Excess phosphorus (P) from agriculture is a leading cause of harmful and nuisance algal blooms in many freshwater ecosystems. Throughout much of the midwestern United States, extensive networks of subsurface tile drains remove excess water from fields and allow for productive agriculture. This enhanced drainage also facilitates the transport of P, particularly soluble reactive phosphorus (SRP), to adjacent streams and ditches, with harmful consequences. Thus, reducing SRP loss from tile-drained cropland is a major focus of regional and national efforts to curb eutrophication and algal blooms. The planting of cover crops after crop harvest is a conservation practice that has the potential to increase retention of fertilizer nutrients in watersheds by extending the growing season and limiting bare ground in the fallow season; however, the effect of cover crops on SRP loss is inconsistent at the field-scale and unknown at the watershed-scale. In this study, we conducted a large-scale manipulation of land cover in a small, agricultural watershed by planting cover crops on >60% of croppable acres for six years and examining changes in SRP loss through tile drains and at the watershed outlet. We found reduced median SRP loss from tiles with cover crops compared to those without cover crops, particularly during periods of critical export from January to June. Variation in tile discharge influenced SRP loss, but relationships were generally weaker in tiles with cover crops (i.e., decoupled) compared to tiles without cover crops. At the watershed outlet, SRP yield was highly variable over all seasons and years, which complicated efforts to detect a significant effect of changing land cover on SRP export to downstream systems. Yet, watershed-scale planting of cover crops slowed cumulative SRP losses and reduced SRP export during extreme events. Overall, this study demonstrates the potential for cover crops to alter patterns of SRP loss at both the field- and watershed-scale.

Growing switchgrass (Panicum virgatum L.) as an intercrop in managed loblolly pine (Pinus taeda L.) plantations has emerged as a potential source of bioenergy feedstock. Utilizing land resources between pine trees to produce an energy crop can potentially reduce the demand for land resources used to produce food; however, converting conventionally managed forest land to this new intercropping system constitutes changes in land use and associated management practices, which may affect the environmental and economic sustainability of the land. The overall objective of this project is to evaluate the environmental effects of large-scale forest bioenergy crop production and utilize these results to optimize cropping systems in a manner that protects the important ecosystem services provided by forests while contributing to the development of a sustainable and economically-viable biomass industry in the southeastern United States.

Agricultural land use in the Midwestern U.S. is the major source of nitrogen (N) causing recurring hypoxia in the northern Gulf of Mexico. Despite efforts to reduce losses, N export from tile-drained, agricultural watersheds throughout the Corn Belt persists. The use of effective agricultural conservation practices can reduce N loss from fields, yet little is known about how field-scale implementation will translate into watershed-scale reductions in N export. In this study, we used a sampling approach with high spatial and temporal resolution to quantify changes in tile drain load and watershed export of nitrate (NO3--N) after planting cover crops on > 60% of croppable acres in a small, agricultural watershed. We found that median NO3--N losses from tiles draining fields with cover crops were 69-90% lower than tiles draining fields without cover crops during winter/spring. Measured instantaneous flow was the major driver of NO-3-N losses from tile drains, though results suggest that this relationship differed between tiles with and without cover crops in spring. The signature of cover crops at the field-scale was evident in watershed NO3--N export, particularly during times of elevated flows; median daily NO3--N exported in elevated flows was 18-22% lower during years with watershed-scale planting of cover crops compared to years without. Nevertheless, changes in watershed NO3--N export were smaller than the observed reductions in tile drain loads. Results indicate that tile drain reductions directly reflected the influence of cover crops at the field-scale while watershed export integrated both past and present management, ultimately complicating attempts to distinguish the effect of conservation efforts at larger spatial scales.

Western Lake Erie Basin (WLEB) is the most intensively farmed region of the Great Lakes. Because of the flat topography and poorly-drained soils many farmers rely on drainage management practices (e.g., subsurface tile drainage, ditch channelization) to maintain productive agriculture. However, these practices also facilitate the delivery of excess nutrients and sediments to Lake Erie, which have been linked to recurring harmful algal blooms (HABs) and associated environmental degradation. Implementation of inset floodplains in formerly channelized waterways via the two-stage ditch can improve water quality but the efficacy has been tested using only implementation in short reaches. Watershed models are critical tools for assessing watershed-scale implementation and as such can guide effective management. We evaluated the effectiveness of the two-stage ditch in improving water quality in the River Raisin Watershed (RRW), a major subbasin in the WLEB, combining empirical measurements for nutrient reductions from two-stage ditches across the Midwest with output from a Soil Water Assessment Tool (SWAT) model. We modeled two-stage implementation in 25, 50, and 100% of headwater reaches in the RRW, and found that the practice could reduce total annual NO3--N export by 2, 5 and 10%, respectively. The two-stage was even more effective at reducing total phosphorus (TP) export, which was reduced by 12, 20 and 31%, respectively. Compared to other conservation practices, nutrient reduction efficiency for the two-stage ditch was good, both in terms of percent load reduction and cost, but watershed-scale adoption will be required in order to achieve significant nutrient reductions as called for by policymakers. (C) 2017 Elsevier B.V. All rights reserved.

Subsurface tile drainage has been used around the globe to lower the water table and drain soils that are seasonally or perennially wet making them suitable for agriculture and/or increasing productivity. However, tile drainage systems have a negative impact on water quality of adjacent streams and ditches due to the transport of excess fertilizer nutrients like nitrogen (N) and phosphorus (P) from fields. To support nutrient management and conservation practices like drain water management (DWM), accurate delineation of the agricultural area drained by tiles is critical for quantifying nutrient yields (nutrient mass per area per time) to downstream water bodies. In this study, we tested Geographic Information System decision tree classification (GIS DTC) and satellite remote sensing based methods (i.e., image differencing) to determine tile drainage area in an agricultural watershed, Shatto Ditch Watershed (SDW) in Indiana, USA. Using these techniques, we estimated that 79% of the cultivated area of SDW is tile drained with 94% accuracy according to the image differencing approach whereas 55% is classified as tile drained with an accuracy of 75% based on estimates from the DTC approach with the most relaxed rule thresholds (where tiles exist on <= 4% slope with poorly and moderately well drained soils). Using satellite imagery to characterize tile drained area at a high resolution over large geographical extent shows promise and will be important for accurately quantifying nutrient yields from tiles which will inform management and conservation efforts to reduce excess nutrient export to downstream water bodies. (C) 2017 Elsevier B.V. All rights reserved.

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. (C) 2016 Elsevier B.V. All rights reserved.

In the Mississippi River Basin (MRB), practices that enhance drainage (e.g., channelization, tile drainage) are necessary management tools in order to maintain optimal agricultural production in modern farming systems. However, these practices facilitate, and may speed the delivery of excess nutrients and sediments to downstream water bodies via agricultural streams and ditches. These nonpoint sources contribute to elevated nutrient loading in the Gulf of Mexico, which has been linked to widespread hypoxia and associated ecological and economic problems. Research suggests agricultural drainage ditches are important links between farm fields and downstream ecosystems, and application of new management practices may play an important role in the mitigation of water quality impairments from agricultural watersheds. In this article, we describe how researchers and producers in the MRB are implementing and validating novel best management practices (BMPs) that if used in tandem could provide producers with continued cropping success combined with improved environmental protection. We discuss three BMPs low-grade weirs, slotted inlet pipes, and the two-stage ditch. While these new BMPs have improved the quality of water leaving agricultural landscapes, they have been validated solely in isolation, at opposite ends of the MRB. These BMPs have similar function and would greatly benefit from stacked incorporation across the MRB to the benefit of the basin as a whole.

Expansion of ethanol production has led to regional-scale cultivation of cellulosic biofuel crops, such as switchgrass (Panicum virgatum L.), on agriculturally marginal lands. A range of forest-based solutions are also being evaluated, especially in the southeastern U.S. However, there may be unanticipated environmental consequences, including changes in water export when managing forests to accommodate biofuel demands at a regional scale. We used the Soil Water Assessment Tool (SWAT) to simulate effects of regional-scale conversion of loblolly pine (Pinus taeda L.) plantations to switchgrass biofuel production on stream flow in the similar to 5 million ha Tombigbee River Watershed in the southeastern U.S. Greater than 50% of the Tombigbee Watershed is forested, with 20% of the watershed supporting primarily loblolly pine forests. We modified the SWAT model by adding five age classes of loblolly pine trees, to more accurately represent existing forested systems. We found that maximum conversion of loblolly pine to switchgrass, affecting 7% of the watershed, represented an extreme land-use change and resulted in a 4% increase in annual stream flow. The more operationally and economically feasible option of converting young (<= 4 yrs) and old (>= 16 yrs) loblolly pine stands to switchgrass on < 8% slope (2% of the watershed) resulted in a 2% increase in stream flow. Changes in annual stream flow were driven primarily by alterations in evapotranspiration (ET). Seasonal changes in stream flow were attributed to complex interactions among water-balance components of ET, surface flow, and groundwater flow. (C) 2015 Elsevier Ltd. All rights reserved.

Within the southeast Canada and northeast USA region, a peak in sulphate (SO4 2−) concentration has been reported for some streams following periods of substantial catchment drying during the summer months (ON, Canada; VT, NH and NY, USA). However, it is currently unclear if a SO4 2− response to seasonal drying is widespread across the broader region, or to what extent the level of response varies among catchments. In our study, SO4 2− response to seasonal drying was compared in 20 catchments from 11 locations across southeastern Canada (ON, QC and NS) and northeastern USA (NH, NY, VT, WV and ME). Using long-term monitoring data of stream discharge and chemistry, the number of days for each month of the dry season (# d) when discharge (Q) was below a threshold level (25th percentile; Q25) was calculated for each catchment to give a measure of ‘seasonal dryness’ (# d Q < Q25). A SO4 2− response score (rs) was then calculated for each catchment based on linear regression analysis of # d Q < Q25 versus either the annual SO4 2− concentration, or the residual of annual SO4 2− concentration as a function of time (year). The final rs values for each catchment provided an estimate of the proportion of variation in annual SO4 2− concentration which could be explained by seasonal drying (possible rs range = 0–1). Of the 20 catchments, 13 exhibited some level of a SO4 2− response to seasonal drying (rs = 0.04–0.72) with an additional two catchments exhibiting a SO4 2− response for one or more seasons. SO4 2− response scores were positively related to percent wetland area (w) (rs = 1.000 − 0.978e−0.054* w , r 2 = 0.44) and percent saturated area (sat) (rs = 0.481 − 0.488e−0.101* sat, r 2 = 0.54) indicating that wetlands/saturated areas were an important driver of regional variation in the SO4 2− response to seasonal drying. Our results suggest that any shift towards drier summers as a result of climate change could impact SO4 2− dynamics in a large number of catchments throughout the region.