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Soil health and water quality improvement are major goals of sustainable agricultural management systems, yet the connections between soil health and water quality impacts remain unclear. In this study we conducted an initial exploratory assessment of the relationships between soil chemical, physical, and biological properties and edge-of-field water quality across a network of 40 fields in Ohio, USA. Discharge, dissolved reactive P (DRP), total P (TP), and nitrate (NO 3 ) losses associated with precipitation events via surface runoff and tile drainage were monitored. Agronomic soil tests and a suite of soil health indicators were measured, then predictive relationships between the field average soil properties and tile drainage and surface runoff discharge and DRP, TP, and nitrate loads were explored with random forest and multiple linear regression approaches. Among the soil health indicators, water extractable C and N were consistently found to be positively related to tile nitrate loads, but other soil health indicators had little or inconsistent importance for water quality impacts. Several other soil properties were important predictors, particularly soil P pools for surface and tile DRP and TP losses as well as Mehlich-3 (M3) extractable Fe and Al for surface and tile discharge. Thus, we did not observe strong evidence that soil health was associated with improved edge-of-field water quality across the edge-of-field monitoring network. However, additional studies are needed to definitively test the relationships between a broader array of soil health metrics and water quality outcomes., (© 2021 Los Angeles Regional Water Quality Control Board. Journal of Environmental Quality © 2021 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. This article has been contributed to by US Government employees and their work is in the public domain in the USA.)

Crayfishes (Decapoda) are common inhabitants of agricultural headwater streams in the Midwestern USA that have been impacted by physical habitat degradation and contamination by agricultural pollutants. The frequency and severity of injuries within crayfish communities are indicators of crayfish aggression, which is influenced by physical, chemical, and biotic factors. Previous studies have not evaluated the relationships of the frequency and severity of crayfish injuries with physical habitat quality, water quality, and biotic factors within agricultural headwater streams. Understanding these relationships will assist with determining if crayfish injury variables can serve as an indicator of physical habitat quality or water quality in these small degraded streams. We sampled crayfishes, documented the frequency and type of injuries, and measured instream habitat and water chemistry in 2014 and 2015 within 12 agricultural headwater streams in Indiana, Michigan, and Ohio. We documented five native crayfish species from 1641 adult captures. The most abundant species were Faxonius rusticus, Faxonius immunis, and Faxonius propinquus. Linear mixed effect model analyses indicated that four crayfish injury response variables were positively correlated (p < 0.05) with crayfish density, physical habitat quality, and water velocity diversity and that crayfish injury response variables were more strongly correlated with crayfish density than physical habitat quality or water quality. Our results indicate that response variables describing the severity and frequency of crayfish injuries can be effective indicators of physical habitat quality in agricultural headwater streams.

The Phosphorus Index (PI) has been the cornerstone for phosphorus (P)-based management and planning over the past twenty years, yet field-scale evaluation of many state PIs has been limited. In this study, P loads measured in surface runoff and tile discharge from 40 agricultural fields in Ohio with prevailing management practices were used to evaluate the Ohio PI. Annual P loads were highly variable among fields (dissolved reactive P: 0.03-4.51 kg ha, total P: 0.03-6.88 kg ha). Both measured annual dissolved reactive P ( = 0.36, < 0.001) and total P ( = 0.25, < 0.001) loads were significantly related to Ohio PI score. The relationship between measured load and PI score substantially improved when averaged annual field values were used (dissolved reactive P: = 0.71, total P: = 0.73), indicating that the Ohio PI should be utilized to evaluate average annual risk of P loss, rather than as an annual risk tool. Comparison between the Ohio PI and other established local and national metrics resulted in large differences in potential P management recommendations for the monitored fields. In the near term, revision of Ohio PI risk categories and management recommendations using local P loading thresholds is needed. To meet the minimum criteria for state PI tools, future research efforts should focus on using measured field data (i) to incorporate new input factors (i.e., P application timing and leaching potential) into the Ohio PI, and (ii) to calibrate and validate the Ohio PI to provide better P risk assessments and management recommendations., (Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.)

Macropores connecting surface soils to tile drains can alter water and nutrient transport through the subsurface. In this study, laboratory rainfall simulations with artificial macropores combined with edge‐of‐field monitoring were used to evaluate surface‐to‐tile drain connectivity and phosphorus (P) transport as a function of antecedent moisture conditions. Laboratory rainfall simulations using repacked soil boxes with different macropore layouts (i.e., no macropore, surface‐connected macropores, and disconnected macropores) were used to examine changes in water sources and flow pathways to tile drains with varying degrees of connectivity and antecedent wetness. Water, tracer, and P fluxes from a tile‐drained field were also monitored to quantify linkages among water flow pathways, antecedent wetness, and P delivery to tile drains. Both laboratory and field results showed that surface‐to‐tile drain connectivity was important for water transport through the subsurface under both dry and wet antecedent conditions. When soil conditions were dry, discharge was minimal and primarily comprised of event water that bypassed the soil matrix. Increasing wetness resulted in similar event water transport, but greater mobilization of stored pre‐event water and greater discharge; thus, the dominant source of tile water and the magnitude of tile discharge were substantially altered with changing antecedent moisture. Field data revealed that changes in drainage water source and discharge with increasing wetness impacted dissolved P transport. Dissolved P concentration decreased and loading increased with increasing wetness. Findings indicate that greater mobilization of pre‐event water under wet antecedent conditions acted as both a hydrologic and chemical buffer for subsurface dissolved P transport. Comparison of study results to water quality data from a larger edge‐of‐field network suggest that relationships between antecedent moisture conditions, water flow pathways, and P transport from the current study are broadly applicable across tile‐drained fields. Understanding processes controlling P delivery to tile drains has direct applicability for conservation practice implementation and improving process representation in models. [ABSTRACT FROM AUTHOR]

Abstract Harmful Algal Blooms (HABs), which were largely absent from Lake Erie from the 1980s until the mid-late 1990s, have been growing steadily worse in intensity. While much of the phosphorus loading into the lake prior to 1972 was caused by point-source pollution, approximately 88% to 93% of current loading comes from nonpoint sources, of which agriculture is the dominant land use. A reduction target of 860 metric tons, or 40% of the total phosphorus spring loading in 2008, has been set with the expectation that such a reduction could limit the size and associated impact of HABs in 9 out of every 10 years. We review the effectiveness of recommended practices aimed at reducing phosphorus loss in agriculture and pair this knowledge with behavioral data on likely adoption to identify how best to achieve the reduction target. The data suggests that the target is feasible as a majority of the farming population is willing to consider many of the recommended practices. However, increases in adoption over time have been minimal, and farmers will need better cost-benefit information, site-specific decision support tools, and technical assistance in order to more rapidly adopt and execute the placement of recommended practices. A combination of voluntary and mandatory approaches may be needed, but policies and programs promoting voluntary adoption should be designed to better target known barriers and maximize voluntary program effectiveness. [ABSTRACT FROM AUTHOR]

Abstract: In contrast to spatial inequality, there are currently no methods for leveraging information on temporal inequality to improve conservation efficacy. The objective of this study was to use Lorenz curves to quantify temporal inequality in surface runoff and tile drainage, identify controls on nutrient loading in these flowpaths, and develop design flows for structural conservation practices. Surface runoff (n = 94 site‐years) and tile drainage (n = 90 site‐years) were monitored on 40 fields in Ohio. Results showed, on average, 80% of nitrate‐nitrogen, soluble reactive phosphorus (P), and total P loads occurred between 7 and 12 days per year in surface runoff and between 32 and 58 days per year in tile drainage. Similar temporal inequality between discharge and load provided evidence that loading was transport‐limited and highlighted the critical role hydrologic connectivity plays in nutrient delivery from tile‐drained fields. Design flow criterion for sizing structural practices based on load reduction goals was developed by combining Lorenz curves and flow duration curves. Comparing temporal inequality between fields and the Maumee River, the largest tributary to the western Lake Erie Basin, revealed challenges associated with achieving watershed load reduction goals with field‐scale conservation. In‐field (i.e., improved nutrient and water management), edge‐of‐field (i.e., structural practices), and instream practices will all be required to meet nutrient reduction goals from tile‐drained watersheds. [ABSTRACT FROM AUTHOR]

Abstract Phosphorus (P) losses from agricultural soils are a growing economic and water-quality concern in the Lake Erie watershed. While recent studies have explored edge-of-field and watershed P losses related to land-use and agricultural management, the potential for soils developed from contrasting parent materials to retain or release P to runoff has not been examined. A field-based study comparing eight agricultural fields in contrasting glacial landscapes (hummocky coarse-textured till-plain, lacustrine and fine-textured till-plain) showed distinct physical and geochemical soil properties influencing inorganic P (P i) partitioning throughout the soil profile between the two regions. Fields located on the coarse-textured till-plain in mid-western Ontario, Canada had alkaline calcareous soils with the highest Total-P i concentrations and the majority of soil P i stored in an acid-soluble pool (up to 91%). In contrast, loosely to moderately soluble P i concentrations were higher in soils of the lacustrine and fine-textured till-plain in southwestern Ontario, northeast Indiana and northwestern Ohio, US. Overall, soils on the lacustrine and fine-textured till-plain had a greater shrink swell-capacity, likely creating preferential flow to minimize P i interaction with the more acidic, lower carbonate and lower sorption capacity soils. These differences in soil P i retention and transport pathways demonstrate that in addition to management, the natural landscape may exert a significant control on how P i is mobilized throughout the Lake Erie watershed. Further, results indicate that careful consideration of region-specific hydrology and soil biogeochemistry may be required when designing appropriate management strategies to minimize P i losses across the lower Great Lakes region. [ABSTRACT FROM AUTHOR]

Field observations that quantify agricultural phosphorus (P) losses are critical for the development of P reduction strategies across the Eastern Corn Belt region of North America. Within this region, surface water bodies including Lake Erie are sensitive to non-point P loadings. It is therefore imperative to quantify the impact of agricultural crop production on surface and subsurface water quality. This study characterized discharge, P concentrations, and P loads in surface runoff and subsurface drainage from 38 edge-of-field research sites in Ohio. Over the four-year study period, 31 ± 16% (mean ± one standard deviation) of annual precipitation became subsurface discharge while 7 ± 8% became surface discharge. Subsurface discharge accounted for 81 ± 23% of annual discharge, 71 ± 26% of annual dissolved reactive phosphorus (DRP) load, and 69 ± 27% of annual total phosphorus (TP) load. A P balance was also developed using management and loading data from the study sites. Under prevailing management practices, P removal (i.e., surface losses, subsurface losses, crop uptake) was greater than P input (i.e., atmospheric deposition, fertilizer application) on 60% of fields. Even so, further reduction of edge-of-field P losses will likely be necessary to meet watershed-scale P load recommendations. Findings suggest that balancing P inputs with crop uptake may not be sufficient to reduce edge-of-field losses due to a combination of legacy P and high-intensity rainfall events. Implementation of management practices targeting P-source will be needed in conjunction with practices at the edge-of-field targeting P-transport in order to meet recommended P loading targets in the Eastern Corn Belt region. [ABSTRACT FROM AUTHOR]

Subsurface tile drains influence watershed fluxes of nitrogen, phosphorus, and pesticides, but few studies have examined the role of subsurface tile drains and drainage water management practices on watershed dissolved organic carbon (DOC) export. The objective of this study was therefore to quantify the contribution of subsurface tile drains to watershed DOC export and to evaluate the effect of drainage water management of DOC concentrations and loads in tile-drained fields. Discharge and DOC concentration were measured at the outlet of an agricultural headwater watershed (3.9 km 2 ) in Ohio, USA and all of the subsurface tile drains (6 total) within the watershed over an 8-year period. Results showed that DOC concentration in both subsurface tile drains and stream water were highly variable (0.1–44.4 mg L −1 ), with mean DOC concentrations ranging from 5.7 to 8.2 mg L −1 . Intra-annual variability in subsurface tile drain and watershed hydrology yielded seasonal differences in DOC loading. Over the study period, 81.7% and 92.4% of watershed and subsurface tile drain DOC loading, respectively, occurred during 20% of the time, typically during winter and spring high flow events. Mean annual DOC loading from the drainage network was 19.6 kg ha −1 , while mean annual DOC loading at the watershed outlet was 43.9 kg ha −1 . On average, subsurface tile drainage comprised 33% of monthly watershed DOC export (<1–82%). Implementing drainage water management at one of the subsurface tile drains decreased discharge (179 mm; 22%) and DOC loading (6.8 kg ha −1 ; 26%) compared to an adjacent free draining subsurface tile drain. Findings from this study demonstrate the utility of simultaneously monitoring solute fluxes from both field and watershed scales, and indicate that subsurface tile drains are a significant source of DOC to headwater agricultural streams. Further, results suggest that drainage water management can significantly decrease DOC losses from tile-drained fields. [ABSTRACT FROM AUTHOR]

Understanding the processes controlling phosphorus (P) export from agricultural watersheds is essential for predicting and mitigating adverse environmental impacts. In this study, discharge, dissolved reactive P load, total P load, and suspended sediment time-series data (1975–2014) from two Lake Erie tributaries, the Maumee and Sandusky rivers, were evaluated to determine whether hydrologic or biogeochemical processes were responsible for observed patterns in P export. Findings indicate that hydrologic processes in these watersheds controlled P loading patterns, as P export was transport-limited (i.e., P loading was strongly correlated to watershed discharge) and P concentrations exhibited effective chemostatic behavior (i.e., low variability in concentration relative to discharge). The nature and behavior of observed P transport likely stems from a large, ubiquitous source of P present within each watershed as results were similar to those found for geogenic constituents (i.e., silica). Results suggest that changes in both precipitation patterns (e.g., precipitation variability) and watershed hydrologic response (e.g., water residence time) are likely explanations for observed increases in water and P loading in the Maumee and Sandusky watersheds. Future P loading in these watersheds should be expected to continue to be proportional to water flux as long as the magnitude and availability of the P source remains at its current level. Current P management strategies may therefore need to be reevaluated to better balance agricultural P requirements and watershed P loadings. [ABSTRACT FROM AUTHOR]

The Agricultural Policy Environmental eXtender (APEX) model is the scientific basis for the Nutrient Tracking Tool (NTT). NTT is an enhanced version of the Nitrogen Trading Tool, a user-friendly web-based computer program originally developed by the USDA. NTT was developed to estimate reductions in nutrient losses to the environment associated with alternative practices. The relatively easy access and ease with which the interface can be used has provided opportunities to demonstrate NTT in locations throughout the country; however, the absence of a clearly defined, consistent approach to parameterization and validation has raised questions over the reliability and consistency of simulated results. In this study: guidelines for parameterization and validation of APEX were developed based on literature review findings and the authors’ experience; and a case study was provided to illustrate how the developed guidelines are applied. The developed guidelines are in the form of recommendations covering essential phases of model simulation studies as well as a clear interpretation of model performance evaluation criteria thresholds and model simulation performance results. These guidelines were successfully applied in the central Ohio case study. The most sensitive water yield parameters and their respective reasonable range of values were determined. Simulated monthly and annual water yield values were within 5% and 15% of observed values during the calibration and validation periods, respectively. Overall, the developed guidelines together with the illustrative case study example are intended to serve as the framework to parameterize and validate APEX to support nation-wide deployment of NTT. This framework can be easily modified and used in additional APEX and other modeling studies. [ABSTRACT FROM AUTHOR]

Elevated phosphorus (P) concentrations in subsurface drainage water are thought to be the result of P bypassing the soil matrix via macropore flow. The objectives of this study were to quantify event water delivery to tile drains via macropore flow paths during storm events and to determine the effect of tillage practices on event water and P delivery to tiles. Tile discharge, total dissolved P (DP) and total P (TP) concentrations, and stable oxygen and deuterium isotopic signatures were measured from two adjacent tile-drained fields in Ohio, USA during seven spring storms. Fertilizer was surface-applied to both fields and disk tillage was used to incorporate the fertilizer on one field while the other remained in no-till. Median DP concentration in tile discharge prior to fertilizer application was 0.08 mg L−1 in both fields. Following fertilizer application, median DP concentration was significantly greater in the no-tilled field (1.19 mg L−1) compared to the tilled field (0.66 mg L−1), with concentrations remaining significantly greater in the no-till field for the remainder of the monitored storms. Both DP and TP concentrations in the no-till field were significantly related to event water contributions to tile discharge, while only TP concentration was significantly related to event water in the tilled field. Event water accounted for between 26 and 69% of total tile discharge from both fields, but tillage substantially reduced maximum contributions of event water. Collectively, these results suggest that incorporating surface-applied fertilizers has the potential to substantially reduce the risk of P transport from tile-drained fields. [ABSTRACT FROM AUTHOR]

The article discusses the challenge faced by the state of Ohio of maintaining agricultural production while protecting the environment and critical ecosystem services and cites the need to understand better the effect of agricultural practices on water quality in artificially drained landscapes. Topics discussed include the establishment of a monitoring network dedicated to quantifying the impacts of agricultural practices on edge-of-field water quality.

Summary Accurate estimates of annual nutrient loads are required to evaluate trends in water quality following changes in land use or management and to calibrate and validate water quality models. While much emphasis has been placed on understanding the uncertainty of nutrient load estimates in large, naturally drained watersheds, few studies have focused on tile-drained fields and small tile-drained headwater watersheds. The objective of this study was to quantify uncertainty in annual dissolved reactive phosphorus (DRP) and nitrate-nitrogen (NO 3 -N) load estimates from four tile-drained fields and two small tile-drained headwater watersheds in Ohio, USA and Ontario, Canada. High temporal resolution datasets of discharge (10–30 min) and nutrient concentration (2 h to 1 d) were collected over a 1–2 year period at each site and used to calculate a reference nutrient load. Monte Carlo simulations were used to subsample the measured data to assess the effects of sample frequency, calculation algorithm, and compositing strategy on the uncertainty of load estimates. Results showed that uncertainty in annual DRP and NO 3 -N load estimates was influenced by both the sampling interval and the load estimation algorithm. Uncertainty in annual nutrient load estimates increased with increasing sampling interval for all of the load estimation algorithms tested. Continuous discharge measurements and linear interpolation of nutrient concentrations yielded the least amount of uncertainty, but still tended to underestimate the reference load. Compositing strategies generally improved the precision of load estimates compared to discrete grab samples; however, they often reduced the accuracy. Based on the results of this study, we recommended that nutrient concentration be measured every 13–26 h for DRP and every 2.7–17.5 d for NO 3 -N in tile-drained fields and small tile-drained headwater watersheds to accurately (±10%) estimate annual loads. [ABSTRACT FROM AUTHOR]

Phosphorus (P) loss from agricultural fields and watersheds has been an important water quality issue for decades because of the critical role P plays in eutrophication. Historically, most research has focused on P losses by surface runoff and erosion because subsurface P losses were often deemed to be negligible. Perceptions of subsurface P transport, however, have evolved, and considerable work has been conducted to better understand the magnitude and importance of subsurface P transport and to identify practices and treatments that decrease subsurface P loads to surface waters. The objectives of this paper were (i) to critically review research on P transport in subsurface drainage, (ii) to determine factors that control P losses, and (iii) to identify gaps in the current scientific understanding of the role of subsurface drainage in P transport. Factors that affect subsurface P transport are discussed within the framework of intensively drained agricultural settings. These factors include soil characteristics (e.g., preferential flow, P sorption capacity, and redox conditions), drainage design (e.g., tile spacing, tile depth, and the installation of surface inlets), prevailing conditions and management (e.g., soil-test P levels, tillage, cropping system, and the source, rate, placement, and timing of P application), and hydrologic and climatic variables (e.g., baseflow, event flow, and seasonal differences). Structural, treatment, and management approaches to mitigate subsurface P transport--such as practices that disconnect flow pathways between surface soils and tile drains, drainage water management, in-stream or end-of-tile treatments, and ditch design and management--are also discussed. The review concludes by identifying gaps in the current understanding of P transport in subsurface drains and suggesting areas where future research is needed. [ABSTRACT FROM AUTHOR]

The 75 year legacy database including discharge, sediment loss, land management, and meteorological data for the USDA-ARS Riesel Watersheds, Riesel, TX, USA has been available on the web for more than a decade () and used in numerous studies and publications; however, only recently have these data been added to the Sustaining the Earth's Watersheds, Agricultural Research Data System (STEWARDS) database (). In addition, water quality data including dissolved inorganic N and P compounds measured from more than 1000 storm runoff events, 1300 base flow sampling events (lateral subsurface return flow or seepage flow), and 157 precipitation events through 2012 were added. The objectives of this manuscript are to present relevant background information on these data, summarize the data collection and analysis methodology, present the measured data along with cursory analyses, and convey the commitment of the USDA-ARS Riesel Watersheds to long-term data accessibility and database enhancement for water quality data and research. [ABSTRACT FROM AUTHOR]

Highlights: [•] Information on pesticide mixtures within agricultural headwater streams is limited. [•] Pesticide mixtures were documented in channelized agricultural headwater streams in Ohio for 5 years. [•] Pesticide mixtures consisted mostly of herbicide or herbicide–fungicide mixtures. [•] Seasonal trends in pesticide mixtures differed annually. [•] Pesticide mixtures did not differ among watershed sizes ranging from 0.7 to 4.5km2. [Copyright &y& Elsevier]

Chlorothalonil concentrations exceeding acute toxicity levels for certain organisms have been measured in surface water discharge events from managed turf watersheds. The duration of exceedence and the timing of these events related to precipitation/runoff and time since application, however, have not been explored. Chlorothalonil concentrations were measured from discharge waters draining a managed turf watershed in Duluth, Minnesota, USA, between 2003 and 2009. The median chlorothalonil concentration was 0.58 µg/L. Approximately 2% of all measured concentrations exceeded the 7.6 µg/L median lethal concentration (LC50) acute toxicity level for rainbow trout. One-twentieth the LC50 concentration, equivalent to the level of concern (0.38 µg/L) for endangered species, was exceeded 31% of the time during the present study. The concentrations that exceeded the LC50 threshold were associated with eight rainfall/runoff events. Low dose exposures are a more important biological concern than acute occurrences. Exceedence concentrations associated with acute effects were significantly ( p < 0.05) correlated to time since application and were measured only in the fall following extensive application. A conflict exists between the transportability of chlorothalonil as suggested by its chemical properties and the data collected in the present study. With respect to course-wide golf course application, avoiding application until after the major autumn rainfall period but before the first snow coverage is recommended to reduce occurrence of chlorothalonil concentrations that exceed toxic levels associated with acute and chronic levels of concern. Environ. Toxicol. Chem. 2013;32:684-691. © 2012 SETAC [ABSTRACT FROM AUTHOR]

Headwater streams constitute the majority of watersheds in the United States and many in the midwest have been channelized for agricultural drainage. Public health implications of water chemistry and aquatic insects within channelized and unchannelized headwater streams have not been explored. We sampled water chemistry and aquatic insects in two channelized and two unchannelized headwater streams in central Ohio from December 2005 until November 2008. Maximum concentrations of ammonium, nitrate plus nitrite, and chlorothalonil were greater in channelized streams. Nitrate plus nitrite and atrazine also exceeded drinking water standards more often in channelized streams. Maximum concentrations of simazine and the percentage of times it exceeded the drinking water standards were greater in unchannelized streams. The predicted hazard potential of nutrient and pesticide mixtures was greater in channelized streams. Mosquito abundance did not differ between stream types. Chironomid abundance was greater in channelized streams. Biting dipterans did not exhibit consistent abundance trends and only differed between stream types in the summer and fall. Our results suggest that if whole stream uptake of nutrients and pesticides is minimal in channelized headwater streams then nutrient and pesticide inputs from these streams may impact downstream drinking water sources. Our results also suggest channelized and unchannelized headwater streams are not serving as a significant source of mosquitoes. [ABSTRACT FROM AUTHOR]

• DWM reduced drainage outflow and total water loss. • DWM reduced seasonal nitrate concentrations and annual nitrate loads. • The magnitude of DWM effectiveness remains uncertain, especially in fields prone to seepage and runoff losses. • Combining measured and modeled data allowed robust analysis of DWM effectiveness. Subsurface (tile) drainage is a necessary practice for economic crop production in humid, poorly drained regions of the world. Drainage water management (DWM), also known as controlled drainage, is among the suite of practices designed to mitigate water quality issues associated with subsurface drainage. Studies evaluating DWM generally include field experiments or simulation models to estimate water quality impacts. Combining field studies with model simulations can provide a more comprehensive assessment. Furthermore, using multiple approaches can provide a range of effectiveness rather than a single estimate, which can help define the uncertainty associated with DWM effectiveness. The goal of this study was to demonstrate the variability in estimated DWM effectiveness using 10 years of measured data and a calibrated hydrologic model. The study field, located in central Ohio, was under a free drainage (FD) mode from 2005 through 2008, and under DWM from 2009 through 2014. We used three approaches to compare discharge and nitrate concentrations and loads: before-and-after, paired-field, and DRAINMOD-NII simulated scenarios. Based on the three evaluation approaches, DWM increased surface runoff by 50% (∼13 mm), reduced annual drainage discharge between 8 and 23% (∼19 to 69 mm), annual mean NO 3 -N concentrations between −1 and 2.5%, and NO 3 -N loads between 9 and 25% (∼2.8 to 10.3 kg ha−1 yr−1). DWM also reduced the frequency of drainage discharge, and increased magnitudes of surface runoff, evapotranspiration, and seepage losses. The true magnitude of DWM effectiveness remains somewhat uncertain, especially in fields prone to seepage and runoff losses. However, using a combined assessment approach can help address the uncertainty associated with estimated DWM effectiveness at watershed and regional scales. [ABSTRACT FROM AUTHOR]

Several structural, treatment, and management approaches exist to minimize phosphorus (P) transport from agricultural landscapes (e.g., cover cropping and conservation tillage). However, many of these practices are designed to minimize particulate P transport and are not as effective in controlling dissolved P (DP) losses. Phosphorus removal structures employ a P sorption material (PSM) to trap DP from flowing water. These structures have been successful in treating surface runoff by utilizing aluminum (Al)-treated steel slag, but subsurface tile drainage has never been tested with this material. The goal of this study was to evaluate the performance and economics of a ditch-style P removal structure using Al-treated steel slag for treating agricultural subsurface drainage discharge. The structure treated subsurface drainage water from a 4.5 ha agricultural field with elevated soil test P levels. Overall, the structure removed approximately 27% and 50% of all DP and total P (TP) entering the structure, respectively (i.e., 2.4 and 9.4 kg DP and TP removal). After an initial period of strong DP removal, the discrete DP removal became highly variable. Flow-through analysis of slag samples showed that the slag used to construct the structure was coarser and less sorptive compared to the slag samples collected prior to construction that were used to design and size the structure. Results of this study highlight the importance of correctly designing the P removal structures using representative PSMs. [ABSTRACT FROM AUTHOR]

Eutrophication due to elevated nitrogen (N) and phosphorus (P) loss from croplands remains one of the most pressing water quality issues throughout the world. Understanding the effect of implementing conservation management practices is critical for meeting nutrient reduction goals as well as informing conservation programs and policies. A before-after-control-impact (BACI) analysis was used to evaluate the individual and combined effect of cover crops and manure application rate on discharge and nutrient loss using six water years (WY2014-WY2019) of measured data across four distinct drainage zones (1X–NCC; 1X–CC; 2X–NCC; 2X–CC) within an Ohio, USA, crop production field. White mustard significantly reduced mean monthly nitrate (NO 3 −-N) concentration regardless of manure application rate (i.e., 65 m3 ha−1 and 130 m3 ha−1). However, neither the use of white mustard, doubling manure rate, or the combination of the two had a significant impact on mean monthly drainage discharge, dissolved-reactive P (DRP), or total P (TP) loss. Seasonal analysis confirmed that NO 3 −-N concentration in the cover crop zones was signficantly less in fall, winter, and spring. However, significant increases in spring discharge, NO 3 −-N, DRP, and TP loads as well as TP concentration were noted with cover crop and greater manure rate treatments. These findings confirm that cover crops have a reducing effect on NO 3 −-N concentration but may not have any effect on addressing P concerns. Further research is warranted; however, this study highlights that the resource concern (e.g., N or P) should be considered prior to implementing cover crops as a conservation management practice. • Individual and combined effects of cover crop and manure rate on tile nutrient loss were assessed. • Cover crop (i.e., white mustard) reduced nitrate concentration in tiles under two manure rates. • The impact of white mustard on phosphorus loss was variable across seasons. • Trade-offs between nitrogen and phosphorus loss should be examined before planting cover crops. [ABSTRACT FROM AUTHOR]

Subsurface tile drainage is recognized as a significant source of sediment and particulate phosphorus (PP) in the midwestern U.S. However, the role of subsurface flow pathway and source water connectivity dynamics on sediment transport is poorly understood. The overarching objective of this study was to investigate sediment and PP loading dynamics for a midwestern subsurface tile drained agroecosystem and assess the governing flow pathway and water sources impacting subsurface sediment loads. In this study, we used a recently-developed framework that couples event-based hydrograph recession and specific conductance-end-member mixing analysis (SC-EMMA) to assess governing drivers of sediment transport through tile. We collected high-frequency specific conductance, turbidity, and subsurface discharge data from an edge-of-field (EOF) tile main located in northwestern Ohio for 15 months. Multiple linear regression (MLR) analysis and hysteresis analysis were employed to evaluate the impact of pathway-connectivity dynamics on flow-weighted mean Total Suspended Solids (TSS) concentrations. The MLR analysis showed that quickflow of new water (Q quick-new) had the highest flow-weighted mean sediment concentrations, and that concentrations associated with quickflow of old water (i.e., matrix-macropore exchange) were variable. Analysis using the hysteresis index (HI) showed that hysteresis characteristics (magnitude and direction) for separated hydrographs using the pathway-connectivity framework deviated from HI values of subsurface discharge (Q tile) and highlighted the importance of Q quick-new through much of the monitoring period. For events immediately following tillage and cover crop application in Fall 2019, we found Q quick-old was the primary form of preferential flow, peak sediment concentrations coincided with Q quick-old , and event sediment loadings during these events decreased relative to the previous fall. The findings suggest that reducing preferential transport of new water may be an effective strategy for reducing sediment and particulate P loadings at the edge-of-field. • Particulate P loadings in tile drainage are governed by sediment transport dynamics. • Hydrograph separation improves prediction of sediment concentration. • Quickflow of new water was the primary driver of sediment and PP delivery to tile. • Cover crops and tillage alter tile sediment hysteresis patterns and loadings. [ABSTRACT FROM AUTHOR]

Viable large-scale crop production in the United States requires artificial drainage in humid and poorly drained agricultural regions. Excess water removal is generally achieved by installing tile drains that export water to open ditches that eventually flow into streams. Drainage water management (DWM) is a conservation practice that allows farmers to artificially raise the outlet elevation of a field’s drain tile and can reduce nutrient loss during wet periods by storing more water in the field. We intended to assess the effectiveness of DWM to reduce drainage discharge and nutrient loads and additionally identify predictor variables that influence DWM effectiveness. We compared managed (i.e., DWM) and free draining records using paired t -tests, and identified factors associated with DWM effectiveness using a multiple linear regression approach. T-test results indicated that DWM was highly effective in reducing drainage water discharge and nutrient losses via drain tiles as tile discharge volumes were reduced on average 46%, while tile nitrate loads were reduced by 48%. In addition, total phosphorus and dissolved reactive phosphorus loads were reduced by 55% and 57%, respectively. Based on regression results, we found that several aspects of farm and tile drain management were associated with DWM effectiveness, while site specific landscape characteristics were less likely to predict effectiveness. While DWM is effective as a conservation practice to reduce discharges of water and nutrients from drain tiles, we also identified several knowledge gaps. Future research should investigate effects of DWM on water and nutrients lost in other pathways such as surface runoff, preferential flow, groundwater recharge and biological uptake, and also focus more attention on phosphorus as there is a paucity of research on this topic. [ABSTRACT FROM AUTHOR]