Impact of Suppression of Floating Aquatic Vegetation on Canal Sediment Properties in South Florida.

A significant portion of phosphorus (P) loads discharged from the Everglades Agricultural Area (EAA) in south Florida is in organic particulate forms from biologic sources during farm drainage events. This study was initiated on eight farms to investigate the role of suppressing floating aquatic vegetation (FAV), such as water lettuce (Pistia stratiotes), on the formation of denser, inorganic sediments and recalcitrant P forms in farm canal sediments. It is hypothesized that with FAV suppression, more light penetrates the water column, potentially allowing for the co-precipitation of P with calcium and magnesium (Ca-Mg) into less labile, more recalcitrant minerals. Also as FAV is suppressed, redox potential can be increased by higher levels of dissolved oxygen, promoting the sorption of P with iron and aluminum minerals to form denser compounds. 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, as well as sediments exported with drainage water during drainage events. Treatment canals implement aggressive FAV suppression, while control canals operate under normal management practices. In addition, x-ray diffraction (XRD) analysis was used to assess the spatial and temporal change in mineral composition of canal sediment. 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, while labile P has the lowest. There are no significant changes found between P pools over two treatment years.