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Engineered carbon‐based nanoparticles are increasingly used for environmental, industrial, and medical purposes. Thus, understanding their interaction with and transport through materials is important. We examine the impact of nanoparticle hydrophobicity and porous medium surface area on the transport of carbon nanoparticles through sand‐packed columns under saturated and unsaturated conditions. The fluorescent carbon nanoparticles (FCNs) used in this study, synthesized from citric acid and ethanolamine, exhibit synthesis‐temperature‐dependent hydrophobicity. To quantify the impact of hydrophobicity on retention, we use FCNs synthesized at four temperatures: 190°C (FCN190), 210°C (FCN210), 230°C (FCN230), and 250°C (FCN250). Several observations are noted. First, the more hydrophobic particles (FCN230 and FCN250) attain lower outlet concentrations and mass recovery than more hydrophilic particles (FCN190 and FCN210). For instance, while 77% of the FCN190 was recovered after passing through a fine‐sand‐packed column, only 23% of the FCN250 was recovered. Second, sand surface area significantly impacts FCN recovery. A 17‐fold increase in sand surface area yields a 30% decrease in the recovery of FCN210. Third, no significant difference in the mass recovery of the FCNs was observed between the unsaturated and saturated conditions, which is attributed to the small size of the FCNs relative to the water film thickness surrounding sand grains. Fourth, the particle transport model in HYDRUS‐1D successfully simulated FCN transport, showing approximately a tenfold increase in the attachment coefficient for hydrophobic FCNs. In summary, through experiments and modeling, we show that hydrophobicity is a major factor impacting FCN transport. Key Points: The synthesis‐temperature‐dependent hydrophobicity reduces the transport of fluorescent carbon nanoparticles through sand‐packed columnsA two‐kinetic sites transport model describes the transport of fluorescent carbon nanoparticles in porous mediaFluorescent carbon nanoparticles are not trapped in the meniscus under unsaturated conditions at the tested moisture contents [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]

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]

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]

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]

Accelerated sediment concentration has become a pervasive feature in developing countries and has substantially impacted lake ecosystem functioning. Despite this, very few comprehensive studies have examined the changes in sedimentation over the time that agriculture intensified greatly with the increasing population. This study aims to fill this gap using historical and recent bathymetric surveys to determine sediment deposition and link these to watershed development. With its unique ecology, Lake Tana that was pristine less than 100 years ago, is one of these systems experiencing increasing sediment concentrations. A detailed bathymetric survey was conducted in late 2017 and compared with bathymetric surveys conducted in 1940, 1987, and 2006. The result shows that in the past 77 years, Lake Tana's depth decreased an average of 28 ± 11 cm, equivalent to nearly 0.9 ± 0.4 Tg (million tons). Sediment deposition was 2.8 ± 2.3 mm a−1 between 1940 and 1987, when the agricultural intensification started. It almost doubled to 5.0 ± 3.7 mm a−1 after that. Spatially, the sediment deposition was most significant in areas near the major river inlets where 2 to 10 km long peninsulas were formed. The increase in sediment deposition is primarily driven by newly formed valley bottom gullies formed after deforestation disturbed the hydrological equilibrium, and watershed outflow increased. [ABSTRACT FROM AUTHOR]

Land degradation in developing countries is exacerbating hardpan development that causes the formation of perched watertable, which in turn results in increased runoff and erosion. To reduce overland flow and erosion, percolation through the hardpan needs to be improved. One successful way to achieve this is ripping off the hardpan and plausibly liming. However, in the highlands of Ethiopia, there is little information available on these two techniques. The objectives of this study were, therefore, to determine the effects of ripping off degraded soils on runoff and erosion rates and whether liming would improve the effectiveness of ripping. A field study was conducted in the Anjeni watershed. Thirty‐two experimental runoff plots were installed across the watershed. Conventional tillage at 15 cm depth and ripping to 30, 45, and 60 cm depths were applied with and without lime amendments. Results showed that ripping to 60 cm depth resulted in a significant reduction of runoff. However, liming increased runoff response, on average by 10%. In contrast to the reduction in runoff amounts, an increase in ripping depth increased the amount of soil loss especially during the first storms at the beginning of the monsoon rainy season. Liming significantly decreased soil loss by up to 35%. Although plots with deep ripping plus liming had greater runoff production than other plots, soil loss was less. Overall, the findings suggest that deep ripping has promise but more research is needed before widely implemented. [ABSTRACT FROM AUTHOR]

Feeding 9 billion people in 2050 will require sustainable development of all water resources, both surface and subsurface. Yet, little is known about the irrigation potential of hillside shallow aquifers in many highland settings in sub‐Saharan Africa that are being considered for providing irrigation water during the dry monsoon phase for smallholder farmers. Information on the shallow groundwater being available in space and time on sloping lands might aid in increasing food production in the dry monsoon phase. Therefore, the research objective of this work is to estimate potential groundwater storage as a potential source of irrigation water for hillside aquifers where lateral subsurface flow is dominant. The research was carried out in the Robit Bata experimental watershed in the Lake Tana basin which is typical of many undulating watersheds in the Ethiopian highlands. Farmers have excavated more than 300 hand dug wells for irrigation. We used 42 of these wells to monitor water table fluctuation from April 16, 2014 to December 2015. Precipitation and runoff data were recorded for the same period. The temporal groundwater storage was estimated using two methods: one based on the water balance with rainfall as input and baseflow and evaporative losses leaving the watershed as outputs; the second based on the observed rise and fall of water levels in wells. We found that maximum groundwater storage was at the end of the rain phase in September after which it decreased linearly until the middle of December due to short groundwater retention times. In the remaining part of the dry season period, only wells located close to faults contained water. Thus, without additional water sources, sloping lands can only be used for significant irrigation inputs during the first 3 months out of the 8 months long dry season. [ABSTRACT FROM AUTHOR]

While hydrological science has made great strides forward during the last 50 years with the advance of computing power and availability of satellite images, much is unknown about the sustainable development of water for irrigation, domestic use, and livestock consumption for millions of households in the developing world. Specifically, quantification of shallow underground water resources for irrigation in highland regions remains challenging. The objective is to better understand the hydrology of highland watersheds with sloping hillside aquifers. Therefore, we present a subsurface flow model for hillside aquifers with recharge that varied from day to day. Recharge to the aquifer was estimated by the Thornthwaite Mather procedure. A characteristic time was identified for travel time of water flowing from the upper part of the hillside to the river or well. Using the method of characteristics, we found that the height of shallow groundwater level can be predicted by determining the total recharge over the characteristic time divided by drainable porosity. We apply the model to farmer‐dug wells in the Ethiopian highlands using observed rainfall, potential evaporation, and a fitted travel time. We find that the model performs well with maximum water table heights being determined by the soil surface and minimum heights by the presence or absence of volcanic dikes downhill. Our application shows that unless the water is ponded behind a natural or artificial barrier, hillslope aquifers are unable to provide a continuous source of water during the long, dry season. This clearly limits any irrigation development in the highlands from shallow sloping groundwater. Plain Language Summary: The population in the Ethiopian highlands, similar to other developing countries, is rapidly increasing. In order to have enough food during the year, most families grow their food crops during the rainy season. More food can be grown by irrigation during the dry season. We mathematically tested and observed data of eight wells as to whether shallow aquifers on the sloping lands can store sufficient water during the rainy season so it can be used for irrigation after the rains have stopped. We found that groundwater on sloping soils is only available during the whole year when volcanic‐derived subsurface barriers prevent flow downslope. Key Points: A novel parsimonious model was developed for shallow hillslope groundwater tablesShallow groundwater depth in wells can be predicted from the recharge and the drainable porosityHillslope aquifers cannot supply water for irrigation at end of the dry monsoon phase unless a downhill obstruction to flow is present [ABSTRACT FROM AUTHOR]

Sustainable development in degraded landscapes in the humid tropics requires effective soil and water management practices. Coupled hydrological‐erosion models have been used to understand and predict the underlying processes at watershed scale and the effect of human interventions. One prominent tool is the parameter‐efficient distributed (PED) model, which improves on other models by considering a saturation‐excess runoff generation driving erosion and sediment transport in humid climates. This model has been widely applied at different scales for the humid monsoonal climate of the Ethiopian Highlands, with good success in estimating discharge and sediment concentrations. However, previous studies performed manual calibration of the involved parameters without reporting sensitivity analyses or assessing equifinality. The aim of this article is to provide a multiobjective global sensitivity analysis of the PED model using automatic random sampling implemented in the SAFE Toolbox. We find that relative parameter sensitivity depends greatly on the purpose of model application and the outcomes used for its evaluation. Five of the 13 PED model parameters are insensitive for improving model performance. Additionally, associating behavioural parameter values with a clear physical meaning provides slightly better results and helps interpretation. Lastly, good performance in one module does not translate directly into good performance in the other module. We interpret these results in terms of the represented hydrological and erosion processes and recommend field data to inform model calibration and validation, potentially improving land degradation understanding and prediction and supporting decision‐making for soil and water conservation strategies in degraded humid landscapes. [ABSTRACT FROM AUTHOR]

Core Ideas: A simple multiregion model predicts herbicide transport well using tracer data.A chloride tracer is used to characterize the preferential flow paths.A surface layer in the model distributes water and solutes to the preferential pathways. Simulation of preferential flow remains a challenge despite being a recognized phenomenon. With short‐interval data, we adapted and tested the preferential flow model (PFM) to simulate the vertical transport of herbicides to lower soil layers. The PFM divides the soil profile into a top distribution zone and a conveyance zone below. The distribution zone acts as a reservoir, with an exponential loss of solutes to the conveyance zone. In the conveyance zone, water and solutes move as convective–dispersive flow through multiple flow paths—preferential and matrix—to shallow groundwater. Our field experiment was performed on a structured Hudson silty clay loam soil (a fine, illitic, mesic Glossaquic Hapludalf) that exhibits preferential flow. The site was instrumented with a variety of soil water samplers placed at depths of 60 cm to monitor the volume and quality of the leachate. Agronomic application of atrazine [6‐chloro‐N‐ethyl‐N′‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine] and 2,4‐D [2‐(2,4‐dichlorophenoxy)acetic acid] was used, followed by 75 cm of controlled and natural rainfall over 100 d. In addition, Cl− was applied as a conservative tracer. All samplers monitored during this period showed a fast breakthrough of solutes consistent with the occurrence of preferential flow, with two groups of breakthrough curves observed. By fitting the Cl− breakthrough curve for each group, PFM input parameters were estimated including water velocity in preferential flow paths and the fraction of water moving through each flow path. With two additional parameters for herbicide adsorption and degradation rates, the model successfully simulated the extent of preferential flow of herbicides. [ABSTRACT FROM AUTHOR]

Abstract: Soil erosion, with significant contributions from gullies, is a serious problem in the Ethiopian highlands. The objective of this paper is to examine patterns of discharge and sediment transport in the Ethiopian highlands, and to provide an initial assessment of whether soil and water conservation practices (SWCP) can reduce sediment loads in watersheds with actively eroding gullies. The study was conducted in the 414‐ha Ene‐Chilala watershed with a unimodal sub‐humid monsoon climate and actively eroding gullies in the valley bottoms. In 2013 and 2014, the local community was mandated to install upland infiltration furrows and farmers voluntarily rehabilitated six gully heads and protected 16 m of eroding stream banks. Discharge and sediment concentration were measured in two upslope watersheds and at the outlet. Since median infiltration capacity in the uplands was always greater than the rainfall intensity, saturation excess and interflow were main runoff pathways. After 175 mm cumulative rainfall, the groundwater table reached the surface in the valley bottoms, restricting infiltration, and runoff was generated as saturation excess overland flow and flowed through active gullies out of the watershed. Upland rill erosion on ploughed land early in the rain phase, and gully erosion in saturated valley bottoms thereafter, were sources of sediment in the rivers. The mandated infiltration furrows installed on the contour overtopped and damaged cropland. The off‐contour furrows increased streamflow. Gully rehabilitation of an upland gully effectively reduced stream sediment concentration in the upland weir. However, there was little benefit at the watershed outlet since the stream picked up the unconsolidated sediment from the failing banks in the downstream porting of the watershed. Therefore, soil conservation programs that in addition to installing upland practices, rehabilitate the main sediment source (gullies) appear to be the most effective approach to reducing in‐stream suspended sediment concentrations. © 2018 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Grasses and trees are often used to stabilize gully banks. However, the effectiveness of such biological conservation measures has not been investigated for the Ethiopian highlands. This study investigates the reinforcement that plant roots may provide to strengthen gully banks in Ethiopia. The root systems of 26 indigenous and exotic plant species of 3 plant life forms (grasses, shrubs, and trees) were sampled, and root tensile strength and distribution were determined. The RipRoot model was used to quantify the additional cohesion derived from the plant roots. Among all tested roots, Eleusine floccifolia (grass), Tephrosia vogelii (tree), and Rosa abyssinica (shrub) had the strongest roots for each life form. The root volumetric ratio (root volume divided by soil volume) in the top 0.6 m of soil ranged from 0.03% to 0.46%. Roots of Digitaria abyssinica provided the maximum added cohesion (10.6 kPa) over this depth. For a given plant species, root volumetric ratio had a greater effect on additional cohesion than root tensile strength. Plant species with a fibrous root system provided greater additional cohesion values in the top 0.6 m (on average 3.4 vs. 1.7 kPa for tap root systems) and could potentially enhance gully bank stability for shallow gullies more than plants having a tap root system. To effectively rehabilitate larger gullies, plants should be integrated with other gully rehabilitation measures, such as regrading of gully banks and structural measures such as check dams to trap sediments, thereby reducing the effective gully bank height relative to rooting depth. [ABSTRACT FROM AUTHOR]

Abstract: Land use changes in many landscapes result in gully formation, carving up agricultural land and playing a large role in filling up downstream reservoirs by connecting uplands with rivers. This includes the Ethiopian highlands. Our objective is to begin investigating the interaction of upland and gully erosion and to quantify the portion of eroded sediment originating from a gully to prioritize erosion control practices. For this purpose, a 5‐m deep valley bottom gully of the 13‐ha catchment in the Debre Mawi watershed in the subhumid Ethiopian highland near Lake Tana was selected. The upstream and downstream gully discharge and sediment concentrations were measured over a 2‐year period. The results show that the sediment concentration at the outlet was about 10 times greater than at the inlet. The sediment budget calculation showed that about over 90% of the sediment at the outlet originated from within the gully. Hysteresis analysis of the sediment concentration discharge relationship showed that sediment supply from the upland was limited, but sediment was always available to be eroded and transported in the gully because of bank failures and headcut retreat. Thus, to reduce sediment loads in rivers and consequent adverse downstream impacts, designing cost‐effective measures to treat gullies should be a priority in the subhumid Ethiopian highlands. [ABSTRACT FROM AUTHOR]

Abstract: Predicting the impact of urbanization on the hydrology of peri‐urban catchments remains a challenge. Using data from nine streamflow gauges installed in a small Portuguese catchment, this study investigates the streamflow responses over a 3‐year period. The catchment comprises unique nested sub‐catchments, characterized by varying proportions of non‐urban land‐use (17–97%) and impermeable surfaces (6–36%), distances between the urban areas and the stream network and storm drainage systems (piped versus dispersed) and overlying distinct lithologies consisting of sandstone and limestone. The results show that in the peri‐urban catchment (39% urban and 22% impervious surfaces) most water infiltrated and annual storm runoff varied between 9% and 13% of rainfall. In urban sub‐catchments (≈50% urban), 29% of rainfall became storm runoff on sandstone and 17% on limestone. In sub‐catchments with more than 80% forest, storm runoff coefficients were averaged 6% independent of the lithology. Sub‐catchments with storm runoff drainage systems and downslope urban areas had shorter response times (<20 min) than dispersed urban sub‐catchments, in which part of the runoff infiltrated, and the response time was up to 1 h. Baseflow contributed between 25–33% upstream and 37–38% downstream of the sandstone total runoff, but was less than 5% in limestone areas independent of location. Hydrological impacts of urbanization may be minimized in planning through disconnecting the urban areas from the stream network, thereby enabling runoff from impervious areas to infiltrate into the soil in downstream forest patches before reaching the stream. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Worldwide, soil erosion has greatly decreased agricultural productivity and continues unabatedly despite decades of developing sustainability and soil conservation strategies. Current strategies need integrated interdisciplinary perspectives to develop more effective measures, especially in degrading mountainous landscapes where rising sediment concentrations persist. By comparing spatio‐temporal field observations and community perceptions with the Geographic Information System (GIS)‐based universal soil loss equation (USLE), this study critically examined theorized erosion patterns (by USLE) in a degraded landscape (Shanko Bahir, Ethiopia) to improve soil conservation strategy development. Daily hydro‐sedimentological data (showing 792 mm of rainfall leading to 3·2 Mg ha−1 y−1 of sediment yield) revealed mild but variable erosion patterns in 2012. Overlooking hydrology hindered the USLE's suitability for conservation planning. For instance, the median infiltration rate (33 mm h−1) was rarely exceeded (3·5% of events), meaning runoff‐induced erosion risk were not well predicted spatio‐temporally by the USLE R‐factor. Conversely, heterogeneous local perspectives explicitly considered accumulated runoff, saturation (“the water at the top level rests on the bottom”), fertility, and gullies as drivers of erosion (“black soil breaks and forms gorges”). Additionally, they designated steeper mono‐cropped lands as at risk (incidentally also highlighted by USLE). Observational evidence showed steeper midslope areas decreasing in topsoil depth by 14 mm, flatter downslope areas by 0·8 mm, and the mild upslope areas increasing 2 mm. Operationalizing effective soil conservation strategies will require expanding beyond (USLE‐based) technical knowledge to incorporate local stakeholders and consider the main hydrological processes causing erosion in sub‐humid mountainous landscapes: saturated pathways, downslope saturation, subsurface flow, and gully formation. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Hardpan is a major cause of land degradation that affects agricultural productivity in developing countries. However, relatively, little is known about the interaction of land degradation and hardpans. The objective of this study was, therefore, to investigate soil degradation and the formation of hardpans in crop/livestock-mixed rainfed agriculture systems and to assess how changes in soil properties are related to the conversion of land from forest to agriculture. Two watersheds (Anjeni and Debre Mewi) were selected in the humid Ethiopian highlands. For both watersheds, 0-45 cm soil penetration resistance (SPR, n = 180) and soil physical properties (particle size, soil organic matter, pH, base ions, cation exchange capacity, silica content, bulk density and moisture content) were determined at 15 cm depth increments for three land uses: cultivated, pasture and forest. SPR of agricultural fields was significantly greater than that of forest lands. Dense layers with a critical SPR threshold of ≥2000 kPa were observed in the cultivated and pasture lands starting at a depth of 15-30 cm but did not occur in the undisturbed forest land. Compared with the original forest soils, agricultural fields were lower in organic matter, cation exchange capacity, and exchangeable base cations; more acidic; had a higher bulk density and more fine particles (clay and silt); and contained less soluble silica. Overall, our findings suggest that soil physical and chemical properties in agricultural lands are deteriorated, causing disintegration of soil aggregates, resulting in greater sediment concentration in infiltration water that clogged up macro-pores, thereby disconnecting deep flow paths found in original forest soils. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In many parts of the world, watershed management practices have been extremely effective. However, implementation of soil and water conservation technologies in the humid African highlands, while beneficial in the short term, were remarkably unsuccessful in the long term. Insights from community knowledge perspectives have revealed that alternative methods are needed. Although conservation practices are designed to conserve water in semi-arid areas, safely draining excess water is needed in humid areas. The objective of this paper is to review current watershed management approaches used in humid regions as exemplified by those used in Ethiopian highlands and then based on these findings propose more effective practices. Although current government sponsored practices primarily protect the hillsides, direct run-off is generated from areas that become saturated on valley bottoms near rivers and on specific parts of the hillsides with degraded soils (or with highly permeable surface soils) and with perched water tables on slowly permeable horizons at shallow depths. In these areas, direct run-off is increasing with deforestation and the soil degradation, demanding additional drainage ways that evolve in the form of gullies. Therefore, watershed management interventions for erosion control should prioritize revegetation of degraded areas, increasing sustainable infiltration, and rehabilitating gullies situated at saturated bottomlands. [ABSTRACT FROM AUTHOR]

Landscape response to drivers of change is more visible and noticeable in deltas and floodplains than in upstream. Here, we address the changes of Lake Tana basin by investigating the delta development of Gumara River and sediment deposition in the Fogera floodplain over a 58-year period when agricultural land expanded, agriculture intensified, and flooding of the alluvial plain became more frequent. Old maps show that delta formation before the 1950s was minimal, indicating that the sediment contributed by the rivers to the lake was small. However, during the last 58 years, the delta has expanded continuously. When considering the same lake level (2·68 m) from 1984 to 2014, the delta has expanded an average of 5 ha annually, and by considering different lake levels and corresponding delta areas, the delta increased in height an average of 3 cm annually. While the growth of the delta was approximately linear, the sediment concentration in the river doubled in the last 30 years, indicating more efficient sediment trapping in the floodplain as a result of higher lake levels, rising river beds, and farmers intervening with the course of the river near the shore. Unless effective river restoration and catchment-based treatment measures are put in place, the capacity of the rivers will further reduce and aggravate the flooding of the floodplain, causing more sediment deposition in the river channel and on the floodplain. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Controlling soil erosion is important for maintaining land productivity and reducing sedimentation of reservoirs in the Ethiopian highlands. To gain insights on sediment loss patterns, magnitude of peak sediment events, and their contribution to annual loads, hydrometric and sediment concentration data were collected for five years (2010 - 2014) from the 95-ha Debre Mawi and four nested catchments (located 30 km south of Lake Tana). Soil and water conservation practices (SWCPs) consisting of soil bunds with 50-cm-deep furrows were implemented in the third year, which made it possible to examine the effects of SWCPs on peak sediment loads. The results show that a 10-min event causes soil loss of up to 11·4 Mg ha−1, which is 22% of the annual sediment yield. Thirty to seventy-five percent (up to 30 Mg ha−1day−1) of the sediment yield was contributed by the greatest daily flow in each year. The contribution increases to 86% for the two largest daily flows. SWCP interventions reduced sediment loss by half but did not affect the relative contribution of peak events to annual loads. Because of gully erosion, peak sediment loads at the outlet of the entire catchment were greater (up to 30 Mg ha−1day−1) as compared to the nested catchments without gullies (0·5 to 8 Mg ha−1day−1). Consequently, to reduce sediment loss, conservation measures should be designed to decrease runoff during large storms. This can be attained by deepening furrows on unsaturated hillsides and reducing the entrainment of unconsolidated sediment from failed gully banks. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Groundwater levels are declining at unsustainable levels in many areas of the world. To secure this resource for future generation, well-documented groundwater level observations are needed to derive recharge rates and sustainable withdrawal amounts. Although groundwater is routinely monitored in most of the world, relatively little information is available in sub-Saharan Africa including the Ethiopian highlands where groundwater irrigation could greatly increase food security. To obtain sustainable withdrawal rates for the wet Ethiopian highlands, we selected the Fogera plain in the Lake Tana basin with a sub-humid climate. Weekly groundwater levels were measured in 32 abandoned shallow wells over a 2-year period in 2014 and 2015. Our observations showed that in the 2 years, the groundwater level reached the surface during the rainy monsoon phase around first week of August. At the end of the dry monsoon phase in May, the average groundwater table was at 4 m depth. The amount of water removed by evaporation during the dry phase was 850 mm year−1. This is replenished through recharge during the wet phase. Rain in excess of the recharge and evaporation is stored on the surface or converted to overland flow. The groundwater flowed slowly towards the lake, but water passing the lakeshore was not a significant term in the water balance of the plain. Irrigation from groundwater seems to be sustainable especially when rivers flood periodically. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Long-term erosion monitoring data in the Ethiopian highlands are only available from the Soil Conservation Research Program (SCRP) watersheds including the Anjeni watershed. The 113 ha Anjeni watershed was established in 1984 and fanya juu terraces were installed in 1986. Runoff and erosion data are available from three different plot sizes and at the watershed outlet. The objective of this study was to investigate how erosion processes and sediment rating parameters vary with plot size and the progression of the rainy monsoon phase. We analyzed runoff and sediment loss data from 40 plots and the watershed outlet. The dataset included erosion data from 24 newly constructed plots (3 m length) during the rainy monsoon phase of 2012 and 2013, and 16 long-term plots (with 12, 16, 22, and 24% slopes and 3, 15 and 30 m lengths) and the watershed outlet during the period between 1986 to 1990. Sediment concentration ( C) was fitted to runoff ( Q) using a power regression equation ( C = aQ b). Sediment concentration and yield increased with increasing plot length from 3 m to 15 m, but sediment yield decreased as plot length increased to 30 m.The coefficients ( a and b) were affected by plot size and the progression of the rainy monsoon phase. As plot size increases, the a value increased, while the b value decreased. Greater a values were observed during the beginning of the monsoon phase, while values of b were greater towards the end of the monsoon phase. Overall findings suggest that erosion from cultivated fields is primarily controlled by transport limitations at the beginning of the monsoon phase, while towards the end of the monsoon phase, as surface covers emerge, sediment availability will be reduced, and thus sediment source would be a limitation. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In the northern highlands of Ethiopia, gully erosion is severe. Despite many efforts to implement gully prevention measures, controlling gully erosion remains a challenge. The objective is to better understand the regional gully erosion processes and to prevent gully head retreat. The study was conducted in the Ene-Chilala catchment in the sub-humid headwaters of the Birr River located southwest of Bahir Dar, Ethiopia. Twelve gully heads were monitored during the 2014 and 2015 rainy monsoon phase. We measured gully head morphology and retreat length, soil shear strength, ground water table levels, and catchment physical characteristics. Two active gully head cuts were treated in 2014 and an additional three head cuts in 2015 by regrading their slope to 45° and covering them with stone riprap. These treatments halted the gully head advance. The untreated gullies were actively eroding due to groundwater at shallow depths. The largest head retreat was 22.5 m, of which about half occurred in August of the first year when the surrounding soil was fully saturated. Lowering both the water table and protecting the gully heads can play a key role in reducing gully expansion and soil loss due to gully erosion in the Ethiopian highlands. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Rapid population growth and agricultural intensification have been directly associated with land degradation and with visible deterioration in water quality in the Ethiopian lakes. Assessing the extent and origin of pollution is cumbersome because of the lack of measurements for water quality parameters. This paper reports on the dissolved phosphorus (DP) concentrations in Lake Tana and its tributaries during 3 years from 2010 to 2012 and the four rainy months in 2014. Concentrations in the headwaters, at the gaging station, at the river mouth, near shore (littoral), and in the open lake (pelagic) were measured for the four major rivers. DP concentration in the rivers was on the average 0·32 mg l−1, and DP in the lake was much lower with an average concentration of 0·10 mg l−1. Temporally, DP concentrations were greater in the rainy phase of the monsoon than in the dry phase from November through March. Moreover, an upward trend in DP concentrations is coinciding with the area expansion of water hyacinths in the lake. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Saturation-excess runoff is the major runoff mechanism in humid well-vegetated areas where infiltration rates often exceed rainfall intensity. Although the Soil and Water Assessment Tool (SWAT) is one of the most widely used models, it predicts runoff based mainly on soil and land use characteristics, and is implicitly an infiltration-excess runoff type of model. Previous attempts to incorporate the saturation-excess runoff mechanism in SWAT fell short due to the inability to distribute water from one hydrological response unit to another. This paper introduces a modified version of SWAT, referred to as SWAT-Hillslope (SWAT-HS). This modification improves the simulation of saturation-excess runoff by redefining hydrological response units based on wetness classes and by introducing a surface aquifer with the ability to route interflow from 'drier' to 'wetter' wetness classes. Mathematically, the surface aquifer is a nonlinear reservoir that generates rapid subsurface stormflow as the water table in the surface aquifer rises. The SWAT-HS model was tested in the Town Brook watershed in the upper reaches of the West Branch Delaware River in the Catskill region of New York, USA. SWAT-HS predicted discharge well with a Nash-Sutcliffe Efficiency of 0.68 and 0.87 for daily and monthly time steps. Compared to the original SWAT model, SWAT-HS predicted less surface runoff and groundwater flow and more lateral flow. The saturated areas predicted by SWAT-HS were concentrated in locations with a high topographic index and were in agreement with field observations. With the incorporation of topographic characteristics and the addition of the surface aquifer, SWAT-HS improved streamflow simulation and gave a good representation of saturated areas on the dates that measurements were available. SWAT-HS is expected to improve water quality model predictions where the location of the surface runoff matters. [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]

Planning effective landscape interventions is an important tool to fight against land degradation and requires knowledge on spatial distribution of runoff. The objective of this paper was to test models that predict temporal and spatial distribution of runoff. The selected models were parameter-efficient semi-distributed watershed model (PED-WM), Hydrologiska Byrans Vattenbalansavdelning integrated hydrological modeling system (HBV-IHMS), and Soil and Water Assessment Tool (SWAT). We choose 7-km2 Awramba watershed in the Lake Tana basin with detailed hydrological information for testing these models. Discharge at the outlet, rainfall, and distributed information on infiltration rates, water table, and extent of the saturated area were collected from 2013 to 2015. The maximum saturated area was 6·5% of the watershed. Infiltration rates exceeded rainfall intensities 91% of the time. Hence, saturation excess runoff was the main runoff mechanism. Models were calibrated for the rainy seasons in 2013 and 2014 and validated for 2015. For daily flow validation, the PED-WM model (Nash-Sutcliff efficiency, NSE = 0·61) outperformed HBV-IHMS (NSE = 0·51) and SWAT (NSE = 0·48). Performance on monthly time step was similar. Difference in model behavior depended on runoff mechanism. In PED-WM, saturation excess is the main direct runoff process and could predict the maximum extent of the saturated area closely at 6·9%. HBV-IHMS model runoff simulation depended on soil moisture status and evapotranspiration, and hence was able to simulate saturation excess flow but not the extent of the saturated area. SWAT, where infiltration excess is the main runoff mechanism, could only predict the monthly discharges well. This study shows that prevailing runoff mechanisms and distribution of runoff source areas should be used for proper model selection. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Increasing population and intensification of agriculture increase erosion rates and often result in severe land degradation and sedimentation of reservoirs. Finding effective management practices to counteract the increasing sediment load is becoming increasingly urgent especially in the Ethiopian highlands where the construction of the hydroelectric Grand Renaissance Dam on the Blue Nile is underway. In this paper, we examine the results of 9 years of a watershed experiment in which discharge and sediment losses were observed in the 113 ha Anjeni watershed of the Blue Nile Basin. The study period encompasses conditions before, during, and after the installation of graded Fanya- Juu ('throw uphill' bunds) soil and water conservation practices (SWCP), which had the ultimate goal of creating terraces. We use a saturation-excess runoff model named the parameter-efficient distributed model as a mathematical construct to relate rainfall with discharge and sediment losses at the outlet. The parameter-efficient distributed model is based on landscape units in which the excess rainfall becomes direct runoff or infiltrates based on topographic position or hardpan characteristics. Deviations in this rainfall-discharge-sediment loss relationship are ascribed to the changes in infiltration characteristics caused by SWCPs on the hillslopes. With this technique, we found that in the Anjeni basin, the Fanya-Juu SWCPs are only effective in increasing the infiltration and thereby reducing the direct runoff and sediment concentrations in the first 5 years. At the end of the 9-year observation period, the direct runoff and sediment concentrations were barely reduced compared to the levels before SWCP were installed. In addition, we found that the model structure based on landscape units was able to represent the varying runoff and erosion processes during the 9 years well by varying mainly the portion of degraded land (and thereby representing the effectiveness of the Fanya-Juu to reduce runoff by increasing infiltration). [ABSTRACT FROM AUTHOR]

Intensifying agriculture in Africa is degrading the water quality of rivers and lakes, thereby, threatening the sustainable use of water resources. In Lake Tana in the Ethiopian highlands, the first signs of eutrophication were recently observed. Since relatively little is known about the non-point source pollution in sub-Saharan Africa, the objective was to examine non-point sources phosphorus contribution of an agricultural watershed near Lake Tana. The 7-km2 Awramba watershed was selected. Dissolved phosphorus concentration (DPC) in groundwater and soil-available phosphorus was measured at three landscape positions and discharge, sediment, and DPC at the outlet. The results indicated that DPC in groundwater was most elevated in the periodically saturated valley bottoms while available P was the greatest in the cropped fields at mid-slope. The DPC increased with discharge. During base flow the concentration in the stream was similar to that in ground water. The results were consistent with other hydrological watershed studies in which the major source of runoff, erosion, and phosphorus originated from valley bottom lands. Hence, converting the periodically saturated areas in the stream corridor to buffer zones with reduced P input can be an important tool in reducing P from rural watersheds in the Ethiopian highlands. [ABSTRACT FROM AUTHOR]

Denitrifying bioreactors have been suggested as effective best management practices to reduce nitrate and nitrite (NOx) in largescale agricultural tile drainage. This study combines experiments in flow-through laboratory reactors with in situ continuous monitoring and experiments in a pair of field reactors to determine the effectiveness of reactors for small-scale agriculture in New York. It also compares the use of a typical woodchip media with a woodchip and biochar mixture. Laboratory results showed linear increase in NOx removal with both increased inflow concentration and increased residence time. Average removal of NOx in weekly monitoring of field reactors over the course of two growing seasons was 3.23 and 4.00 g N m-3 d-1 for woodchip and woodchip/biochar reactors, respectively. Removal of NOx during two field experimental runs was similar to in situ monitoring and did not correlate with laboratory experiments. Factors that are uncontrollable at the field scale, such as temperature and inflow water chemistry, may result in more complex and resilient microbial communities that are less specialized for denitrification. Further study of other controlling variables, other field sites, and other parameters, including microbial communities and trace gas emissions, will help elucidate function and applicability of denitrifying bioreactors. [ABSTRACT FROM AUTHOR]

In temperate climates, a significant fraction of annual emissions of N2O from agricultural land can occur during soil thaw in late winter and early spring. The objective of this study was to determine the impact of land use change from long-term fallow grassland to managed perennial grass crops on these thaw-related N2O emissions and to identify field-scale drivers that influence emissions. Using static chambers, we monitored mid-afternoon N2O fluxes during the 2013 spring thaw from 27 March to 7 April, observing fallow grassland and second-year reed canarygrass (Phalaris arundinaceae L., 'Bellevue') across a short topographical gradient. Soil temperature, soil moisture, and residual aboveground biomass were also observed, as were hourly air temperature and precipitation. Fluxes of N2O were generally low (-9.8 to 21.3 mg N2O-N m-2 h-1) except for one observation of 77.6 mg N2O-N m-2 h-1. Hot-moment analysis, non-parametric statistical tests, and ANOVA results showed that downslope positions converted to managed and fertilized grass had significantly higher N2O emissions than the fallow and upslope positions. We found that these downslope managed grass sites had mean soil moisture of 75.0% water-filled pore space and less insulating residual aboveground biomass than the fallow grassland. Our results suggest that converting fallow grassland to managed perennial grass cropping systems for bioenergy or other uses could increase spring-thaw N2O emissions in wetness- prone areas. [ABSTRACT FROM AUTHOR]

Gully erosion reduces agricultural productivity by destroying valuable land resources, increases sediment concentrations, reduces water quality, and fills up reservoirs. Gully rehabilitation has proven to be challenging especially in the high-rainfall areas of the Ethiopian Highlands and has therefore had limited success. This paper describes a successful low-cost gully rehabilitation effort with community participation in the Birr watershed in the Blue Nile basin that begun in early 2013. Initially, farmers were reluctant to participate for religious reasons, but with the aid of local priests and respected elders, community discussions, and a visit to a rehabilitated gully, a consensus was reached to rehabilitate a 0·71-ha upland gully. The rehabilitation measures consisted of regrading the gully head at a 45° slope, constructing low-cost check dams from locally available materials, and planting Pennisetum purpureum grass and Sesbania sesban. At the end of the first post-implementation rainy season, 2,200 tons of soil was conserved by the constructed check dams and newly planted vegetation, compared with soil losses of 680 and 560 tons in two untreated, nearby gullies. In 2014, an additional 3,100 tons of soil was conserved. In 2013, the marginal rate of return (MRR) on the gully rehabilitation investment was 2·6 based on the value of increased forage production alone. When we include trapped soil nutrient values, the rehabilitation MRR was increased to 10. Although these numbers are impressive, the best proof of the success was that farmers on their own initiative rehabilitated an additional five gullies in 2014. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In nondegraded watersheds of humid climates, subsurface flow patterns determine where the soil saturates and where surface runoff is occurring. Most models necessarily use infiltration-excess (i.e., Hortonian) runoff for predicting runoff and associated constituents because subsurface flow algorithms are not included in the model. In this article, we modify the Water Erosion Prediction Project (WEPP) model to simulate subsurface flow correctly and to predict the spatial and temporal location of saturation, the associated lateral flow and surface runoff, and the location where the water can re-infiltrate. The modified model, called WEPP-UI, correctly simulated the hillslope drainage data from the Coweeta Hydrologic Laboratory hillslope plot. We applied WEPP-UI to convex, concave, and S-shaped hillslope profiles, and found that multiple overland flow elements are needed to simulate distributed lateral flow and runoff well. Concave slopes had the greatest runoff, while convex slopes had the least. Our findings concur with observations in watersheds with saturation-excess overland flow that most surface runoff is generated on lower concave slopes, whereas on convex slopes runoff infiltrates before reaching the stream. Since the WEPP model is capable of simulating both saturation-excess and infiltration-excess runoff, we expect that this model will be a powerful tool in the future for managing water quality. [ABSTRACT FROM AUTHOR]

We present a conceptual framework that relates agricultural best management practice ( BMP) effectiveness with dominant hydrological flow paths to improve nonpoint source ( NPS) pollution management. We use the framework to analyze plot, field and watershed scale published studies on BMP effectiveness to develop transferable recommendations for BMP selection and placement at the watershed scale. The framework is based on the location of the restrictive layer in the soil profile and distinguishes three hydrologic land types. Hydrologic land type A has the restrictive layer at the surface and BMPs that increase infiltration are effective. In land type B1, the surface soil has an infiltration rate greater than the prevailing precipitation intensity, but there is a shallow restrictive layer causing lateral flow and saturation excess overland flow. Few structural practices are effective for these land types, but pollutant source management plans can significantly reduce pollutant loading. Hydrologic land type B2 has deep, well-draining soils without restrictive layers that transport pollutants to groundwater via percolation. Practices that increased pollutant residence time in the mixing layer or increased plant water uptake were found as the most effective BMPs in B2 land types. Matching BMPs to the appropriate land type allows for better targeting of hydrologically sensitive areas within a watershed, and potentially more significant reductions of NPS pollutant loading. [ABSTRACT FROM AUTHOR]

Experimental research in the Ethiopian highlands found that saturation excess induced runoff and erosion are common in the sub-humid conditions. Because most erosion simulation models applied in the highlands are based on infiltration excess, we, as an alternative, developed the Parameter Efficient Distributed (PED) model, which can simulate water and sediment fluxes in landscapes with saturation excess runoff. The PED model has previously only been tested at the outlet of a watershed and not for distributed runoff and sediment concentration within the watershed. In this study, we compare the distributed storm runoff and sediment concentration of the PED model against collected data in the 95-ha Debre Mawi watershed and three of its nested sub-watersheds for the 2010 and 2011 rainy seasons. In the PED model framework, the hydrology of the watershed is divided between infiltrating and runoff zones, with erosion only taking place from two surface runoff zones. Daily storm runoff and sediment concentration values, ranging from 0.5 to over 30 mm and from 0.1 to 35 g l−1, respectively, were well simulated. The Nash Sutcliffe efficiency values for the daily storm runoff for outlet and sub-watersheds ranged from 0.66 to 0.82, and the Nash-Sutcliffe efficiency for daily sediment concentrations were greater than 0.78. Furthermore, the model uses realistic fractional areas for surface and subsurface flow contributions, for example between saturated areas (15%), degraded areas (30%) and permeable areas (55%) at the main outlet, while close similarity was found for the remaining hydrology and erosion parameter values. One exception occurred for the distinctly greater transport limited parameter at the actively gullying lower part of the watershed. The results suggest that the model based on saturation excess provides a good representation of the observed spatially distributed runoff and sediment concentrations within a watershed by modelling the bottom lands (as opposed to the uplands) as the dominant contributor of the runoff and sediment load. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Obtaining representative meteorological data for watershed-scale hydrological modelling can be difficult and time consuming. Land-based weather stations do not always adequately represent the weather occurring over a watershed, because they can be far from the watershed of interest and can have gaps in their data series, or recent data are not available. This study presents a method for using the Climate Forecast System Reanalysis (CFSR) global meteorological dataset to obtain historical weather data and demonstrates the application to modelling five watersheds representing different hydroclimate regimes. CFSR data are available globally for each hour since 1979 at a 38-km resolution. Results show that utilizing the CFSR precipitation and temperature data to force a watershed model provides stream discharge simulations that are as good as or better than models forced using traditional weather gauging stations, especially when stations are more than 10 km from the watershed. These results further demonstrate that adding CFSR data to the suite of watershed modelling tools provides new opportunities for meeting the challenges of modelling un-gauged watersheds and advancing real-time hydrological modelling. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The Soil and Water Assessment Tool ( SWAT) model (Arnold et al., 1998) is a popular watershed management tool. Currently, the SWAT model, actively supported by the U.S. Department of Agriculture and Texas A&M, operates only on Microsoft® Windows, which hinders modelers that use other operating systems ( OS). This technical note introduces the Comprehensive R Archive Network ( CRAN) distributed ' SWATmodel' package which allows SWAT 2005 and 2012 to be widely distributed and run as a linear model-like function on multiple OS and processor platforms. This allows researchers anywhere in the world using virtually any OS to run SWAT. In addition to simplifying the use of SWAT across computational platforms, the SWATmodel package allows SWAT modelers to utilize the analytical capabilities, statistical libraries, modeling tools, and programming flexibility inherent to R. The software allows watershed modelers to develop a simple hydrological watershed model conceptualization of the SWAT model and to obtain a first approximation of the minimum expected results a more complicated model should deliver. As a proof of concept, we test the SWAT model by initializing and calibrating 314 U.S. Geological Survey stream gages in the Chesapeake Bay watershed and present the results. [ABSTRACT FROM AUTHOR]

Pore velocity-dependent dynamic contact angles provide a mechanism for explaining the formation of fingers/columns in porous media. To study those dynamic contact angles when gravity is present, rectangular capillary tubes were used to facilitate observation of the complete interface without geometric distortion. Results show that the Hoffman (1975) relationship between dynamic contact angle and water velocity applies to gravity-affected flow fields, and that it (when adjusted for nonzero static contact angles) can be used to model dynamic capillary pressures for unstable wettings fronts in porous media by assuming that (1) pressure at the wetting front is discontinuous, (2) the flow field behind the fingertip is highly heterogeneous, and (3) the front line advances one or a few pores at the time. We demonstrate the utility of the Hoffman relationship for porous media with a published infiltration experiment by calculating the capillary pressure successfully at the unstable wetting front as a function of the flux of water in the finger and the grain size diameter. [ABSTRACT FROM AUTHOR]

Recent works have indicated that climate change in the northeastern United States is already being observed in the form of shorter winters, higher annual average air temperature, and more frequent extreme heat and precipitation events. These changes could have profound effects on aquatic ecosystems, and the implications of such changes are less understood. The objective of this study was to examine how future changes in precipitation and temperature translate into changes in streamflow using a physically based semidistributed model, and subsequently how changes in streamflow could potentially impact stream ecology. Streamflow parameters were examined in a New York City water supply watershed for changes from model-simulated baseline conditions to future climate scenarios (2081-2100) for ecologically relevant factors of streamflow using the Indicators of Hydrologic Alterations tool. Results indicate that earlier snowmelt and reduced snowpack advance the timing and increase the magnitude of discharge in the winter and early spring (November-March) and greatly decrease monthly streamflow later in the spring in April. Both the rise and fall rates of the hydrograph will increase resulting in increased flashiness and flow reversals primarily due to increased pulses during winter seasons. These shifts in timing of peak flows, changes in seasonal flow regimes, and changes in the magnitudes of low flow can all influence aquatic organisms and have the potential to impact stream ecology. [ABSTRACT FROM AUTHOR]

To explain the dynamic behavior of the matric potential at the wetting front of gravity driven fingers, we take into account the pressure across the interface that is not continuous and depends on the radius of the meniscus, which is a function of pore size and the dynamic contact angle θd. θd depends on a number of factors including velocity of the water and can be found by the Hoffman-Jiang equation that was modified for gravity effects. By assuming that water at the wetting front imbibes one pore at a time, realistic velocities are obtained that can explain the capillary pressures observed in unstable flow experiments in wettable and water repellent sands. [ABSTRACT FROM AUTHOR]

Rain-on-snow (ROS) runoff events are important hydro-meteorological phenomenon due to their association with flooding. The severity of ROS runoff events depends on the magnitude of the precipitation, air temperature elevation, snow water equivalent (SWE), and areal extent of the antecedent snowpack. Examining the consequences of these factors acting together creates challenges for both flood prediction and flood risk assessments. This study provides information on the spatial patterns, and seasonality of ROS events in New York. We examine the spatial and temporal variability of ROS events for water years 2004 to 2012 from SNOw Data Assimilation System products for New York. Liquid and solid precipitation, snow depth, snowmelt, SWE, maximum and minimum temperature, hydrograph characteristics, and annual peak flow are examined. There is significant positive correlation of ROS days and ROS triggered events with elevation and negative correlation of these events with increasing air temperature. Our study shows that ROS events are dominant in high elevation areas of Adirondack and Catskill regions, and their distribution varies with month. Cumulative runoffs from ROS events are generally greater than the rain-only runoff events. The majorities of annual peak flows in the study watersheds are the results of ROS events and lasted from a few days to many weeks. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Describing the distribution of aquatic habitats and the health of biological communities can be costly and time-consuming; therefore, simple, inexpensive methods to scale observations of aquatic biota to watersheds that lack data would be useful. In this study, we explored the potential of a simple "hydrogeomorphic" model to predict the effects of acid deposition on macroinvertebrate, fish, and diatom communities in 28 sub-watersheds of the 176-km² Neversink River basin in the Catskill Mountains of New York State. The empirical model was originally developed to predict stream-water acid neutralizing capacity (ANC) using the watershed slope and drainage density. Because ANC is known to be strongly related to aquatic biological communities in the Neversink, we speculated that the model might correlate well with biotic indicators of ANC response. The hydrogeomorphic model was strongly correlated to several measures of macroinvertebrate and fish community richness and density, but less strongly correlated to diatom acid tolerance. The model was also strongly correlated to biological communities in 18 sub-watersheds independent of the model development, with the linear correlation capturing the strongly acidic nature of small upland watersheds (< 1 km²). Overall, we demonstrated the applicability of geospatial data sets and a simple hydrogeomorphic model for estimating aquatic biological communities in areas with stream-water acidification, allowing estimates where no direct field observations are available. Similar modeling approaches have the potential to complement or refine expensive and timeconsuming measurements of aquatic biota populations and to aid in regional assessments of aquatic health. [ABSTRACT FROM AUTHOR]

We present a method to integrate a process-based (PB) snowmelt model that requires only daily temperature and elevation information into the Soil and Water Assessment Tool (SWAT) model. The model predicts the spatiotemporal snowpack distribution without adding additional complexity, and in fact reduces the number of calibrated parameters. To demonstrate the utility of the PB model, we calibrate the PB and temperature-index (TI) SWAT models to optimize agreement with stream discharge on a 46-km2 watershed in northwestern Idaho, United States, for 10 individual years and use the calibrated parameters for the year with the best agreement to run the model for 15 remaining years. Stream discharge predictions by the PB and TI model were similar, although the PB model simulated snowmelt more accurately than the TI model for the remaining 15-year period. Spatial snow distributions predicted by the PB model better matched observations from LandSat imagery and a SNOTEL station. Results for this watershed show that including PB snowmelt in watershed models is feasible, and calibration of TI-based watershed models against discharge can incorrectly predict snow cover. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) emissions were monitored using the micrometeorologi- cal eddy covariance technique from manure-fertilized cropland on a large dairy farm in New York State in 2006 to 2009. Nitrous oxide emissions demonstrated episodic behavior with intermittent short-duration peak fluxes up to 39.7 mg N2O-N m-2 d-1, whereas most of background fluxes during the annual agricultural cycle were below 6.5 mg N2O-N m-2 d-1. This paper discusses temporal variability of measured N2O emissions using a "hot moment" approach. To identify and quantify peak events as potential hot moments and to determine whether or not they could be treated statistically as outliners, N2O daily fluxes were analyzed by the box plot method using multiple thresholds. Peak events exceeding outlier thresholds contributed up to 51% of cumulative annual N2O emissions, although they represented <7% of the total observation time. Individual N2O peaks were also categorized by their duration, as single day spikes and multiday events. The highest contributing instances were multiday N2O peaks during summer precipitation and early spring thaw, largely enhanced by manure fertilization. These high-intensity emission events demonstrated repetitive seasonal responses to a combination of environmental factors and were therefore identified as hot moments. Abrupt rises in both temperature and soil moisture appeared to trigger major hot moments, whereas the availability of manure N controlled their magnitude. In the absence of strong correlations between time-series of individual environmental factors and N2O emissions, the hot moment approach can be a promising tool for the integrated analysis of most significant N2O events in cultivated fields receiving manure applications. [ABSTRACT FROM AUTHOR]

The article presents a study which investigates the water quality and economic consequences of protecting runoff-generating areas from agriculture with chosen best management practices (BMPs). The study shows that to install barnyard BMPs and to convert runoff-prone agricultural land to buffers are both effective in reducing dissolved P loss from one single-farm watershed with the use of a net present value analysis (NPV) and the variable Source Loading Function model. The marginal costs of increasing buffer size and the spatial location of the BMPs in association with the runoff producing areas were discovered to be the most critical considerations for profitability and water quality.

Private wells in Cayuga and Orange counties in New York were sampled to determine the occurrence of pesticide contamination of groundwater in areas where significant pesticide use coincides with shallow or otherwise vulnerable groundwater. Well selection was based on local groundwater knowledge, risk modeling, aerial photo assessments, and pesticide application database mapping. Single timepoint samples from 40 wells in each county were subjected to 93-compound chromatographic scans. All samples were nondetects (reporting limits ≤1 μg/L), thus no wells from either county exceeded any of 15 state groundwater standards or guidance values. More sensitive enzyme-linked immunosorbent assays (ELISA) found two wells with quantifiable atrazine in each county (0.1-0.3 μg/L), one well with quantifiable diazinon (0.1 μg/L) in Orange County, and one well with quantifiable alachlor (0.2 μg/L) in Cayuga County. Trace detections (<0.1 μg/L) in Cayuga County included atrazine (five wells), metolachlor (six wells), and alachlor (one well), including three wells with multiple detections. All 12 Cayuga County wells with ELISA detections had either corn/grain or corn/forage rotations as primary surrounding land uses (although 20 other wells with the same land uses had no detections) and all quantified detections and most trace detections occurred in wells up to 9-m deep. Orange County trace (<0.1 μg/L) ELISA detections (atrazine three wells, diazinon one well, and metolachlor five wells) and quantified detections were only generally associated with agricultural land uses. Finding acceptable drinking water quality in areas of vulnerable groundwater suggests that water quality in less vulnerable areas will also be good. [ABSTRACT FROM AUTHOR]

Most semi-distributed watershed water quality models divide the watershed into hydrologic response units (HRU) with no flow among them. This is problematic when watersheds are delineated to include variable source areas (VSAs) because it is the lateral flows from upslope areas to downslope areas that generate VSAs. Although hydrologic modellers have often successfully calibrated these types of models, there can still be considerable uncertainty in model results. In this paper, a topographic-index-based method is described and tested to distribute effective soil water holding capacity among HRUs, which can be subsequently adjusted using the watershed baseflow coefficient. The method is tested using a version of the Soil and Water Assessment Tool (SWAT) model that simulates VSA runoff and is applied to two watersheds: a New York State (NYS) watershed, and one in the head waters of the Blue Nile Basin (BNB) in Ethiopia. Daily streamflow predicted using effective soil water storage capacities based only on the topographic index were reassuringly accurate in both the NYS watershed (daily Nash Sutcliffe ( E) = 0·73) and in the BNB ( E = 0·70). Using the baseflow coefficient to adjust the effective soil water storage capacity only slightly improved streamflow predictions in NYS ( E = 0·75) but substantially improved the BNB predictions ( E = 0·80). By comparison, the standard SWAT model, which uses the traditional look-up tables to determine a runoff curve number, performed considerably less accurately in un-calibrated form ( E = 0·51 for NYS and E = 0·45 for BNB), but improved substantially when explicitly calibrated to streamflow measurements ( E = 0·76 for NYS and E = 0·67 for the BNB). The calibration method presented here provides a parsimonious, systematic approach to using established models in VSA watersheds that reduces the ambiguity inherent in model calibration. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Eddy covariance and static chambers are different-scale methods for monitoring agricultural N20 that, when used together on heterogeneous agricultural landscapes, can help identify flux sources and sinks and evaluate the effect of management interventions on landscape-scale N2O emissions. This study compared the N2O flux data obtained by eddy covariance and static chambers during a short-term N2O measurement campaign from two adjacent agricultural treatments: alfalfa (Medicago sativa L.) and corn (Zea mays L.) fields. Wind direction data from micrometeorological observations were used to downscale the integrated eddy covariance N2O flux and estimate the treatment contributions. The N2O data from static chambers installed on each treatment were used to verify the partitioned eddy covariance fluxes. Both methods consistently showed greater emissions for the alfalfa field, which received more N fertilizer earlier in the growing season. Two methods were also compared with respect to the landscape-integrated N2O flux measured at the eddy covariance mast location. Upscaling the chamber N2O fluxes was performed by totaling the contributions from individual chambers weighted toward the source area share associated with their field locations using a simple footprint model. The comparison of the chambers' total to the measured eddy covariance emissions showed a difference of 7 to 33% between the methods. The best agreement was observed when the integrated eddy covariance flux was associated with uniform wind direction and a homogeneous source area. The results suggest that localization of the flux source using wind directions and footprint information can help in comparing different-scale N2O emissions. [ABSTRACT FROM AUTHOR]

Watershed scale hydrological and biogeochemical models rely on the correct spatial-temporal prediction of processes governing water and contaminant movement. The Soil and Water Assessment Tool (SWAT) model, one of the most commonly used watershed scale models, uses the popular curve number (CN) method to determine the respective amounts of infiltration and surface runoff. Although appropriate for flood forecasting in temperate climates, the CN method has been shown to be less than ideal in many situations (e.g. monsoonal climates and areas dominated by variable source area hydrology). The CN model is based on the assumption that there is a unique relationship between the average moisture content and the CN for all hydrologic response units (HRUs), and that the moisture content distribution is similar for each runoff event, which is not the case in many regions. Presented here is a physically based water balance that was coded in the SWAT model to replace the CN method of runoff generation. To compare this new water balance SWAT (SWAT-WB) to the original CN-based SWAT (SWAT-CN), two watersheds were initialized; one in the headwaters of the Blue Nile in Ethiopia and one in the Catskill Mountains of New York. In the Ethiopian watershed, streamflow predictions were better using SWAT-WB than SWAT-CN [Nash-Sutcliffe efficiencies (NSE) of 0·79 and 0·67, respectively]. In the temperate Catskills, SWAT-WB and SWAT-CN predictions were approximately equivalent (NSE > 0·70). The spatial distribution of runoff-generating areas differed greatly between the two models, with SWAT-WB reflecting the topographical controls imposed on the model. Results show that a water balance provides results equal to or better than the CN, but with a more physically based approach. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Agriculture often is considered to be a contributor of soluble reactive phosphorus (SRP) and nitrate-N (NO3--N) to surface waters. This research analyzed SRP and NO3--N concentrations in groundwater and in a creek fed by groundwater on a valley dairy farm in the Cannonsville basin of the New York City (NYC) watershed. A total of 37 groundwater piezometers were installed to depths of 0.3 to 1.5 m. Water-table depth and concentrations of SRP, NO3--N, dissolved organic carbon (DOC), and dissolved oxygen were measured at regular intervals over a three-year period. A multivariate mixed model analysis of variance indicated that the SRP and NO3--N concentrations were controlled primarily by three classes of variables: environmental variables, including precipitation and water table depth; source variables, including manure applied and crop type; and chemical variables, including DOC and dissolved oxygen concentrations in groundwater. The highest groundwater concentrations of NO3--N and SRP were found at the shallowest water-table depths, which has implications for agricultural nutrient management in areas with shallow groundwater. [ABSTRACT FROM AUTHOR]