Abstract:
Phosphorus (P) is a limiting nutrient for seagrass and phytoplankton growth in Florida Bay. Dissolved phosphate concentrations in Bay waters are often at nanomolar levels. Shallow sediment represents the largest P reservoir because its carbonate sediment can strongly retain P. Sediment can act as a source or a sink of P to the overlying water depending on its P content. Utilizing sequential extraction technique this study provided the first spatial distribution of different forms of P in Florida Bay sediment. Total sediment P was fractionated into five different pools: (1) exchangeable (2) Fe-bound (3) biogenic carbonate (4) detrital apatite, and (5) refractory organic P. A strong gradient of decreasing P concentration was observed from the west (14.6 *mol g-1) to east (1.2 *mol g-1) across central Bay. The spatial pattern is consistent with distribution of both seagrass and phytoplankton that are limited by available P in the bay.
To study sediment-water exchange process, sorption experiments were conducted to quantify the capacity (zero equilibrium phosphate concentrations) and intensity (the distribution coefficients) of sediments in the exchange process. The study also quantified the effect of temperature and salinity on the exchange process and provided the first quantitative relationships between sorption parameters and the content of sediment P.
The quantitative relationships can be used to predict the dissolved phosphate concentration in the water column, particulary during sediment re-suspension events in the bay. They can also be used to predict the buffing capacity of the bay to external loading of P.
