Quantifying Chloride Retention in Urban Stormwater Management Ponds Using a Mass Balance Approach

Abstract Chloride (CI) from runoff containing deicing salts is retained in watersheds after deicing ends, resulting in deleterious effects on aquatic biota. Stormwater management ponds (SWMPs) are known to impact pollutant transport. However, there is little information on what role SWMPs play in the timing and magnitude of CI transport in urban watersheds. This study quantifies the mass of CI retained in two urban SWMPs over varying timescales and the in-stream response to CI-laden pond outflows. The findings suggest that SWMPs likely play a role in watershed-scale CI retention. In the receiving creek, CI pulses corresponded to CI release from the pond. The results of this study suggest that SWMPs concentrate spatially distributed salt inputs and modify the timing and magnitude of their release to receiving streams. This study will help parameterize the role of SWMPs in watershed-scale CI transport models and geospatial models of salt vulnerable areas.