Dynamic stormwater management to mitigate phosphorous export

Altered stormwater flow characteristics and associated changes in nutrient and sediment fluxes due to urbanization threaten the water quality of many water bodies. For example, particle-bound phosphorus in stormwater runoff adds to the nutrient pool that can produce harmful algal blooms, and the associated particulate material can endanger fish and other living organisms in surface waters by increasing turbidity. While many studies have investigated how Total Solids (TS) particle size distributions vary in urban stormwater and the associated design criteria for Best Management Practices (BMPs) to remove TS, few studies have included different forms of phosphorus and their association with particle sizes to characterize design criteria to specifically maximize Total Phosphorus (TP) removal. This highlights a gap in our understanding of how the particle size distributions of TP and TS are related, and how these particle size distributions vary within and between storm events. Bridging this knowledge gap can improve design methods for BMPs specifically targeting phosphorus removal. This study characterizes within event (i.e., hourly) TP and TS particle size distributions and associated fluxes from urban catchments in the City of Cambridge, Massachusetts, to characterize potential TP and TS removal based on four different diversion and treatment strategies. The stormwater diversion strategies integrate new insights on temporal variations in particle size distributions and mass loading characteristics. In terms of diverted stormwater, the volume of stormwater treated tends to control more than what water is treated (e.g., first flush, event high flows, or smaller event flows). Based on the event data obtained in this study, considering flow volume different diversion approaches are optimal for TP vs TS, but treatment combined with particles sizes < 100 μm is best for both TP and TS.