HR: 0800h
AN: H41D-0335    [Abstracts]
TI: Investigations into the \delta $^{15}$N and \delta $^{13}$C of POM, Primary Producers, and Filter Feeders in the Florida Keys Coral Reef Tract
AU: * Lamb, K A
EM: klamb@rsmas.miami.edu
AF: Rosenstiel School of Marine and Atmospheric Science, 4600 Rickenbacker Causeway, Miami, FL 33149 United States
AU: Swart, P K
EM: pswart@rsmas.miami.edu
AF: Rosenstiel School of Marine and Atmospheric Science, 4600 Rickenbacker Causeway, Miami, FL 33149 United States
AB: In order to examine the possible influences of anthropogenic wastes on the Florida Keys coral reef tract, water column particulate organic matter \(POM\), primary producers, and filter feeders were sampled from within the coastal waters of the reef tract, and analyzed for \delta $^{15}$N and \delta $^{13}$C isotopic composition. The POM was found to have a mean \delta $^{15}$N value of +4.13\permil (\pm 1.03\permil\) and a mean \delta $^{13}$C value of -19.93\permil (\pm 0.58\permil). The \delta $^{13}$C values for POM across the entire reef tract were heavier inshore \(avg \delta $^{13}$C = -18.29\permil \(\pm 1.04\permil\)\) and became lighter offshore \(avg \delta $^{13}$C = -21.41\permil \(\pm 0.89\permil\)\), which is consistent with influences from benthic algae/seagrass closer to shore in contrast to open-marine influences offshore. The \delta $^{15}$N values for POM were neither temporally nor spatially interrelated, as the data showed no clear trend moving in either the inshore or offshore direction. Instead, our \delta $^{15}$N values for POM reflect a combined influence from nitrogen fixation \(\approx0\permil\), zooplankton and other suspended particles, and not anthropogenic wastes \($>$+10\permil\), as other authors claim. The mean isotopic composition of various primary producers suggests a nitrogen fixation source of nutrients to the reef system ({\it Halimeda sp.} (\delta $^{15}$N = 2.43\permil; \delta $^{13}$C = -18.04\permill), {\it Dictyota sp.} (\delta $^{15}$N = +2.86\permil; \delta $^{13}$C = -16.30\permil), {\it Thalassia sp.} (\delta $^{15}$N = 2.39\permil; \delta $^{13}$C = -10.32\permil)), while filter feeders were found to have a mean isotopic composition more similar to POM values (sponge \delta $^{15}$N = 4.95\permil; \delta $^{13}$C = -18.02\permil). Our data simply do not appear to show evidence of anthropogenic influence on the Florida Keys reef tract. Further more, we suggest that \delta $^{15}$N values of +4\permil, which have recently been suggested to indicate anthropogenic influences are not, in fact, indicative of sewage.
DE: 1871 Surface water quality
DE: 1030 Geochemical cycles (0330)
DE: 1040 Isotopic composition/chemistry
DE: 1050 Marine geochemistry (4835, 4850)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting