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The potential impacts of climate change on BMP effectiveness were investigated using SWAT simulations for an agricultural watershed that drains into the Chesapeake Bay in the U.S. Northeast climate region. Critical source areas (CSAs) for sediments, nitrogen, and phosphorus, identified for current and future climate (SRES scenarios A1B and A2), were classified by density to support BMP prioritization schemes. BMPs were designed for these CSAs and tested against current and future climate using SWAT simulations to evaluate their robustness. A second set of BMPs was designed by optimization for all agricultural and urban lands in the study watershed and was similarly tested for robustness. In both cases, the design goal was for the watershed's water quality response to meet the bay TMDLs once BMPs were implemented. Results indicated that density 2 and 3 CSAs (hotspots exporting excess amounts of 2 or 3 constituents) may be good prioritization targets, but reaching the bay TMDLs would still require targeting all CSAs. BMPs designed for CSAs under current climate were effective to reach bay TMDLs under current climate but not under scenarios A1B and A2. BMPs designed for CSAs under scenario A2 were effective to reach the bay TMDLs under all climates, except for nitrogen under A2. Similarly, BMPs optimized for agricultural and urban lands, when designed for current climate, were effective in meeting TMDLs for current climate only. Optimizing these BMPs for future climate produced a design that met TMDLs under both current and future climates, except for nitrogen with future climate. However, in this case, the nitrogen TMDL was exceeded by a smaller amount than in the CSA design. It was concluded that, in the U.S. Northeast, BMPs designed to remediate water quality problems under current climate will be insufficient to maintain water quality with climate change. Increased annual rainfall and storm intensity will increase the proportion of watershed area needing BMPs, and current hotspots will generate excess amounts of new constituents that will require re-design of existing BMPs. Community-based participatory strategies will likely be required to foster BMP adoption and sustain water quality gains in the Chesapeake Bay region. [ABSTRACT FROM AUTHOR]

In recent years, riparian buffers have become known as one of the most effective best management practices for nonpoint-source pollution. However, establishment of riparian buffer systems with respect to plant species and their position in the buffer zone has not been investigated due to lack of efficient evaluation methods for the analysis of water quality improvement with established riparian buffers. To solve this problem, the SWAT-REMM prototype version was developed by researchers in Canada. In the SWAT-REMM prototype version, many riparian-related input parameters are not directly read from the local input data. Thus, a SWAT-REMM enhancement was developed by improving three major limitations of the prototype version of SWAT-REMM: (1) riparian buffers at designated reaches in the watersheds, (2) riparian buffers using local soil properties at the riparian buffer zone along reaches, and (3) multiple weather stations in a larger-scale watershed. The enhanced SWAT-REMM version was applied to the Bonggok watershed in Korea. This study investigated riparian buffers with different widths (10 m, 5 m, and 1 m) along the slope. Total nitrogen reduction ranged from 14.8% to 54.0% in each catchment for 10 m widths. Total nitrogen reduction ranged from 6.9% to 31.6% in each catchment for 1 m widths. The reduction efficiency was not simply proportional to the width of buffers. This study evaluated the enhanced SWAT-REMM simulation of water quality improvement. Based on this research, the enhanced SWAT-REMM can be used to evaluate water quality improvement by riparian buffers at various watersheds worldwide using local data. In particular, simulation of riparian buffers at user-designated reaches in a watershed enables simulation of riparian buffers in watersheds experiencing frequent flooding where no riparian buffers can be established. It is expected that the enhanced SWAT-REMM can be used to determine economical and environmentally optimum riparian buffer scenarios. [ABSTRACT FROM AUTHOR]

Cropland best management practice recommendations often combine tillage and nutrient application improvements to reduce nutrient losses with surface runoff. This study used the Soil and Water Assessment Tool (SWAT) model to evaluate nutrient runoff yields from conventional-till and no-till management practices with surface and deep-banded fertilizer application in a sorghum-soybean rotation. The model was calibrated for three field plots (0.39 to 1.46 ha) with different combinations of practices and validated for three field plots (0.40 to 0.56 ha) during 2001 to 2004. Daily performance of the calibrated SWAT model in simulating total N for all treatments was satisfactory for median-based Nash-Sutcliffe model efficiency (Ef* of 0.54 to 0.64), good to very good for percent bias (PBIAS of 31% to 7%), and satisfactory to good for median-based root mean square error to observations standard deviation ratio (RSR* of 0.72 to 0.62). Performance was slightly lower and more variable for total P calibration (Ef* of 0.42 to 0.62, PBIAS of-48% to 2%, and RSR* of 0.76 to 0.62). Monthly statistics improved for total P runoff yield compared to daily performance, but changed little for total N runoff yields, probably due to the stronger influence of outliers in the N data. Based on validation results, SWAT was more robust in simulating total N runoff yields from the treatment with less soil disturbance (NT/SB) and total P for the two treatments with more soil disturbance (NT/DB and TILL). A major concern was that SWAT predicted greater annual average total N runoff yields for no-till treatments than for tilled treatments, which was contrary to measured values at the study site. This reinforces a fundamental research issue that tillage system effects on nutrient losses are still very much uncertain and thus may not be properly modeled. The SWAT model generally underpredicted monthly total N yields for all treatments in the higher-precipitation months of May and June and overpredicted total N and total P yields from September through November. Calibration for N and P resulted in identical calibration parameters for NPERCO (1.0), RSDCO (0.05), BIOMIX (0.2), PPERCO (10), PHOSKD (175), and UBP (50) regardless of tillage practice or fertilizer application method. Together with results that calibrated parameters for runoff (CN, Ksat, AWC) and erosion (Cmin) differed among the treatments, this study found that differences in nutrient yields among tillage and fertilizer management may be adequately modeled with SWAT by calibrating runoff and sediment yields only, and that further calibration of nutrient parameters may not improve model results. [ABSTRACT FROM AUTHOR]

In 2006, bacterial pathogens were the leading cause of water quality concerns in the U.S. With more than 300 water bodies in the state of Texas failing to meet water quality standards because of bacteria, managing bacteria pollution commanded the attention of regulatory agencies, researchers, and stakeholders across Texas. In order to assess, monitor, and manage water quality, it was necessary to characterize the sources of pathogens within the watershed. The objective of this study was to develop a spatially explicit method to estimate potential E. coli loads in Plum Creek watershed in east central Texas. Locations of contributing non-point and point sources in the watershed were defined using Geographic Information Systems (GIS). By distributing livestock, wildlife, wastewater treatment plants, septic systems, and pet sources, the bacterial load in the watershed was spatially characterized. Contributions from each source were quantified by applying source specific bacterial production rates, and ranking of each contributing source was assessed for the entire watershed. Cluster and discriminant analyses were used to identify similar regions within the watershed for selecting appropriate best management practices. Based on the statistical analysis and the spatially explicit method, four clusters of subwatersheds were found and characterized. The analysis provided a basis for development of spatially explicit identification of best management practices (BMPs) to be applied within the Watershed Protection Plan (WPP). [ABSTRACT FROM AUTHOR]

Nitrate nitrogen (NO3-N) enriched water originates from subsurface drains or "tiles" that underlay many fields in the Corn Belt and is the primary source of NO3-N to surface waters in this region. To better assess the fate and transport of nutrients, such as NO3-N, the tile drain and pothole components of SWAT (Soil and Water Assessment Tool) were enhanced and modified in the previous component of this study. In this study, the environmental and economic impacts of various best management practice (BMP) scenarios often adopted by local farmers to reduce sediment and nutrient loadings (in particular NO3-N) were evaluated using the modified SWAT (SWAT-M) and FEM (Farm-level Economic Model) models. Measured values of water quality indicators from the Walnut Creek watershed (WCW) located in central Iowa were used to verify the capability of SWAT-M to predict the impact of late-spring nitrate test (LSNT) and rye cover crop management on NO3-N reduction at the subbasin level. The results obtained from SWAT-M simulation results, similar to field measurement data, indicated a 25% reduction in NO3-N under the LSNT scenario. FEM results indicated a corresponding increased annual cost of $6/ha across all farms in the watershed. Simulation of other scenarios, including winter cover cropping and a combination of LSNT and cover cropping at different adoption rates within WCW, resulted in a progressive reduction in sediment and nutrient losses as adoption rates increased. Use of the rye cover crop added about $25/ha to $35/ha to the annual cost of the average farm, indicating that some cost-share support may be necessary to encourage farmers to use winter cover crops. [ABSTRACT FROM AUTHOR]

Environmental models are used to assess and evaluate various best management practices (BMPs) at field (e.g., Agricultural Policy/Environmental eXtender, APEX) and watershed (e.g., Soil and Water Assessment Tool, SWAT) levels. However, models such as SWAT and APEX are only capable of simulating, mechanistically, a limited number of BMP scenarios individually. Therefore, this study was conducted to: (1) develop an automated program referred to as SWAPP to convert SWAT files to and from APEX format and simulate SWAT and APEX simultaneously, and (2) to evaluate this program using measured data from the upper North Bosque River watershed in central Texas. In this study, SWAT (version 2000) and APEX (version 2110) were utilized within SWAPP. Simulations from SWAT alone (SWAT-A) and the combined SWAT and APEX models in SWAPP were compared with the historical measured data collected in the upper North Bosque River (UNBR) watershed. In the first phase of this study, SWAT-A was applied to simulate all land uses in the UNBR watershed. In the second phase, stream flow and losses of sediment and nutrients from all crop and pasture lands within the UNBR watershed were simulated by APEX. The results obtained from APEX, and remaining land uses in the UNBR watershed (e.g., urban) simulated by SWAT, were then routed to the outlet of the watershed using the SWAT routing function. The measured flow, sediment, and nutrients at three sites within the UNBR watershed were simulated by SWAT-A and the combined SWAT and APEX within SWAPP for the period of January 1994 through July 1999. The results obtained from the three sites within the UNBR watershed indicate that the pattern (Nash-Sutcliffe efficiencies, E) and average monthly values of flow and loadings predicted by the combined SWAT and APEX within SWAPP were similar, and in some cases (mainly for sediment and nutrients loadings) closer to the measured values, as compared to SWAT-A. For instance, the E values for flow obtained from SWAPP ranged from 0.65 to O. 74, while those from SWAT-A ranged from 0.55 to O. 75. The E value for sediment loading at three sampling sites ranged from 0.55 to O. 74 for SWAPP, as compared to 0.41 to O. 72 for SWAT-A, and the E values for nutrient loadings ranged from -0.04 to 0.88 for SWAPP, compared to -0.74 to 0.82 for SWAT-A. The results obtained from this study indicated that the SWAPP program not only improved the modeling results, but also provides an opportunity to utilize APEX within the SWAPP program for simulating management practices, such as multicropping or filter strips, at the field level, whereas SWAT alone currently has limited capability to simulate these practices. In addition, SWAPP can be used to rapidly convert SWAT data files, generated from Geographical Information System (GIS) layers, to APEX data file format. [ABSTRACT FROM AUTHOR]

Structural best management practices (BMPs) that reduce soil erosion and nutrient losses have been recommended and installed on agricultural land for years. A structural BMP is expected to be fully functional only for a limited period after installation, after which degradation of the BMP is likely to lead to a reduction in the water quality improvement provided by the BMP. Assessing the impact of BMPs on water quality is of widespread interest, but no standard methods exist to determine the water quality impact of structural BMPs, particularly as the impact changes through time. The objective of this study was to determine the long-term (∼20 year) impact of structural BMPs in two subwatersheds of Black Creek on sediment and phosphorus loads using the Soil and Water Assessment Tool (SWAT) model The BMPs were represented by modifying SWAT parameters to reflect the impact the practice has on the processes simulated within SWAT, both when practices are fully functional and as their condition deteriorates. The current condition of the BMPs was determined using field evaluation results from a previously developed BMP condition evaluation tool. Based on simulations in the two subwatersheds, BMPs in good condition reduced the average annual sediment yield by 16% to 32% and the average annual phosphorus yield by 10% to 24%. BMPs in their current condition reduced sediment yield by only 7% to 10% and phosphorus yield by 7% to 17%. [ABSTRACT FROM AUTHOR]

This article introduces a collection of papers from the fourth biennial ASABE 21st Century Watershed Technology Conference and Workshop: Improving Water Quality and the Environment, held in Hamilton, New Zealand, on November 3-6, 2014. This Special Collection consists of three articles selected from the 47 meeting papers. The technical presentations at the conference focused on solving spatial and temporal water quality and quantity problems and addressed topics such as watershed management in developing countries, water quality standards, agricultural best management practice (BMP) effectiveness, emerging problems, impact of extreme weather conditions, biological monitoring, increasing stakeholder involvement, political and economic implications, watershed implementation planning, forest and rangeland water quality issues, and water resources education. At first glance, these topics seem quite diverse. A more detailed look suggested that the "big data" and data mining themes of the last conference in Bari, Italy, continued to develop. [ABSTRACT FROM AUTHOR]