Phosphorus Characterization In the Everglades Agricultural Area Canal Sediments.

The Everglades Agricultural Area (EAA) located in South Florida is situated between Lake Okeechobee and the Everglades National Park. Nutrient enrichment from the EAA particularly P is thought to be responsible for the ecosystem changes in the Everglades. Best Management Practices (BMP) in the EAA are implemented since 1995 to reduce the P loads. Despite the success of the BMPs, there are concerns about accumulated sediments in the canals of the EAA that can be a potential P source to the overlying water column affecting the water quality in downstream ecosystems. Our objective was to characterize the sediments in the canals to their potential P release into the water column. We sampled three farm canals and three main district canals which drain the EAA farms and also supply irrigation water. Organic matter content, pH, bulk density, and total P for the sediments were determined at various depths. The pH of the sediments varied from 7.1 to 8.0. Organic matter content of the canals ranged from 20 to 70%.  Phosphorus was extracted into different pools using a fractionation scheme employed for sediments. The HCl extractable P was the dominant fraction with 59% to 70% of TP followed by residue-P fraction (17% to 34% of TP). This indicates that the majority of the inorganic P compounds in these sediments exist as bound to Ca and Mg which are generally a stable. The high HCl-P fraction may be due to the limestone bedrock bedrock of the EAA. The NaOH extractable P fraction was lower than the HCl–P and residue–P, but it may be subject to rapid flux. The NaOH extractable inorganic P may be affected by changes in redox of sediments, while NaOH extractable organic P may be subject to microbial transformations.