Soil-derived dissolved organic matter and nutrient sources from urban stormwater control measures

There has been significant investment in stormwater control measures (SCM) to reduce erosion, filter pollutants, and mitigate peak storm flows within urban watersheds. SCMs have variable hydrologic connectivity to downstream waterbodies where SCMs may rapidly export water during storm events but dry up in-between events and these alternating wet/dry cycles influence the biogeochemical processes that occur in SCM soils. While the performance of SCMs has been evaluated for nutrient removal, less is known about the potential for mobilization of nutrients and dissolved organic matter (DOM) that accumulate in SCM soils. Because of the significant aquatic ecosystem and human health implications related to excess DOM and nutrients, further work is needed to understand how urban SCMs and wetland soils may be impacting downstream water quality. Water-soluble organic matter (WSOM) was extracted from SCM and urban wetland soils located in the Rappahannock River watershed, part of the larger Chesapeake Bay watershed in the Mid-Atlantic region, to assess the potential mobilization of DOM and nutrients from SCM soils. We found low quantities of readily released organic matter and nutrients regardless of SCM type. WSOM concentration and composition did not vary spatially within SCMs. However, SCM surface water had plant-like signatures and was more aromatic compared to WSOM, indicating that organic matter processing occurs as water moves through SCM soil media. Monthly sampling of SCM soils suggests WSOM and nutrient quantities peak when SCMs are dry. When accounting for spatial extent, SCMs likely serve as smaller potential sources of carbon to downstream aquatic ecosystems relative to larger naturally occurring urban wetlands. Exploring the potential soil-derived DOM in SCMs and urban wetlands furthers our knowledge of how urban systems influence DOM concentration and composition, while examining the performance of SCMs relative to natural soil systems.