Field assessment of bacteria and nutrient removal by vegetative filter strips

Strategies are sought to reduce the impact of nonpoint sources of pollution,including fecal bacteria,and meet TMDL criteria.Vegetative filter strips(VFSs)are one such strategy,though the data of VFS function under field conditions,particularly for fecal bacteria,are limited.The objective of this study was to evaluate the efficiencies in removing fecal bacteria,N,and P from VFSs installed to treat contaminated runoff from a working feedlot.VFSs were found to be effective in removing a broad range of constituents from beef feedlot runoff pretreated by a settling basin.The first 30 m provided most or all of the reductions found within the 150 m VFSs studied:reductions average 85%of inflow water,85%of sediment,77%of N,and 84%of P.Fecal bacteria removal by the VFSs was about one order of magnitude:reductions at 30 m ranged from 83.5%for FC and FS to 91%for E.coli.On the site being studied,this provided an important level of protection and reduced surface-flow concentrations of fecal coliforms to below the 200 CFU/100 mL(coliform-forming units,CFU)water-quality standard for Kansas.

A validation of WEPP water quality routines in uniform and nonuniform agricultural hillslopes

Current watershed-scale,nonpoint source pollution models do not represent the processes and impacts of agricultural best management practices on water quality with sufficient detail.A Water Erosion Pre-diction Project-Water Quality(WEPP-WQ)model was recently developed which is capable of simulating nonpoint source pollutant transport in nonuniform hillslope conditions such as those with BMPs.However,WEPP-WQ has not been validated for these conditions,and prior validation work only eval-uated calibrated performance rather than uncalibrated performance,with the latter being most relevant to model applications.This study evaluated uncalibrated and calibrated model performance in two plot-scale,artificial rainfall studies.179 observations were compared to corresponding WEPP-WQ simulations of runoff,sediment yield,and soluble and particulate nutrient forms for both nitrogen and phosphorus.Uncalibrated validation results were mixed for the different field conditions,model configurations,and prediction variables.Nash-Sutcliffe Efficiencies for uncalibrated simulations of uniform conditions were generally greater than 0.6 except for soluble nitrogen predictions which were poor.Simulations of nonuniform conditions were generally'unsatisfactory'except for runoff predictions which were quite good(NSE=0.78).Performance was improved substantially for almost all endpoints with calibration.Some exceptions to this occurred because the objective function for calibration was based on log-space differences so as to more equally-weight calibration of unsaturated conditions that tend to produce lesser runoff volumes and sediment yields.Calibrated results for both uniform and nonuniform condi-tions were generally'satisfactory'or'good'according to widely accepted model performance criteria.