Biogeochemical soil dynamics under the influence of various urban runoffs

Soils in urban settings are introduced daily to runoffs containing various oxidants and reductants that may alter biogeochemical dynamics and microbial community composition. In this study, we characterize these runoff-associated impacts by exposing an undisturbed soil to wastewater, road, and roof runoff, in both oxic and anoxic conditions. Our results demonstrate that the soil microbial community underwent significant changes depending on the type of runoff and that runoff-associated redox reactions induced metal leaching, particularly for Cu, Ni, and Zn. Road runoff resulted in the highest metal leaching measured. The introduction of wastewater, an electron donor rich fluid, imposed the most substantial changes to soil. Wastewater-associated changes include higher concentrations of Myo-IHP, a P form that accumulates in soil and is hydrolyzed overtime, releasing bioavailable PO43- to groundwater. In addition, wastewater was linked to consumption of natural soil organic matter (OM) and metal leaching via OM oxidation, which is the main sink for Cu, Ni, and Zn in soils. Overall, even though these experiments were conducted with both soils and runoffs that were relatively low in metal concentrations, leaching was induced by runoff-associated redox dynamics. Soil and groundwater regulations should consider soil dynamics as a current threat to groundwater quality, via metal leaching, in urban and populated settings.