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ROLE OF THE PHOTO-FENTON REACTION IN THE PRODUCTION OF HYDROXYL RADICALS AND PHOTOBLEACHING OF COLORED DISSOLVED ORGANIC MATTER IN A COASTAL RIVER OF THE SOUTHEASTERN UNITED STATES
Citation:
White, E. M., P. P. Vaughan, AND R G. Zepp. ROLE OF THE PHOTO-FENTON REACTION IN THE PRODUCTION OF HYDROXYL RADICALS AND PHOTOBLEACHING OF COLORED DISSOLVED ORGANIC MATTER IN A COASTAL RIVER OF THE SOUTHEASTERN UNITED STATES. AQUATIC SCIENCES 65(4):402-414, (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:
Photochemical reactions involving colored dissolved organic matter (CDOM) in natural waters are important determinants of nutrient cycling, trace gas production and control of light penetration into the water column. In this study the role of the hydroxyl radical ((OH)-O-.) in CDOM photodegradation was explored as well as the contribution of photo-Fenton chemistry to (OH)-O-. formation. Photochemically produced (OH)-O-. was observed under aerobic and dioxygen-depleted conditions in highly colored, acidic natural water samples obtained from a freshwater reach of the Satilla River, a river in the southeastern United States. Net aerobic (OH)-O-. formation along with the production of hydrogen peroxide and Fe(II) provided evidence of photo-Fenton produced (OH)-O-.. A reduction in (OH)-O-. production in the presence of iron chelators further suggests the importance of iron and the photo-Fenton reaction in this water. Apparent quantum yield values for the photochemical production of (OH)-O-. were determined from 300-320 nm. In addition, the relationship between (OH)-O-. photoproduction and effects of irradiation on the optical properties of CDOM was examined. Changes in the light absorption and fluorescence properties of water samples from the Satilla River and other natural waters were compared to (OH)-O-. production rates. The ability of constituents of Satilla River water, principally the dissolved organic matter, to scavenge (OH)-O-. was also considered. Results indicate that the photo-Fenton reaction accounts for more than 70% of total photochemical (OH)-O-. production in Satilla River water. Given the significant levels of (OH)-O-. produced in this water, it is possible that (OH)-O-. influences CDOM photobleaching.