Floating Aquatic Vegetation Suppression Effects on Discharged and 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 the form of organic particulates from biological sources during farm drainage events. This study was initiated on four treatment-control farm pairs over a five year period to investigate the role of suppressing floating aquatic vegetation (FAV), such as water lettuce (Pistia stratiotes), on the formation of more recalcitrant inorganic P forms in farm canal sediments. Treatment canals implemented aggressive FAV suppression, while control canals operated under normal management practices. It is hypothesized that with FAV suppression, co-precipitation of P with calcium and magnesium (Ca-Mg) into less labile, more recalcitrant minerals is increased due to more light penetrating the water column, while P sorption with iron and aluminum increases with higher dissolved oxygen and redox potential. Phosphorus fractionation was used to measure labile and recalcitrant P pools in the eight farm canal sediments at the 0-2.5 cm depth, as well as particulates exported with drainage water during pumping events. On most farms, sediment residue and Ca-Mg-bound P pools had the highest percent of total P ranging from 23.6 to 73.4% for Ca-Mg-bound and 6.1 to 63.6% residue P, while labile P had the lowest between 0.5 to 5.5%. In the discharged particulates, Ca-Mg-bound-P had the highest percentage (28.2 to 61.0%) and labile P was the lowest (0.9 to 19.1%). While labile P was the smallest pool, it was higher in the discharged particulates than canal sediments. The generation of denser inorganic mineral P may reduce P transport out of farm canals and reduce P loads into the downstream Everglades ecosystem.