Urbanization can degrade the natural function of soil through stripping of topsoil, vegetation removal, and compaction by heavy equipment. The result is an exposed, compacted subsoil with low fertility and infiltration, which leads to increased erosion and sediment loss, and impedes vegetation establishment. Strategic compost incorporation to disturbed, degraded urban soils may provide benefit to soil properties. Our research evaluated the effectiveness of different compost incorporation rates and compost sources as a stormwater control measures (SCMs). Two laboratory-scale experiments investigated the effect of compost incorporation rate on (1) saturated hydraulic conductivity (Ks) and (2) nutrient and heavy metal export patterns. First, results from the Ks experiments demonstrated that level of soil compaction (soil porosity) was a more important factor than compost rate for determining Ks. Compacted, low porosity soils with 50% compost by volume had significantly reduced Ks compared to medium and high porosity soils with no compost. Second, results from nutrient and heavy metal export experiments show stormwater largely did not increase the pollutant loads compared to DI water with compost incorporation. Compost rate does however influence pollutant transport and may retain most heavy metals when infiltrating stromwater. Next, a greenhouse experiment considered vegetation quantity with two sources of compost at varying rates. A compost application rate ≥10% by volume improved biomass production. Soil crusting was additionally mitigated in all compost treatments. Lastly, a field experiment determined the effects of compost incorporation on stormwater runoff volume, runoff quality (turbidity and total suspended solids [TSS]), infiltration rate (IR), bulk density, and vegetation establishment over the course of one year. Compost incorporation did not alter runoff quantity or quality compared to a tilled, no compost treatment. As compost rate was increased, bulk density decreased, vegetation biomass increased, and infiltration rates increased. More vegetation biomass was produced in the certified compost-amended treatments compared to treatments with the uncertified compost-amendment. Overall, the results of these studies suggest that the direct impact of tillage on soil properties is the primary factor affecting stormwater movement through soil. Compost incorporation has the greatest soil physical property improvement on heavier (more clay) soils and can improve vegetation establishment and growth, which is necessary for long-term erosion control. Tillage appears to be a viable option for reducing runoff volumes in compacted soils.
