EVALUATION OF COMPOST BLANKETS FOR EROSION CONTROL AND RUNOFF WATER QUALITY ON A CONSTRUCTED HILLSLOPE IN SOUTHERN CALIFORNIA

Compost blankets are useful for reducing sediment exports from soils cleared and compacted by construction activity, but their effectiveness as a water quality measure has not been evaluated for semi-arid conditions. This field study evaluated greenwaste and biosolids fine (<9.5 mm) compost blankets for their effectiveness in curbing soil erosion and maintaining runoff water quality following three consecutive natural rain storms on a 3:1 constructed hillslope in southern California. Both runoff concentration and mass losses for sediments, total dissolved solids (TDS), total suspended solids (TSS), turbidity, nutrient exports, and metal exports through runoff were evaluated for each of the three storms. Cumulative totals across all three storms were also calculated. A nonparametric Kaplan-Meier approach was adapted to deal with nondetects observed in trace metal analysis in order to calculate the cumulative metal losses. Composts significantly reduced runoff and associated sediment loads compared to untreated controls. Mean runoff was 77% and 92% less for greenwaste and biosolids compost, respectively, relative to the control. Respective TSS exports were 88.5% and 97% less. TDS losses were 81% less from biosolids, but greenwaste did not differ significantly from the control. Biosolids contributed more NH4+-N and suspended P but less dissolved P than the other treatments. Dissolved trace metals were seldom detected in runoff, except for Cu and Zn, but detected losses were greatest from the controls. Greenwaste compost released the smallest amounts of suspended metals. Fine-textured greenwaste and biosolids composts are effective for erosion control under semi-arid conditions.