Citation:

ZEPP, R. G. AND R. JONES. FACTORS INFLUENCING LIGHT-INDUCED MORTALITY OF ENTEROCOCCI IN SEDIMENT SUSPENSIONS. Presented at ASLO 2007 Aquatic Sciences Meeting, Santa Fe, NM, February 04 - 09, 2007.

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:

Contamination of recreational waters by pathogenic microorganisms occurs through complex, poorly understood interactions involving variable microbial sources, hydrodynamic transport, arid microbial fate processes. Fecal indicator bacteria such as enterococci have been used to assess such contamination. Here we report laboratory studies of the sorption and light-induced mortality of enterococci in suspensions of sediments from streams and ponds in the Piedmont region of the southeastern United States. The studies indicated that enterococci are strongly associated with the suspended and bottom sediments of these systems. Size fractionation studies indicated that the bacteria were predominantly partitioned to clay-sized sediments that are readily suspended in the water column by currents or wind action. Direct exposure of the sorbed bacteria to solar radiation resulted in rapid mortality of the enterococci with half-lives of a few minutes. In the dark, mortality half-lives were much longer, on the order of several days. Other studies indicated that the UV component of the solar radiation was mainly responsible for inducing mortality.

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