Temperature,redox, and amendments alter wetland soil inorganic phosphorus retention dynamics in a Laurentian Great Lakes priority watershed

Surface water phosphorus loading must be reduced to improve water quality and decrease harmful algal blooms. Many wetlands have a natural capacity to retain inorganic reactive PO₄^3? via soil sorption. However, soil PO₄^3? retention capacity is finite and may be limited by soil legacy phosphorus effects in agricultural and urban areas. This study evaluated soil PO₄^3? retention in soils from a wetland constructed on former agricultural land in the Lake Erie, Maumee River watershed targeted for nutrient load reduction. Soil PO₄^3? sorption isotherms were evaluated under cool (10 °C), warm (22°), aerobic, and anaerobic treatments to determine changes in PO₄^3? retention due to environmental conditions and estimate seasonal changes in PO₄^3? sorption. The soils displayed a strong capacity for PO₄^3? retention by sorption. However, results indicate that cooler temperatures and anaerobic conditions decreased PO₄^3? sorption and lowered retention rates at PO₄^3? concentrations observed in the region. Soil amendment experiments investigated opportunities to increase PO₄^3? retention because many soils display elevated phosphorus concentrations due to historic land use, limiting their ability to adsorb additional PO₄^3?. Amendments increased PO₄^3? retention capacity compared to unamended soils in the presence of high PO₄^3? concentrations, suggesting soil PO₄^3? retention can be improved in areas where natural storage capacity has been exhausted. Results from this study can inform natural resources managers in the Laurentian Great Lakes and elsewhere when identifying potential nutrient reduction wetland locations and assist with developing operational guidelines to optimize PO₄^3? retention and water quality improvements using wetlands.