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MICROBIAL COMMUNITY DIVERSITY AND CARBON UTILIZATION IN ESTUARINE ECOSYSTEMS OF SOUTHEASTERN U.S.A.
Citation:
Molina, M. MICROBIAL COMMUNITY DIVERSITY AND CARBON UTILIZATION IN ESTUARINE ECOSYSTEMS OF SOUTHEASTERN U.S.A. Presented at Invited Speaker, University of Puerto Rico, Humacao, Puerto Rico, September 21, 2002.
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:
Estuaries are very dynamic ecosystems with regard to the transport and transformation of organic matter. Detrital organic matter is abundant in most estuaries, however, the dynamics of detritus utilization is not well understood. Two questions that remain unanswered are the sources of the detrital material and how the detritus is utilized by the different consumer groups in both the water column and surface sediments. A combination of phospholipid fatty acid analysis (PLFA) and compound specific isotope analysis (CSIA) was used to provide information on the possible sources, distribution, and transformation of sedimentary organic matter in the Altamaha and Savannah River estuaries in GA. Total PLFA concentration, a measurement of microbial biomass and community structure, was similar in both rivers. The highest microbial biomass was observed in the mesohaline zone apparently in response to an input of labile organic matter at the mixing zone. Microbial community structure differed significantly both as a function of time and type of river. Selective utilization of C sources by specific microbial groups was demonstrated with CSIA. This analysis indicated that Gram positive bacteria degraded 13C-enriched material (marine C), whereas Gram negative bacteria assimilated higher concentrations of C3 material. In general, the results indicated that estuarine systems under the influence of large riverine inputs are subjected to seasonal regimes of microbial C cycling in response to changes in rain episodes and river discharge. However, the seasonal variability of the system was readily altered by anthropogenic alterations to river flow and other land use changes; which then produced a shift in the natural C cycling at the sediment-water interface of the estuarine continuum.