Controlling Floating Aquatic Vegetation to Reduce Labile Phosphorus Pools in Drainage Canal Sediments.

A significant portion of phosphorus (P) loads exiting the Everglades Agricultural Area (EAA) basin in south Florida is in organic particulate forms from canal sediments during farm drainage events. This study was initiated to investigate the role of controlling floating aquatic vegetation (FAV), such as water lettuce (Pistia stratiotes), on the formation of denser inorganic sediments and recalcitrant P forms on eight farms. It is hypothesized with FAV removal, more light penetrates the water column, potentially allowing for the co-precipitation of P with calcium and magnesium (Ca-Mg) into less labile minerals and reducing the accumulation of labile organic P in sediments. With FAV removal, more oxygen is present, possibly increasing redox potential and P-sorption. This change in redox potential can increase the capacity of iron and aluminum (Fe-Al) minerals to sorb P into more recalcitrant forms. Phosphorus fractionation was used to measure labile and recalcitrant P pools in eight farm canal sediments at the 0-2.5 cm depth in the EAA. Treatment canals implement aggressive FAV control, while control canals operate under normal management practices. The generation of denser inorganic mineral P may reduce P transport out of farm canals and reduce P loads into the downstream Everglades ecosystem. On all farms, residue and Ca-Mg-bound P pools have the highest concentration, and labile P has the lowest. There are no significant changes found between P pools on the farms over the sampling periods so far. In addition, x-ray diffraction (XRD) analysis is being used to assess the spatial and temporal change in mineral composition of canal sediment. In the future, sediments exported with drainage water will be subject to P-fractionation analysis to assess the speciation of P exported during pumping events.