Optimizing compost incorporation for stormwater infiltration, runoff quality, and vegetation establishment in post-construction soils

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. A progression of experiments were conducted to determine the optimal compost incorporation rates to improve stormwater infiltration, runoff quality, and vegetation establishment. Two laboratory-scale experiments investigated the effect of compost incorporation rate on (1) saturated hydraulic conductivity (Ks) and (2) pollutant 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 pollutant export experiments show stormwater largely did not increase the pollutant loads compared to DI water with compost incorporation. Additionally, results from adsorption and desorption experiments show compost-soil blends have a high capacity to sorb and retain pollutants. Next, a greenhouse experiment considered vegetation quantity and quality with varying rates of compost. There were no differences in the timeliness of vegetation germination between treatments. Higher rates of compost were found to have more vegetation cover and produce more biomass. Lastly, a field experiment determined the effects of compost incorporation on stormwater runoff, runoff quality (sediment loss and pollutant loads), infiltration rate (IR), and vegetation establishment over the course of a growing season. Compost incorporation did not alter runoff quantity or quality compared to a tilled, no compost treatment. More vegetation biomass was produced in compostamended treatments compared to treatments without compost incorporation. 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 may be beneficial to improve vegetation coverage, which is necessary for long-term erosion control. Tillage appears to be a viable option for reducing runoff volumes in compacted soils.