HR: 0800h
AN: H31B-1297    [Abstracts]
TI: Assessing the Effects of Land use Change on Southwest Florida Estuaries Using Stable Isotopes of Organic Carbon
AU: * Dvorak, M
EM: mdvorak@iastate.edu
AF: Iowa State University, Department of Geological and Atmospheric Sciences 253 Science 1, Ames, IA 50010 United States
AU: Mora, G
EM: gmora@iastate.edu
AF: Iowa State University, Department of Geological and Atmospheric Sciences 253 Science 1, Ames, IA 50010 United States
AU: Surge, D
EM: donna64@unc.edu
AF: University of North Carolina, Department of Geological Sciences Campus Box #3315, Mitchell Hall, Chapel Hill, NC 27599 United States
AB: Many estuaries in southwestern Florida, including those within Rookery Bay National Estuarine Research Reserve (RBNERR), have different land-use characteristics that have resulted in the fragmentation of natural landscapes and changes in estuarine ecosystem structure. Although water quality monitoring is in place within the reserve, the effects of agriculture and residential development on the estuarine ecosystems are unknown. Four estuaries within RBNERR that are experiencing different types of disturbance were chosen to examine the potential impacts of land-use change on primary productivity. One of these estuaries is relatively undisturbed, thereby serving as our control site. To determine how land use is affecting estuarine productivity, we measured concentrations of particulate organic matter (POM) and chlorophyll-a. Since POM could also come from terrestrial sources, we measured carbon isotope values of POM because terrestrial POM typically shows values lower than -25%. Because tidal fluctuations could affect POM values, samples were collected for both high and low tide. We found that the carbon isotope composition of POM ranges from -12 to -36% in the studied estuaries. The more negative values occur in the freshwater end members and indicate a terrestrial source of organic matter, whereas the less negative values were found near the saltwater end member and likely indicate aquatic sources of POM. Initial results also show that there is an increase in terrestrial sources of POM during low tide. This pattern is consistent across all four estuaries. POM maximum concentrations are on average 176 ug/L higher across all estuaries during low tide, indicating an increase in terrestrial sources of POM as well as an increase in primary production. Henderson Creek has a watershed dominated by residential and urban development and has an average maximum POM concentration that is 447 ug/L higher than the other three estuaries. These high POM concentrations, combined with elevated chlorophyll-a concentrations and lower carbon isotope composition of POM, strongly indicate increased primary productivity in Henderson Creek. These results suggest that anthropogenic changes in land use on this watershed resulted in the observed increase in primary productivity.
DE: 0442 Estuarine and nearshore processes (4235)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0478 Pollution: urban, regional and global (0345, 4251)
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1803 Anthropogenic effects (4802, 4902)
SC: Hydrology [H]
MN: Fall Meeting 2005