Citation:

ZEPP, R. G., R. JONES, J. WILLIS, M. J. CYTERSKI, AND M. MOLINA. PREDICTIVE MODELING OF LIGHT-INDUCED MORTALITY OF ENTEROCOCCI FAECALIS IN RECREATIONAL WATERS. Presented at Society of Environmental Toxicology and Chemistry Annual Meeting, Milwaukee, WI, November 11 - 15, 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:

One approach to predictive modeling of biological contamination of recreational waters involves the application of process-based approaches that consider microbial sources, hydrodynamic transport, and microbial fate. This presentation focuses on one important fate process, light-induced mortality. Fecal indicator bacteria such as enterococci have been used to assess possible contamination of beaches and other recreational waters. Past studies have indicated that sunlight plays an important role in altering concentrations of culturable enterococci and other indicator microorganisms in beach environments. Here we report studies of the light-induced mortality of one species of enterococci, Enterococci faecalis, under various conditions in Nanopure and natural waters. Direct exposure of the bacteria to solar radiation in all waters 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. Mortality rates of E. faecalis were determined in a series of irradiations of the bacteria that used simulated solar radiation that was passed through light filters that blocked different parts of the ultraviolet and visible spectral region. The mortality rates and spectral irradiance were then analyzed by the Rundel techllique to develop biological weighting functions (BWFs) for the light-induced mortality. The BWFs were then combined with other data concerning underwater solar spectral irradiance to model the light-induced mortality of E. faecalis in selected recreational waters.

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