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PHOTOCHEMICAL AND BIOLOGICAL DEGRADATION OF CDOM IN WATERS FROM SELECTED COASTAL REGIONS OF THE SOUTHEASTERN UNITED STATES
Citation:
Zepp, R G., M. A. Moran, E. White, AND E. Stabenau. PHOTOCHEMICAL AND BIOLOGICAL DEGRADATION OF CDOM IN WATERS FROM SELECTED COASTAL REGIONS OF THE SOUTHEASTERN UNITED STATES. Presented at 2002 Ocean Sciences Meeting, Honolulu, HI, February 11-15, 2002.
Impact/Purpose:
The overall objective of this task is to develop quantitative relationships for assessing the vulnerability of aquatic resources to global change. The task will contribute experimental and modeling tools for assessments of the interactions of global climate and UV changes with coral reefs and selected watersheds and estuaries in the U.S. These activities are contributing primarily to two APGs in the ecosystems component of the Global Change Research Multiyear Plan: the 2006 APG (APG 3) on building the capacity to assess global change impacts on coastal aquatic ecosystems, including coral reefs and estuaries and the 2004 APG (APG 2) on building capacity to assess and respond to global change impacts on selected watersheds. One major task objective is to assess interactions of global warming and UV exposure that are contributing to the observed coral bleaching and disease. Our lab is working with scientists at the NHEERL Gulf Ecology Lab to characterize UV exposure and effects at several coral reef sites. Other research in this task is examining the interactions between UV-induced breakdown of refractory organic matter in estuaries and coastal areas that enhance UV penetration into the water and concurrently form biologically-labile nitrogen-, phosphorus- and carbon-containing substances that stimulate productivity and microbial activity. This task also involves research in central Brazil that is part of the Large Scale Biosphere Atmosphere Experiment (LBA). The objectives of this project are to assess the impacts of land use and climatic changes on soil nutrient cycles and microbiota, trace gas exchange and water quality in the Brazilian cerrado. This work involves a close collaboration between EPA and a group of scientists from the Department of Ecology, University of Brasilia, Brazil. Other objectives of this task are to assess the interactions of land use and climate changes with the ecological functioning of streams in watersheds of the Piedmont region of the southestern U.S.
Description:
Biological and photochemical degradation of colored dissolved organic matter (CDOM) were investigated in controlled experiments using waters from southeastern U.S. estuaries, from the Mississippi River plume and Gulf of Mexico, and from the coastal shelf region in the Florida Keys. Results of the experiments generally indicated that photoreaction results in decreases in the absorption and fluorescence of terrestrially- derived CDOM as well as CDOM derived from seagrasses. Changes in both absorption spectra (increased spectral slope coefficients) and excitation-emission spectra (hypsochromic shifts) also were observed. Terrestrially-derived CDOM photoreacts to produce biologically-labile photoproducts (BLPS) that were measured using cumulative bacterial oxygen consumption during post irradiation-incubation as an index. The spectral slopes of apparent quantum yield spectra for BLP production were similar to those observed for carbon monoxide production and BLP production rates in sunlight were of the same order of magnitude as those for direct DIC photoproduction. Comparisons of photobleaching and BLP production rates for terrestrially-derived CDOM in the Mississippi River plume on the Gulf of Mexico surface and for algal- derived CDOM in chlorophyll maxima below the surface indicate that these two primary CDOM sources may have quite different photoreactivity. Photobleaching and BLP production for the algal derived CDOM were significantly slower. than for the terrestrially-derived CDOM from two sites in the plume west of the mouth of the Mississippi River.