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U.S. Department of the Interior
Geochemical Productivity Monitoring in Florida Bay
Calcification, photosynthesis, and respiration were measured during winter (March) and Summer (September) of 1999 on seagrass beds located in basins near Buchanon Bank (latitude 24o 55.416' N, longitude 80o 45.942' W) and Russell Bank (latitude 25o 03.756' N, longitude 80o 36.850' W) using the SHARQ. Geochemical parameters including pH, dissolved oxygen, fluorescence, and temperature were measured continuously through the SHARQ's flow-through analytical system (Figure 6 and 7) throughout the duration of incubation periods (from 20-28 hours). Water samples were removed from sample ports every 4 hours for alkalinity measurements via the Gran titration method using methods of Millero (1979). Dissolved oxygen, pH and alkalinity data were used to calculate rates of net calcification, photosynthesis, and respiration for each 4-hour interval between alkalinity measurements during incubation periods. Productivity parameters were calculated using the alkalinity anomaly technique (Smith and Key, 1975) and carbonate system equations of Millero (1979), whereby concentration of each parameter/T x SHARQ volume/SHARQ surface area = g C m-2 s-1. Sample interval rates were then used to calculate net daily production rates that were then used to derive average hourly rates of calcification, photosynthesis, and respiration.
Preliminary results indicate net dissolution of carbonate sediments in basins near Russell and Buchanon Banks ranging from approximately - 6 x 10-3 to - 0.11 g CaCO3/m2/hr, shown graphically as negative calcification values (Figure 8). Photosynthesis shows seasonal variation in both basins with highest rates of photosynthesis occurring during winter. It must be noted, however, that salinity and temperature were high relative to annual averages in both basins during summer measurements (salinity 42 and temperature 28.5-31oC near Russell Bank, and salinity 36.5 and temperature 28.2-29oC near Buchanon Bank). Additionally, a summer algal bloom near Russell Bank reduced photosynthetically active radiation (PAR) to 8% of surface values from water surface to bottom (4 ft. depth). These conditions are likely to have stressed the benthos resulting in net oxygen consumption and negative photosynthesis values for both sites, and higher respiration values for the basin near Russell Bank shown in Figure 8.
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U.S. Department of the Interior, U.S. Geological Survey
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Last updated: 04 September, 2013 @ 02:03 PM (KP)