Influence of stormwater control measures on water quality at nested sites in a small suburban watershed

Stormwater control measures (SCMs) are designed to mitigate the deleterious impacts of urban runoff on the water quality of receiving waters. To assess the cumulative effects of SCMs at the watershed scale, we monitored longitudinal changes in storm discharge and stream water chemistry at high temporal resolution in a suburban headwater stream in Charlotte, NC. SCMs significantly decreased or stabilized instream concentrations of reactive solutes (nitrate, soluble reactive phosphorus, and dissolved organic carbon) relative to the upstream control site. However, SCM outflows minimally influenced concentrations of less reactive solutes (major ions) which increased with urbanization. Additionally, instream concentration variability correlated with antecedent moisture conditions – representative of watershed storage availability – highlighting the role that SCM storage availability plays in the timing of solute delivery to the stream. Our results show that SCMs decrease instream concentrations of biogeochemically reactive solutes but the mitigation potential is temporally dynamic and influenced by antecedent conditions.