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Earth's water resources are critical for supporting livelihoods and food security but are being increasingly overexploited to support global agriculture. Diversifying cropping systems could potentially resolve unsustainable water use but trade‐offs with other aspects of sustainability and food security have not yet been assessed. We performed a detailed analysis of 31 different field crop rotations conducted during 1990–2019 in the North China Plain, to assess the potential impact of crop diversification on actual evapotranspiration (ETa), changes in regional groundwater table, grain yield, economic output, and water use efficiency (WUE) and to identify configurations that can achieve co‐benefits across multiple dimensions. We found that a combination of lowering the cropping index (i.e., harvest frequency), incorporating fallow periods, and introducing higher‐value crops into the currently dominant winter wheat–summer maize double cropping system can reduce growing season ETa by as much as 31%, mitigate groundwater decline by 19% or more, and increased economic output and economic WUE by more than 11% and 3%, respectively. We also found that multiple diversified wheat‐maize–based rotations—all with rotation lengths greater than 2 years—achieve co‐benefits across all evaluated dimensions. This study provides new empirical evidence of the opportunities for diversified crop rotations to balance the multiple objectives of food production, sustainable groundwater use, and farmer profitability. Extending this solution to other water‐stressed agricultural regions could be an effective strategy in achieving more sustainable food production system globally. [ABSTRACT FROM AUTHOR]

Agricultural production in the North China Plain with rainfall of less than 500 mm$yr-1 has been steadily increasing over the past 40 years, with the groundwater levels decreasing at a rate of over 1 m$yr-1. In this paper, it is demonstrated theoretically that the water level in the aquifer can be expressed as a function of agricultural production and the sum of water added as rainfall and imported from outside the basin. Therefore, the most effective measures to halt groundwater depletion are importing water, decreasing cropping intensity and growing less thirsty crops. Irrigation improvements, mulching and agronomic measures that could increase the yield per unit area have less of an impact on solving the declining groundwater levels. [ABSTRACT FROM AUTHOR]

Evapotranspiration (ET) is the major component of the hydrology cycle. Satellites provide a convenient way for gathering information to estimate regional ET. The most widely applied method for converting the instantaneous satellite measurement to daily scale assumes that evaporative fraction (EF), defined as the ratio of ET to the available energy, is constant during the daytime. However, this method was proved to underestimate the daily ET. This study implemented a theoretically improved EF algorithm to calculate daily ET with the decoupling factor method based on the Penman‐Monteith and McNaughton‐Jarvis equations. Seven improved algorithms were developed by assuming that various parameters remain constant during the day. The satellite‐based ET estimates were compared with seven local flux tower measurements in China. The results showed that: (a) The original ET method calculated the daily evaporation more accurately than the other algorithms. However, the good fit was based on two compensating inaccuracies. Compared to the flux tower measurement, the original ET method underestimated the daily EF by 26% and overestimated the daily net radiation by 30%. (b) Six of the seven proposed algorithms underpredicted the daily ET by 30%–60%, mainly due to the inaccurate daily net radiation. (c) The algorithm that assumed that the instantaneous decoupling parameter Ω∗ was equal to its daily value method calculated EF and ET with relative errors of 8% and 10% separately when the inaccurate estimated daily net radiation was replaced by the observed flux tower data. Plain Language Summary: The water that evaporates from the land surface sustains the hydrological cycle that replenishes the world's freshwater resources. Scientists and water managers are therefore interested in quantifying the water that evaporates each day. It is especially true for China that has one of the lowest water reserves in the world. Satellites that provide coverage of all the land surface would be ideal for recording evaporation if we could scale up the instantaneous satellite measurements to a daily scale. The current scale‐up methods available have not been widely tested. In this manuscript, we test the available methods and show how they can be improved for China. Key Points: This article improved satellite‐based daily evapotranspiration calculations for ChinaA decoupling parameter method was used in the daily evaporation fraction algorithm [ABSTRACT FROM AUTHOR]

Abstract: Modeling two-phase flow in proton exchange membrane (PEM) fuel cells is hampered by a lack of conceptual understanding of flow patterns in the gas diffusion layer (GDL). In this paper, pore-scale visualizations of water in different types of GDLs were used to improve current understanding of flow and transport phenomena in PEM fuel cells. Confocal microscopy was used to capture the real-time transport of water, and pressure micro-transducers were installed to measure water breakthrough pressures. Three types of fuel cell GDLs were examined: TO series (Toray Corp., Tokyo, Japan), SGL series (SGL Carbon Group, Wiesbaden, Germany), and MRC series (Mitsubishi Rayon Corp., Otake City, Japan). The visualizations and pressure measurements revealed that despite difference in “pore” structures in the three types of GDLs, water followed distinct flow paths spanning several pores with characteristics similar to the “column flow” phenomena observed previously in hydrophobic or coarse-grained hydrophilic soils. The results obtained from this study can aid in the construction of theories and models for optimizing water management in fuel cells. [Copyright &y& Elsevier]

Abstract: Grain production shortfalls in northern Ethiopia are commonly associated with occurrence of intra-seasonal dry spells or droughts and rapid land degradation which adversely impact crop yields. Suitable practices that use available rainwater more efficiently to mitigate impact of dry spells on crops and that protect soil are needed to stabilize and improve grain yields in the predominately rainfed agriculture. During three cropping seasons on-farm experiments tested conservation tillage techniques implemented with oxen-drawn plows on clay loam soil. Tested tillage techniques are subsoiling, open and tied ridges, no till, and conventional tillage with the local maresha plow (the control). Effectiveness in improving root zone soil moisture, limiting soil erosion, and improving sorghum (Sorghum bicolor (L.) Moench.) and chickpea (Cicer arietinum L.) grain yield were determined. Results demonstrate that performance of the tillage techniques varied with seasonal rainfall distribution and intensity and land slope gradient. Tied and open ridge increased seasonal root zone soil moisture 15–24%. Subsoiling slightly (3%) increased and no till slightly decreased soil moisture but were not statistically different from conventional tillage. Tied ridge and no till significantly reduced seasonal soil loss by up to 11Mgha−1 during seasons with moderate intensity storms, but during a season with high intensity storms tied ridge on over 9% slope gradient increased soil loss (up to 35Mgha−1). The increased soil disturbance of subsoiling led to higher soil loss rates (up to 32Mgha−1) than conventional tillage during all seasons. Grain yield decreased and runoff and erosion rates increased rapidly with increasing land slope gradient. During a season with moderate intensity rainfall open and tied ridge increased sorghum yield by 67–73% over the control (730kgha−1) while no till decreased yield by 25%. During a season when high intensity rainfall events damaged the ridges, subsoiling had the best sorghum yield with 42% increase over the control (1430kgha−1). Poor early season rainfall and fungus attacks resulted in low chickpea yields (200–320kgha−1) and statistically insignificant differences between tillage methods. Overall results of the study suggest that on slopes below 8% gradient oxen-drawn ridge tillage and subsoiling, to a lesser degree, can effectively improve conditions that mitigate impact of short dry spells especially during seasons with less intense rainfall events. [Copyright &y& Elsevier]

Abstract: The topography, hydroperiod, water table, and selected edaphic characteristics are described for Piermont Marsh, an irregularly flooded tidal marsh in the Hudson River Estuary, New York, USA. Despite variations in microtopography, overall the marsh is flat, and although the observations were conducted at a high point in the Estuary''s 18.6 year metonic cycle, its surface was only inundated 10–12 times a month. Observations of spatial differences in the saturated hydraulic conductivity and surface infiltration rates are also discussed. ‘Edge’ portions of the marsh are characterized by a slightly higher, more uniform, more structured, less organic, and less hydrologically conductive substrate than found in the marsh interior. Preferential flow is facilitated by macropores in the creekbank wall. The water table is close to the marsh surface for a lesser percentage of the lunar month in the marsh ‘edge’ when compared to the interior, where it is almost always within 10cm of the surface. The extent to which the spatial variability of these hydrologic characteristics determines the marsh''s ability to provide various ecosystem services is also discussed and the implications of these observations on tidal marsh restoration efforts briefly presented. [Copyright &y& Elsevier]

Abstract: During the last 25 years there has been a great interest in deriving aquifer characteristics from outflow data. This analysis has been mainly based of the drainage of a horizontal aquifer after sudden drawdown, using the Boussinesq approximation. Following the general approach of Brutsaert and Lopez [Brutsaert W, Lopez, JP. Basin-scale geohydrologic drought flow features of riparian aquifers in the southern Great Plains. Water Resour Res 1998;34(2):233–40], it was determined that for this geometry the aquifer behavior could be characterized by dQ/dt ∝ Q 3 for small t and by dQ/dt ∝ Q 3/2 for large t. It was remarked that dQ/dt ∝ Q for large t is often observed. In practice, it is also difficult to determine if dQ/dt ∝ Q 3 for small t because this behavior can only be observed over a very short period. Here, we present a similar analysis of aquifer behavior based on the more fundamental Laplace solution for penetrated aquifers. It has been shown that also when the drain does not fully penetrate the aquifer, the solution still produces good results [Szilagyi, J. Sensitivity analysis of aquifer parameter estimations based on the Laplace equation with linearized boundary conditions. Water Resour Res 2003;39(6)]. The Laplace solution quickly shows that dQ/dt ∝ Q for t →∞ and dQ/dt ∝ Q ∞ for t →0, after sudden drawdown. This analysis reconfirms previous findings concerning long-time behavior. More importantly, the analysis shows that the exponent B in dQ/dt ∝ Q B does not have a fixed limited value for short times for the given geometry. Further analysis, however, shows that under certain conditions the relation dQ/dt ∝ Q 3 is retained for 0≪ t <1. Detailed examination of the Laplace solution also shows under which types of recharge dynamics a well-identifiable transition takes place between short- and long-term behavior. As long as such a clear transition exists, the aquifer characterization method proposed earlier by Brutsaert and Lopez [Brutsaert W, Lopez, JP. Basin-scale geohydrologic drought flow features of riparian aquifers in the southern Great Plains. Water Resour Res 1998;34(2):233–40] can be applied. It is shown that for a sharp pulse input, the Laplace solution gives similar results as presented by Brutsaert and Lopez [Brutsaert W, Lopez, JP. Basin-scale geohydrologic drought flow features of riparian aquifers in the southern Great Plains. Water Resour Res 1998;34(2):233–40]. For a smooth pulse, the transition becomes unclear. What is “smooth” and “sharp” depends on input and aquifer characteristics, whereby shallow aquifers give clearer transitions than deep aquifers for the same input. The analysis shows that when rain ceases suddenly after the aquifer has come into equilibrium with a steady rain input, a usable transition in the relation between dQ/dt and Q can be found as well. Researchers can use the present analysis to assess whether specific aquifers and recharge events can be used for the previously suggested characterization method. [Copyright &y& Elsevier]

Abstract: In order to assess the reliability of the springs near Matalom, Leyte, Philippines as a sustainable source of drinking water, we measured precipitation and outflow of five small and two large springs for the region for a period of a year and analyzed the recession spring flow data. Although monthly spring flow follows a similar pattern to that of the rainfall, the regression relationship between both parameters is poor except for the smallest spring. To determine the dry season spring flow behavior, we analyzed the spring flow data with a mechanistic recession flow model originally developed for prediction of stream drought flow in the northeastern U.S. by Brutsaert and Nieber in 1977. The model describes the dry season spring flow well assuming that the aquifer behaves as a linear reservoir. The analysis shows that the flow “half-life” for the springs is about one month. By adding the individual spring flows to derive a watershed outflow we were able to evaluate how well the simple watershed geometry underlying the analysis of Brutsaert and Nieber [Regionalized drought flow hydrographs from a mature glaciated plateau. Water Resour Res 1977;13(3):637–43] applies to the more complex watersheds. [Copyright &y& Elsevier]

The movement of water and potential pollutants in the vadose zone of fluvial deposits is often difficult to predict because fine-over-coarse layers may behave as capillary barriers, funneling water and dissolved solutes into concentrated preferential flow paths. Capillary barriers have been studied in laboratory experiments and by mathematical analysis with well-defined boundaries but little is known about water and solute movement in naturally layered soils. This paper demonstrates how naturally occurring capillary barriers affect water and solute movement. Experiments were carried-out in a river valley near Amherst, MA and on a prehistoric beach near Cornell University in Ithaca, NY. Dye tracer and chloride were initially applied near the soil surface, followed by intermittent rainfall over several weeks. After 2–6 weeks the blue dye, soil water content, and chloride concentration distributions in the soil profile were examined by excavating a trench and photographing and sampling the exposed soil face. At both sites, the infiltrating water was diverted and flowed laterally over a relatively coarse layer. At the Cornell site, flow broke through the fine–coarse interface into the coarse layer at a few points along the barrier. The primary breakthrough at the Cornell site occurred at a horizontal section of the interface, 2 m down-slope from the point of dye application. The capillary diversions generally agreed with current theory, however, the flow patterns were difficult to predict accurately without more detailed information about the soil layering characteristics. [Copyright &y& Elsevier]

Insufficient sub-surface hydraulic data from watersheds often hinders design of water resources structures. This is particularly true in developing countries and in watersheds with low population densities because well-drilling to obtain the hydraulic data is expensive. The objective of this study was to evaluate the applicability of ‘Brutsaert’ recession flow analysis to steeper and more arid watersheds than those that were previously used. Using daily streamflow data (1962–1992), a modified version of the analysis was used to estimate the subsurface hydraulic parameters of four semi-arid, mountainous watersheds (204–764 km2) near Oaxaca, Mexico. In this analysis, a dimensionless recession curve (DRC) was translated to best-fit observed recession flow (Q) data. The basin-wide hydraulic parameters were directly related to the magnitude of the translation used to fit the DRC to the data. One unique aspect of this study was too few high flow data to confidently fit the DRC to the data via previously published protocols. We, thus, proposed using three different approaches for translating the DRC in order to establish a range for the hydraulic parameters. Our analyses predicted a narrow range of basin-wide hydraulic parameters that were near regionally measured values and consistent within commonly published values for similar geology, suggesting that the Brutsaert method is applicable to arid, mountainous basins like those used here. This method potentially provides a cost-effective alternative to traditional geohydrological field methods for determining groundwater parameters. [Copyright &y& Elsevier]

Watersheds, in many parts of the world, consist of sloping soils with a dense subsoil at shallow depth. Very few measurement techniques exist for realistically determining hydraulic properties in situ on these hillside soils. A hillslope infiltrometer, open at the bottom, top, and downhill sides, was developed that can measure the vertical saturated conductivity of the horizon sequence and lateral hydraulic conductivity of the horizon most conductive to water. The infiltrometer was tested on the steeply sloping soils in Honduras. Increasing rainfall intensities were applied and lateral flow rate was measured in several troughs at the downslope end of the hillslope infiltrometer. Vertical infiltration rates for the horizon sequence and lateral conductivity were calculated at each rainfall rate after steady state conditions were established. The hillslope infiltrometer proved useful in the characterization of subsurface flow on the steep slopes in Honduras. [ABSTRACT FROM AUTHOR]

Soil and water conservation practices are increasingly being considered for curbing non-point source pollution from agricultural land. Several studies have demonstrated that stream power is a simple and good predictor of soil detachment and transport and can be used to predict the effect of soil and water conservation practices on soil loss. Our objective was, therefore, to develop a simple water erosion simulation model that is physically based on stream power, handles vegetation in terms of contact cover, and considers the settling velocity characteristics of the eroding sediment. The model assumes that rill flow can occur on hillslope segments with net erosion, but on segments with net deposition sheet flow is assumed. Input parameters include the depositability of the soil, rill shape, rill density, net precipitation, and an empirical power function describing the decrease of sediment concentration with vegetative cover increase. The model was evaluated by comparison of predicted and observed relationships between sediment concentration, slope, and vegetative residue cover in two experimental studies using simulated rainfall: one that involved erosion plots with various uniform slopes and levels of vegetative cover, and another that involved the observation of soil movement on mechanically shaped concave, uniform, and convex slopes with negligible vegetation. Without calibration, the model appeared to represent soil erosion relationships observed in these studies and is simple enough to be included in grid-based variable source hydrology models. [Copyright &y& Elsevier]

The article discusses the research study conducted to examine the synthesis and analysis of conservation effects assessment projects for improved water quality. Topics discussed include effect of timing, location, and suite of implemented agricultural conservation practices, relationship of conservation practices and water quality in watersheds, and social and economic factors that facilitate or impede implementation of conservation practices.

Examines the first-order model of the US Environmental Protection Agency for predicting losses from the zone of incorporation as part of risk assessment. Simulation of the loss of trace metals from the surface of soil layer; Factors governing the mobility of metals.

The often rapid arrival of pesticides at the ground water has been explained by the concept of preferential movement of water and solutes through the soil. To facilitate understanding of these transport processes, a drainage study was conducted by applying a nonadsorbed tracer to plots drained by subsurface drains. Three management practices were employed: no-till, conventional-till, and conventional-till with incorporation of the tracer. The plots were irrigated with 71–203 mm of water. Drainage line outflow and tracer concentration in the outflow were monitored for up to 52 hr. The resulting soil profiles were analyzed for tracer concentration. The main effect of plowing and incorporating the tracer was a more uniform concentration in the resulting profile. A simple mixing-layer model was used to predict the rate at which the tracer was transported out of the root zone into the layers below. The model was found to be in reasonable agreement with drainage outflow patterns, especially from the incorporated plots. These results may be helpful for future development of best-management practices for controlling the effects of agriculture on environmental pollution. [ABSTRACT FROM AUTHOR]

Simple methods for predicting runoff from watersheds are important in engineering practice, particularly in flood forecasting and water-balance calculation. In this paper, we illustrate that the often used SCS runoff curve-number approach in its most elementary form can be derived from assuming that only the saturated areas contribute to direct runoff. With this approach the initial abstraction or the amount of water required before runoff starts is equal to air-filled pore space per unit area for the most shallow soil in the watershed. Air-filled pore space throughout the year was calculated with aid of the simple water balance employing the Thornthwaite-Mather procedure for the most shallow soil in the watershed. By plotting the effective precipitation defined as the amount of precipitation minus the initial abstraction against the observed runoff for two watersheds in Australia and three in the northeastern United States we found that the SCS curve-number equation in its elementary form fitted the data well. [ABSTRACT FROM AUTHOR]

Minasny et al. (2020) proposed enhancing future global soil science research by examining the role of soils in global ecosystem functioning. They argued in particular that meaningful collaboration between high- and low-income countries is essential to generate new knowledge and facilitate capacity building. In this commentary, we provide an account of our experience with an effective cooperative research and training partnership between Cornell University and Bahir Dar University in Ethiopia. We note that, in addition to the willingness and commitment of the scientists to cooperate, support and flexibility of senior university administrators is essential for international cooperation to succeed. We illustrate these points describing our experience and show that these cooperative efforts are evolving incrementally and in many cases do not follow well-laid-out programs. [ABSTRACT FROM AUTHOR]

Phosphonate‐based herbicides are extensively used in agriculture. Glyphosate was long considered immobile in soils due to strong complexation with metal oxides, but detection in agricultural effluents and surface waters points to glyphosate mobilization and transport. In particular, mechanisms of glyphosate adsorption and subsequent mobility from runoff‐prone soils enriched in quartz have not been fully elucidated. Here we used theoretical and experimental approaches to gain new insights on the soil mobility of glyphosate and two other phosphonate herbicides, glufosinate and fosamine. Molecular modeling simulations of optimized adsorbate complexes of the phosphonate herbicides with quartz and montmorillonite revealed Ca‐enhanced interactions for all three herbicides at both mineral interfaces, weak binding of Na‐complexed phosphonate herbicides on quartz, and more favorable interactions for glufosinate and fosamine with Na‐montmorillonite than for glyphosate. We conducted adsorption and desorption experiments to evaluate the mobility of glyphosate on quartz‐enriched agricultural soils. Consistent with our theoretical findings, adsorption experiments conducted with CaCl2 resulted in greater than a twofold increase in glyphosate retention compared with experiments with NaCl. The desorption experiments revealed release of about 30–90% of the initially bound glyphosate into solution, whereby Ca in the desorption solution promoted glyphosate mobility compared with Na. Furthermore, in all conditions, the relative initial wetness of the agricultural soil was correlated positively with the enhanced glyphosate mobilization, consistent with field‐scale reports that herbicide applied to soils following rain events were prone to runoff. Core Ideas: ■Herbicide adsorption mechanisms on minerals depends on compound chemical structures.■Only diffuse layer suspension occurs with a lack of surface adsorption on Na‐quartz.■Glufosinate and fosamine have stronger binding than glyphosate on Na‐montmorillonite.■Ca‐complexed herbicides have enhanced adsorption on both montmorillonite and quartz.■Experimental data with quartz‐enriched agricultural soils are consistent with simulation results. [ABSTRACT FROM AUTHOR]

Presents a study which determined the possible use of the ground-penetrating radar (GPR) as an in situ water sensor on sandy soils. Importance of the robust and noninvasive techniques for in situ measurement of soil water content; How the soil's dielectric constant was compared as measured by GPR and time domain reflectometry (TDR); Proposal of a calibration equation relating soil water to GPR-measured dielectric constants.

Soil and water conservation structures, promoted by local and international development organizations throughout rural landscapes, aim to increase recharge and prevent degradation of soil surface characteristics. This study investigates this unexamined relationship between recharge, water table depths, and soil surface characteristics (nutrients) in a small sub-watershed in the northwestern Ethiopian highlands. These highland watersheds have high infiltration rates (mean 70 mm hr −1 , median 33 mm hr −1 ), recharging the shallow unconfined hillslope aquifer with water transport occurring via subsurface pathways down the slope. The perched water tables reflect the subsurface flux and are deep where this flux is rapid in the upland areas (138 cm below surface). Soil saturation and overland flow occur when the subsurface flux exceeds the transport capacity of the soil in the lower downslope areas near the ephemeral stream (19 cm below surface). Land use is directly related to the water table depth, corresponding to grazing and fallowed (saturated) land in the downslope areas and cultivated (unsaturated) land in the middle and upper parts where the water table is deeper. Kjeldahl Total Nitrogen (TN), Bray II available phosphorus (AP), and exchangeable potassium (K + ) averages exhibit different behaviors across slope, land use transects, or saturation conditions. TN was moderate to low (0.07% ± 0.04) in various land uses and slope regions. Bray II AP had very low concentrations (0.25 mg kg −1  ± 0.26) among the different slope regions with no significant differences throughout (p > .05). The exchangeable cation (K + , Ca 2+ , Mg 2+ ) concentrations and pH, however, were greater in non-cultivated (seasonally saturated) lands and in a downslope direction (p < .001, p < .005, p < .05, and p < .005, respectively). These results show that the perched groundwater plays an important role in influencing land use, the amount of water seasonally available for crop growth, and exchangeable cations, but have no clear effect on the concentration of the two primarily applied nutrients in fertilizers (N, P). [ABSTRACT FROM AUTHOR]

This study employed geomorphometric analysis to characterize the four major watersheds (Gilgel Abay, Gumara, Rib, and Megech) of Lake Tana sub-basin, Ethiopia, and prioritize the watersheds for the implementation of SWC practices using GIS and remote sensing techniques. Also, the study analyzed streamflow and sediment data recorded at the outlets of each watershed to associate the geomorphometric prioritization result with recordings of the watersheds. Geomorphometric analysis results indicated that the Rib watershed is the most susceptible watershed for soil erosion and should be prioritized for the implementation of SWC practices. The analysis of streamflow and suspended sediment concentration suggest that the Rib watershed had the second maximum sediment yield (14.3 t ha−1 yr−1) compared to the other three watersheds. This is because of the low streamflow response of the watershed compared with the Gumara watershed which had the highest sediment yield (18.9 t ha−1 yr−1). [ABSTRACT FROM AUTHOR]

With the increasing consumer awareness and knowledge about safe and healthy food, it is imperative to develop 'green' crops with reduced fertilizer application for quality food production, environmental protection and sustainable agricultural development. This study systematically evaluated and compared the water footprint (WF) including WFblue, WFgreen and WFgrey of eight crops including wheat, maize, rice, sweet potato, soybean, millet, mung bean and sorghum under green and traditional cultivation in the Huang-Huai-Hai farming region. The data came from 252 onsite questionnaires conducted in 2018 for land under green and traditional cultivation by 19 green planting companies and farming cooperatives with green food production certification authorized by the government of China. The results revealed that, compared to traditional cultivation, green cultivation under reduced N fertilizer application (1) decreased crop yields by 3–13%; (2) reduced the average WFtotal by 29% to 1168 m3 t−1 and average WFgrey by 57% to 419 m3 t−1 with no significant differences in WFblue and WFgreen; (3) decreased the WFtotal of maize by 55%, rice by 41%, wheat by 27%, mung bean by 31%, sorghum by 24%, sweet potato by 19%, millet by 17% and soybean by 17%. The WFgrey proportion of WFtotal under green cultivation ranged from 27–57% and contributed the most to the decline in WFtotal. This study offers insight into the impact of green cultivation on water requirements and pollution relative to traditional cultivation. Precision N fertilizer application and improved N use efficiencies on-farm are important pathways to sustainable agricultural development. [ABSTRACT FROM AUTHOR]

Modeling of suspended sediment emission into freshwater lakes is challenging due to data gaps in developing countries. Existing models simulate sediment concentration at a gauging station upstream and none of these studies had modeled total suspended solids (TSS) emissions by inflowing rivers to freshwater lakes as there are no TSS measurements at the river mouth in the upper Blue Nile basin. In this study a 10 year TSS time series data generated from remotely sensed MODIS/Terra images using established empirical relationship is applied to calibrate and validate a hydrology model for Lake Tana in Upper Blue Nile Basin. The result showed that at a monthly time scale TSS at the river mouth can be replicated with Nash–Sutcliffe efficiency (NS) of 0.34 for calibration and 0.21 for validation periods. Percent bias (PBIAS) and ratio of the root-mean-square error to the standard deviation of measured data (RSR) are all within range. Given the inaccessibility and costliness to measure TSS at river mouths to a lake the results found here are considered useful for suspended sediment budget studies in water bodies of the basin. [ABSTRACT FROM AUTHOR]

Summary In response to anthropogenic disturbances, alluvial rivers adjust their geometry. The alluvial river channels in the upper Blue Nile basin have been disturbed by human-induced factors since a longtime. This paper examines channel adjustment along a 38-km stretch of the Gumara River which drains towards Lake Tana and then to the Blue Nile. Over a 50 years period, agriculture developed rapidly in the catchment and flooding of the alluvial plain has become more frequent in recent times. The objectives of this study were to document the changes in channel planform and cross-section of the Gumara River and to investigate whether the changes could have contributed to the frequent flooding or vice versa. Two sets of aerial photographs (1957 and 1980) were scanned, and then orthorectified. Recent channel planform information was extracted from SPOT images of 2006 and Google Earth. Channel planform and bed morphology (vertical changes) were determined for these nearly 50 years period. The vertical changes were determined based on aggradation along a permanent structure, historic information on river cross-sections at a hydrological gauging station, and field observations. The results indicate that the lower reach of Gumara near its mouth has undergone major planform changes. A delta with approx. 1.12 km 2 of emerged land was created between 1957 and 1980 and an additional 1 km 2 of land has been added between 1980 and 2006. The sinuosity of the river changed only slightly: negatively (−1.1% i.e. meandering decreased) for the period from 1957 to 1980 and positively (+3.0%) for the period 1980–2006. Comparison of cross-sections at the hydrological gauging station showed that the deepest point in the river bed aggraded by 2.91 m for the period 1963–2009. The importance of sediment deposition in the stream and on its banks is related to land degradation in the upper catchment, and to artificial rising of Lake Tana level that creates a backwater effect and sediment deposition in Gumara River. Direct anthropogenic impacts (irrigation activities and building of dykes along the river banks) have contributed to the huge deposition in the river bed. Where the abstraction of water for irrigation is intensive, seepage water through the banks has contributed to river bank failure. In general, this study showed that changes to the planform at the mouth of the river and to the riverbed level are substantial. Moreover, the study indicated that the flood carrying capacity of the Gumara River channel has diminished in recent times. [ABSTRACT FROM AUTHOR]

• A high-speed camera observed gravity-driven unstable finger formation. • At the fingertip, water advances intermittently one pore at a time. • Pore invasions occur at high velocities. • High velocities increase dynamic contact angles. • Greater contact angles reduce the matric potential at the front and cause instability. The imbibition of fluids in porous media has been studied widely. Still, processes of preferential flow under gravity due to instability at the wetting front, crucial in groundwater contamination, have yet to be fully understood. Recent theories using dynamic contact angles could describe unstable flow phenomena but have not been proven experimentally. Therefore, infiltration experiments in small sand-filled chambers were conducted to explore the effect of dynamic contact angles. A high-speed camera recorded pore invasion at the unstable imbibition liquid front. A tensiometer recorded the matric potential. The results show that water moved in milliseconds through a small pore at the wetting front, followed by a stationary period. The maximum observed pore water velocity was 25 cm/s, exceeding the saturated hydraulic conductivity by three orders of magnitude. The relationship between dynamic contact angle and water velocity found by Hoffman in glass tubes could describe which was observed in soils. [Display omitted] [ABSTRACT FROM AUTHOR]

The importance of soils to society has gained increasing recognition over the past decade, with the potential to contribute to most of the United Nations' Sustainable Development Goals (SDGs). With unprecedented and growing demands for food, water and energy, there is an urgent need for a global effort to address the challenges of climate change and land degradation, whilst protecting soil as a natural resource. In this paper, we identify the contribution of soil science over the past decade to addressing gaps in our knowledge regarding major environmental challenges: climate change, food security, water security, urban development, and ecosystem functioning and biodiversity. Continuing to address knowledge gaps in soil science is essential for the achievement of the SDGs. However, with limited time and budget, it is also pertinent to identify effective methods of working that ensure the research carried out leads to real‐world impact. Here, we suggest three strategies for the next decade of soil science, comprising a greater implementation of research into policy, interdisciplinary partnerships to evaluate function trade‐offs and synergies between soils and other environmental domains, and integrating monitoring and modelling methods to ensure soil‐based policies can withstand the uncertainties of the future. Highlights: We highlight the contributions of soil science to five major environmental challenges since 2010.Researchers have contributed to recommendation reports, but work is rarely translated into policy.Interdisciplinary work should assess trade‐offs and synergies between soils and other domains.Integrating monitoring and modelling is key for robust and sustainable soils‐based policymaking. [ABSTRACT FROM AUTHOR]

Summary: Recently, the interactions between soil structure and microbes have been associated with water transport, retention and preferential or column flow development. Of particular significance is the potential impact of microbial extracellular polymeric substances (EPS) on soil porosity (i.e., hydraulic conductivity reduction or bioclogging) and of exudates from biota, including bacteria, fungi, roots and earthworms on the degree of soil water repellency. These structural and surface property changes create points of wetting instability, which under certain infiltrating conditions can often result in the formation of persistent preferential flow paths. Moreover, distinct differences in physical and chemical properties between regions of water flow (preferential flow paths) and no-flow (soil matrix) provide a unique set of environmental living conditions for adaptable microorganisms to exist. In this review, special consideration is given to: (1) the functional significance of microbial activity in the host porous medium in terms of feedback mechanisms instigated by irregular water availability and (2) the related physical and chemical conditions that force the organization and formation of unique microbial habitats in unsaturated soils that prompt and potentially perpetuate the formation of preferential flow paths in the vadose zone. [ABSTRACT FROM AUTHOR]

Summary: Current urban water quality models rely on empirical, catchment-scale functions of particulate wash-off that do not clearly represent the governing physical erosion and transport processes. We proposed a saltation-type wash-off model in which particles are repeatedly ejected from an impervious surface by raindrop impacts and are transported laterally by overland flow while settling back to the surface. The rate that particles are ejected is proportional to rain intensity and the spatial density of particles on the surface. We found that for low particle spatial densities, ejection is proportional to spatial density, but for high spatial densities, the ejection rate is independent of spatial density. We tested our model against data from small (10.5×80cm) flume experiments in which rain intensity and upslope overland flow could be independently controlled. We used a rough flume surface (∼1mm roughness element height) and sand particles (diameter=500–590μm). Rainfall rates, upslope overland flow rates, and initial particle amounts were varied among experiments with ranges of, 4.2–7.8cmh−1, 300–565mL min−1, and 0.01–0.07gcm−2, respectively. The model predictions agreed well with the experiments (R 2 >0.85). This work provides a basis for developing new, uniquely mechanistic models for predicting “wash-off” from urban surfaces. [Copyright &y& Elsevier]

Water resource management in West Africa is often a complicated process due to inadequate resources, climatic extremes, and insufficient hydrological information. Insufficient data hinder sustainable watershed management practices, one of the top priorities in the Volta River Basin. This research properly fills in missing data by modeling the hydrological distribution in the Volta River Basin. On average, discharge gages across the basin are missing 20 percent of their monthly data over 20 years. Two methods were used to supplement missing data: a statistically linear model and a conceptual hydrological model. A linear equation, developed from the regression of precipitation and runoff, was used to evaluate the quality of existing data. The hydrological model separates the system into root and groundwater zones. Measured values were used to calibrate the hydrological model and to validate the statistical model. The quality of existing data was analyzed and organized for usability. Accuracy of the hydrological model was also evaluated for its effectiveness using R² and standard error. It was found that the hydrological model was an improvement from the linear model on a monthly basis; R² values improved by as much as 0.5 and monthly error decreased. Monthly predictions of the hydrological model were used to fill gaps of measured data sets. [ABSTRACT FROM AUTHOR]

Although both raindrop driven processes and diffusion play important roles in the transfer of chemicals from soil to surface runoff, current transport models either do not consider the two processes together, or use ‘effective’ parameters with uncertain physical definitions. We developed a physically based, solute transport model that couples both mechanisms and tested it with laboratory experiments. One unique aspect of this study is that all the parameters were either directly measured or previously published, that is, there was no model ‘calibration’ or ‘fitting.’ Our model assumes that chemicals near the surface of the soil are ejected into runoff by raindrop impact and chemicals deeper in the soil diffuse into a surface layer, or ‘exchange layer,’ via diffusion. The exchange layer depth and transfer processes are derived from the ‘shield’ concept in the Rose soil erosion model (e.g. ). The model''s governing equations were solved numerically and the results agreed well with experimental data (R2>0.90). The model''s sensitivity to various physical and chemical parameters illuminated the importance of both raindrop controlled processes and diffusion on chemical transport from soil to surface runoff. [Copyright &y& Elsevier]

[Display omitted] • Soil and Water Conservation Practices (SWCPs) reduce short-term soil loss. • The long-term effect of many SWCPs is questionable, especially in humid regions. • Forestation is effective; gully sediment losses negate upstream SWCP benefits. • Watershed simulations of SWCP overestimate the decrease in offsite soil loss. • SWCPs should also be evaluated by long-term experiments in catchments. Soil and water conservation have been traditionally part of farming practices for thousands of years. Despite massive efforts to implement modern soil and water conservation practices (SWCPs) in the Ethiopian Highlands, soil erosion increased after the 1970s when social and political events led to a remarkable change in land use. This review aims to critically analyze the impact of conservation practices on soil loss and crop yield and highlight research and modeling gaps. In doing so, 120 published articles on experimental and simulated soil losses in the Ethiopian Highlands were retrieved from the refereed literature. We found that most published experimental studies evaluating SWCPs lasted less than five years in areas of less than 100 ha. Most modeling studies were over short periods, too; some models simulated soil loss over large areas. The literature analysis for these short-term experimental studies showed that SWCP decreased soil loss on individual sites and increased crop yield in semi-arid regions. Simulated sediment concentration increased as a function of watershed size, while observed soil losses did not follow this trend. Moreover, the decrease in soil loss due to the soil and water conservation practices on small plots was also greatly overestimated. Consequently, past research and current modeling techniques are inconclusive on the effectiveness of SWCPs in large catchments over periods exceeding five years and those with active gullies. Additional long-term experimental studies in catchments are required to evaluate whether SWCPs can decrease sediment loads. [ABSTRACT FROM AUTHOR]

Given the critical role of water in rural development, it is essential to quantify water use by various sectors. Reportedly, a significant water loss during the dry monsoon phase is by Eucalyptus trees in the Ethiopian highlands but few quantitative studies have been carried out. In our study in the Fogera plain near Lake Tana, consumptive water use of a small Eucalyptus patch was calculated from the fluctuating diurnal water table observations for two dry monsoon phases. During the dry monsoon phase in 2014, the groundwater table declined linearly at a rate of 2.6 cm d−1 and in 2015 the decline was 2.5 cm d−1. Daily fluctuations in groundwater were around 20 cm. Translating changing groundwater levels in precise evapotranspiration rates was cumbersome because of uncertainty in the value of drainable porosity. We concluded that the evapotranspiration over the small Eucalyptus patch was at a minimum 3.4 mm d−1 but more likely around 10 mm d−1 at the end of the dry phase. The 10 mm d−1 is twice the reference evaporation rate. This is in accordance with advection aridity approach where the actual evaporation of isolated patches with access to groundwater in dry environments can evaporate at twice the reference rate. The current and future extent of Eucalyptus patches and forests need, therefore, be considered in the management of the groundwater resource. [ABSTRACT FROM AUTHOR]

• Phosphorus (P) reduction in streams was analyzed based on data and SWAT-HS model. • SWAT-HS gave good predictions for daily streamflow, monthly P and sediment loads. • Pastures are the largest contributor of both soluble and particulate P in streams. • P is mostly exported from near-stream areas, particularly from pastures. • Point and non-point source P control programs are effective in NYC watersheds. New York City (NYC)'s drinking water reservoirs supply over four billion liters each day to over nine million consumers in NYC and upstate communities. In the last 25 years, the City has invested nearly $2 billion in watershed protection programs (WPPs) to maintain high source water quality, allowing NYC to avoid filtration for 90% of the supply. This study involves the use of a model to evaluate the impact of WPPs on phosphorus (P) loading in the Cannonsville Reservoir watershed, one of the unfiltered water supply sources. The model is SWAT-Hillslope (SWAT-HS), a modified version of the Soil and Water Assessment Tool (SWAT) that can realistically predict variable source runoff processes. We applied the SWAT-HS model to this watershed to test its ability to simulate conditions observed after the implementation of watershed protection and evaluate the impact of point and non-point source WPPs on watershed export of P. When applied to a 12-year period of WPP implementation, SWAT-HS predicted streamflow very well with a daily Nash Sutcliffe Efficiency (NSE) of 0.85 at the calibrated outlet and values ranging from 0.56 to 0.78 at six other locations within the watershed. Moreover, the monthly predictions of soluble P (total dissolved P), particulate P, and sediment (total suspended solids) were good with NSE of over 0.73. Model simulations indicated that the dominant source of soluble P was pastures while particulate P originated from both from croplands and pastures. A significant quantity of P was derived from near-stream areas, particularly from pastures where cattle spent time grazing and had access to streams. SWAT-HS was also used to estimate what the P export would have been over this 12-year period without WPP implementation. Point and non-point source programs were found to be important for P control, with non-point source controls most effective during high streamflow, and point source controls more beneficial at low flow. [ABSTRACT FROM AUTHOR]

• Forested and revegetated regions show greater levels of hydraulic flux and nutrients. • Greater K s and lower ρ b throughout the upper parts of this Andean watershed. • For common pedotransfer functions, these soils' Ks are significantly underestimated. • Conservation initiatives are coinciding with improved soil surface characteristics. Understanding catchment sediment or solute transport frequently relies on understanding of soil nutrient conditions and physical properties. This study investigates hydropedological patterns in a tropical catchment by understanding soil nutrient and soil surface changes. Soil nutrient concentrations and hydraulic properties were measured from the La Vega micro watershed in the southwestern Colombian Andes at 16 distributed locations in four elevation ranges (between 1450 and 1700 m a.s.l.). The site is a part of a conservation partnerships which implements programs and monitor impacts. Soil samples were analyzed for total nitrogen (TN), Bray II-available phosphorus, exchangeable cations, pH, organic matter, and texture. Soil hydraulic conductivities at two depths (0–5 cm and 5–10 cm) were determined in conservation implementation areas (enclosures and natural regrowth). In the upper elevation range, regrowth of natural vegetation was found on deep soils (∼3 m) with moderate infiltration (26 cm hr−1), the lowest bulk density (0.92 g cm−3), and the highest TN (0.4%). The lowest elevation (mixed land use of grazing and riparian forests with deep profiles) had the lowest infiltration (4 cm hr−1), highest bulk density (1.02 g cm−3), and the lowest TN (0.26%). In the middle elevation ranges, conserved tropical forest vegetation were located on shallow soil depths with high organic matter (∼6%) and high infiltration (86 cm hr−1). The lowest infiltration rate average (2.3 cm hr−1) exceeded the estimated erosive regional precipitation intensity (∼2.5 cm hr−1) about 60% of the time, while the median infiltration rate (10 cm hr−1) exceeded rainfall intensities 94% of the time, indicating that infiltration excess and saturation excess runoff mechanisms are both present. Coupling data with sediment concentration and solute concentration patterns can help discern correlations between scales and will help to monitor effectiveness of conservation programs aimed at sustaining ecosystem services. [ABSTRACT FROM AUTHOR]

• SWAT-C predicts dissolved organic carbon (DOC) export from variable source areas. • Remotely sensed data reduced uncertainty in model predictions. • DOC predictions are sensitive to soil properties. • DOC flux is more sensitive to increases in precipitation than air temperature. Dissolved organic carbon (DOC) in surface water influences the global carbon cycle, ecosystem productivity, and water quality in potable water supply systems. Few physically based watershed models can simulate carbon cycling and predict DOC in surface waters under the influence of natural and anthropogenic drivers. In this work we transform the SWAT-Carbon (C) model to simulate DOC from variable source runoff areas in a humid forested watershed in the northeastern United States. Remotely sensed data were used to parameterize and simulate forest growth and evapotranspiration. The calibrated model accurately simulated streamflow and DOC flux at six sites across the watershed compared to measured data. The DOC predictions across sites showed model sensitivity to soil properties, particularly soil depth and available water capacity. The spatial distribution of DOC export across the watershed followed the pattern of surface runoff from variable source areas. Model sensitivity of DOC flux showed greater sensitivity to changes in precipitation than temperature. The overall good performance of the model makes it a valuable tool for watershed-scale modeling of DOC to understand the influence of climate and watershed management towards developing mitigation strategies. The methods presented in this study can be used in forested watersheds in regions where runoff from variable source areas is important for water quality predictions. [ABSTRACT FROM AUTHOR]

Abstract Atrazine and nitrate NO 3 - N are two agricultural pollutants that occur widely in surface and groundwater. One of the pathways by which these pollutants reach surface water is through subsurface drainage tile lines. Edge-of-field anaerobic denitrifying bioreactors apply organic substrates such as woodchips to stimulate the removal of NO 3 - N from the subsurface tile waters through denitrification. Here we investigated the co-removal of NO 3 − N and atrazine by these bioreactors. Laboratory experiments were conducted using 12-L woodchips-containing flow-through bioreactors, with and without the addition of biochar, to treat two concentrations of atrazine (20 and 50 μg L−1) and NO 3 − N (1.5 and 11.5 mg L−1), operated at four hydraulic retention time, HRT, (4 h, 8 h, 24 h, 72 h). Additionally, we examined the effect of aerating the bioreactors on atrazine removal. Furthermore, we tested atrazine removal by a field woodchip denitrifying bioreactor. The removal of both NO 3 − N and atrazine increased with increasing HRT in the laboratory bioreactors. At 4 h, the woodchip bioreactors removed 65% of NO 3 − N and 25% of atrazine but, at 72 h, the bioreactors eliminated all the NO 3 − N and 53% of atrazine. Biochar-amended bioreactors removed up to 90% of atrazine at 72-h retention time. We concluded that atrazine removal was primarily via adsorption because neither aeration nor NO 3 − N levels had an effect. At 4-h retention time, the field bioreactors achieved 2.5 times greater atrazine removal than the laboratory bioreactors. Our findings thus highlighted hydraulic retention time and biochar amendments as two important factors that may control the efficiency of atrazine removal by denitrifying bioreactors. In sum, laboratory and field data demonstrated that denitrifying bioreactors have the potential to decrease pesticide transport from agricultural lands to surface waters. Graphical abstract Image 1 Highlights • Edge-of-field mitigation of atrazine and nitrate was investigated. • Woodchip bioreactors simultaneously removed nitrate and atrazine. • Biochar amendment increased atrazine removal. • Nitrate and atrazine removal by the bioreactors followed first-order kinetic rates. [ABSTRACT FROM AUTHOR]

Highlights • Soil moisture and yield were observed for 6-year grain, forage and bioenergy crops. • Potential bioethanol production and groundwater decline were calculated. • Sorghum rotation produced more bioethanol per unit of groundwater decline. • Net groundwater withdrawal for perennial switchgrass was the smallest. Abstract Managing the complex demands on available energy, food and water is a fundamental challenge for a world with increasingly tenuous resource pools. The North China Plain's groundwater crisis has become increasingly serious due to decades-long over-exploitation for irrigation to pursue high grain yield. This combined challenge motivated investigation of ways to mitigate the groundwater table decline while fostering the use of renewable bioenergy resources. To provide insights about tradeoffs among water, food and energy, we performed a six-year experiment from 2010 to 2015 in the North China Plain where groundwater use, biomass and biofuel production and water use efficiency were compared for four cropping systems. They are winter wheat-summer maize (WM, grains, 1-year cycle), ryegrass–sweet sorghum (RS, forage plus bioenergy crops, 1-year cycle), winter wheat–summer maize→ ryegrass–sweet sorghum (WMRS, forage, bioenergy plus grain crops, 2-year cycle), and perennial switchgrass (SG, bioenergy crop). Actual evapotranspiration (ET a) and recharge to groundwater were calculated and validated using observed soil moisture contents. Results showed ET a of the cropping systems were statistically similar ranging from 694 to 730 mm yr−1 with the exception of switchgrass which was significantly less at 504 mm yr-1. The water table was projected to decline by about 1.3 m yr-1 for all three multi-crop rotations and 0.4 m yr-1 for switchgrass. In terms of bioethanol production per unit land and per unit ET a , the ryegrass-sweet sorghum (RS) rotation performed best with 25.0 m3 ha-1 and 5.7 L m-3 outperforming the yearly winter wheat–summer maize (WM) rotation (11.7 m3 ha-1 and 3.3 L m-3) and switchgrass (11.4 m3 ha-1 and 2.6 L m-3). The multiple year rotation of winter wheat–summer maize→ ryegrass–sweet sorghum (WMRS) yielded 16.9 m3 bioethanol per hectare and 4.3 L m-3 bioethanol per m3 ET a. When optimizing bioethanol against net groundwater depletion, RS and switchgrass outperformed the two grain-based rotations with 15.5 L and 14.4 L of bioethanol per m3 of depleted groundwater, ahead of WMRS at 10.9 L m-3 and WM at 9.1 L m-3. These results are significant for setting governmental policies on sustainable use of groundwater by various crop mixes. [ABSTRACT FROM AUTHOR]

Abstract Soil is a critical medium that governs hydrological processes in a landscape; however, soil data quality and resolution are not given much emphasis during watershed modeling and developing practical management practices, especially in data scarce regions such as in the Ethiopian highlands. This is primarily because measuring most soil parameters is costly, laborious, and at times impractical. Infiltration models and Pedotransfer functions (PTFs) may bridge this gap by estimating such complex soil parameters from easily measurable ones. However, most infiltration models and PTFs were developed for temperate regions and there is no comprehensive experimental or modeling work done to evaluate the robustness of such approaches in the Ethiopian highlands. Therefore, this study aims to i) evaluate the performance of three infiltration models, namely Horton, Koistakov, and Philip in simulating soil infiltration rates and ii) test the reliability of nine PTFs in estimating saturated hydraulic conductivity and soil moisture contents at field capacity and permanent wilting point in a case study in the Anjeni watershed. Soils in the Anjeni watershed on average contain higher percentages of clay and silt with 42 and 34%, respectively; and have acidic pH and low organic matter. Steady infiltration rate (f s) and saturated hydraulic conductivity (Ks) ranged between 0.19 and 30.6 mm h−1 and 0.19 and 3.3 mm h−1, respectively. All the three infiltration models fitted observed data very well with R2 and Nash-Sutcliffe efficiency (NS) values between 0.95 and 0.97 each. While the Horton and Koistakov models had the same R2 and NS values, the Horton provided smaller Mean Absolute Error (MAE) and Root Mean Square Error (RMSE) values. Some of the tested PTFs showed promising results in estimating saturated hydraulic conductivity and soil moisture content; however, all PTFs showed limitations which warrant further evaluation using observed data. This study showed that soil hydrologic parameters vary significantly even within a small area, and widely available soil datasets (e.g., Africa Soil Information Service (AfSIS) and FAO Harmonized World Soil Database) fail to reflect actual field conditions. This suggests that emphasis should be given to soil data quality and resolution during watershed modeling, and land and water management planning. Highlights • The FAO and African Soil Information Service (AfSIS) datasets did not accurately represent field soil conditions • XRD test results showed that most soils in the Anjeni watershed were mixtures of kaolinite, illite, and quartz • The Horton, Koistakov, and Philip infiltration models fitted observed data very well • Pedotransfer functions could be viable options in data scarce regions liken in the Ethiopian highlands • There was no difference in performances between PTFs developed based on observations from temperate and African regions • Tested PTFs showed some limitations which warrant further evaluation using observed data [ABSTRACT FROM AUTHOR]

Abstract The effect of long-term versus short-term water content on soil organic carbon (SOC) mineralizability was evaluated in a six-week incubation trial. Soils were sampled from field sites in upstate New York used for rain-fed bioenergy crop production: nitrogen (N)- fertilized reed canarygrass, switchgrass, switchgrass + N, as well as a broadleaf-grass fallow. Within each cropping system, natural moisture gradients due to topography and subsoil structure allowed us to sample across regions with high (0.5 g g−1), mid (0.4 g g−1) and low (0.3 g g−1) water content. Moisture of the laboratory incubations was adjusted mimicking the three average field moisture levels in a full factorial design. Increasing laboratory moisture in the incubations increased cumulative carbon mineralization per unit soil (C mineralization) and cumulative C mineralization per unit SOC (C mineralizability) (main effect p < 0.0001), indicating that lower average moisture as found at this site on average limited mineralization but higher average moisture did not. C mineralizability at high field moisture was 31% (25-42%) lower than at low field moisture across all cropping systems, regardless of moisture adjustment in the incubation. The mean slow C pool size of soils from high field moisture sites (997.1 ± 0.1 mg C g−1 C) was 0.2% greater than that of soils from low field moisture sites (p < 0.0001), obtained by fitting a double-exponential model. The mean residence time of the slow mineralizing C pool for soils from low field moisture sites was 5.5 ± 0.1 years, in comparison to 8.0 ± 0.1 years for soils from high field moisture sites (p < 0.0001). While permanganate-oxidizable carbon (POXC) per unit SOC (r = 0.1) was positively correlated to C mineralizability, wet aggregate stability (r = −0.2) was negatively correlated to C mineralizability. Above-ground biomass did not affect C mineralizability (p > 0.05) and root biomass marginally influenced (p = 0.05) C mineralizability after correcting for soil texture variations. Additionally, after correcting for soil texture variations and biomass inputs, C mineralizability significantly decreased with higher field moisture (p = 0.02), indicating possible stabilization mechanisms through mineral interactions of SOC under high water content. Bulk contents of pedogenic iron and aluminum determined by oxalate extraction did not clearly explain differences in mineralizability. However, exchangeable calcium and magnesium contents were significantly (p < 0.0001) greater in high moisture soils than soils with lower moisture. Additionally, cumulative C mineralizability at 6 weeks was negatively correlated to calcium (r = −0.7) and magnesium (r = −0.6) and mean residence time of the modeled slow pool correlated positively with calcium (r = 0.4). Therefore, cation bridging by retained or illuviated base ions was more important than redox changes of iron as a stabilization mechanism in this experiment. Highlights • Soil organic carbon (SOC) was highest in bioenergy plantations under high moisture. • SOC mineralizability was 25–42% lower from high field moisture compared to low field moisture. • Mineralization increased with higher moisture in laboratory incubation. • Above-ground biomass or root biomass did not affect C mineralizability. • Aggregate stability was negatively correlated to C mineralizability. • Base cation contents negatively correlated with mineralizability. [ABSTRACT FROM AUTHOR]

The control of soil moisture, vegetation type, and prior land use on soil health parameters of perennial grass cropping systems on marginal lands is not well known. A fallow wetness-prone marginal site in New York (USA) was converted to perennial grass bioenergy feedstock production. Quadruplicate treatments were fallow control, reed canarygrass (Phalaris arundinaceae L. Bellevue) with nitrogen (N) fertilizer (75 kg N ha−1), switchgrass (Panicum virgatum L. Shawnee), and switchgrass with N fertilizer (75 kg N ha−1). Based on periodic soil water measurements, permanent sampling locations were assigned to various wetness groups. Surface (0-15 cm) soil organic carbon (SOC), active carbon, wet aggregate stability, pH, total nitrogen (TN), root biomass, and harvested aboveground biomass were measured annually (2011-2014). Multi-year decreases in SOC, wet aggregate stability, and pH followed plowing in 2011. For all years, wettest soils had the greatest SOC and active carbon, while driest soils had the greatest wet aggregate stability and lowest pH. In 2014, wettest soils had significantly (p < 0.0001) greater SOC and TN than drier soils, and fallow soils had 14 to 20% greater SOC than soils of reed canarygrass + N, switchgrass, and switchgrass + N. Crop type and N fertilization did not result in significant differences in SOC, active carbon, or wet aggregate stability. Cumulative 3-year aboveground biomass yields of driest switchgrass + N soils (18.8 Mg ha−1) were 121% greater than the three wettest switchgrass (no N) treatments. Overall, soil moisture status must be accounted for when assessing soil dynamics during feedstock establishment. [ABSTRACT FROM AUTHOR]

Watershed responses are affected by the watershed characteristics and rainfall events. The characteristics of soil layers are among the fundamental characteristics of a watershed and they are input to hydrologic modeling similar to topography and land use/cover. Although the roles of soils have been perceived, there are limited studies that quantify the role of soil characteristics on watershed runoff responses due to the lack of field datasets. Using two adjacent watersheds (Ribb and Gumara) which have a significant different runoff response with a similar characterstics except geological settings (including soil characteristics), we studied the effects of soil characteristics on runoff and water balance. The Soil and Water Assessment Tool (SWAT) was used to simulate the surface runoff response at the outlet of the watershed and the optimal model parameters distribution was tested with a non-parametric test for similarity. Results indicated that SWAT model captured the observed flow very well with a Nash-Sutcliffe Efficiency (NSE) of greater than 0.74 and with a PBIAS of less than 10% for both calibration and validation period. The comparison of the optimal model parameter distributions of the SWAT model showed that the watershed characteristics could be uniquely defined and represented by a hydrologic model due to the differences in the soils. Using field observations and modeling experiments, this study demonstrates how sensitive watershed hydrology is to soils, emphasizing the importance of accurate soil information in hydrological modeling. We conclude that due emphasis should be given to soil information in hydrologic analysis. [ABSTRACT FROM AUTHOR]

In many developing countries and remote areas of important ecosystems, good quality precipitation data are neither available nor readily accessible. Satellite observations and processing algorithms are being extensively used to produce satellite rainfall products (SREs). Nevertheless, these products are prone to systematic errors and need extensive validation before to be usable for streamflow simulations. In this study, we investigated and corrected the bias of Multi-Sensor Precipitation Estimate–Geostationary (MPEG) data. The corrected MPEG dataset was used as input to a semi-distributed hydrological model Hydrologiska Byråns Vattenbalansavdelning (HBV) for simulation of discharge of the Gilgel Abay and Gumara watersheds in the Upper Blue Nile basin, Ethiopia. The result indicated that the MPEG satellite rainfall captured 81% and 78% of the gauged rainfall variability with a consistent bias of underestimating the gauged rainfall by 60%. A linear bias correction applied significantly reduced the bias while maintaining the coefficient of correlation. The simulated flow using bias corrected MPEG SRE resulted in a simulated flow comparable to the gauge rainfall for both watersheds. The study indicated the potential of MPEG SRE in water budget studies after applying a linear bias correction. [ABSTRACT FROM AUTHOR]

Denitrifying bioreactors are increasingly being used for nitrate removal from agricultural drainage water. Filled with carbon substrates, often woodchips, denitrifying bioreactors provide a favorable anaerobic environment for denitrification. Despite performing well in loess soils in the Midwestern United States, field bioreactors have not yet been evaluated in shallow soils over glacial till that are characteristic for the Northeastern United States. This study, therefore, investigates the performance of bioreactors and provides design criteria for shallow soil with flashy discharges. Paired bioreactors, one filled with woodchips and one with a mixture of woodchip and biochar, were installed in tile drained fields in three landscapes in New York State. The bioreactors were monitored for a three-year period during which, the flow rate, temperature, nitrate ( N O 3 − − N ), sulfate ( S O 4 2 − − S ) and dissolved organic carbon (DOC) were measured. Results showed that the average N O 3 − − N removal efficiency during the three years of observations was about 50%. The N O 3 − − N removal rate ranged from 0 in winter to 72 g d −1 m −3 in summer. We found that biochar was only effective during the first year in enhancing denitrification, due to the ageing. An index for carbon availability related to N O 3 − − N removal was developed. During winter, availability of the DOC was a limiting factor in bioreactor performance. Finally, to aid in the design of bioreactors, we developed generalizable relationships between the removal efficiency and hydraulic retention time and temperature. [ABSTRACT FROM AUTHOR]

Agricultural intensification has increased crop productivity but simplified production and reduced cropping system diversity. In recent decades, the intensified wheat–maize rotation in the North China Plain has sharply decreased the groundwater table, with associated environmental and biodiversity issues. Understanding whether increasing cropping system diversity stabilizes productivity, improves resilience, and reduces adverse environmental impacts is critical. This study quantified the water requirements of nine staple crops from 1960 to 2020, established 15 alternative crop rotations, and evaluated the resilience of each rotation in the Cangzhou area, a typical groundwater deletion funnel area. The results showed that reducing cropping density (harvests per year) from 2 to 1.5 decreased the average annual water requirement and irrigation demand by 14 % and 33 %, respectively. Summer soybean alternated with maize and rotated with wheat did not reduce groundwater use but increased profitability and protein production. Spring mung bean–summer millet-based multi-rotations had higher precipitation coupling degrees (8 % in wet years, 17 % in normal years, and 56 % in dry years) and profitability (1.1–2.4 times) than the wheat–maize rotation. The spring potato–summer millet rotation in one year had the greatest profitability, the highest equivalent yield to wheat, and the highest water use efficiency (WUE), while spring maize rotated with winter wheat–summer soybean performed best for protein content, energy output, and WUEs. This study identified 11 alternative rotations with a higher comprehensive evaluation index than the conventional wheat–maize rotation based on entropy-TOPSIS considering 12 indicators. Spring mungbean is not suitable for inclusion in the crop rotation when solely cultivated in one year due to mismatched rainfall. Beyond wheat and maize, soybean, millet, and potato are promising crops for innovative multi-year multi-crop rotations to enhance crop diversification, maximize system outputs, and minimize groundwater and energy depletion. This study's analysis could be extended to develop robust and diverse crop rotations with multiple co-benefits in other water-stressed agricultural regions. • Water requirements of nine staple crops from 1960 to 2020 was quantified. • 15 diversified crop rotations were redesigned and established. • Multi-dimensional outcomes of each rotation were evaluated for synergies and tradeoff. • Reducing cropping density mitigated groundwater table decline. • Wheat-maize rotations involving soybean, millet and potato achieved multiple co-benefits. [ABSTRACT FROM AUTHOR]

Knowledge of preferential flow in heterogeneous environments is essential for enhanced hydrocarbon recovery, geothermal energy extraction, and successful sequestration of chemical waste and carbon dioxide. Dual tracer tests using nanoparticles with a chemical tracer could indicate the preferential flow. A dual-permeability model with a high permeable core channel surrounded by a low permeable annulus was constructed and used to determine the viability of an inert carbon nanoparticle tracer for this application. A series of column experiments were conducted to demonstrate how this nanoparticle tracer can be used to implement the dual tracer tests in heterogeneous environments. The results indicate that, with the injection rate selected and controlled appropriately, nanoparticles together with a chemical tracer can assess the preferential flow in heterogeneous environments. The results also implement the dual tracer tests in heterogeneous environments by simultaneously injecting chemical and nanoparticle tracers. [ABSTRACT FROM AUTHOR]

Agricultural water conservation is important in arid and semi-arid areas where water resources are deficient and agriculture irrigation accounts for a high proportion of water use. Thus, efficient deficit irrigation methods, which the supplied water is less than potential evapotranspiration have been developed. In semi-arid areas, groundwater can contribute to crop’s water consumption but less is known about impact of deficit irrigation on the contribution. We conducted, therefore, a two-year field experiments with deficit flood irrigation for maize in an arid district with shallow groundwater in China. Four irrigation practices were tested with water applied at approximately 82.5%, 75%, 67.5% and 60% of the 540 mm potential evapotranspiration (PET) in 2014 and the 500 mm in 2013 over the crop growing season. We found that the upward flux between soil water and groundwater varied from 5 mm with input water of 488 mm to 60 mm with input water of 353 mm. The yield of maize decreased by only 15% from 10.0 to 8.5 t/ha for the WS treatment (irrigated at 60% of PET) compared with the WH treatment (irrigated at 82.5% of PET) due to more groundwater contribution to the crop growing with less irrigation. As a consequence, the water use efficiency (WUE), defined as quotient of the yield and plant evapotranspiration was not significantly different among different irrigation treatments. However, the irrigation water use efficiency (IWUE), which is the yield per unit of water applied, increased significantly with the decreasing amount of water applied due to the contribution of upward fluxes. The implication is that deficit irrigation enhances the contribution of groundwater to crop water use and will not produce an obvious reduction of yield within a stable shallow groundwater level. [ABSTRACT FROM AUTHOR]

Accurate prediction of hydrological models requires accurate spatial and temporal distribution of rainfall. In developing countries, the network of observation stations for rainfall is sparse and unevenly distributed. Satellite-based products have the potential to overcome this shortcoming. The objective of this study is to compare the advantages and the limitation of commonly used high-resolution satellite rainfall products (Climate Forecast System Reanalysis (CFSR) and Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA) 3B42 version 7) as input to hydrological models as compared to sparsely and densely populated network of rain gauges. We used two (semi-distributed) hydrological models that performed well in the Ethiopian highlands: Hydrologiska Byråns Vattenbalansavdelning (HBV) and Parameter Efficient Distributed (PED). The rainfall products were tested in two watersheds: Gilgel Abay with a relatively dense network of rain gauge stations and Main Beles with a relatively scarce network, both are located in the Upper Blue Nile Basin. The results indicated that TMPA 3B42 was not be able to capture the gauged rainfall temporal variation in both watersheds and was not tested further. CFSR over predicted the rainfall pattern slightly. Both the gauged and the CFSR reanalysis data were able to reproduce the streamflow well for both models and both watershed when calibrated separately to the discharge data. Using the calibrated model parameters of gauged rainfall dataset together with the CFSR rainfall, the stream discharge for the Gilgel Abay was reproduced well but the discharge of the Main Beles was captured poorly partly because of the poor accuracy of the gauged rainfall dataset with none of the rainfall stations located inside the watershed. HBV model performed slightly better than the PED model, but the parameter values of the PED could be identified with the features of the landscape. [ABSTRACT FROM AUTHOR]

Hotspots of nitrous oxide (N2O) emission are thought to contribute substantially to annual emissions from agricultural soils. We observed N2O fluxes from fertilized and unfertilized C3 and C4 perennial grasses on a wet silt loam soil in New York, United States during the growing season in 2013, 2014 and 2015 using static chambers. Analysis of N2O hotspots within the research plots revealed that hotspots contributed between 34.3 and 39.1% of the total emissions and constituted between 0.8% and 5.0% of all flux observations. Hotspots were more frequent and of greater magnitude in the fertilized treatments and occurred when soil temperature was greater than 9.1°C and soil moisture was between about 40% and 80% water filled pore space (WFPS). A single chamber location in the fertilized switchgrass treatment was consistently a hotspot for N2O emission, suggesting that hotspots maintain a stable spatial pattern over extended periods. The maximum magnitude of N2O hotspot emission exhibited a relationship to soil temperature that is similar to that of the microbial growth rate constant. [ABSTRACT FROM AUTHOR]