CUERE Fall 2024 Seminar Series

Chesapeake Bay Program Office

Consensus on the contribution of different flows and sources to nitrogen export across gradients in urbanization is vital to optimize management strategies leveraging source reductions, stormwater controls, and restorations. We investigated how solute loading and sources varied across flows and land-use in the North Carolina Piedmont using a combination of high frequency monitoring (5 study catchments), stable nitrate isotope analysis (12 catchments), and periodic baseflow grab sampling (27 catchments). We found that across low to moderate development intensity catchments, baseflows contributed most of the N load, with up to 75% baseflow contribution from septic served catchments. Stormflows mobilized and mixed many surface and subsurface nitrate sources. However, multiple lines of evidence suggest that wastewater was the largest contributor to nonpoint source baseflow loading across both septic and sewer served catchments. The hydrogeomorphic position of sanitary infrastructure was the best predictor of baseflow loading and we estimated that up to 92% of the nonpoint source baseflow load comes from low and medium development intensity catchments within our study region. Research from across globe corroborates the importance of subsurface flows and wastewater to urbanized watershed nonpoint source loading. Together, these findings suggest that while urbanization increases surface stormflows, it also enriches subsurface flows with N primarily from leaky sanitary infrastructure. These subsurface loads are not treated by surface water management practices primarily targeted to surface stormflows. Effective management will require balancing improvements to green and grey infrastructure, addressing lower development intensity catchments, and stream/riparian restorations.