SS3.04 Biogeochemistry of DOC/DON in a Watershed Context
Date: Wednesday, June 12, 2002
Time: 2:45:00 PM
Location: Carson B
 
OpsahlSP, J. W. Jones Ecological Research Center, Newton, USA, stephen.opsahl@jonesctr.org
 
SURFACE WATER/GROUNDWATER MIXING AND MICROBIAL METABOLISM OF DISSOLVED ORGANIC MATTER IN A SHALLOW KARST ECOSYSTEM
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The Upper Floridan Aquifer is a shallow karst feature of the southeastern US landscape, which serves as both a major source and sink of water, dissolved organic matter (DOM), and nutrients to adjacent freshwater and coastal ecosystems. Yet studies of ecosystem function in subterranean waters such as the Upper Floridan Aquifer lag far behind those of rivers, lakes and wetlands, and basic biogeochemical processes such as DOM and nutrient dynamics remain poorly understood. Sites were identified along the Lower Flint River in southwestern Georgia where large exchanges of water occur through direct conduits between the river and the aquifer. A suite of inorganic compounds (cations, anions, nutrients) and organic matter properties (DOC, lignin phenols, UV/visible absorbance) proved useful for distinguishing aquifer water from river water. In spite of low DOC concentrations in the aquifer, rates of microbial metabolism based on oxygen consumption were at times equivalent to those measured in the river indicating more dynamic groundwater biogeochemistry than expected. Results will be discussed in terms of controls on microbial metabolism, and how these are influenced by regional climatic events.