A review of ecosystem services from edge-of-field practices in tile-drained agricultural systems in the United States Corn Belt Region.

Edge-of-field management practices that reduce nutrient pollution from tile drainage while contributing habitat and other ecosystem services are needed to enhance agricultural systems in the US Corn Belt Region. In this review, we identified edge-of-field and catchment scale agricultural conservation practices for intercepting and treating tile drainage. The reviewed conservation practices were (1) controlled drainage, also known as drainage water management (USDA-NRCS Code 554); (2) drainage water recycling (USDA-NRCS Code 447); (3) denitrifying bioreactors (USDA-NRCS Code 605); (4) saturated buffers (USDA-NRCS Code 604); and (5) constructed or restored wetlands designed for water quality improvement (USDA-NRCS Code 656) herein referred to as water quality wetlands. We examined 119 studies that had information on one or more of the following ecosystem services: water retention, water quality improvement (e.g., nitrate, phosphate, sediment, or pesticide retention), wetland habitat (for birds, aquatic organisms, and pollinators), crop yield improvement, and other benefits (e.g., recreation, education, aesthetic appreciation, greenhouse gas retention). We found the five edge-of-field practices were all effective at removing nitrate with varying degrees of other potential benefits and disservices (e.g., greenhouse gas production). Drainage water recycling and water quality wetlands have the potential to provide the most co-benefits as they provide surface water systems for capturing surface flows in addition to tile drainage while also potentially providing habitat and recreation opportunities. However, the following research needs are identified: 1) the disservices and benefits associated with drainage water recycling have not been adequately evaluated; 2) surface flow dynamics are understudied across all reviewed management practices; 3) a complete accounting of phosphorus species and flow pathways for all management practices is needed; 4) field evaluations of the habitat benefit of all management practices are needed; and 5) greenhouse gas dynamics are understudied across all management practices. While all management practices are expected to reduce nitrate loads, addressing these knowledge gaps will help inform holistic management decisions for diverse stakeholders across the US Corn Belt.

Integrating ACPF and SWAT to Assess Potential Phosphorus Loading Reductions to Lake Erie: A Case Study.

Lake Erie is threatened by eutrophication and harmful algal blooms due to excess nutrient loading from agricultural sources. To reduce nutrient loading to Lake Erie, widespread adoption of agricultural conservation practices (ACPs) has been proposed. However, identifying appropriate and effective locations for ACP placement has been challenging. Another challenge is understanding how effective the ACPs are in reducing nutrient loading and achieving water quality goals. Therefore, identifying the most effective ACPs, as well as spatially optimal placement of ACPs to achieve the maximum environmental benefit, is of paramount importance. The main objective of this study was to integrate the Agricultural Conservation Planning Framework (ACPF) with the Soil and Water Assessment Tool (SWAT) to assess the potential effectiveness of ACPs developed by ACPF in reducing phosphorous losses from an agriculturally dominated small watershed within the Western Lake Erie Basin. ACPF was used to develop a series of ACP opportunity plans, which were then integrated into a calibrated SWAT model. SWAT simulation of ACPF developed ACP opportunity plans for grassed waterways (GWs), contour buffer strips (CBSs), water and sediment control basins (WASCOBs), nutrient removal wetlands (NRWs), and farm ponds (FPs) revealed various reductions in sediment, soluble reactive phosphorus (SRP), and total phosphorus (TP) at the watershed-scale. The simulation of individual ACP opportunity plans revealed that GW resulted in the greatest annual average SRP and TP reductions (19% and 30%, respectively), followed by CBS (16% and 22%), and WASCOB (13% and 16%); NRWs were the most effective at reducing sediment (56%) but increased SRP (27%). Combined GW, CBS, and WASCOB opportunity plans resulted in the greatest reduction of SRP (34%), while the combination of all ACP opportunity plans resulted in the greatest reduction of TP (49%) and sediment (78%).

SWAT model application for evaluating agricultural conservation practice effectiveness in reducing phosphorous loss from the Western Lake Erie Basin.

Lake Erie is threatened by eutrophication and harmful algal blooms due to excess nutrient loading from agricultural sources. Agricultural conservation practices (ACPs) have been developed and implemented to reduce nutrient losses but estimating ACP effectiveness is challenging. The Soil and Water Assessment Tool (SWAT) has been used to investigate ACP effectiveness for water quality improvement. Many SWAT applications have been developed by different investigators to evaluate ACP effectiveness for reducing nutrient, particularly phosphorus (P), loading in the agriculturally-dominated Western Lake Erie Basin (WLEB). Our objective is to establish what has been achieved by past modeling research and make suggestions for future applications and improvements. We synthesized the findings of 28 SWAT modeling studies within the WLEB. Models generally performed satisfactorily against accepted criteria for streamflow and sediment, but performance for P loads, like soluble reactive P, was mostly "unsatisfactory". The "unsatisfactory" performance maybe due to imperfections and idealizations in model formulations and/or parameterization. Thus, simulations of P transport and transformation processes need improvement. In addition, model parameter selection is the key part of model set-up. Most SWAT modeling studies used default values during initial set-up, then performed calibration and validation. It was found that the calibrated P related parameter values varied widely across different studies, even within the same watershed with some values unrealistic for the study areas. The phenomena of different combinations of model parameters producing similar outputs indicates equifinality. Equifinality in the baseline model may impact results when ACPs are incorporated. Furthermore, the unrealistic values used in ACP assessment undermine the credibility of ACP effectiveness. Future model applications should try to re-examine the calibrated P parameters and make sure they are realistic for the study area as well as reduce equifinality by constraining the model with characterization of watershed conditions, better understanding of hydrologic processes, and parameter values based on real-world observations. In summary, future model applications should focus on improving P transport and transformation processes, using measured watershed characteristics for parameterization, and improving reflections of climate change, which could result in more accurate assessments of ACP effectiveness to meet targeted goals.