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PHOTOREACTIONS IN SURFACE WATERS AND THEIR ROLE IN BIOGEOCHEMICAL CYCLES
Citation:
Zepp, R G. PHOTOREACTIONS IN SURFACE WATERS AND THEIR ROLE IN BIOGEOCHEMICAL CYCLES. Presented at American Society of Limnology and Oceanography Aquatic Sciences Meeting, Albuquerque, NM, February 12-16, 2001.
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:
During the past decade significant interest has developed in the influence of photochemical reactions on biogeochemical cycles in surface waters of lakes and the sea. A major portion of recent research on these photoreactions has focused on the colored component of dissolved organic matter, referred to as CDOM. Photodegradation of CDOM contributes to loss of its UV and visible absorbance and fluorescence. Such "photobleaching", through interactions with climate-sensitive processes such as stratification, enhances the penetration of harmful UV-B radiation into surface waters and can influence the remote sensing of ocean color. In addition to these spectral effects, photoreactions of CDOM alter its biological availability and isotopic composition. Photochemical reactions in surface waters also enhance the cycling of metals such as iron, manganese, copper, and mercury, and result in the direct production of carbon dioxide, carbon monoxide, volatile hydrocarbons, nitrogen oxides, and sulfur-containing gases. This talk will use selected case studies to illustrate approaches that are being used to investigate these intriguing photoreactions in the laboratory and field.