Role of Aquatic Vegetation On Phosphorus Loads in the Everglades Agricultural Area.

Farm canals in the Everglades Agricultural Area (EAA) contain an abundance of floating and submerged aquatic vegetation (FAV, SAV). These species flourish in waters with high phosphorus (P) concentrations preventing the co-precipitation of P with the underlying limestone bedrock. Two most common variety of vegetation are water lettuce (Pistia stratiotes), and filamentous algae (Lyngbya sp.). Although these weeds are recognized as nuisance due to their ability to multiply and spread rapidly in open waters, they also serve as a P sink. To test the effects of FAV and SAV on water quality, a lysimeter experiment was stocked with water lettuce and filamentous algae over a 28-d period. Results would help quantify the uptake of various P fractions by these two aquatic species. The P concentration in all treatments reduced significantly after each water exchange. Treatments without sediments showed a higher efficiency for P removal, implying that the accumulation of sediments in farm canals could have a negative effect on exiting P loads. The presence of vegetation resulted in a reduction in water column P concentration; however this will only serve as a short‐term sink because of their high turn‐over rate. Results from the experiment were up-scaled to field conditions, where eight farms were monitored and sampled. The buildup of highly labile, organic, P-enriched sediments in farms canals within the EAA has been associated with the production of FAV. During drainage events, these particulates are susceptible to transport and contribute to the overall P load. A five step P-fractionation process was used to distinguish the recalcitrant versus the labile forms of P present in the particulates and compared to the individual farm canal sediments.