|GALL, HEATHER - Pennsylvania State University|
|SCHULTZ, DANIEL - Pennsylvania State University|
|Veith, Tameria - Tamie|
|MEJIA, ALFONSO - Pennsylvania State University|
|HARMAN, CIARAN - Johns Hopkins University|
|RAJ, CIBIN - Pennsylvania State University|
|PATTERSON, PAUL - Pennsylvania State University|
Submitted to: Stochastic Environmental Research and Risk Assessment (SERRA)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2017
Publication Date: 1/5/2018
Citation: Gall, H.E., Schultz, D., Veith, T.L., Goslee, S.C., Mejia, A., Harman, C., Raj, C., Patterson, P.H. 2018. The effects of disproportional load contributions on quantifying vegetated filter strip sediment trapping efficiencies. Stochastic Environmental Research and Risk Assessment (SERRA). 1-12. https://doi.org/10.1007/s00477-017-1505-x.
Interpretive Summary: Vegetated filter strips, which are grass strips next to agricultural fields, are used to trap sediments and nutrients in the water coming off the field. Due to the time and cost in collecting long-term data on how well these filter strips work, estimates for their effectiveness vary widely and may be too high. We used a model that simulates rainfall, soil wetness, runoff, and sediment and nutrient trapping to provide 1000 years of results based on historical weather data for each of 12 soil textures. After using two different methods to analyze the results, we found that current values for filter strip effectiveness may be as much as 20% too high in clay soils. This study shows the need for care when assigning filter strip effectiveness and provides visual graphics for how the effectiveness values change based on soil texture.
Technical Abstract: Vegetated filter strips (VFSs) are a best management practice (BMP) commonly implemented adjacent to row-cropped fields to trap overland transport of sediment and other constituents present in agricultural runoff. Although they have been widely adopted, insufficient data exist to understand their short and long-term effectiveness. High inter-event variability in performance has been observed, yet the majority of studies report average removal efficiencies over observed or simulated events, ignoring the disproportional effects of loads into and out of VFSs over longer periods of time. We argue that due to positively correlated sediment concentration-discharge relationships, disproportional contribution of runoff events transporting sediment over the course of a year (i.e., temporal inequality), decreased performance with increasing flow rates, and effects of antecedent moisture condition, VFS removal efficiencies over annual time scales may be significantly lower than reported per-event averages. By applying a stochastic approach, we investigated the extent of disparity between reporting average efficiencies from each runoff event over the course of one year versus the total annual load reduction. Additionally, we examined the effects of soil texture, concentration-discharge relationship, and VFS slope in contributing to this disparity, with the goal of revealing potential errors that may be incurred by ignoring the effects of temporal inequality in quantifying VFS performance. Simulation results suggest that ignoring temporal inequality can lead to overestimation of annual performance by as little as < 2% and to as much as > 20%, with the greatest disparities observed for clay soils.