Evaluation of compost/mulch as highway embankment erosion control in Louisiana at the plot-scale

Total suspended solids (TSS) and associated turbidity in runoff water are considered the most problematic nonpoint source pollutant of Louisiana surface waters. With high precipitation in Louisiana, attention should be given to controlling highway right-of-way erosion. The use of compost/mulch for erosion control enhances soil conservation and substantially reduces erosion. The main objective of this study was to assess the effect of compost/mulch placement on runoff water quality on roadsides. Our hypothesis was that the use of compost/mulch would significantly reduce TSS and turbidity in runoff from highway right-of-ways in Louisiana. Two locations constituting four sites and eight individual plots were chosen: one in an active highway construction area and another in an established area plagued by continual rill and sheet erosion. Thicknesses of compost/mulch (5 and 10 cm), slope inclination (10-34%), and tillage practices (till vs. no-till) were evaluated. Runoff, triggered by storm water events, was collected using ISCO auto-samplers from June 2010 to August 2011 and the samples were analyzed for TSS, turbidity, biochemical oxygen demand, electrical conductivity, and pH. The results of factor analysis showed that the compost/mulch thickness was the most influential variable affecting water quality. Two samples t-test results indicated that TSS and turbidity were significantly different across all comparative variables: construction activities, compost/mulch applications, and tillage practices. The results confirmed the effectiveness of compost/mulch cover as a successful best management practice. Specifically decreases in TSS of 70% and 74% were achieved for the 5 cm and 10 cm compost/mulch application when compared to no compost/mulch, respectively. Light tillage application increased TSS as much as 67%. Therefore, light tillage is not recommended since it decreased the effectiveness of compost/mulch in reducing runoff and sediment losses. (C) 2012 Elsevier B.V. All rights reserved.