Parameterizing Functions of Soil-Water Soluble Reactive Phosphorus Flux for an Ecohydrological Model of Formerly Drained Riparian Wetlands in the Lake Champlain Basin

Elevated phosphorus (P) concentrations in numerous freshwater lakes in North America are leading to a higher frequency of potentially harmful cyanobacteria blooms. Lake Champlain is an example and in 2016 the U.S. EPA passed a stringent P total maximum daily load limit for the Vermont tributaries to the lake. Wetland restoration may help reduce P loading by increasing water and sediment retention and over 4000 potential wetland restoration sites have been identified in Vermont. Most candidate sites overlay historically drained agricultural fields with potentially high existing amounts of legacy soil P. The fate and transport of this legacy soil P will be affected by hydrologic modifications. We are developing a wetland biogeochemical process model to be used in conjunction with hydraulic models (e.g., HEC-RAS) to estimate the effect of restoration activity on floodplain P balance. This poster focuses on the development of functions that relate soil properties of Vermont wetlands to P sorption dynamics and soluble reactive P (SRP) diffusion rates across the soil-water interface. As expected, results from spring flood monitoring and lab simulated floods indicate that soil-to-water SRP flux is greater under lower floodwater oxygen conditions and negatively correlated with time since farming. Future research will whether simple soil tests (e.g., water extractable P) and/or widely collected state soil test data (e.g., Modified Morgan extractable P, Al, Fe used in the Northeast) could be used to estimate flux parameters in process models that simulate the effects of wetland restoration on P dynamics.