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The assessment of BMP (best management practice) impacts using a watershed model has helped to establish a watershed conservation and protection plan that is projected to be required by government and decision makers. Cedar Creek watershed, located southeast of Dallas, Texas, was included in the 303(d) list as an impaired watershed due to high pH values. A number of efforts have been made to develop watershed protection plans by the North Central Texas Water Quality (NCTXWQ) project team. Tarrant Region Water District (TRWD) has monitored the water quality in the reservoir and found that chlorophyll-a has been increasing at an annual rate of 3.85%. Chlorophyll-a is a good indicator of algae growth, and TRWD, with 18 years of monitoring, revealed that the increase of chlorophyll-a needs to be a primary focus of the watershed protection plats. A stakeholder group and the project team suggested that total phosphorous (TP) reduction from the watershed should be targeted at 35% of current loading in order to preserve the water quality in the reservoir. In previous studies, flow and nutrients in the watershed were calibrated using SWAT (Soil and Water Assessment Tool). In addition, sensitivity analyses for each BMP were conducted such that each BMP was simulated in the model at a 100% adoption rate. The cost-effectiveness of each BMP was estimated and ranked by TP reduction. In this study, using the calibrated model and the cost-effectiveness analyses of the BMPs, the initially selected BMPs were simulated in SWAT to identify the reduction rate at the watershed outlet (reservoir) using a marginal adoption rate and to illustrate the spatially distributed impacts' of each BMP at the subbasin scale. The results show that simulation of the eight selected BMPs in subbasins with higher TP loading cats achieve the 35% reduction goal at the reservoir. [ABSTRACT FROM AUTHOR]

Best management practices (BMPs) have been implemented on a farm-by-farm basis within the Cannonsville Reservoir watershed (CRW) as part of a New York City watershed-wide BMP implementation effort to reduce phosphorus (P) loads to the water supply reservoirs. Monitoring studies have been conducted at selected locations and at the watershed outlet on one of the farms, which spans an entire subwatershed within the CRW, with the aim of quantifying effectiveness of the BMPs installed on the farm. This study applied the Soil and Water Assessment Tool (SWAT) and a recently developed BMP characterization tool to the farm over pre- and post-BMP installation periods with the object of determining the extent to which model results incorporating all installed BMPs match observed data, and the individual impact of each of the BMPs installed on the farm. The SWAT model generally performed well at the watershed level for flow, sediment, and phosphorus simulations. Annual Nash-Sutcliffe (NS) coefficients for the components ranged between 0.56 and 0.80, while monthly NS coefficients ranged between 0.45 and 0.78. The model also performed well at the field level, with simulated in-field P loads closely matching observed data. Because the fields had various combinations of BMPs installed on them, it was difficult to separate out individual BMP impacts based on SWAT simulations. It was, however, possible to determine the effects of BMP combinations such as nutrient management plans and rotations (31% dissolved P; 25% total P). For dissolved P, integration of BMP tool efficiencies allowed individual BMP impacts to be incorporated while still maintaining the same level of representation as was obtained using model simulations. As the SWAT model is often used with little or no post-BMP data to verify simulation results, this study served to validate SWAT model suitability for evaluating BMP impacts. The BMP tool was found to suitably complement the model by providing insights into individual BMP impacts, and providing BMP efficiency data where the model was lacking. [ABSTRACT FROM AUTHOR]

Soil erosion from agricultural lands and the subsequent transport of sediment and sediment-bound nutrients (particularly P) are serious problems contributing to surface water pollution and threatening agricultural sustainability. Raindrop impact on bare soil destabilizes soil aggregates and leads to surface sealing, increasing runoff volumes and soil loss. Surface-applied polyacrylamide (PAM) decreases soil erosion by stabilizing the soil structure and reducing surface sealing. Previous research has shown that surface-applied PAM reduces erosion at relatively high application rates (20 to 80 kg ha-l). The purpose of this study was to evaluate the effectiveness and longevity of a new liquid/emulsion PAM formulation to reduce runoff, sediment, and P loss from rainfed agricultural fields. The formulation was applied using a hand sprayer at a low PAM rate of 5 kg ha-1 (13,333 L of solution ha-1). Plot-scale field rainfall simulations (75 mm ha-1) were conducted on individual test plots at three test intervals (rainfall simulated 2 days, 3 weeks, and 10 weeks after DAM application) on two soil types (Ashdale silt loam and Plano silt loam). The new polymer formulation, Soil Net EM-1000-50, reduced runoff volumes an average of 100% at the 2-day test interval, 59% at the 3-week test interval, and 55% at the 10-week test interval. Overall, larger rainfall depths were applied to treatment plots prior to runoff generation compared to controls. The most significant differences were observed at the 2-day test interval, when an average of 141 mm of rainfall was applied to the PAM-treated plots before runoff started, compared to 82 mm for the controls. These runoff reductions are not only important in terms of erosion but may also enhance water supply through increased infiltration. Sediment loss was reduced an average of 100% at the 2-day test interval, 80% at the 3-week test interval, and 74% at the 10-week test interval. Phosphorus loss was reduced an average of 100% at the 2-day test interval, 75% at the 3-week test interval, and 83% at the 10-week test interval. The polymer treatment was more effective on the Ashdale silt loam, which had received manure during the two years preceding the rainfall simulations. Manure application was the primary difference between the two soils (manure was not applied to the Plano silt loam), suggesting that the PAM treatment reacts more favorably to manured soils. The low cost of this new PAM technology (approx. $25 ha-1) coupled with its success in reducing runoff, sediment, and P loss over a 10-week period, make EM-1000-50 an attractive and economically feasible management practice for agricultural producers in rainfed regions. [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]