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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]

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]

Silage bunker runoff can be a very polluting substance and is increasingly being treated by vegetative treatment areas (VTAs), but little information exists regarding nutrient removal performance of systems receiving this wastewater. Nutrient transport through the shallow subsurface of three VTAs (i.e. one VTA at Farm WNY and two VTAs at Farm CNY) in glaciated soils containing a restrictive layer (i.e., fragipan) was assessed using a mass balance approach. At Farm WNY, the mass removal of ammonium was 63%, nitrate was 0%, and soluble reactive phosphorus (SRP) was 39%. At Farm CNY, the mass removal of ammonium was 79% in the West VTA, but nitrate and SRP increased by 200% and 533%, respectively. Mass removal of ammonium was 67% in the East VTA at Farm CNY; nitrate removal was 86% and SRP removal was 88%. The East VTA received a much higher nutrient loading, which was attributed to a malfunctioning low-flow collection apparatus within the settling basin. Results demonstrate that nutrient reduction mechanisms other than vegetative uptake can be significant within VTAs. Even though increases in nitrate mass were observed, concentrations in 1.65m deep wells indicated that groundwater impairment from leaching of nitrate was not likely. These results offer one of the first evaluations of VTAs treating silage bunker runoff, and highlight the importance of capturing concentrated low flows in VTA systems. [Copyright &y& Elsevier]

Vegetative treatment areas (VTAs) are commonly being used as an alternative method of agricultural process wastewater treatment. However, it is also apparent that to completely prevent discharge of pollutants to the surrounding environment, settling of particulates and bound constituents from overland flow through VTAs is not sufficient. For effective remediation of dissolved agricultural pollutants, VTAs must infiltrate incoming wastewater. A simple water balance model for predicting VTA soil saturation and surface discharge in landscapes characterized by sloping terrain and a shallow restrictive layer is presented and discussed. The model accounts for the cumulative effect of successive rainfall events and wastewater input on soil moisture status and depth to water table. Nash–Sutcliffe efficiencies ranged from 0.65 to 0.81 for modeled and observed water table elevations after calibration of saturated hydraulic conductivity. Precipitation data from relatively low, average, and high annual rainfall years were used with soil, site, and contributing area data from an example VTA for simulations and comparisons. Model sensitivity to VTA width and contributing area (i.e. barnyard, feedlot, silage bunker, etc.) curve number was also investigated. Results of this analysis indicate that VTAs should be located on steeper slopes with deeper, more-permeable soils, which effectively lowers the shallow water table. In sloping landscapes (>2%), this model provides practitioners an easy-to-use VTA design and/or risk assessment tool that is more hydrological process-based than current methods. [Copyright &y& Elsevier]

Planners advocate best management practices (BMPs) to reduce loss of sediment and nutrients in agricultural areas. However, the scientific community lacks tools that use readily available data to investigate the relationships between BMPs and their spatial locations and water quality. In rural, humid regions where runoff is associated with saturation-excess processes from variable source areas (VSAs), BMPs are potentially most effective when they are located in areas that produce the majority of the runoff. Thus, two critical elements necessary to predict the water quality impact of BMPs include correct identification of VSAs and accurate predictions of nutrient reduction due to particular BMPs. The objective of this research was to determine the effectiveness of BMPs using the Variable Source Loading Function (VSLF) model, which captures the spatial and temporal evolutions of VSAs in the landscape. Data from a long-term monitoring campaign on a 164-ha farm in the New York City source watersheds in the Catskills Mountains of New York state were used to evaluate the effectiveness of a range of BMPs. The data spanned an 11-year period over which a suite of BMPs, including a nutrient management plan, riparian buffers, filter strips and fencing, was installed to reduce phosphorus (P) loading. Despite its simplicity, VSLF predicted the spatial distribution of runoff producing areas well. Dissolved P reductions were simulated well by using calibrated reduction factors for various BMPs in the VSLF model. Total P losses decreased only after cattle crossings were installed in the creek. The results demonstrated that BMPs, when sited with respect to VSAs, reduce P loss from agricultural watersheds, providing useful information for targeted water quality management. [Copyright &y& Elsevier]

Abstract: Researchers have noted that current water quality protection strategies, like nutrient management plans, lack a sound hydrological underpinning for pollutant transport processes. This is especially true for areas like the northeastern U.S. where copious research has shown that variable source area hydrology largely governs runoff generation. The goal of this study was to develop a scientifically justified method to identify the locations that generate overland flow. Furthermore, this methodology must be computationally simple enough that it can be utilized or incorporated into nutrient management plans and other established water quality tools. We specifically tested the reliability of the ‘distance from a stream,’D s, and the ‘topographic index,’λ, to predict areas with a high propensity for generating overland flow, i.e. hydrologically sensitive areas (HSA). HSAs were defined by their probability of generating runoff, P sat, based on 30 year simulations using a physically based hydrological model. Using GIS, each location''s P sat was correlated with D s and λ. We used three Delaware Co., NY watersheds in the New York City watershed system with areas varying in size from 1.6 to 37km2 and with forested and agricultural land uses. The topographic index gave stronger, more regionally consistent correlations with P sat than did D s. Equations correlating λ and P sat for each month are presented and can be used to estimate hydrological sensitivity in the region surrounding our study watersheds, i.e. in Delaware Co. This work is currently being incorporated into an Internet Mapping System to facilitate user-friendly, on-line identification of HSAs. [Copyright &y& Elsevier]

A nine-year (2010–2018) field study in the Debre Mawi watershed was conducted to understand the effect of governmentally-imposed and farmer-initiated conservation practices. The watershed is in the sub-humid Ethiopian Highlands which experience high and increasing erosion rates despite years of conservation efforts. Consequently, reservoirs are filling up with sediment and soil degradation is enhanced, calling for the evaluation of conservation practices currently in use. The few past long-term experimental studies on structural practices are inconclusive. In addition, only anecdotal information is available for streamflow and sediment loss. Precipitation, stream discharge, and suspended sediment concentrations were recorded manually in the Debre Mawi watershed during the nine-year period. Groundwater depth and total saturated area measurements were taken for selected periods. From 2012 to 2014, government-mandated conservation practices were constructed, which consisted of 50-cm-deep infiltration furrows with bunds downslope. These furrows were filled in with sediment by 2018. At the same time, the acreage of eucalyptus trees planted by farmers on the most vulnerable lands tripled to 5% of the total area with most trees fully grown in 2018. Runoff coefficients and sediment concentrations decreased steadily throughout the nine years. In the saturated bottomlands, the observations suggested that government-sponsored infiltration furrows in the saturated bottomlands were ineffective and may concentrate flows and enhance gully erosion, while eucalyptus trees appear effective. The results of this observational study point to both the potential benefits of conservation practices in this sub-humid tropical highland region and to emerging long-term risks. If structural conservation is to be pursued in watersheds like Debre Mawi, due attention must be given to the safe removal of excess water from the valley bottoms. The vegetative farmer-initiated practice of planting eucalyptus trees effectively reduced streamflow and erosion, but at the same time, might dry up wells during the dry monsoon phase which should be investigated further. Image 1 • Acreage of eucalyptus planted by farmers increased three-fold in nine years. • Observed runoff and sediment yield declined with increased acreage of eucalytus. • Dry phase eucalyptus evaporation delayed saturation excess runoff in rain phase. • Infiltration furrows were not maintained, filled up, and appeared ineffective. • Groundwater irrigation is feasible when lava dikes block subsurface downhill flow. [ABSTRACT FROM AUTHOR]

Land resources in developing countries are facing intense degradation due to deforestation and subsequent loss of organic matter from continuous tillage that causes soil erosion and gulley formation. The Ethiopian highlands are especially and severely affected. One of the land and water management practices to counteract this problem, fenced areas to prevent livestock access (called exclosures), has been in practice for the last few decades in the semi-arid highlands of Ethiopia but its effect on degraded landscapes has not been well researched -- especially in the sub-humid and humid highlands. The aim of this study is to evaluate the effects of exclosures on improving degraded landscapes in the sub-humid highlands. The research was carried out in the Ferenj Wuha watershed, in the northwestern sub-humid Ethiopian highlands, where land and water management practices were implemented starting in 2011. Vegetation was inventoried and aboveground biomass, carbon and nutrient stock determined for communal grazing land, exclosures and for other uses. In addition, soil samples were collected for nutrient analysis. Our results show that exclosures have a richer and more diverse set of plant species compared to communal grazing land. Establishment of an exclosure also enhanced organic carbon, total nitrogen and available phosphorus. Over a six-year period, aboveground biomass increased by 54 Mg ha−1 (or 81%) at the watershed scale because of the conversion of communal grazing land to exclosures. The improvement in soil nutrients due to exclosures, in turn, increased carbon and nutrient stock. The results support regeneration of degraded landscapes by restoring vegetation, soil fertility, carbon and nutrient stocks in the Northwestern highlands of Ethiopia. However, additional research is required to more accurately quantify these improvements because current research efforts that sample only the surface soils seem to indicate that the capacity of exclosures to increase soil carbon storage is decreasing when annual rainfall is increasing. Image 1 • Ethiopian Highlands are degraded due to continuous cultivation after deforestation. • Exclosures that keep cattle out, improve degraded soils. • Exclosures increase soil organic carbon and nitrogen but not available phosphorus. • Increasing rainfall decreases effectiveness of soil carbon storage in surface 20 cm of soil. • Exclosures should be sampled over entire rooting depth for proper evaluation. [ABSTRACT FROM AUTHOR]