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PHOTOREACTIVITY OF CHROMOPHORIC DISSOLVED ORGANIC MATTER (CDOM) DERIVED FROM DECOMPOSITION OF VARIOUS VASCULAR PLANT AND ALGAL SOURCES
Citation:
Zepp, R G., M. A. Moran, AND D. Koopmans. PHOTOREACTIVITY OF CHROMOPHORIC DISSOLVED ORGANIC MATTER (CDOM) DERIVED FROM DECOMPOSITION OF VARIOUS VASCULAR PLANT AND ALGAL SOURCES. Presented at 225th American Chemical Society National Meeting, New Orleans, LA, March 23-27, 2003.
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:
Chromophoric dissolved organic matter (CDOM) in aquatic environments is derived from the microbial decomposition of terrestrial and microbial organic matter. Here we present results of studies of the spectral properties and photoreactivity of the CDOM derived from several organic matter sources found in watersheds and coastal regions of the Southeastern United States. The species examined were derived from microbial decomposition of litter from two woody vascular plants (live oak, loblolly pine), two non-woody vascular plants (Spartina, the sea grass Thalassia) and the algal species Synechococcus. Absorption properties of the algal CDOM were significantly different that those of the CDOM derived from the terrestrial, vascular plant sources. For example, the spectral slope coefficient of the UV-visible spectra ranged from 0.028 nm(-1) for the Synechococcus CDOM to 0.010-0.015 nm(-1) for the vascular plant derived CDOM. Photoreaction of all the CDOM on exposure to simulated solar radiation resulted in increases in the spectral slope coefficients and blue shifts in their excitation-emission fluorescence spectra. The photodegradation rate constant of the Synechococcus CDOM, judged by its photobleaching at 350 nm, was almost an order of magnitude greater than that of the terrestrially derived CDOM. Exposure of CDOM from these sources produced measurable biologically labile photoproducts, even in extensively degraded material.