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INFLUENCE OF DISSOLVED ORGANIC MATTER ON AGROCHEMICAL PHOTOREACTIONS IN AQUATIC ENVIRONMENTS
Zepp, R G., E. White, AND P. P. Vaughan. INFLUENCE OF DISSOLVED ORGANIC MATTER ON AGROCHEMICAL PHOTOREACTIONS IN AQUATIC ENVIRONMENTS. Presented at 221st American Chemical Society National Meeting, San Diego, CA, April 1-5, 2001.
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.
Pioneering studies by Don Crosby and co-workers demonstrated that the sunlight-induced dissipation of agrochemicals in water often is strongly affected by natural constituents in the water such as nitrate and dissolved organic matter. In this presentation, the focus is on the role played by the colored component of dissolved organic matter, referred to as CDOM, in (a) controlling the availability of solar UV radiation in aquatic systems and (b) initiating indirect agrochemical photoreactions. CDOM, which is a mixture of lignocellulose-derived polyelectrolytes that are derived mainly from the decay of terrestrial vegetation, constitutes the majority of the organic carbon in most freshwater, estuarine and coastal environments. On irradiation, CDOM and its complexes with metals such as iron, produce excited state and reactive oxygen species that mediate indirect reactions. This talk will discuss recent approaches that are being used to study these intriguing photoreactions in the laboratory and field with particular emphasis on factors affecting the production of hydroxyl radicals.