Erosion control and storm water quality from straw with pAm, mulch, and compost blankets of varying particle sizes

Compost and mulch blankets have been widely used for slope stabilization and erosion control at construction sites; however, the majority of research on these erosion control blankets has failed to meet state or federal specifications for particle size distribution. The primary objective of this study was to determine how blending wood mulch with compost may affect its performance as an erosion control practice relative to a straw blanket with polyacrylamide (PAM). The secondary objective of this study was to determine if particle size distribution of the organic erosion control blanket affects runoff, erosion, and vegetation establishment. Researchers concluded that the greater percent of compost used in an erosion control blanket, the lower the total runoff and the slower the runoff rate. Compost erosion control blankets retained 80% of the simulated rainfall applied and reduced cumulative storm runoff by 60%, while the wood mulch blankets reduced runoff by 34% and straw with PAM by 27%. Conversely, the greater the percent of mulch used in the erosion control blanket, the lower the sediment and suspended sediment load. However, any combination of compost and mulch reduced runoff volume, runoff rate, and soil loss relative to a straw blanket with polyacrylamide. The average cover management factor (C factor) for the straw with PAM was 0.189, the compost blanket was 0.065, and the mulch blanket was 0.013. Researchers also concluded that particle size distribution of the compost and mulch blankets was the leading parameter that reduced soil loss and runoff. If particle size distribution specifications are not followed, total soil loss can be four times greater, suspended solids can be five times greater, and turbidity can be eight times greater, relative to blankets that meet particle size distribution specifications. Nitrogen and phosphorus loading from mineral fertilizer used with conventional straw blankets may lead to increased nutrient loading of receiving surface water relative to the compost and mulch blankets. The straw blanket with fertilizer increased total Kjeldahl nitrogen loading by more than 8,000%, the compost blanket increased total Kjeldahl nitrogen by 340%, and the mulch blanket by 18% relative to the control. Although the bare soil and mulch blanket treatments did not contribute any soluble phosphorus (P) to runoff, relative to the compost blanket, the soluble P load from the straw blanket with PAM was 3,800% greater. Results from this study may be used to revise particle size specifications for compost erosion control blankets and to help regulators and design professionals determine which type of erosion control best management practice is best for their particular application.