Assessment of runoff water quality for an integrated best management practice system in an agricultural watershed

Abstract

To better understand, implement, and integrate best management practices (BMPs) in agricultural watersheds, critical information on their effectiveness is required. A representative agricultural watershed, Beasley Lake, was used to compare runoff water quality draining through an integrated system of BMPs from row crop cultivated subdrainages as part of the national Conservation Effects Assessment Project (CEAP). From 2011 to 2014, runoff samples were collected across three subdrainages representing two integrated BMPs and three subdrainages representing row crop cultivation. Best management practice sites studied were two vegetated drainage ditches (east [EDV] and west [WDV]) that subsequently flowed into a vegetated sedimentation pond (SP). A suite of critical water quality parameters were assessed and included total suspended solids (TSS), total phosphorus (TP), total nitrogen (TN), nitrate-nitrogen (NO₃-N), ammonium-nitrogen (NH₄-N), and orthophosphate-phosphorus (PO₄-P). During the four-year study period, integrated BMPs were effective at mitigating TSS runoff loads relative to row crop, but less effective at mitigating nutrient runoff loads. Runoff from WDV and SP were only moderately effective in mitigating nutrients in runoff with only TN and TP consistently reduced relative to row crop. Effectiveness of BMPs were primarily a result of the amount of area in tillage practices and crops planted relative to BMP within subdrainage basin area. Decreasing tillage:BMP and/or crop:BMP area ratios produced a subsequent decrease in runoff loads with the exception of NH₄-N and PO₄-P.