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Spatial and Temporal Variability of Solar Ultraviolet Exposure of Coral Assemblages in the Florida Keys: Importance of Colored Dissolved Organic Matter
Citation:
ZEPP, R. G., G. C. SHANK, E. STABENAU, K. W. PATTERSON, M. J. CYTERSKI, W. S. FISHER, E. BARTELS, AND S. L. ANDERSON. Spatial and Temporal Variability of Solar Ultraviolet Exposure of Coral Assemblages in the Florida Keys: Importance of Colored Dissolved Organic Matter. LIMNOLOGY AND OCEANOGRAPHY. American Society of Limnology and Oceanography, Lawrence, KS, 53(5):1909-1922, (2008).
Impact/Purpose:
The overall objective of this task is to develop quantitative relationships for assessing the vulnerability of aquatic ecosystems (freshwater and coastal) and their services 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. and Brazil These activities are contributing to two APGs in the ecosystems focus area of the Global Change Research Multiyear Plan: the 2008 APG (APG 2) on developing information and tools that managers will use in their decision-making about how to adapt to the effects of global change on aquatic ecosystems; and the 2010 APG (APG 3) on providing information and models that will support development of biocriteria for corals. 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 in the Florida Keys. This collaboration will contribute to one ERD APM in 2006 and three joint NERL-NHEERL APMs in the 2008 - 2010 period. Other research is examining the effects of changing climate and UV on microbial activity in waters close to beaches in the U.S. Work is being completed on the interactions of land use and climate changes with the ecological functioning of streams in watersheds of the southeastern U.S. The task also includes two sub-tasks that are funded mainly by funds-in IAGs. One sub-task funded by NASA involves research in central Brazil that is part of the Large Scale Biosphere Atmosphere Experiment (LBA). This work involves a close collaboration between EPA and a group of scientists from the Department of Ecology, University of Brasilia, Brazil. 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. Another sub-task funded by the Office of Naval Research is examining interactions between nitrogen and organic substances in aquatic ecosystems that produce the colored dissolved organic matter (CDOM) that controls penetration of solar UV radiation into coastal waters.
Description:
Solar UV radiation can have deleterious effects on coral assemblages in tropical and subtropical marine environments. We present evidence that UV exposure of coral reefs in the Florida Keys is controlled primarily by chromophoric dissolved organic matter (CDOM) in waters overlying the reefs. Diffuse attenuation coefficients (Kd) were determined using downwelling vertical profiles of UV and visible radiation obtained at sites located in the Middle and Lower Keys and the Dry Tortugas. Significant linear correlations were observed between dissolved organic carbon (DOC) and Kd values in the UV spectral region (305 - 380 nm) for inshore and reef tract sites but no significant correlations between Kd and DOC were found further offshore in bluewater sites.
