Legacy Phosphorus Assessment in the Western Lake Erie Basin – Phase 2 (FY25 UK)

Abstract/Scope of Work In phase I of the Western Lake Erie Basin (WLEB) legacy phosphorus (P) assessment, various approaches were used to quantify the magnitude of legacy P loss from fields and watersheds. Results have shown that 50-80% of dissolved reactive P (DRP) loss through subsurface leachate is the result of legacy P in these landscapes (Osterholz et al., 2022; Williams et al., 2022; Williams et al., 2023; Osterholz et al., in review). The project examined P desorption kinetics through laboratory flow-through experiments (Penn et al., 2022), the spatial distribution of legacy P stores within a headwater watershed (Mumbi et al., in review), and P transformations and transport in agricultural ditches (Casillas-Ituarte et al., 2019). Studies were also performed that present a laboratory study examining the effect of rainfall intensity and antecedent soil moisture on legacy P leaching losses, the use of P isotopes for tracing legacy P transport, the effect of hotspots on field and watershed P loss, and P adsorption kinetics. This is in addition to the sample and data contributions to the USDA National Legacy P Project (e.g., national legacy soil P quantification, APLE and SWAT modeling efforts, and laboratory method development). The consistent concept that spans across individual projects and studies has been the importance of the interaction between soil chemistry and hydrology for controlling legacy P in the WLEB. As a result, in phase II of the project, we plan to dive deeper into this interaction to better understand the processes controlling both legacy P magnitude and transport, and also expand our work to include particulate P losses.