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Soluble reactive phosphorus stream loads decrease following legacy sediment removal in a restored floodplain, Big Spring Run, PA
Citation:
Wilhelm, J., J. Weitzman, P. Mayer, R. Walker, Ann Keeley, AND Ken Forshay. Soluble reactive phosphorus stream loads decrease following legacy sediment removal in a restored floodplain, Big Spring Run, PA. American Geophysical Union Annual Meeting, Washington, District Of Columbia, December 10 - 13, 2018.
Impact/Purpose:
Increases in downstream concentrations of soluble reactive phosphorus (SRP) in streams and rivers can degrade regional water quality, and lead to longstanding water issues like eutrophication. At Big Spring Run (BSR) located in Lancaster, Pennsylvania, an ecosystem restoration was undertaken to remove legacy sediment generated from previous historic development damming effects, with the aim to reduce nutrient loads and improve water quality. We evaluated seasonal response of SRP and other water quality parameters in surface and groundwater at a restored floodplain. A mass balance model of upstream compared to downstream surface water SRP loads showed overall net retention (upstream-downstream load) within the floodplain system with a decrease in SRP flux observed from pre-restoration (16282.4 kg yr-1 ± 1642.7) (mean±s.e.) to post-restoration (10264.4 kg yr-1 ± 707.7). We determine changes of SRP concentrations following restoration, and assess whether the restored floodplain is stablizing through chelation, solubilization, and reduction of metal bound P through complexation. The purpose of this study is to assess soluble reactive phosphorous output from the basin to determine the drivers loading SRP to the system following legacy sediment removal. Understanding soluble reactive phosphorous response to a restored floodplain system will help watershed managers and policy makers to make decisions about restoration practices as a nutrient management approach.
Description:
Soluble reactive phosphorus (SRP) is the labile form of phosphorus (P) used by plants and algae and often attributed to eutrophication and water quality degradation. In streams with deeply incised banks, often associated with downcutting of legacy sediments, stream water and groundwater are physically separated from the floodplain, which limits plant uptake. When legacy sediments are removed, the surface water and groundwater are better connected to plant and algal uptake because of the renewed connectivity with the restored hydric floodplain, but there is also potential for mobilization of previously sorbed and unavailable P due to the formation of anoxic conditions. The stated purpose of restorations involving legacy sediment removal is to reduce sediment and nutrient loads. Here we evaluated the seasonal response of SRP and other water quality parameters in surface and groundwater at Big Spring Run (BSR) in Lancaster, Pennsylvania, where a legacy sediment removal/floodplain wetland restoration project has been monitored since 2008 (restoration completed November 2011). Our study found that the relative contribution of SRP constituents from upstream to downstream systems decreased overtime in response to legacy sediment removal. A mass balance model of upstream compared to downstream surface water SRP loads showed overall net retention (upstream-downstream load) within the floodplain system with a decrease in SRP flux observed from pre-restoration (16282.4 kg yr-1 ± 1642.7) (mean±s.e.) to post-restoration (10264.4 kg yr-1 ± 707.7), a net reduction of 37%. We found that immediately following restoration, winter and spring SRP concentrations were lowest, but increased over time. Three years following restoration, summer and fall SRP values were generally lower. We discuss possible mechanisms of mobilization and retention of SRP including solubilization, uptake, and the effects of reducing-conditions by post-restoration monitoring during 2008-2011. Our evaluation of post-restoration conditions of SRP is intended to inform future decisions about similar restoration practices, and reveal benefits and trade-offs of restoration as a nutrient management approach.