Water--Phosphorus content

Different physiochemical processes control phosphorus storage in subtropical versus temperate estuaries; however, few studies are available on sediment phosphorus storage from the subtropics. In this study, solid-phase phosphorus pools of northeastern Florida Bay's sediments were examined by sequential chemical extractions, separating phosphorus into exchangeable, iron-bound, calcium-bound, and residual organic fractions. Calcium-bound phosphorus was the dominant fraction, accounting for approximately 60% of the total phosphorus and 93% of the inorganic phosphorus. Residual organic phosphorus was the second dominant fraction, accounting for 37% of the total phosphorus. In contrast to calcium-bound and residual organic phosphorus, the concentration of iron-bound phosphorus was low, indicating a limited role of iron in long-term phosphorus storage. The fine-grained carbonate sediments of Florida Bay probably account for the large pool of calcium-bound phosphorus, while the proximity of the mangroves to the northeastern section of the Bay may account for the high residual organic pool of phosphorus.

Phosphorus exchange between sediment-water system was observed under molecular diffusion and turbulent condition. Some experiments were focused on adsorption behavior under common environmental factors (e.g., temperature, salinity and pH). The sediment suspension was found to have a significant effect on phosphorus movement to the upper layer water. Higher temperature increased the release of phosphorus from kaolinite and lake sediments, and the effect was almost nil for bentonite. Temperature effect was pronounced on kaolinite where relatively higher release of phosphorus observed. Salinity effect on lake sediments was not significantly important for release or adsorption. Bentonite showed a release of phosphorus after addition of salts. Adsorption on kaolinite was found higher at pH 4.7-5.0. The study was also focused on the estimation of phosphorus partitioning due to molecular diffusion and turbulent mixing. The observed behavior of the phosphorus exchange under different conditions showed an agreement with the observations by the other investigators.