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Composts as Post-Fire Erosion Control Treatments and Their Effect on Runoff Water Quality

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Transactions of the ASABE. 56(2): 423-435. (doi: 10.13031/2013.42692) @2013
Authors:   David M. Crohn, Vijayasatya N. Chaganti, Namratha Reddy
Keywords:   Composts Erosion control Fires Metals Mulches Nutrients Sediment Water quality.

Abstract. Erosion from fire-damaged wildlands poses a significant water quality concern. Deprived of vegetation, runoff intensifies, which escalates exports of sediments and other pollutants. Used as mulches, composts shield the soil surface and reduce runoff by absorbing water and promoting infiltration. This field study considered three types of compost used as mulches following the controlled burn of coastal sage scrub vegetation. Nine treatments considered a coarse greenwaste compost (>9.5 mm), a fine greenwaste compost (<9.5 mm), and a biosolids co-compost, each of which was surface-applied to 2.5 and 5 cm mulch depths, along with a final treatment of incorporation of 5 cm of material into 8 cm of soil. Results were aggregated from four sequential natural storm events on 2.5:1 steepness replicated plots, with the runoff sampled for sediment, nutrients, and metals. A novel non-parametric Kaplan-Meier approach was adapted to sum metal samples falling below detection limits. Compared to untreated controls, compost use effectively controlled runoff, sediment, nutrient, and metal exports after fire removed the vegetation from the slope. Runoff, total dissolved solids (TDS), total suspended solids (TSS), and total solids (TS) were reduced by averages of 86%, 88%, 80%, and 97%, respectively. Suspended metals were typically reduced by 93% to 95%. Compost use also reduced turbidity and, in most cases, nutrient exports. Mulching and soil incorporation were, in general, equally effective. Applying 5 cm mulches offered no performance advantage over 2.5 cm mulches, and in the case of biosolids compost 5 cm performed less well, contributing more dissolved solids, ammonium-N, and dissolved metals (Cd, Cr, Cu, and Mo) than the 2.5 cm treatment. Greenwaste compost particle size did not significantly affect runoff, and results for the coarse and fine greenwaste composts were similar. Compost mulches appear to be an effective means of reducing pollution from soils following wildfires.

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