Nutrient over enrichment and eutrophication in Florida Bay are believed to be the cause of the degradation of water quality which are evidenced by the mass mortality of turtle grass and nuisance algal blooms. Existing nutrient data indicate that nitrogen, mainly as ammonia, is abundant and phosphorus becomes the limiting nutrient. Therefore the supply of phosphate is critical to the onset and sustainment of phytoplankton blooms. The Florida Bay is a tropical estuary, which differs from a temperate one. Biogenic calcium carbonates, calcite and aragonite, are major components of the sediments and of the suspended matter. The adsorption and coprecipitation of phosphate on the suspended matter may play an important role in the cycling and transport of nutrients in Florida Bay. The release of phosphate from the suspended matter may be the source of this nutrient for the onset and sustainment of the algae bloom. In order to understand the fate of anthropogenic and natural phosphorus in the Florida Bay, the role of suspended calcium carbonate on its cycling and transport needs to be studied. 

Previous studies have shown that phosphate is strongly adsorbed on the surface of calcite and aragonite (Cole et al, 1953, de Kanel and Morse, 1978, Gaudette, 1980). This adsorption has been used to explain why calcium carbonate-rich sediments contain low concentrations of dissolved phosphate in their pore waters. Among the various natural particles goethite (iron oxide) has the strongest adsorption capacity for phosphate (Hingston et al. 1974; Khalid et al, 1977, Berner, 1973). Therefore, the content of iron hydroxide in the sediments and suspended matter is an important factor in regulating the adsorption capacity.

The resuspension of sediments has been speculated as a mechanism to supply the phosphate to the water column by desorption of phosphate from the solid surface. Krom and Berner (1980) have shown that the desorption is more rapid than adsorption in anoxic marine sediments. There presently are no data available for desorption kinetics of phosphate from calcium carbonate particles. To understand the dynamics of phosphate cycling and quantify its flux in Florida Bay, it is necessary to measure the adsorption and desorption kinetics of phosphate on the suspended matter in the Bay. We proposed to study the kinetics of adsorption and desorption of phosphate on the surface of suspended particles collected in Florida Bay.

There presently are little systematic measurements of the carbonate system in Florida Bay water. An understanding of the carbonate system in the Bay is important in the determination of the saturation state of calcite and aragonite particles that can adsorb phosphate as well as examining the uptake of inorganic carbon by phytoplankton. The carbonate system can be characterized (Millero, 1995) by measuring two of the variables that control the system (pH, TA, total alkalinity; TCO₂, total carbonate; and pCO₂, the partial pressure of CO₂). The carbonate system can be affected by the precipitation and dissolution of calcium carbonates and the production and destruction of phytoplankton. Measurements of pH are also important in understanding the dynamic nature of biogeochemical processes, and reflect the state of all the acid-base systems present in the water. The eutrophication induced phytoplankton bloom, hence the intensive photosynthesis, can locally decrease the pCO₂ and increase the pH. Lapointe et al. (1996) have reported a pH value of 9.4 in Florida Bay water which was due to this effect. The precipitation of calcium carbonate may occur at this high pH in seawater already supersaturated with respect to calcium carbonate (Berner and Morse, 1974). The precipitation of calcium carbonate has been reported to be triggered by phytoplankton blooms in some shallow lakes (Murphy, et al., 1983). This suggests that the precipitation of calcium carbonate caused by phytoplankton blooms may play an important role in the cycling and transport of nutrients in Florida Bay through adsorption and coprecipitation of nutrient compounds (e.g., PO₄^3- and NH₄⁺) on the suspended matter. Studies are needed to examine how the inorganic formation of calcium carbonate can control the fate of anthropogenic produced nutrients in the Florida Bay.

To understand the carbonate system in Florida Bay, we plan to make measurements of carbonate parameters (pH, TA, and TCO₂) in Florida Bay. Measurements of these three carbonate parameters simultaneously will insure the internal consistency of measurements from individual parameters. The pCO₂ can be calculated from these measured values using thermodynamic relationships (Millero, 1995). These measurements can be used to calculate the saturation state of calcium carbonate, and detect the effect that phytoplankton blooms have on the carbonate system in Florida Bay waters.

Our study will be closely linked with Dr. Mark Dortch of the Army Corps of Engineers in the effort to develop a Florida Bay water quality model. The phosphorus cycle in Florida Bay is one of the center piece constituent of this water quality model (Dortch, personal communication, 1997). The model requires the knowledge of partitioning of phosphorus between different reservoirs, such as a water column, suspended matter and sediment; the speciation of phosphorus in each reservoir (organic and inorganic phosphorus) and their biological availability; the influence of pCO₂, total CO₂, pH, salinity, temperature and other environmental factors on the phosphorus transformation between different reservoirs (Mucci, 1986; Burton and Walter, 1990). Our measurements of carbonate parameters, as well as the calculated parameters using our carbonate thermodynamic model (such as the saturation state of calcite and aragonite), will fully characterize the carbonate system in Florida Bay, and provide the essential data for water quality modeling. One of key aspects in the phosphorus cycle is the extent of the release of phosphorus by the desorption process during resuspension events. A study in Lake Okeechobee indicates that resuspended sediment increases particulate phosphorus in the water column during resuspension, but little of the particulate phosphorus is in a dissolved form. Total phosphorus in the water column rapidly drops off following cessation of resuspension due to the settling of particulate matter (Dortch, personal communication, 1997). The kinetics of adsorption and desorption will be different in seawater media (Cole et al, 1953, de Kanel and Morse, 1978). Our laboratory and field studies will provide the useful parameters for modeling the phosphorus cycle in Florida Bay.