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Phosphorus retention in stormwater control structures across streamflow in urban and suburban watersheds
Citation:
Duan, S., T. Newcomer-Johnson, AND S. Kaushal. Phosphorus retention in stormwater control structures across streamflow in urban and suburban watersheds. WATER. MDPI, Basel, Switzerland, 8:390, (2016).
Impact/Purpose:
Excess phosphorus (P) from human activities contributes to the degradation of water quality in streams and coastal areas nationally and globally. Stormwater control structures and stream restoration may be important management approaches to improve water quality by increasing the capacity of streams and water bodies to process and/or remove P. However, the efficacy of restoration and stormwater methods varies widely, leading to uncertainty about which approach is more effective and under what circumstances. Therefore, we examined changes in P retention in restored streams and stormwater control structures in the Baltimore MD metro area, a highly urbanized ecosystem with high P inputs. Effectiveness in P uptake and removal were highly variable over space and time. For example, P changed from retention during high flows to negative, indicating release during low flows, possibly due to a combination of factors including hydrology, physical sedimentation, biogeochemical mobilization. Cultivation of macrophytes and/or frequent sediment dredging may provide potential solutions to managing P in urban watersheds. Our study is intended to provide guidance for watershed managers to select the most cost effective approaches for nutrient management under various conditions. This study was not done a priori under an existing RAP task but parallels the focus of SSWR 4.03 - Science to Improve Nutrient Management Practices, Metrics of Benefits, Accountability and Communication
Description:
Recent studies have shown that stormwater control measures (SCMs) are less effective at retaining phosphorus (P) than nitrogen. We compared P retention between two urban/suburban SCMs and their adjacent restored stream reaches at the Baltimore Long-Term Ecological Study (LTER) site, and examined changes in P retention in SCMs across flow conditions. Results show that when compared with free-flowing stream reaches, the SCMs had significantly lower dissolved oxygen (%DO) and higher P concentrations, as well as lower mean areal retention rates and retention efficiencies of particulate P (PP). In the SCMs, PP areal retention rates and retention efficiencies changed from positive (indicating retention) during high flows to negative (indicating release) during low flows. We partially attribute the changing roles of SCMs from a PP sink to a PP source across flows due to SCM hydrologic mass balances, as well as physical sedimentation during high flows vs biogeochemical mobilization during low flows due to %DO reduction. This study demonstrates that in suburban/urban SCMs, P retained during high flow events can be released by P mobilizations during low flows. Cultivation of macrophytes and/or frequent sediment dredging provide potential solutions to retain both P and nitrogen in urban SCMs.