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OFR-00-361 > introduction
U.S. Department of the Interior
Geochemical Productivity Monitoring in Florida Bay
The production and transport of biogenic carbonate sediments plays a key role in developing mud banks and altering circulation patterns in Florida Bay. Accurate measurements of sediment accumulation and production rates are required to determine how these processes have changed during the last century in response to anthropogenic influences. Estimates of sediment accumulation rates and annual production rates based on standing crop and turnover of various calcifying species are available from previous research (Stockman et al., 1967; Nelson and Ginsburg, 1986; Bosence, 1989; Frankovich and Zieman, 1994). However, a discrepancy exists between long-term accumulation rates and short-term productivity measurements. For example, Stockman et al. (1967) estimated an average carbonate sediment accumulation rate of 8.0 cm/1000 years using sediment thickness to Pleistocene bedrock and dates of the start of marine sedimentation at given localities. Bosence (1989) presents the most comprehensive calculation of short-term average carbonate sediment production rates in Florida Bay banks and lakes of 1,023 g m-2 yr-1 from standing crop surveys, growth rates, and short-term growth measurements of a variety of carbonate sediment producing organisms. This average production rate corresponds to an accumulation rate of 88.2 cm/1000 years, 910% more sediment than has accumulated based on Stockman et al.Ěs (1967) estimates. Clearly there is a large discrepancy between long term sediment accumulation and short-term productivity rates that cannot be accounted for by previous work on sediment dissolution rates (Walter et al., 1993; Walter and Burton, 1990) or transport of sediment out of the Bay. This suggests that either recent productivity rates have increased perhaps due to a change in water quality, accumulation measuring techniques under-estimate rates, or productivity measurement techniques over-estimate sediment production. Independent measures of sediment accumulation and productivity using different techniques are required to determine whether this incongruity is due to measurement and calculation techniques or to an actual change in productivity of the Bay. Identifying potential changes in sediment production resulting from anthropogenic influences is essential for predicting the effects of future resource management actions on the health of Florida Bay.
We have performed short-term productivity measurements in Florida Bay, including net calcification, photosynthesis, and respiration, using geochemical techniques that have proven successful for measuring production in carbonate reef and seagrass bed ecosystems (Smith, 1973; Barnes, 1983; Barnes and Devereux, 1984; Frankignoulle and Distéche (1984), Gattuso et al., 1993). Determining productivity geochemically provides an independent measure of sediment production that incorporates all carbonate producing species in a given area and dissolution of sediments, unlike standing crop and turnover methods which are based on select species and do not consider loss of sediment to dissolution.
Carbonate sedimentation and organic productivity (calcification, photosynthesis and respiration) are most effectively determined from precise, in situ measurements of alkalinity, pH, temperature, conductivity, and air:sea CO2 and O2 gas fluxes (Smith and Key, 1975; Millero, 1979; Barnes, 1983; Gattuso et al., 1993; Millero et al., 1993). Productivity was determined in basins by measuring temporal geochemical changes in a large incubation chamber called the Submersible Habitat for Analyzing Reef Quality (SHARQ) deployed on seagrass beds located in basins near Buchanon and Russell Banks. Productivity on Russell Bank was determined using an upstream/downstream sampling strategy to measure spatial geochemical changes across the bank.
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SOFIA Project: Geochemical Monitoring of Restoration Progress
U.S. Department of the Interior, U.S. Geological Survey
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Last updated: 15 January, 2013 @ 12:43 PM (KP)