Water management practices in South Florida are already being altered in an effort to restore the Everglades and Florida Bay. Resulting changes in water chemistry will first affect biogeochemical processes, and may result in changes in species distributions (such as seagrass, algae, etc.) in the Bay. Monitoring changes in biogeochemical processes is critical to early identification of ecological response to restoration and predicting changes in species distribution within the Bay.

We have developed and tested techniques for measuring critical biogeochemical processes in the Bay including carbonate sediment production by calcifying organisms and dissolution, photosynthesis, and respiration (referred to collectively as productivity). Carbonate sedimentation and organic productivity are most effectively determined from precise, in situ measurements of alkalinity, pH, temperature, conductivity, and air:sea CO₂ and O₂ gas fluxes. Productivity on Russell Bank was determined in July 1998 and March 1999 using an "upstream/downstream" technique for measuring spatial geochemical changes. Sontek current meters were deployed on the banks to characterize current velocity and direction. Geochemical parameters were measured at upstream and downstream stations along north/south transects across the bank every 4 hours. Maximum rates of productivity during incubation periods were used to calculate rates of calcification, photosynthesis, and respiration. Productivity in basins adjacent to Buchanon and Russell Banks was determined in March 1999 by measuring temporal geochemical changes over 24 hour periods in a large, in situ incubation chamber that isolates the mass of water overlying benthic substrate. Basin water was turbid due to sediment resuspension from winter storms.

Preliminary results of Russell bank productivity measurements indicate maximum rates of net calcification of 0.54 g CaCO₃ m^-2day^-1 during July and 0.18 g CaCO₃ m^-2day^-1 during March. Estimates of annual production rates from these measurements suggest net sediment accumulation rates of approximately 0.1 mm yr ^-1 . Maximum rates of photosynthesis in Russell Bank ranged from 0.03 g carbon m^-2day^-1 in March to 0.67 g carbon m^-2day^-1 in July. Results of basin productivity measurements indicate net dissolution of carbonate sediments during turbidity events resulting from sediment resuspension. Net rates of photosynthesis for basins were -0.3 g carbon m^-2day^-1 near Buchanon Bank (indicating that respiration dominates over photosynthesis) and 0.08 g carbon m^-2day^-1 near Russell Bank. Rates of carbonate sediment production and photosynthesis measured geochemically are similar to rates determined by measuring accumulated calcium carbonate sediments and standing crops of seagrasses in the Bay. These field investigations indicate that geochemical productivity measurements are an effective measure of these biogeochemical processes.

Biogenic calcification, photosynthesis, and respiration are sensitive to changes in water quality including salinity and nutrients. Monitoring these biogeochemical processes as water quality changes during restoration efforts can be used as an effective ecological performance measure for restoration progress, and will provide insight into the link between biological function and environmental quality.

(This abstract was taken from "Programs and Abstracts - 1999 Florida Bay and Adjacent Marine Systems Science Conference". (PDF, 1 MB))

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