HYDROGEOLOGY DIVISION BIRDSALL-DREISS LECTURE ABSTRACTS
Groundwater as an Ecosystem
Management of groundwater resources has traditionally focused on human needs for domestic, industrial, and agricultural water supply. In recent years, however, there has been an increasing recognition of the importance of the "ecological services" provided by groundwater discharge to streams, wetlands, and lakes. This recognition comes at a time of increasing human demands resulting from population growth, and as expanding urban areas limit rates of groundwater recharge. In the U.S., water shortages have been experienced in both in the arid west and in areas that are generally considered to be water rich such as the Midwest and Florida. While management strategies that allow for temporary overdraft of aquifers may offer an economically efficient option to satisfy human needs, ecosystems that rely on groundwater discharge can be sensitive to even small declines in water levels. Developing groundwater management strategies that meet human needs while protecting critical ecosystems is a delicate balancing act, and requires improved understanding of the relationships between ecosystem function and groundwater hydrology and geochemistry.
This talk will discuss several case histories related to the role of groundwater in ecosystem preservation and restoration. Research projects in several watersheds near Madison, WI have explored the hydrogeologic controls on spring flow and the effects of municipal pumping and reduced recharge on the springs. Results of these studies are being used in an interdisciplinary effort to identify urbanization alternatives that minimize negative hydrologic impacts on springs and wetland habitat. Another study, in a lowland savannah along the Lower Wisconsin River, demonstrates the effects of stage control by upstream dams on spatial patterns of groundwater discharge to the river and adjacent floodplain. Groundwater discharge into wetland areas results in loss of agriculturally derived nitrate. This suggests strategies for restoration of riparian wetlands and dam management that could reduce nitrogen fluxes from the Upper Midwest to the Mississippi River. The final case history will review groundwater management strategies that are included in a 7.8 billion dollar, 20+ year program, to restore the Florida Everglades.
of Groundwater in Uncontaminated and Contaminated Aquifers
Hydrogeologists are accustomed to finding large spatial and temporal variations in groundwater chemistry as a result of contaminant migration. During characterization of "background" conditions in these aquifers, however, it is often assumed that only one or a small number of wells are adequate for assessing pristine groundwater chemistry. This talk will present results of multilevel sampling in shallow aquifers in a variety of hydrogeologic settings that demonstrate the prevalence of fine scale spatial and short-term temporal variability in major ions and redox sensitive species such as oxygen, nitrate and iron. The sites include several in unconsolidated sediments and two in fractured bedrock: one a carbonate aquifer in Wisconsin and the other in a shale/carbonate aquifer in Tennessee. The geochemical heterogeneity of groundwater at these field sites reflects a combination of distinct flow paths and geochemical and biogeochemical reactions that occur during transport. In many cases the observed geochemical signatures can be used as natural tracers to delineate flow paths. Identification of the background heterogeneity, as well as understanding the controlling physical and geochemical processes, is important to interpretation of changes induced by introduction of contaminants. A case study of gasoline contaminants in a sandy aquifer in Wisconsin demonstrates the applications of these principles to assessing the potential for intrinsic and enhanced biodegradation under aerobic and anaerobic conditions.