubs over 74 years on grazed and protected grasslands. Livestock are effective agents of mesquite dispersal and mesquite plants have lateral roots extending well beyond the canopy. We therefore hypothesized that mesquite distributions would be (a) random on grazed areas mainly due to cattle dispersion and clustered on protected areas due to decreased dispersal and interspecific interference with grasses; and (b) that clustered or random distributions at early stages of encroachment would give way to regular distributions as stands matured and density-dependent interactions intensified. Assessments in 1932, 1948 and 2006 supported the first hypothesis, but we found no support for the second. In fact, clustering intensified with time on the protected area and the pattern remained random on the grazed site. Although shrub density increased on both areas between 1932 and 2006, we saw no progression toward a regular distribution indicative of density-dependent interactions. We propose that processes related to seed dispersal, grass-shrub seedling interactions, and hydrological constraints on shrub size interact to determine vegetation structure in grassland-to-shrubland state changes with implications for ecosystem function and management.

Description: Aquifer hydraulic properties such as hydraulic conductivity ( K ) are ubiquitously heterogeneous and typically only a statistical characterization can be sought. Additionally statistical anisotropy at typical characterization scales is the rule. Thus, regardless of the processes governing solute transport at the local (pore) scale, transport becomes non-Fickian. Mass-transfer models provide an efficient tool that reproduces observed anomalous transport; in some cases though, these models lack predictability as model parameters cannot readily be connected to the physical properties of aquifers. In this study we focus on a multi-rate mass-transfer model (MRMT), and in particular the apparent capacity coefficient (β), which is a strong indicator of the potential of immobile zones to capture moving solute. We aim to find if the choice of an apparent β can be phenomenologically related to measures of statistical anisotropy. We analyzed an ensemble of random simulations of three-dimensional log-transformed multi-Gaussian permeability fields with stationary anisotropic correlation under convergent flow conditions. It was found that apparent β also displays an anisotropic behavior, physically controlled by the aquifer directional connectivity, which in turn is controlled by the anisotropic correlation model. A high hydraulic connectivity results in large β values. These results provide new insights into the practical use of mass-transfer models for predictive purposes.

Description: Ecological Applications, Volume 0, Issue 0, Ahead of Print. Mounting evidence now shows that fishing activity modifies both heritable life-history traits and ecological processes in harvested populations. However, ecological and evolutionary changes are intimately linked and can occur on the same time-scale, and few studies have investigated their combined effect on fish population dynamics. Here, we contrast two population subunits of a harvested fish species in the Northeast Atlantic, the European hake (Merluccius merluccius), in the light of the emerging field of evolutionary demography, which considers the interacting processes between ecology and evolution. The two subunits experienced similar age/size truncation due to size-selective fishing, but displayed differences in key ecological processes (recruitment success) and phenotypic characteristics (maturation schedule). We investigate how temporal variation in maturation and recruitment success interactively shape the population dynamics of the two subunits. We document that the two subunits of European hake displayed different responses to fishing in maturation schedules, possibly because of the different level of adaptive phenotypic plasticity. Our results also suggest that high phenotypic plasticity can dampen the effects of fisheries-induced demographic truncation on population dynamics, whereas a population subunit characterized by low phenotypic plasticity may suffer from additive effects of ecological and life-history responses. Similar fishing pressure may thus trigger contrasting interactions between life history variation and ecological processes within the same population. The presented findings improve our understanding of how fishing impacts eco-evolutionary dynamics, which is a keystone for a more comprehensive management of harvested species.

Description: Ecological Applications, Volume 0, Issue 0, Ahead of Print. Conservation practitioners, faced with managing multiple threats to biodiversity and limited funding, must prioritize investment in different management actions. From an economic perspective, it is routine practice to invest where the highest rate of return is expected. This return-on-investment (ROI) thinking can also benefit species conservation, and researchers are developing sophisticated approaches to support decision-making for cost-effective conservation. However, applied use of these approaches is limited. Managers may be wary of 'black-box' algorithms or complex methods that are difficult to explain to funding agencies. As an alternative, we demonstrate the use of a basic ROI analysis for determining where to invest in cost-effective management to address threats to species. This method can be applied using basic geographic information system and spread sheet calculations. We illustrate the approach in a management-action prioritization for a biodiverse region of eastern Australia. We use ROI to prioritize management actions for two threats to a suite of threatened species: habitat degradation by cattle grazing and predation by invasive red foxes (Vulpes vulpes). We show how decisions based on cost-effective threat management depend upon how expected benefits to species are defined and how benefits and costs co-vary. By considering a combination of species richness, restricted habitats, species vulnerability, and costs of management actions, small investments can result in greater expected benefit compared with management decisions that consider only species richness. Furthermore, a landscape management strategy that implements multiple actions is more efficient than managing only for one threat or more traditional approaches that don't consider ROI. Our approach provides transparent and logical decision-support for prioritizing different actions intended to abate threats associated with multiple species; it is of use when managers need a justifiable and repeatable approach to investment.

Description: Ecological Applications, Volume 0, Issue 0, Ahead of Print. Fire is becoming a pervasive driver of environmental change in Amazonia and is expected to intensify, given projected reductions in precipitation and forest cover. Understanding of the influence of post-deforestation land cover change on fires in Amazonia is limited, even though fires in cleared lands constitute a threat for ecosystems, agriculture, and human health. We used MODIS satellite data to map burned areas annually between 2001 and 2010. We then combined these maps with land cover and climate information to understand the influence of land cover change in cleared lands and dry season severity on fire occurrence and spread in a focus area in the Peruvian Amazon. Fire occurrence, quantified as the probability of burning of individual 232m spatial resolution MODIS pixels was modeled as a function of the area of land cover types within each pixel, drought severity, and distance to roads. Fire spread, quantified as the number of pixels burned in 3x3 pixel windows around each focal burned pixel, was modeled as a function of land cover configuration and area, dry season severity, and distance to roads. We found that vegetation regrowth and oil palm expansion are significantly correlated with fire occurrence but that the magnitude and sign of the correlation depend on drought severity, successional stage of regrowing vegetation and oil palm age. Burning probability increased with the area of non-degraded pastures, fallow, and young oil palm and decreased with larger extents of degraded pastures, secondary forests and adult oil palm plantations. Drought severity had the strongest influence on fire occurrence overriding the effectiveness of secondary forests but not of adult plantations to reduce fire occurrence in severely dry years. Overall, irregular and scattered land cover patches reduced fire spread but irregular and dispersed fallows and secondary forests increased fire spread during dry years. Results underscore the importance of land cover management for reducing fire proliferation in this landscape. Incentives for promoting natural regeneration and perennial crops in cleared lands might help reduce fire risk if those areas are protected against burning in early stages of development and during severely dry years.

Description: Sintered nanoceramics of Pr -doped lanthanum hafnate, La 2 Hf 2 O 7 : Pr , were prepared by means of a high-pressure sintering technique using nanopowders made by Pechini method. Structure, morphology, and spectroscopic properties of the ceramics compared to the starting powder are presented and discussed. Emission and excitation spectra recorded at room temperature as well as at 7 K using synchrotron radiation are presented together with results of luminescence kinetics measurements. In ceramics, at 7 K, the Pr 3+ luminescence from 3 P 0 (blue-green, green, and red region) and 1 D 2 (red) levels is accompanied by a broad-band emission located in the 380–530 nm range of wavelengths, whereas powders gives only the Pr 3+ -related luminescence. Depending on the excitation wavelength, the broad-band emission maximum moves between 430 and 470 nm indicating superposition of at least two components. In sintered nanoceramics, the lifetimes of Pr 3+ emissions from 3 P 0 and 1 D 2 levels were by 10%–20% shorter compared to the powder. The existence of different luminescence centers was proved by the selective emission decays examination. The fast 5 d → 4 f luminescence of Pr 3+ was not observed from either of the two types of La 2 Hf 2 O 7 :Pr materials.

Description: In this paper, an operational algorithm is proposed for the mapping of surface moisture over the northern and central parts of Tunisia, in North Africa. A change detection approach is applied, using 160 multi-incidence Envisat ASAR Wide Swath images acquired in the horizontal polarization over a 7-year period. Parameterization of this algorithm is considered for three classes of vegetation cover density (NDVI〈0.25, 0.25〈NDVI〈0.5 and NDVI〉0.5), retrieved from SPOT-VGT decadal images. A relative soil moisture index, ranging between 0 (for the driest surfaces) and 1 (for saturated soils), is proposed for each date, with a resolution of 1 km. The retrieved soil moistures are validated by means of ground measurements based on continuous thetaprobe measurements, as well as low resolution (25 km) ERS and ASCAT soil moisture products from the Vienna University of Technology (TU Wien). A qualitative relationship between spatio-temporal variations of moisture and precipitation is also discussed.

Description: Ecological Applications, Volume 0, Issue 0, Ahead of Print. There is a growing need for operational biodiversity mapping methods to quantify and to assess the impact of climate change, habitat alteration and human activity on ecosystem composition and function. Here, we present an original method for the estimation of α- and β-diversity of tropical forests based on high-fidelity imaging spectroscopy. We acquired imagery acquired over high-diversity Amazonian tropical forest landscapes in Perú with the Carnegie Airborne Observatory and developed an unsupervised method to estimate the Shannon Index (H') and variations in species composition using Bray-Curtis Dissimilarity (BC) and non-metric multidimensional scaling (NMDS). An extensive field plot network was used for the validation of remotely sensed α- and β-diversity. Airborne maps of H' were highly correlated with field α-diversity estimates (r = 0.86), and BC was estimated with demonstrable accuracy (r = 0.61-0.76). Our findings are the first direct and spatially-explicit remotely sensed estimates of α- and β-diversity of humid tropical forests, paving the way for new applications using airborne and space-based imaging spectroscopy.

Description: Ecological Applications, Volume 24, Issue 1, Page 229-233, January 2014.

Description: Ecological Applications, Volume 24, Issue 1, Page 181-195, January 2014. Stable isotopes are valuable tools for partitioning the components contributing to ecological processes of interest, such as animal diets and trophic interactions, plant resource use, ecosystem gas fluxes, streamflow, and many more. Stable isotope data are often analyzed with simple linear mixing (SLM) models to partition the contributions of different sources, but SLM models cannot incorporate a mechanistic understanding of the underlying processes and do not accommodate additional data associated with these processes (e.g., environmental covariates, flux data, gut contents). Thus, SLM models lack predictive ability. We describe a process-based mixing (PBM) model approach for integrating stable isotopes, other data sources, and process models to partition different sources or process components. This is accomplished via a hierarchical Bayesian framework that quantifies multiple sources of uncertainty and enables the incorporation of process models and prior information to help constrain the source-specific proportional contributions, thereby potentially avoiding identifiability issues that plague SLM models applied to “too many” sources. We discuss the application of the PBM model framework to three diverse examples: temporal and spatial partitioning of streamflow, estimation of plant rooting profiles and water uptake profiles (or water sources) with extension to partitioning soil and ecosystem CO2 fluxes, and reconstructing animal diets. These examples illustrate the advantages of the PBM modeling approach, which facilitates incorporation of ecological theory and diverse sources of information into the mixing model framework, thus enabling one to partition key process components across time and space.

Description: We have investigated the electromechanical response of potassium sodium niobate ( K 0.5 Na 0.5 NbO 3 or KNN) thick films. The high-field strain hysteresis loops and weak-field converse piezoelectric d 33 coefficient of the films were measured and compared with those of KNN bulk ceramics under the same electric field conditions. The converse d 33 values of the thick films and bulk ceramics were equal to 82.5 and 138 pm/V, respectively, at 0.4 kV/mm. The fundamental difference between the piezoelectric response of the KNN films and the ceramics was studied in terms of the effective (“clamped”) piezoelectric d 33 coefficient. The reduction in the piezoelectric d 33 coefficient of the KNN films, resulting from the clamping by the substrate, was compared to lead-based ferroelectric thick films, including Pb ( Zr , Ti ) O 3 (PZT) and (1 −  x ) Pb ( Mg 1/3 Nb 2/3 ) O 3 − x PbTiO 3 (PMN-PT). We propose a possible explanation, based on the particular elastic properties of KNN, for the small relative difference observed between the “clamped” and “unclamped” (“bulk”) d 33 of KNN, in comparison with lead-based systems.

Description: Lead zirconate titanate (PbZr 1 −  x Ti x O 3 , PZT)/epoxy composites with one- dimensional epoxy in PZT matrix (called 3-1 type piezocomposites) have been fabricated by tert-butyl alcohol (TBA)-based directional freeze casting of PZT matrix and afterward infiltration of epoxy. The composites with PZT volume fraction ranging from 0.36 to 0.69 were obtained by adjusting initial solid loading in freeze-casting slurry. The effect of poling voltage on piezoelectric properties of the composites was studied for various volume fraction of PZT phase. With the increasing of PZT volume fraction, relative permittivity (ε r ) increased linearly and piezoelectric coefficient ( d 33 and d 31 ) increased step by step. The resultant composites with 0.57 PZT volume fraction possessed the highest hydrostatic piezoelectric strain coefficient ( d h ) value (184 pC/N), voltage coefficient ( g h ) value (13.6 × 10 −3  V/m Pa), and hydrostatic figure of merit (HFOM) value (2168 × 10 −15  Pa −1 ).

Description: Multiphase borosilicate glass-ceramics represent one candidate to contain radioactive nuclear waste separated from used nuclear fuel. In this work, the thermophysical properties from room temperature to 1273 K were investigated for four different borosilicate glass-ceramic compositions containing waste loadings from 42 to 60 wt% to determine the sensitivity of these properties to waste loading, as-fabricated microstructure, and potential evolutions in microstructure brought about by temperature transients. The thermal expansion, specific heat capacity, thermal diffusivity, and thermal conductivity are presented. The impact of increasing waste loading is shown to have a small but measurable effect on the thermophysical properties between the four compositions, contrasted to a much greater impact observed when transitioning from predominantly crystalline to amorphous systems. Thermal cycling below 1273 K was not found to measurably impact the thermophysical properties of the compositions investigated here.

Description: This paper presents the results of a data based comparative study of several hundred catchments across continental United States belonging to the MOPEX dataset to systematically explore the connection between the flood frequency curve and mean annual water balance. Mean annual water balance is expressed in terms of two similarity measures: (i) the climatic aridity index, AI , which is a measure of the competition between energy and water availability; and (ii) the baseflow index, BFI , which is a measure of total runoff partitioning into surface and subsurface components at the annual time scale. The data analyses showed that the aridity index, AI , has a first order control on the shape of the flood frequency curve (also known as the growth curve), as expressed in terms of both the mean and coefficient of variation ( C v ) of the annual maximum floods, once normalized by catchment size (i.e., specific flood discharge) While the mean annual (specific) flood discharge decreases with increasing aridity, C v increases with increasing aridity. On the other hand, the BFI was found to be a second order control on the flood frequency curve. Higher BFI , meaning higher contributions of subsurface flow to total streamflow, leads to a decrease of the mean annual (specific) flood discharge, and vice versa. The statistically significant relationship between AI and the flood frequency curve and the consistent shift of the growth curves with AI support the use of AI as a similarity measure for regionalization of flood frequency.

Description: The performance of glacio-hydrological models which simulate catchment response to climate variability depends to a large degree on the data used to force the models. The forcing data become increasingly important in high elevation, glacierised catchments where the interplay between extreme topography, climate and the cryosphere is complex. It is challenging to generate a reliable forcing dataset that captures this spatial heterogeneity. In this paper, we analyze the results of a one year field campaign focusing on air temperature and precipitation observations in the Langtang Valley in the Nepalese Himalayas. We use the observed time series to characterize both temperature lapse rates (LRs) and precipitation gradients (PGs). We study their spatial and temporal variability, and we attempt to identify possible controlling factors. We show that very clear LRs exist in the valley and that there are strong seasonal differences related to the water vapor content in the atmosphere. Results also show that the LRs are generally shallower than the commonly used environmental lapse rates. The analysis of the precipitation observations reveal that there is great variability in precipitation over short horizontal distances. A uniform valley wide PG cannot be established and several scale-dependent mechanisms may explain our observations. We complete our analysis by showing the impact of the observed LRs and PGs on the outputs of the TOPKAPI-ETH glacio-hydrological model. We conclude that LRs and PGs have a very large impact on the water balance composition and that short-term monitoring campaigns have the potential to improve model quality considerably.

Description: Ecological Applications, Volume 0, Issue 0, Ahead of Print. Grazing represents one of the most common disturbances in drylands worldwide, affecting both ecosystem structure and functioning. Despite the efforts to understand the nature and magnitude of grazing effects on ecosystem components and processes, contrasting results continue to arise. This is particularly remarkable for the biological soil crust (BSC) communities (i.e. cyanobacteria, lichens and bryophytes), which play an important role in soil dynamics. Here we evaluated simultaneously the effect of grazing impact on BSC communities (resistance) and recovery after livestock exclusion (resilience) in a semiarid grassland of Central Mexico. In particular, we examined BSC species distribution, species richness, taxonomical group cover (i.e., cyanobacteria, lichen, bryophyte) and composition along a disturbance gradient with different grazing regimes (low, medium, high impact) and along a recovery gradient with differently-aged livestock exclosures (short-, medium-, long-term exclusion). Differences in grazing impact and time of recovery from grazing both resulted in slight changes in species richness; however, there were pronounced shifts in species composition and group cover. We found we could distinguish four highly diverse and dynamic BSC species groups: 1) species with high resistance and resilience to grazing, 2) species with high resistance but low resilience, 3) species with low resistance but high resilience, and 4) species with low resistance and resilience. While disturbance resulted in a novel diversity configuration, which may profoundly affect ecosystem functioning, we observed that 10 years of disturbance removal did not lead to the ecosystem structure found after 27 years of recovery. These findings are an important contribution to our understanding of BCS dynamics from a species and community perspective placed in a land use change context.

Description: Many physically-based hydrological/hydrogeological models used for predicting groundwater seepage areas, including topography-based index models such as TOPMODEL, rely on the Dupuit assumption. To ensure the sound use of these simplified models, knowledge of the conditions under which they provide a reasonable approximation is critical. In this study, a Dupuit solution for the seepage length in hillslope cross-sections is tested against a full-depth solution of saturated groundwater flow. In homogeneous hillslopes with horizontal impervious base and constant-slope topography, the comparison reveals that the validity of the Dupuit solution depends not only on the ratio of depth to hillslope length d/L (as might be expected), but also on the ratio of hydraulic conductivity to recharge K/R and on the topographic slope s . The validity of the Dupuit solution is shown to be in fact a unique function of another ratio, the ratio of depth to seepage length d/L S . For d/L S 〈 0.2, the relative difference between the two solutions is quite small (〈 14% for the wide range of parameter values tested), whereas for d/L S 〉 0.2, it increases dramatically. In practice, this criterion can be used to test the validity of Dupuit solutions. When d/L S increases beyond that cut-off, the ratio of seepage length to hillslope length L S /L given by the full-depth solution tends towards a non-zero asymptotic value. This asymptotic value is shown to be controlled by (and in many cases equal to) the parameter R/sK . Generalization of the findings to cases featuring heterogeneity, non-horizontal impervious base and variable-slope topography is discussed.

Description: Isothermal compositional flow models require coupling transient compressible flows and advective transport systems of various chemical species in subsurface porous media. Building such numerical models is quite challenging and may be subject to many sources of uncertainties because of possible incomplete representation of some geological parameters that characterize the system's processes. Advanced data assimilation methods, such as the ensemble Kalman filter (EnKF), can be used to calibrate these models by incorporating available data. In this work, we consider the problem of estimating reservoir permeability using information about phase pressure as well as the chemical properties of fluid components. We carry out state-parameter estimation experiments using joint and dual updating schemes in the context of the EnKF with a two-dimensional single-phase compositional flow model (CFM). Quantitative and statistical analyses are performed to evaluate and compare the performance of the assimilation schemes. Our results indicate that including chemical composition data significantly enhances the accuracy of the permeability estimates. In addition, composition data provide more information to estimate system states and parameters than do standard pressure data. The dual state-parameter estimation scheme provides about 10% more accurate permeability estimates on average than the joint scheme when implemented with the same ensemble members, at the cost of twice more forward model integrations. At similar computational cost, the dual approach becomes only beneficial after using large enough ensembles.

Description: Groundwater-fed irrigation has been shown to deplete groundwater storage, decrease surface water runoff and increase evapotranspiration. Here we simulate soil moisture dependent groundwater-fed irrigation with an integrated hydrologic model. This allows for direct consideration of feedbacks between irrigation demand and groundwater depth. Special attention is paid to system dynamics in order to characterized spatial variability in irrigation demand and response to increased irrigation stress. A total of 80 years of simulation are completed for the Little Washita Basin in Southwestern Oklahoma, USA spanning a range of agricultural development scenarios and management practices. Results show regionally aggregated irrigation impacts consistent with other studies. However, here a spectral analysis reveals that groundwater-fed irrigation is also shown to amplify the annual streamflow cycle while dampening longer-term cyclical behavior with increased irrigation during climatological dry periods. Feedbacks between the managed and natural system are clearly observed with respect to both irrigation demand and utilization when water table depths are within a critical range. Although the model domain is heterogeneous with respect to both surface and subsurface parameters, relationships between irrigation demand, water table depth and irrigation utilization are consistent across space and between scenarios. Still, significant local heterogeneities are observed both with respect to transient behavior and response to stress. Spatial analysis of transient behavior shows that farms with groundwater depths within a critical depth range are most sensitive to management changes. Differences in behavior highlight the importance of groundwater's role in system dynamics in addition to water availability.

Description: Including positive feedbacks in hydrological models has recently been shown to result in complex behavior with multiple steady states. When a large disturbance, say a major drought, is simulated within such models the hydrology changes. Once the disturbance ends the hydrology does not return to that prior to the disturbance, but rather, persists within an alternate state. These multiple steady states (henceforth attractors ) exist for a single model parameterization and cause the system to have a finite resilience to such transient disturbances. A limitation of past hydrological resilience studies is that multiple attractors have been identified using mean annual or mean monthly forcing. Considering that most hydrological fluxes are subject to significant forcing stochasticity and do not operate at such large time scales, it remains an open question whether multiple hydrological attractors can exist when a catchment is subject to stochastic daily forcing. This question is the focus of this paper and it needs to be addressed prior to searching for multiple hydrological attractors in the field. To investigate this, a previously developed semi-distributed hill-slope ecohydrological model was adopted which exhibited multiple steady states under average monthly climate forcing. In this paper, the ecohydrological model was used to explore if feedbacks between the vegetation and a saline water table result in two attractors existing under daily stochastic forcing. The attractors and the threshold between them (henceforth repellor ) were quantified using a new limit cycle continuation technique that up-scaled climate forcing from daily to monthly (model and limit cycle code is freely available). The method was used to determine the values of saturated lateral hydraulic conductivity at which multiple attractors exist. These estimates were then assessed against time-integration estimates, which they agreed with. Overall, multiple attractors where found to exist under stochastic daily forcing. However, changing the climate forcing from monthly to daily did significantly reduce the parameter range over which two attractors existed. This suggests fewer catchments may have multiple attractors than previously considered.

Description: The companion paper showed that multiple steady state groundwater levels can exist within a hill-slope Boussinesq-vegetation model under daily stochastic forcing. Using a numerical limit-cycle continuation algorithm, the steady states (henceforth attractors ) and the threshold between them (henceforth repellor ) were quantified at a range of saturated lateral conductivity values, . This paper investigates if stochastic daily forcing can switch the catchment between both of the attractors. That is, an attractor may exist under average forcing conditions but can stochastic forcing switch the catchment into and out of each of the attractor basins?; i.e. making the attractor emerge . This was undertaken using the model of the companion paper and by completing daily time-integration simulations at six values of the saturated lateral hydraulic conductivity, ; three having two attractors and three having only a deep water table attractor. By graphically analyzing the simulations, and comparing against simulations from a model modified to have only one attractor, multiple attractors were found to emerge under stochastic daily forcing. However, the emergence of attractors was significantly more subtle and complex than that suggested by the companion paper. That is, an attractor may exist but never emerge; both attractors may exist and both may emerge but identifying the switching between attractors was often ambiguous; and only one attractor may exist and but a second temporary attractor may exist and emerge during periods of high precipitation. This subtle and complex emergence of attractors was explained using continuation analysis of the climate forcing rate, and not a model parameter such as . It showed that the temporary attractor existed over a large range of values and this suggests that more catchments may have multiple attractors than suggested by the companion paper. By combining this continuation analysis with the time-integration simulations, hydrological signatures indicative of a switch of multiple attractors were proposed. These signatures may provide a means for identifying actual catchments that have switched between multiple attractors.

Description: ABSTRACT A large-time analytical solution is proposed for the spatial variance and coefficient of variation of the depth-averaged concentration due to instantaneous, cross-sectionally uniform solute sources in pseudo-rectangular open channel flows. The mathematical approach is based on the use of the Green functions and on the Fourier decomposition of the depth-averaged velocities, coupled with the method of the images. The variance spatial trend is characterized by a minimum at the center of the mass and two mobile, decaying symmetrical peaks which, at very large times, are located at the inflexion points of the average Gaussian distribution. The coefficient of variation, which provides an estimate of the expected percentage deviation of the depth-averaged point concentrations about the section-average, exhibits a minimum at the center which decays like t -1 and only depends on the river diffusive time-scale. The defect of cross-sectional mixing quickly increases with the distance from the center, and almost linearly at large times. Accurate numerical Lagrangian simulations were performed to validate the analytical results in pre-asymptotic and asymptotic conditions, referring to a particularly representative sample case for which cross-sectional depth and velocity measurements were known from a field survey. In addition, in order to discuss the practical usefulness of computing large-time concentration spatial moments in river flows, and resorting to directly measured input data, the order of magnitude of section-averaged concentrations and corresponding coefficients of variation was estimated in field conditions and for hypothetical contamination scenarios, considering a unit normalized mass impulsively injected across the transverse section of 81 U.S. rivers.

Description: Ecological Applications, Volume 0, Issue 0, Ahead of Print. The American pika (Ochotona princeps) has become a species of concern for its sensitivity to warm temperatures and potential vulnerability to global warming. We explored the value of radiocarbon dating of fecal pellets to address questions of population persistence and timing of site extirpation. Carbon was extracted from pellets collected at 43 locations in the western Great Basin, USA, including 3 known occupied sites and 40 sites of uncertain status at range margins or where previous studies indicated the species is vulnerable. We resolved calibrated dates with high precision (within several years), most of which fell in the period of the mid-late 20th century "bomb curve." The two-sided nature of the bomb curve renders "far-" and "near-side" dates of equal probability, which are separated by 1-4 decades. We document methods for narrowing resolution to one age range, including stratigraphic analysis of vegetation collected from pika haypiles. No evidence was found for biases in atmospheric 14C levels due to fossil-derived or industrial CO2 contamination. Radiocarbon dating indicated that pellets can persist for 〉59 years; known-occupied sites resolved contemporary dates. Using combined evidence from field observations and radiocarbon-dating, and the Bodie Mountains (Mtns) as an example, we propose a historical biogeographic scenario for pikas in minor Great Basin mountain ranges adjacent to major cordillera wherein historical climate variability led to cycles of extirpation and re-colonization during alternating cool and warm centuries. Using this model to inform future dynamics for small ranges in biogeographic settings similar to the Bodie Mtns, CA, extirpation of pikas appears highly likely under directional warming trends projected for the next century, even while populations in extensive cordillera (e.g., Sierra Nevada, Rocky Mtns, Cascade Range) are likely to remain viable due to extensive, diverse, habitat and high connectivity.

Description: Ecological Applications, Volume 0, Issue 0, Ahead of Print. Studies of predator-prey demographic responses and the physical drivers of such relationships are rare, yet essential for predicting future changes in the structure and dynamics of marine ecosystems. Here, we hypothesize that predator-prey relationships vary spatially in association with underlying physical ocean conditions, leading to observable changes in demographic rates, such as reproduction. To test this hypothesis, we quantified spatio-temporal variability in hydrographic conditions, krill, and forage fish to model predator (seabird) demographic responses over 18 years (1990-2007). We used principal component analysis and spatial correlation maps to assess coherence among ocean conditions, krill, and forage fish, and generalized additive models to quantify interannual variability in seabird breeding success relative to prey abundance. The first principal component of 4 hydrographic measurements yielded an index that partitioned "weak/warm upwelling" and "strong/cool upwelling" years. Partitioning of krill and forage fish time series among shelf and oceanic regions yielded spatially-explicit indicators of prey availability. Krill abundance within the oceanic region was remarkably consistent between years, whereas krill over the shelf showed marked interannual fluctuations in relation to ocean conditions. Anchovy abundance varied on the shelf, and was greater in years of strong stratification/weak upwelling and warmer temperatures. Spatio-temporal variability of juvenile forage fish covaried strongly with each other and with krill, but was weakly correlated with hydrographic conditions. Demographic responses between seabirds and prey availability revealed spatially-variable associations indicative of the dynamic nature of habitat-prey relationships. Quantification of spatially-explicit demographic responses, and their variability through time, demonstrates the possibility of delineating specific critical areas where the implementation of protective measures could maintain functions and productivity of central place foraging predators.

Description: We report a novel oscillatory pressure-assisted hot-pressing process for preparing high-quality ceramics. Compared with the samples prepared by conventional pressureless sintering (PS) and hot-pressing (HP), the zirconia ceramic prepared by oscillatory pressure-assisted hot-pressing (OPAHP) exhibited a higher density, smaller grain size, and more homogeneous structure. More remarkably, the strength of the OPAHP sample reached 1556 MPa, which is much higher than the samples prepared by other two techniques. The results suggest that OPAHP is a more effective technique for preparing high-quality zirconia, which is likely applicable to other material systems.

Description: Two major causes of salt marsh loss are vertical drowning, when sediment accumulation on the platform cannot keep vertical pace with sea level rise, and horizontal retreat, associated with wave-induced marsh boundary erosion. Despite these processes having been extensively documented and modeled, is unclear which loss modality dominates given a set of environmental parameters. A three-point dynamic model was developed to predict marsh loss as a function of sea level rise, allochthonous sediment supply, wind regime, tidal range, and marsh bank and mudflat erodability. Marsh horizontal and vertical evolution was found to respond in opposing ways to wave induced erosion processes. Marsh horizontal retreat was triggered by large mudflats, strong winds, high erodability of marsh bank and mudflat, whereas the opposite conditions acted to reduce the sediment supply to the marsh platform, promoting marsh loss to drowning. With low and moderate rates of sea level rise (~ 5 mm/yr), retreat was found to be a more likely marsh loss modality than drowning. However, conditions associated with marsh retreat also increase the system resilience by transferring sediment on the marsh platform and preventing drowning. Our results suggest the use of a modular strategy for short-term marsh management: selectively protect extensive salt marsh regions by maintaining healthy vegetation on the platform, while allowing other areas to retreat, leveraging the natural resilience embedded in the lateral loss of marsh extent.

Description: Observational data and the Princeton Urban Canopy Model, with its detailed representation of urban heterogeneity and hydrological processes, are combined to study evaporation and turbulent water vapor transport over urban areas. The analyses focus on periods before and after precipitation events, at two sites in the Northeastern United States. Our results indicate that while evaporation from concrete pavements, building rooftops and asphalt surfaces is discontinuous and intermittent, overall these surfaces accounted for nearly 18% of total latent heat fluxes (LE) during a relatively wet 10-day period. More importantly, these evaporative fluxes have a significant impact on the urban surface energy balance, particularly during the 48 hours following a rain event when impervious evaporation is the highest. Thus, their accurate representation in urban models is critical. Impervious evaporation after rainfall is also shown to correlate the sources of heat and water at the earth surface, resulting in a conditional scalar transport similarity over urban terrain following rain events.

Description: The spatial and temporal dynamics of seasonal snow covers play a critical role for many hydrological, ecological, and climatic processes. This paper presents a new, innovative approach to continuously monitor these dynamics using numerous low-cost, standalone snow monitoring stations (SnoMoS). These stations provide snow and related meteorological data with a high temporal and spatial resolution. Data collected by SnoMoS include: snow depth, surface temperature, air temperature and humidity, total precipitation, global radiation, wind speed, and barometric pressure. A total of 99 sensors were placed over the winters 2010/11 and 2011/12 at multiple locations within three 40 - 180 km² basins in the Black Forest region of Southern Germany. The locations were chosen to cover a wide range of slopes, elevations, and expositions in a stratified sampling design. Furthermore, “paired stations” located in close proximity to each other, one in the open and one underneath various forest canopies, were set up to investigate the influence of vegetation on snow dynamics. The results showed that considerable differences in snow depth and, therefore, snow water equivalent (SWE) are present within the study area despite its moderate temperatures and medium elevation range (400 - 1500 m). The relative impact of topographical factors like elevation, aspect, and of different types of forest vegetation were quantified continuously and were found to change considerably over the winter period. The recorded differences in SWE and snow cover duration were large enough that they should be considered in hydrologic and climate models.

Description: Integrated land surface-groundwater models are valuable tools in simulating the terrestrial hydrologic cycle as a continuous system and exploring the extent of land surface–subsurface interactions from catchment to regional scales. However, the fidelity of model simulations is impacted not only by the vegetation and subsurface parameterizations, but also by the antecedent condition of model state variables, such as the initial soil moisture, depth to groundwater and ground temperature. In land surface modeling, a given model is often run repeatedly over a single year of forcing data until it reaches an equilibrium state: the point at which there is minimal artificial drift in the model state or prognostic variables (most often the soil moisture). For more complex coupled and integrated systems, where there is an increased computational cost of simulation and the number of variables sensitive to initialization is greater than in traditional uncoupled land surface modeling schemes, the challenge is to minimize the impact of initialization while using the smallest spin-up time possible. In this study, multi-criteria analysis was performed to assess the spin-up behavior of the ParFlow.CLM integrated groundwater-surface water-land surface model over a 208 km 2 sub-catchment of the Ringkobing Fjord catchment in Denmark. Various measures of spin-up performance were computed for model state variables such as the soil moisture and groundwater storage, as well as for diagnostic variables such as the latent and sensible heat fluxes. The impacts of initial conditions on surface water–groundwater interactions were then explored. Our analysis illustrates that the determination of an equilibrium state depends strongly on the variable and performance measure used. Choosing an improper initialization of the model can generate simulations that lead to a misinterpretation of land surface-subsurface feedback processes and result in large biases in simulated discharge. Estimated spin-up time from a series of spin-up functions revealed that 20 (or 21) years of simulation were sufficient for the catchment to equilibrate according to at least one criterion at the 0.1% (0.01%) threshold level. Amongst a range of convergence metrics examined, percentage changes in monthly values of groundwater and unsaturated zone storages produced a slow system convergence to equilibrium, whereas criteria based on ground temperature allowed a more rapid spin-up. Slow convergence of unsaturated and saturated zone storages is a result of the dynamic adjustment of the water table in response to a physically arbitrary or inconsistent initialization of a spatially uniform water table. Achieving equilibrium in subsurface storage ensured equilibrium across a spectrum of other variables, hence providing a good measure of system-wide equilibrium. Overall, results highlight the importance of correctly identifying the key variable affecting model equilibrium and also the need to use a multi-criteria approach to achieve a rapid and stable model spin-up.

Description: In this paper, we perform a detailed regional analysis of the link between meteorological drought indices and streamflow for a comprehensive Austrian dataset of 47 small to medium-size catchments in humid-temperate climate. Four drought indices considering different components of the catchment water balance are tested. We assess the quality of the link using rank correlation analysis, and the probability of detecting low flow events by hit-scores. Overall, correlations range between 0.4 and 0.8 and differ significantly between regions. A stratified analysis shows that the link is much stronger (i) for summer low flows and droughts than for anomalies in general, and (ii) for more humid than more arid conditions. Under more humid conditions streamflow droughts of small to medium-size catchments are to a large extent generated by climate forcing and therefore well represented by a simple meteorological index. Under increasingly dry conditions, the climate signal gets less predictive and storage properties of the underground become more important. A simple soil moisture accounting scheme (such as those of the Palmer index) can considerably improve the correlations. Overall, we conclude there is a significant link between meteorological drought and streamflow drought, except for catchments where groundwater storage and snow processes are important. The results are encouraging and provide a wealth of information which can profitably be used to set up statistical prediction models to estimate low flows from meteorological time series.

Description: Water resources in the western United States are contingent on interannual variations in snowpack. Interannual snowpack variability has been attributed to large-scale climate patterns including the El Niño-Southern Oscillation (ENSO), however the contribution of snowfall frequency and extreme snowfall events to this variability are less well quantified. Long term records from Snowpack Telemetry and Cooperative Observer Program stations in the eleven western states were used to investigate these relationships by considering the number of snowfall days and snowfall water equivalent (SFE) of extreme snowfall events. The top decile of snowfall events contributed 20-38% of annual SFE, depending on the region. An average of 65% and 69% of the interannual variability in annual SFE was explained by snowfall days and SFE of top decile snowfall events, respectively, with extreme events being a more significant predictor at most stations. The latitudinal dipole in SFE during ENSO phases results from changes in snowfall frequency and extreme events. In the Pacific Northwest, above normal SFE during La Niña winters was a product of both larger contributions from extremes and more snowfall days, while below normal SFE during El Niño winters was primarily associated with a substantial reduction in extremes. Conversely, annual SFE during ENSO phases in the mountains of Arizona was more closely linked to fluctuations in snowfall days than extremes. Results indicate the importance of extreme snowfall events in shaping interannual variability in water resources and suggest that improved predictive ability may inform better water resource management now and in the coming decades.

Description: The formation of a homogeneous Bi 8 TiO 14 phase was successfully achieved in a specimen calcined at 600°C. However, a Bi 4 Ti 3 O 12 secondary phase also developed in specimens calcined at temperatures higher than 600°C, probably because of Bi 2 O 3 evaporation. For specimens sintered above 800°C, a small amount of the Bi 8 TiO 14 phase melted during sintering, with the liquid phase contributing to the densification of the specimens; however, Bi 4 Ti 3 O 12 and Bi 12 TiO 20 secondary phases were still formed in these specimens. The microwave dielectric properties of the Bi 8 TiO 14 phase were considerably affected by variations in the microstructure of the specimens. When the sintering temperature exceeded 825°C, the amount of secondary phases increased, and this decreased the density and Q×f values of the specimens. Bi 8 TiO 14 ceramics sintered at 825°C exhibited promising microwave dielectric properties, with ε r = 47.4, Q×f  =   5370 GHz, and τ f = −16.01 ppm/°C.

Description: Cell-centered finite volume methods are prevailing in numerical simulation of flow in porous media. However, due to the lack of cell-centered finite volume methods for mechanics, coupled flow and deformation is usually treated either by coupled finite-volume-finite element discretizations, or within a finite element setting. The former approach is unfavorable as it introduces two separate grid structures, while the latter approach loses the advantages of finite volume methods for the flow equation. Recently we proposed a cell-centered finite volume method for elasticity. Herein we explore the applicability of this novel method to provide a compatible finite volume discretization for coupled hydro-mechanic flows in porous media. We detail in particular the issue of coupling terms, and show how this is naturally handled. Furthermore, we observe how the cell-centered finite volume framework naturally allows for modeling fractured and fracturing porous media through internal boundary conditions. We support the discussion with a set of numerical examples: The convergence properties of the coupled scheme are first investigated; Secondly, we illustrate the practical applicability of the method both for fractured and heterogeneous media.

Description: The spatiotemporal distribution of Land Surface Temperature (LST) is linked to the partitioning of the coupled surface water and energy budgets. In watersheds with a strong seasonality in precipitation and vegetation cover, the temporal evolution of LST patterns are a signature of the interactions between the land surface and atmosphere. Nevertheless, few studies have sought to understand the topographical and ecohydrological controls on LST in regions of complex terrain. Numerical watershed models, tested against spatially-distributed field and remote sensing data, can aid in linking the seasonal evolution of LST to meteorology, terrain, soil and vegetation. In this study, we use a distributed hydrologic model to explore LST patterns in a semiarid mountain basin during the transition from a dry spring to the wetter North American monsoon (NAM). By accounting for vegetation greening through remotely-sensed parameters, the model reproduces LST and surface soil moisture observations derived from ground, aircraft and satellite platforms with good accuracy at individual sites and as spatial basin patterns. Distributed simulations reveal how LST varies with elevation, slope and aspect and the role played by the seasonal vegetation canopy in cooling the land surface and increasing the spatial variability in LST. As a result, LST is shown to track well with ecosystem-specific changes in vegetation cover, evapotranspiration and soil moisture during the NAM. Furthermore, vegetation greening is shown to modulate the spatial heterogeneity of LST during the NAM that should be considered in subsequent atmospheric studies in regions of complex terrain.

Description: Models of landscape evolution or hydrological processes typically depend on the accurate determination of upslope drainage area from digital elevation data, but such calculations can be very computationally demanding when applied to high-resolution topographic data. To overcome this limitation, we propose calculating drainage area in an implicit, iterative manner using linear solvers. The basis of this method is a recasting of the flow routing problem as a sparse system of linear equations, which can be solved using established computational techniques. This approach is highly parallelizable, enabling data to be spread over multiple computer processors. Good scalability is exhibited, rendering it suitable for contemporary high-performance computing architectures with many processors, such as graphics processing units (GPUs). In addition, the iterative nature of the computational algorithms we use to solve the linear system creates the possibility of accelerating the solution by providing an initial guess, making the method well suited to iterative calculations such as numerical landscape evolution models. We compare this method with a previously proposed parallel drainage area algorithm and present several examples illustrating its advantages, including a continent-scale flow routing calculation at 3 arcsecond resolution, improvements to models of fluvial sediment yield, and acceleration of drainage area calculations in a landscape evolution model. We additionally describe a modification that allows the method to be used for parallel basin delineation.

Description: Ecological Applications, Ahead of Print. Translocation experiments, in which researchers displace animals then monitor their movements to return home, are commonly used as tools to assess functional connectivity of fragmented landscapes. Such experiments are purported to have important advantages of being time efficient and standardizing 'motivation' to move across individuals. Yet, we lack tests of whether movement behavior of translocated birds reflects natural behavior of unmanipulated birds. We compared the routine movement behavior of a tropical hummingbird (Phaethornis guy) to that of experimentally translocated individuals. We tested for differences in site-selection patterns during movement at two spatial scales (point and path levels). We also compared movement rates between treatments. Behaviors documented during translocation experiments reflected those observed during routine movements. At the point level, both translocated and non-translocated birds showed similar levels of preference for mature tropical forest. At the path level, step selection functions showed both translocated and non-translocated hummingbirds avoiding movement across non-forested matrix and selecting streams as movement corridors. Movement rates were generally higher during translocation experiments. However, the negative influence of forest cover on movement rates was proportionately similar in translocation and routine movement treatments. We report the first evidence showing that movement behavior of birds during translocation experiments is similar to their natural movement behavior. Therefore, translocation experiments may be reliable tools to address effects of landscape structure on animal movement. We observed consistent selection of landscape elements between translocated and non-translocated birds, indicating that both routine and translocation movement studies lead to similar conclusions regarding the effect of landscape structure and forest composition on functional connectivity. Our observations that hummingbirds avoid non-forest matrix and select riparian corridors also provides a potential mechanism for pollen limitation in fragmented tropical forest.

Description: Ecological Applications, Ahead of Print. Climate change vulnerability assessments for species of conservation concern often use species distribution and ecological niche modeling to project changes in habitat. One of many assumptions of these approaches is that food web dependencies are consistent in time and environmental space. Species at higher trophic levels that rely on the availability of species at lower trophic levels as food may be sensitive to extinction cascades initiated by changes in the habitat of key food resources. Here we assess climate change vulnerability for Ursus arctos (grizzly bears) in the southern Canadian Rocky Mountains using projected changes to 17 of the most commonly consumed plant food items. We used presence-absence information from 7,088 field plots to estimate ecological niches and to project changes in future distributions of each species. Model projections indicated idiosyncratic responses among food items. Many food items persisted or even increased, although several species were found to be vulnerable based on declines or geographic shifts in suitable habitat. This included Hedysarum alpinum (alpine sweet vetch), a critical spring and autumn root-digging resource when little else is available. Potential habitat loss was also identified for three fruiting species of lower importance to bears: Empetrum nigrum (crowberry), Vaccinium scoparium (grouseberry) and Fragaria virginiana (strawberry). A general trend towards uphill migration of bear foods may result in higher vulnerability to bear populations at low elevations which are also those that are most likely to have human-bear conflict problems. Regardless, a wide diet breadth of grizzly bears, as well as wide environmental niches of most food items, make climate change a much lower threat to grizzly bears than other bear species such as polar bears and panda bears. We cannot exclude, however, future alterations in human behavior and land use resulting from climate change that may reduce survival rates.

Description: Ecological Applications, Ahead of Print. Efforts to test and improve terrestrial biosphere models (TBMs) using a variety of data sources have become increasingly common. However, geographically extensive forest inventories have been under-exploited in previous model-data fusion efforts. Inventory observations of forest growth, mortality, and biomass integrate processes across a range of time scales, including slow time-scale processes such as species turnover, that are likely to have important effects on ecosystem responses to environmental variation. However, the large number (thousands) of inventory plots precludes detailed measurements at each location, so that uncertainty in climate, soil properties, and other environmental drivers may be large. Errors in driver variables, if ignored, introduce bias into model-data fusion. We estimated errors in climate and soil drivers at U.S. Forest Inventory and Analysis (FIA) plots, and we explored the effects of these errors on model-data fusion with the Geophysical Fluid Dynamics Laboratory LM3V dynamic global vegetation model. When driver errors were ignored or assumed small at FIA plots, responses of biomass production in LM3V to precipitation and soil available water capacity appeared steeper than the corresponding responses estimated from FIA data. These differences became non-significant if driver errors at FIA plots were assumed large. Ignoring driver errors when optimizing LM3V parameter values yielded estimates for fine-root allocation that were larger than biometric estimates, which is consistent with the expected direction of bias. To explore if complications posed by driver errors could be circumvented by relying on intensive study sites where driver errors are small, we performed a power analysis. To accurately quantify the response of biomass production to spatial variation in mean annual precipitation within the eastern U.S. would require at least 40 intensive study sites, which is larger than the number of sites typically available for individual biomes in existing plot networks. Driver errors may be accommodated by several existing model-data fusion approaches, including hierarchical Bayesian methods and ensemble filtering methods; however, these methods are computationally expensive. We propose a new approach, in which the TBM functional response is fit directly to the driver-error-corrected functional response estimated from data, rather than to the raw observations.

Description: Ecological Applications, Ahead of Print. Despite intensive monitoring, temporary emigration from the sampling area can induce bias severe enough for managers to discard life-history parameter estimates toward the terminus of the times series (terminal bias). Under random temporary emigration unbiased parameters can be estimated with CJS models. However, unmodeled Markovian temporary emigration causes bias in parameter estimates and an unobservable state is required to model this type of emigration. The robust design is most flexible when modeling temporary emigration, and partial solutions to mitigate bias have been identified, nonetheless there are conditions were terminal bias prevails. Long-lived species with high adult survival and highly variable non-random temporary emigration present terminal bias in survival estimates, despite being modeled with the robust design and suggested constraints. Because this bias is due to uncertainty about the fate of individuals that are undetected toward the end of the time series, solutions should involve using additional information on survival status or location of these individuals at that time. Using simulation, we evaluated the performance of models that jointly analyze robust design data and an additional source of ancillary data (predictive covariate on temporary emigration, telemetry, dead recovery, or auxiliary resightings) in reducing terminal bias in survival estimates. The auxiliary resighting and predictive covariate models reduced terminal bias the most. Additional telemetry data was effective at reducing terminal bias only when individuals were tracked for a minimum of two years. High adult survival of long-lived species made the joint model with recovery data ineffective at reducing terminal bias because of small-sample bias. The naïve constraint model (last and penultimate temporary emigration parameters made equal), was the least efficient, though still able to reduce terminal bias when compared to an unconstrained model. Joint analysis of several sources of data improved parameter estimates and reduced terminal bias. Efforts to incorporate or acquire such data should be considered by researchers and wildlife managers, especially in the years leading up to status assessments of species of interest. Simulation modeling is a very cost effective method to explore the potential impacts of using different sources of data to produce high quality demographic data to inform management.

Description: Ecological Applications, Ahead of Print. Warmer and drier climate over the past few decades has brought larger fire sizes and increased annual area burned in forested ecosystems of western North America, and continued increases in annual area burned are expected due to climate change. As warming continues, fires may also increase in severity and produce larger contiguous patches of high severity. We use remotely sensed burn-severity data from 125 fires in the northern Cascade Range of Washington, USA, to explore relationships between fire size, severity, and the spatial pattern of severity. We examine relationships between climate and the annual area burned and the size of wildfires over a 25-year period. We test the hypothesis that increased fire size is commensurate with increased burn severity and increased spatial aggregation of high severity. We also ask how local ecological controls might modulate these relationships by comparing results over the whole study area (the northern Cascade Range) to those from four ecological subsections within it. We found significant positive relationships between climate and fire size, and between fire size and the proportion of high severity and spatial-pattern metrics that quantify the spatial aggregation of high-severity areas within fires, but the strength and significance of these relationships varied among the four subsections. In areas with more contiguous subalpine forests and less complex topography, the proportion of high severity and spatial aggregation of high severity were more strongly correlated with fire size. If fire sizes increase in a warming climate, changes in the extent, severity, and spatial pattern of fire regimes will likely be more pronounced in higher-severity fire regimes with less complex topography and more continuous fuels.

Description: Ecological Applications, Ahead of Print. Fremont cottonwood (Populus fremonti, Eckenwal.) is a foundation riparian tree species that drives community structure and ecosystem processes in southwestern U.S. ecosystems. Despite its ecological importance, little is known about the ecological and environmental processes that shape its genetic diversity, structure and landscape connectivity. Here, we combine molecular analyses of 82 populations including 1,312 individual trees dispersed over the species' geographical distribution. We reduced the dataset to 40 populations and 743 individuals to eliminate admixture with a sibling species, and used multi-variate restricted optimization and reciprocal causal modeling, to evaluate the effects of river network connectivity and climatic gradients on gene flow. Our results confirmed the following: First, gene flow of Fremont cottonwood is jointly controlled by the connectivity of the river network and gradients of seasonal precipitation. Second, gene flow is facilitated by mid-sized to large rivers, and is resisted by small streams and terrestrial uplands, with resistance to gene flow decreasing with river size. Third, genetic differentiation increases with cumulative differences in winter and spring precipitation. Our results, suggest that ongoing fragmentation of riparian habitats will lead to a loss of landscape level genetic connectivity, leading to increased inbreeding and the concomitant loss of genetic diversity in a foundation species. These genetic effects will cascade to a much larger community of organisms, some of which are threatened and endangered.

Description: Ecological Applications, Ahead of Print. Identifying determinants of the probability and intensity of infections is important for understanding the epidemiology of wildlife diseases, and for managing their impact on threatened species. Chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis, has decimated populations of some amphibians. However, recent studies have identified important environmental constraints on the disease, related to the pathogen's physiological tolerances. In this study, we identified several intrinsic and extrinsic determinants of the probability and intensity of chytrid infections for the threatened Growling Grass Frog (Litoria raniformis) in south-eastern Australia, and used mark-recapture to estimate the effect of chytrid infections on the probability of survival of these frogs. Water temperature and salinity had negative effects on both the probability and intensity of chytrid infections. We coupled models of the infection process with a model of the effect of chytrid infections on the probability of survival to assess variation in the impact of chytridiomycosis between wetlands with differing temperature and salinity profiles. Our results suggest that warm, saline wetlands may be refuges from chytridiomycosis for L. raniformis, and should be priorities for protection. Our results also suggest that management actions that increase water temperature (e.g. reducing canopy shading) and salinity (e.g. complementing inflows with groundwater) could be trialled to reduce the impacts of chytridiomycosis on this species. This and other recent studies highlight the value of research on environmental risk factors for chytridiomycosis.

Description: Ecological Applications, Ahead of Print. Terrestrial soil is a large reservoir of atmospherically deposited mercury (Hg). However, few studies have evaluated the accumulation of Hg in terrestrial ecosystems in the northeastern United States, a region which is sensitive to atmospheric Hg deposition. In this study, we characterize Hg and organic matter in soil profiles from 139 sampling sites for five sub-regions across the northeastern United States, and estimate atmospheric Hg deposition to these sites by combining numerical modeling with experimental data from the literature. We did not observe any significant relationships between current net atmospheric Hg deposition and soil Hg concentrations or pools, even though soils are a net sink for Hg inputs. Soil Hg appears to be preserved relative to organic carbon (OC) and/or nitrogen (N) in the soil matrix, as a significant negative relationship was observed between the ratios of Hg/OC and OC/N (r = 0.54, p 〈 0.0001) that shapes the horizonal distribution patterns. We estimated that atmospheric Hg deposition since 1850 (3.97 mg m-2) accounts for 102% of the Hg pool in the organic horizons (3.88 mg m-2) and 19% of the total soil Hg pool (21.32 mg m-2), except for the Southern New England (SNE) sub-region. The mean residence time for soil Hg was estimated to be 1,800 years, except SNE which was 800 years. These patterns suggest that in additional to atmospheric deposition, the accumulation of soil Hg is linked to the mineral diagenetic and soil development processes in the region.

Description: Ecological Applications, Ahead of Print. Predicting how climate change is likely to interact with myriad other stressors that threaten species of conservation concern is an essential challenge in aquatic ecosystems. This study provides a framework to accomplish this task in salmon-bearing streams of the northwestern United States, where land-use related reductions in riparian shading have caused changes in stream thermal regimes, and additional warming from projected climate change may result in significant losses of coldwater fish habitat over the next century. Predatory non-native smallmouth bass have also been introduced into many northwestern streams and their range is likely to expand as streams warm, presenting an additional challenge to the persistence of threatened Pacific salmon. The goal of this work was to forecast the interactive effects of climate change, riparian management, and non-native species on stream-rearing salmon, and to evaluate the capacity of restoration to mitigate these effects. We intersected downscaled global climate forecasts with a local-scale water temperature model to predict mid- and end-of-century temperatures in streams in the Columbia River basin; we compared one stream that is thermally impaired due to the loss of riparian vegetation and another that is cooler and has a largely intact riparian corridor. Using the forecasted stream temperatures in conjunction with fish-habitat models, we predicted how stream-rearing Chinook salmon and bass distributions would change as each stream warmed. In the highly modified stream, end-of-century warming may cause near total loss of Chinook salmon rearing habitat and a complete invasion of the upper watershed by bass. In the less modified stream, bass were thermally restricted from the upstream-most areas. In both systems, temperature increases resulted in higher predicted spatial overlap between stream-rearing Chinook salmon and potentially predatory bass in the early summer (2-4-fold increase) and greater abundance of bass. We found that riparian restoration could prevent the extirpation of Chinook salmon from the more altered stream, and could also restrict bass from occupying the upper 31 km of salmon rearing habitat. The proposed methodology and model predictions are critical for prioritizing climate-change adaptation strategies before salmonids are exposed to both warmer water and greater predation risk by non-native species.

Description: Ecological Applications, Volume 24, Issue 3, Page 528-538, April 2014. A unique high temporal frequency data set from an irrigated cotton–wheat rotation was used to test the agroecosystem model DayCent to simulate daily N2O emissions from subtropical vertisols under different irrigation intensities. DayCent was able to simulate the effect of different irrigation intensities on N2O fluxes and yield, although it tended to overestimate seasonal fluxes during the cotton season. DayCent accurately predicted soil moisture dynamics and the timing and magnitude of high fluxes associated with fertilizer additions and irrigation events. At the daily scale we found a good correlation of predicted vs. measured N2O fluxes (r2 = 0.52), confirming that DayCent can be used to test agricultural practices for mitigating N2O emission from irrigated cropping systems. A 25-year scenario analysis indicated that N2O losses from irrigated cotton–wheat rotations on black vertisols in Australia can be substantially reduced by an optimized fertilizer and irrigation management system (i.e., frequent irrigation, avoidance of excessive fertilizer application), while sustaining maximum yield potentials.

Description: Ecological Applications, Ahead of Print. Grazing represents one of the most common disturbances in drylands worldwide, affecting both ecosystem structure and functioning. Despite the efforts to understand the nature and magnitude of grazing effects on ecosystem components and processes, contrasting results continue to arise. This is particularly remarkable for the biological soil crust (BSC) communities (i.e. cyanobacteria, lichens and bryophytes), which play an important role in soil dynamics. Here we evaluated simultaneously the effect of grazing impact on BSC communities (resistance) and recovery after livestock exclusion (resilience) in a semiarid grassland of Central Mexico. In particular, we examined BSC species distribution, species richness, taxonomical group cover (i.e., cyanobacteria, lichen, bryophyte) and composition along a disturbance gradient with different grazing regimes (low, medium, high impact) and along a recovery gradient with differently-aged livestock exclosures (short-, medium-, long-term exclusion). Differences in grazing impact and time of recovery from grazing both resulted in slight changes in species richness; however, there were pronounced shifts in species composition and group cover. We found we could distinguish four highly diverse and dynamic BSC species groups: 1) species with high resistance and resilience to grazing, 2) species with high resistance but low resilience, 3) species with low resistance but high resilience, and 4) species with low resistance and resilience. While disturbance resulted in a novel diversity configuration, which may profoundly affect ecosystem functioning, we observed that 10 years of disturbance removal did not lead to the ecosystem structure found after 27 years of recovery. These findings are an important contribution to our understanding of BCS dynamics from a species and community perspective placed in a land use change context.

Description: Ecological Applications, Ahead of Print. Post-fire predictions of forest recovery under future climate change and management actions are necessary for forest managers to make decisions about treatments. We applied the Climate-Forest Vegetation Simulator (Climate-FVS), a new version of a widely used forest management model, to compare alternative climate and management scenarios in a severely burned multi-species forest of Arizona, U.S.A. The incorporation of seven combinations of General Circulation Models (GCM) and emissions scenarios altered long-term (100 years) predictions of future forest condition compared to a No Climate Change (NCC) scenario, which forecast a gradual increase to high levels of forest density and carbon stock. In contrast, emissions scenarios that included continued high greenhouse gas releases led to near-complete deforestation by 2111. GCM-emissions scenario combinations that were less severe reduced forest structure and carbon stock relative to NCC. Fuel reduction treatments that had been applied prior to the severe wildfire did have persistent effects, especially under NCC, but were overwhelmed by increasingly severe climate change. We tested six management strategies aimed at sustaining future forests: prescribed burning at 5, 10, or 20-year intervals, thinning 40% or 60% of stand basal area, and no-treatment. Severe climate change led to deforestation under all management regimes, but important differences emerged under the moderate scenarios: treatments that included regular prescribed burning fostered low density, wildfire-resistant forests composed of the naturally dominant species, ponderosa pine. Non-fire treatments under moderate climate change were forecast to become dense and susceptible to severe wildfire, with a shift to dominance by sprouting species. Current U.S. forest management requires modeling of future scenarios but does not mandate consideration of climate change effects. However, this study showed substantial differences in model outputs depending on climate and management actions. Managers should incorporate climate change into the process of analyzing the environmental effects of alternative actions.

Description: Ecological Applications, Ahead of Print. Digital repeat photography is becoming widely used for near surface remote sensing of vegetation. Canopy greenness, which has been used extensively for phenological applications, can be readily quantified from camera images. Important questions remain, however, as to whether the observed changes in canopy greenness are directly related to changes in leaf-level traits, changes in canopy structure, or some combination thereof. We investigated relationships between canopy greenness and various metrics of canopy structure and function, using five years (2008-2012) of automated digital imagery, ground observations of phenological transitions, leaf area index (LAI) measurements, and eddy-covariance estimates of gross ecosystem photosynthesis from the Harvard Forest, a temperate deciduous forest in the northeastern USA. Additionally, we sampled canopy sunlit leaves on a weekly basis throughout the growing season of 2011. We measured physiological and morphological traits including leaf size, mass (wet/dry), nitrogen content, chlorophyll fluorescence, and spectral reflectance, and characterized individual leaf color with flatbed scanner imagery. Our results show that observed spring and autumn phenological transition dates are well captured by information extracted from digital repeat photography. However, spring development of both LAI and the measured physiological and morphological traits are shown to lag behind spring increases in canopy greenness, which rises very quickly to its maximum value before leaves are even half their final size. Based on the hypothesis that changes in canopy greenness represent the aggregate effect of changes in both leaf-level properties (specifically, leaf color) and changes in canopy structure (specifically, LAI), we developed a two end-member mixing model. With just a single free parameter, the model was able to reproduce the observed seasonal trajectory of canopy greenness. This analysis shows that canopy greenness is relatively insensitive to changes in LAI at high LAI levels, which we further demonstrate by assessing the impact of an ice-storm on both LAI and canopy greenness. Our study provides new insights into the mechanisms driving seasonal changes in canopy greenness retrieved from digital camera imagery. The nonlinear relationship between canopy greenness and canopy LAI has important implications both for phenological research applications and for assessing responses of vegetation to disturbances.

Description: A new solid solution of (1− x ) Pb ( Mg 1/2 W 1/2 ) O 3 – x Pb ( Zn 1/2 W 1/2 )O 3 has been prepared in the form of ceramics by solid-state reaction with composition x up to 30%. It is found that with the substitution of Zn 2+ for Mg 2+ on the B site of the of complex perovskite structure the antiferroelectric (AFE) Curie temperature T C of PMW increases from 40°C ( x  = 0) to 67°C ( x  = 30%), indicating an enhancement of antiferroelectric order, whereas, at the same time, the phase transition becomes more diffuse due to a higher degree of chemical inhomogeneity. X-ray diffraction analysis indicates that the crystal structure adopts an orthorhombic space group ( Pmcn ) with a decrease in lattice parameter a, but an increase in b and c as the Zn 2+ concentration increases. The low dielectric constant (~ 10 2 ), low dielectric loss (tanδ ≈ 10 −3 ), linear-field-induced polarization, and significantly high breakdown field (~ 125 kV/cm) at room temperature make this family of dielectric materials a promising candidate for ceramic insulators.

Description: ABSTRACT Rising development costs and growing concerns over environmental impacts have led many communities to explore more diversified water management strategies. These 'portfolio'-style approaches integrate existing supply infrastructure with other options such as conservation measures or water transfers. Diversified water supply portfolios have been shown to reduce the capacity and costs required to meet demand, while also providing greater adaptability to changing hydrologic conditions. However, this additional flexibility can also cause unexpected reductions in revenue (from conservation) or increased costs (from transfers). The resulting financial instability can act as a substantial disincentive to utilities seeking to implement more innovative water management techniques. This study seeks to design portfolios that employ financial tools (e.g. contingency funds, index insurance) to reduce fluctuations in revenues and costs, allowing these strategies to achieve improved performance without sacrificing financial stability. This analysis is applied to the development of coordinated regional supply portfolios in the 'Research Triangle' region of North Carolina, an area comprising four rapidly growing municipalities. The actions of each independent utility become interconnected when shared infrastructure is utilized to enable inter-utility transfers, requiring the evaluation of regional tradeoffs in up to five performance and financial objectives. Diversified strategies introduce significant tradeoffs between achieving reliability goals and introducing burdensome variability in annual revenues and/or costs. Financial mitigation tools can mitigate the impacts of this variability, allowing for an alternative suite of improved solutions. This analysis provides a general template for utilities seeking to navigate the tradeoffs associated with more flexible, portfolio-style management approaches.

Description: Despite significant advances during the last decades, there are still many processes related to non-equilibrium flow and transport in macroporous soil that are far from completely understood. The use of X-ray for imaging time-lapse 3-D solute transport has a large potential to help advance the knowledge in this field. We visualized the transport of potassium iodide (20 g iodide l -1 H 2 O) front through a small undisturbed soil column (height 3.8 cm, diameter 6.8 cm) under steady-state hydraulic conditions using an industrial X-ray scanner. In addition, the electrical conductivity was measured in the effluent solution during the experiment. We attained a series of seventeen 3-D difference images which we related to iodide concentrations using a linear calibration relationship. The solute transport through the soil mainly took place in two cylindrical macropores, by-passing more than 90% of the bulk soil volume during the entire experiment. From these macropores the solute diffused into the surrounding soil matrix. We illustrated the properties of the investigated solute transport by comparing it to a 1-D convective-dispersive transport and by calculating the temporal evolution of the dilution index. We furthermore showed that the tracer diffusion from one of the macropores into the surrounding soil matrix could not be exactly fitted with the cylindrical diffusion equation. We believe that similar studies will help establish links between soil structure and solute transport processes and lead to improvements in models for solute transport through undisturbed soil.

Description: A semi-analytical grid-free series solution method is presented for modeling 3-D steady-state free boundary groundwater-surface water exchange in geometrically complex stratified aquifers. Continuous solutions for pressure in the subsurface are determined semi-analytically, as is the location of the water table surface. Mass balance is satisfied exactly over the entire domain except along boundaries and interfaces between layers, where errors are shown to be acceptable. The solutions are derived and demonstrated on a number of test cases and the errors are assessed and discussed. This accurate and grid-free scheme can also be a helpful tool for providing insight into lake-aquifer and stream-aquifer interactions. Here, it is used to assess the impact of lake sediment geometry and properties on lake-aquifer interactions. Various combinations of lake sediment are considered and the appropriateness of the Dupuit-Forchheimer approximation for simulating lake bottom flux distribution is investigated. In addition, the method is applied to a test problem of surface seepage flows from a complex topographic surface; this test case demonstrated the method's efficacy for simulating physically realistic domains.

Description: This article is aimed at quantifying and discussing the relative magnitude of key terms of the equation of conservation of turbulent kinetic energy (TKE) in the inter-stem space of a flow within arrays of vertical cylinders simulating plant stems of emergent and rigid vegetation. The spatial distribution of turbulent quantities and mean flow variables are influenced by two fundamental space scales, the diameter of the stems and the local stem areal number-density. Both may vary considerably since the areal distribution of plant stems in natural systems is generally not homogeneous; they are often arranged in alternating sparse and dense patches. The magnitude of the terms of the budget of TKE in the inter-stem space has seldom been quantified experimentally and is currently not well-known. This work addresses this research need. New databases, consisting of three-component LDA velocity series and two-component PIV velocity maps, obtained in carefully controlled laboratory conditions, were used to calculate the terms of the TKE budget. The physical system comprises random arrays of rigid and emergent cylinders with longitudinally varying areal number-density. It is verified that the main source of TKE is vortex shedding from individual cylinders. The rates of production and dissipation are not in equilibrium. Regions with negative production, a previously unreported feature, are identified. Turbulent transport is particularly important along the von Kármán vortex street. Convective rate of change of TKE and pressure diffusion are most relevant in the vicinity of the cylinders.

Description: A major difficulty in modeling multiphase flow in porous media is the emergence of trapped phases. Our experiments demonstrate that gas can be trapped in either single-pores, multi-pores, or in large connected networks. These large connected clusters can comprise up to 8 grain-volumes and can contain up to 50% of the whole trapped gas volume. About 85% of the gas volume is trapped by multi-pore gas clusters. This variety of possible trapped gas clusters of different shape and volume will lead to a better process understanding of bubble-mediated mass transfer. Since multi-pore gas bubbles are in contact with the solid surface through ultra-thin adsorbed water films the interfacial area between trapped gas clusters and intergranular capillary water is only about 80% of the total gas surface. We could derive a significant (R 2 = 0.98) linear relationship between the gas-water-interface and gas saturation. We found no systematic dependency of the front velocity of the invading water phase in the velocity range from 0.1 to 0.6 cm/min corresponding to capillary numbers from 2×10 -7 to 10 -6 . Our experimental results indicate that the capillary trapping mechanism is controlled by the local pore structure and local connectivity and not by thermodynamics, i.e. by the minimum of the Free Energy , at least in the considered velocity range. Consistent with this physical picture is our finding that the trapping frequency (= bubble-size distribution) reflects the pore-size distribution for the whole range of pore radii, i.e. the capillary trapping process is determined by statistics and not by thermodynamics.

Description: Ecological Applications, Ahead of Print. The degree to which recent bark beetle (Dendroctonus ponderosae) outbreaks may influence fire severity and post-fire tree regeneration is of heightened interest to resource managers throughout western North America, but empirical data on actual fire effects are lacking. Outcomes may depend on burning conditions (i.e., weather during fire), outbreak severity, or intervals between outbreaks and subsequent fire. We studied recent fires that burned through green-attack / red-stage (outbreaks 〈 3 yr before fire) and gray-stage (outbreaks 3-15 yr before fire) subalpine forests dominated by lodgepole pine (Pinus contorta var. latifolia) in Greater Yellowstone, Wyoming, USA, to determine if fire severity was linked to pre-fire beetle outbreak severity and whether these two disturbances produced compound ecological effects on post-fire tree regeneration. With field data from 143 post-fire plots that burned under different conditions, we assessed canopy and surface fire-severity, and post-fire tree seedling density against pre-fire outbreak severity. In the green-attack / red stage, several canopy fire-severity measures increased with pre-fire outbreak severity under moderate burning conditions. Under extreme conditions, few fire-severity measures were related to pre-fire outbreak severity, and effect sizes were of marginal biological significance. The percentage of tree stems and basal area killed by fire increased with more green-attack vs. red-stage trees (i.e., the earliest stages of outbreak). In the gray stage, by contrast, most fire-severity measures declined with increasing outbreak severity under moderate conditions, and fire severity was unrelated to outbreak severity under extreme burning conditions. Post-fire lodgepole pine seedling regeneration was unrelated to pre-fire outbreak severity in either post-outbreak stage, but increased with pre-fire serotiny. Results suggest bark beetle outbreaks can affect fire severity in subalpine forests under moderate burning conditions, but have little effect on fire severity under extreme burning conditions when most large wildfires occur in this system. Thus, beetle outbreak severity was moderately linked to fire severity, but the strength and direction of the linkage depended on both endogenous (outbreak stage) and exogenous (fire weather) factors. Closely-timed beetle outbreak and fire did not impart compound effects on tree regeneration, suggesting the presence of a canopy seedbank may enhance resilience to their combined effects.

Description: Ecological Applications, Ahead of Print. Ecological reserves provide important wildlife habitat in many landscapes, and the functional connectivity of reserves and other suitable habitat patches is crucial for the persistence and resilience of spatially structured populations. To maintain or increase connectivity at spatial scales larger than individual patches, conservation actions may focus on creating and maintaining reserves and/or influencing management on non-reserves. Using a graph-theoretic approach, we assessed the functional connectivity and spatial distribution of wetlands in the Rainwater Basin of Nebraska, U.S.A., an intensively cultivated agricultural matrix, at four assumed, but ecologically realistic, anuran dispersal distances. We compared connectivity in the current landscape to the historical landscape and putative future landscapes, and evaluated the importance of individual and aggregated reserve and non-reserve wetlands for maintaining connectivity. Connectivity was greatest in the historical landscape, where wetlands were also the most densely distributed. The construction of irrigation reuse pits for water storage has maintained connectivity in the current landscape by replacing destroyed wetlands, but these pits likely provide suboptimal habitat. Also, because there are fewer total wetlands (i.e., wetlands and irrigation reuse pits) in the current landscape than the historical landscape, and because the distribution of current wetlands is less clustered than that of historical wetlands, larger and longer-dispersing, sometimes non-native species may be favored over smaller, shorter-dispersing species of conservation concern. Because of their relatively low number, wetland reserves do not affect connectivity as greatly as non-reserve wetlands or irrigation reuse pits; however, they likely provide the highest-quality anuran habitat. To improve future levels of resilience in this wetland habitat network, management could focus on continuing to improve the conservation status of non-reserve wetlands, restoring wetlands at spatial scales that promote movements of shorter-dispersing species, and further scrutinizing irrigation reuse pit removal by considering effects on functional connectivity for anurans, an emblematic and threatened group of organisms. However, broader conservation plans will need to give consideration to other wetland-dependent species, incorporate invasive species management, and address additional challenges arising from global change in social-ecological systems like the Rainwater Basin.

Description: Ecological Applications, Ahead of Print. Ecosystem-based management of natural resources involves an explicit consideration of trade-offs among ecosystem services. In marine fisheries, there is the potential for a trade-off between the supporting role of small pelagic fish and cephalopods in food webs, and the provisioning service they play as a major target of fisheries. Because these species play central roles in food webs by providing a conduit of energy from small prey to upper trophic level predators, we hypothesized that trade-offs between these two ecosystem services could be predicted based on energetic properties of predator-prey linkages and food web structure. We compiled information from 27 marine food web models (Ecopath) that included either small pelagic fish or cephalopods, described predator-prey linkages involving these species, and developed a novel analytical framework to estimate how changes in yields of forage species would propagate through food webs and other fisheries. Consistent with expectations, diet overlap between predators and prey was generally low, and predator prey linkages tended to be asymmetric; contribution of these species to predator diets was, on average, larger than the contribution of individual predator stocks to prey mortality. The estimated trade-offs between yields of forage fish and predator species were highly variable when we assumed joint bottom-up and top-down control on predation. Roughly one-third of this variance was related to an interactive effect of fishing and predation intensity; strong trade-offs were predicted when fishing intensity on forage species is high and when predators account for a high proportion of total forage mortality. When trophic connections were presumed to be driven by bottom-up processes, trade-offs were more predictable but generally very small. Contrary to our expectations, trade-offs were not easily predicted from energetic properties, largely because predators of forage species exhibited a high degree of intra-guild predation and also consumed many of the same prey as forage species. Given the limited ability to a priori predict the food web implications of forage fisheries, we suggest that a precautionary risk-based approach be applied to decisions about acceptable biological removals of forage fish and biological targets used for their management.

Description: Ecological Applications, Ahead of Print. Accelerating climate change and other cumulative stressors create an urgent need to understand the influence of environmental variation and landscape features on the connectivity and vulnerability of freshwater species. Here, we introduce a novel modeling framework for aquatic systems that integrates spatially-explicit, individual-based, demographic and genetic (demogenetic) assessments with environmental variables. To show its potential utility, we simulated a hypothetical network of 19 migratory riverine populations (e.g., salmonids) using a riverscape connectivity and demogenetic model (CDFISH). We assessed how stream resistance to movement -- a function of water temperature, fluvial distance, and physical barriers -- might influence demogenetic connectivity and hence population vulnerability. We present demographic metrics (abundance, immigration, and change in abundance) and also genetic metrics (diversity, differentiation, and change in differentiation), and combine them into a single vulnerability index for identifying populations at risk of extirpation. We considered four realistic scenarios that illustrate the relative sensitivity of these metrics for early detection of reduced connectivity: (1) maximum resistance due to high water temperatures throughout the network, (2) minimum resistance due to low water temperatures throughout the network, (3) increased resistance at a tributary junction caused by a partial barrier, and (4) complete isolation of a tributary, leaving resident individuals only. We then apply this demogenetic framework using empirical data for a bull trout metapopulation in the upper Flathead River system, Canada and USA, to assess how current and predicted future stream warming may influence population vulnerability. Results suggest that warmer water temperatures and associated barriers to movement (e.g., low flows, de-watering) are predicted to fragment suitable habitat for migratory salmonids, resulting in the loss of genetic diversity and reduced sizes in certain vulnerable population. This demogenetic simulation framework, which is illustrated in a web-based interactive mapping prototype (http://ptolemy.dbs.umt.edu/pvm/), should be useful for evaluating population vulnerability in a wide variety of dendritic and fragmented riverscapes, helping to guide conservation and management efforts for freshwater species.

Description: Ecological Applications, Ahead of Print. Fire regimes of the Canadian boreal forest are driven by certain environmental factors that are highly variable from year to year (e.g., temperature, precipitation) and others that are relatively stable (e.g., land cover, topography). Studies examining the relative influence of these environmental drivers on fire activity suggest that models making explicit use of inter-annual variability appear to better capture years of climate extremes, whereas those using a temporal average of all available years highlight the importance of land-cover variables. It has been suggested that fire models built at different temporal resolutions may provide a complementary understanding of controls on fire regimes, but this claim has not been tested explicitly with parallel data and modelling approaches. We addressed this issue by building two models of area burned for the period 1980-2010 using 14 explanatory variables to describe ignitions, vegetation, climate, and topography. We built one model at an annual resolution, with climate and some land-cover variables being updated annually, and the other model using 31-year fire "climatology" based on averaged variables. Despite substantial differences in the variables' contributions to the two models, their predictions were broadly similar, which suggests coherence between the spatial patterns of annually varying climate extremes and long-term climate normals. Where the models' predictions diverged, discrepancies between the annual and averaged models could be attributed to specific explanatory variables. For instance, annually updating land cover allowed us to identify a possible negative feedback between flammable biomass and fire activity. These results show that building models at more than one temporal resolution affords a deeper understanding of controls on fire activity in boreal Canada than can be achieved by examining a single model. However, in terms of spatial predictions, the additional effort required to build annual models of fire activity may not always be warranted in this study area. From a management and policy standpoint, this key finding should boost confidence in models that incorporate climatic normals, thereby providing a stronger foundation on which to make decisions on adaptation and mitigation strategies for future fire activity.

Description: Ecological Applications, Ahead of Print. Fire is becoming a pervasive driver of environmental change in Amazonia and is expected to intensify, given projected reductions in precipitation and forest cover. Understanding of the influence of post-deforestation land cover change on fires in Amazonia is limited, even though fires in cleared lands constitute a threat for ecosystems, agriculture, and human health. We used MODIS satellite data to map burned areas annually between 2001 and 2010. We then combined these maps with land cover and climate information to understand the influence of land cover change in cleared lands and dry season severity on fire occurrence and spread in a focus area in the Peruvian Amazon. Fire occurrence, quantified as the probability of burning of individual 232m spatial resolution MODIS pixels was modeled as a function of the area of land cover types within each pixel, drought severity, and distance to roads. Fire spread, quantified as the number of pixels burned in 3x3 pixel windows around each focal burned pixel, was modeled as a function of land cover configuration and area, dry season severity, and distance to roads. We found that vegetation regrowth and oil palm expansion are significantly correlated with fire occurrence but that the magnitude and sign of the correlation depend on drought severity, successional stage of regrowing vegetation and oil palm age. Burning probability increased with the area of non-degraded pastures, fallow, and young oil palm and decreased with larger extents of degraded pastures, secondary forests and adult oil palm plantations. Drought severity had the strongest influence on fire occurrence overriding the effectiveness of secondary forests but not of adult plantations to reduce fire occurrence in severely dry years. Overall, irregular and scattered land cover patches reduced fire spread but irregular and dispersed fallows and secondary forests increased fire spread during dry years. Results underscore the importance of land cover management for reducing fire proliferation in this landscape. Incentives for promoting natural regeneration and perennial crops in cleared lands might help reduce fire risk if those areas are protected against burning in early stages of development and during severely dry years.

Description: Ecological Applications, Ahead of Print. Intraguild predators both feed on and compete with their intraguild prey. In theory, intraguild predators can therefore be very effective as biological control agents of intraguild prey species, especially in productive environments. We investigated this hypothesis using the mixotrophic chrysophyte Ochromonas as intraguild predator and the harmful cyanobacterium Microcystis aeruginosa as its prey. Ochromonas can grow photoautotrophically, but can also graze efficiently on Microcystis. Hence, it competes with its prey for inorganic resources. We developed a mathematical model and parameterized it for our experimental food web. The model predicts dominance of Microcystis at low nutrient loads, coexistence of both species at intermediate nutrient loads, and dominance of Ochromonas but a strong decrease of Microcystis with further nutrient enrichment. We tested these theoretical predictions in chemostat experiments supplied with three different nitrogen concentrations. Ochromonas initially suppressed the Microcystis abundance by 〉 97% compared to the Microcystis monocultures. Thereafter, however, Microcystis gradually recovered to ~20% of its monoculture abundance at low nitrogen loads, but to 50-60% at high nitrogen loads. Hence, Ochromonas largely lost control over the Microcystis population at high nitrogen loads. We explored several mechanisms that might explain this deviation from theoretical predictions, and found that intraspecific interference at high Ochromonas densities reduced their grazing rates on Microcystis. These results illustrate the potential of intraguild predation to control pest species, but also show that the effectiveness of their biological control can be reduced in productive environments.