Biogeochemical Studies of the Upper Floridan Aquifer

Research Team: Dr. Stephen P. Opsahl (Assistant Scientist), David W. Hicks (Scientist), Christopher Wheeler (Research Technician III), Brian Clayton (Monitoring Techinician), and Joanna Jenkins (Research Technician)

Biogeochemistry refers to the movement and transformation of materials in ecosystems as a function of physical, chemical and biological processes. In karst aquifer systems such as the Upper Floridan aquifer, biogeochemical processes play a crucial role in determining the quality of groundwater by reducing excessive nutrients and organic matter that is characteristic of water at the land's surface. Bacterial metabolism is the primary mechanism by which materials are transformed in natural systems. Bacteria use a wide variety of compounds present in surface and groundwaters as sources of energy and nutrients for growth. Biogeochemical studies in groundwater systems are challenging because sophisticated techniques must be used to assess microbial activity and because of the difficulties in obtaining subterranean water samples to work with.

Biogeochemical Studies of the Upper Floridan Aquifer We are currently evaluating the relative importance of predominant microbial pathways involved in groundwater evolution in southwest Georgia. This research is being carried out as part of a preliminary assessment of the Chickasawhatchee Swamp-a large Upper Floridan aquifer discharge/recharge feature in Georgia. A network of groundwater wells is in place at the swamp which allows us to regularly sample shallow and deep groundwater. Water chemistry from surface wetlands, creeks, and groundwater is being sampled for organics (DOC, lignin phenols) and inorganic constituents (nitrate, ammonium, DON, phosphate, cations, anions), and physical properties (conductivity, temperature, oxygen). From this, we can better predict which microbial processes will predominate under a given chemical environment. We are particularly interested in studying the importance of aerobic (heterotrophy, methane oxidation, etc.) versus anaerobic processes (fermentation, methanogenesis, denitrification, iron reduction, etc.), and the specific role that each form of metabolism plays in altering groundwater chemistry. Natural tracers of organic matter (e.g. plant-derived lignins) will be used to identify key pathways of organic matter transport and degradation during surface water/groundwater exchanges. We also plan to do some age dating (CFC's and ³H/³He) of groundwater at both recharge (wetlands and sinks) and discharge (springs) sites.

The long-term future of the Upper Floridan aquifer and its ability to provide an ample supply of clean water to people remain uncertain. Studies such as these will help to understand the critical biogeochemical linkages between surface water and aquifer water and many of the controls that dictate water quality. Demands on the Upper Floridan aquifer will continue to increase in the 21st century, and scientific studies of critical areas including the Chickasawhatchee Swamp and lower Flint River will contribute to the sustainable management of the state's valuable groundwater resources.

Additional Information:

Jenkins, J. C., D.W. Hicks, and S.P. Opsahl. (in review). Large Differences in Nitrogen Chemistry in the Upper Floridan Aquifer in Reference Wells on the Ichauway Ecological Reserve, Newton, Georgia. In: Proceedings of the 2003 Georgia Water Resources Conference. K. J. Hatcher, editor. Institute of Ecology, The University of Georgia, Athens, Georgia.

Funded by: The Joseph W. Jones Ecological Research Center