Publication Date

5-1-2007

Degree Program

Department of Geography and Geology

Degree Type

Master of Science

Abstract

Agricultural land use in areas that are located in karst groundwater basins negatively impact groundwater quality because karst terrains provide multiple, direct hydrologic connections from the surface into karst aquifers. The connections and rapid velocities associated with surface and subsurface flow in karst aquifers allow for contaminants to move quickly into and through a groundwater basin. When groundwater returns to the surface via a spring or springs, any contaminants within the water become part of surface streams and rivers. These in turn, impact water quality in areas located downstream of the spring or springs. The purpose of this study was to identify the source and movement of agricultural contaminants in a karst groundwater basin within the context of local climate, hydrogeology and land use. The study area is a fluvio-karst groundwater basin located in the Corn Belt of northeast Iowa and southeast Minnesota. Land use is predominantly agricultural in nature. Dye tracing, both qualitative and quantitative, resulted in the delineation of the Coldwater Cave Groundwater basin and illustrated that the boundaries of the basin could change as a result of precipitation events. Investigation of basin and aquifer characteristics, stream water temperature monitoring, and evaluation of cave map data and karst feature inventories determined that the surface and subsurface hydrogeology in the study area was very well integrated. Water sampling and analysis documented that agricultural contaminants, specifically nitrates, bacteria, and atrazine impact the quality of the surface water and groundwater within the basin. A ribotyping project that was done in conjunction with the thesis work showed the source of bacteria to be from cattle and humans. Nitrogen isotope analyses indicated that the source of nitrates was from ammonium fertilizers and from septic system wastes. Atrazine, at levels well below the MCL standards established by EPA, and its metabolite deethylatrzine (DEA) were detected in the groundwater year round. Contaminant load was calculated for nitrates, bacteria, and atrazine. Lowest contaminant loads occurred during the winter months of November, December, and January, when freezing temperatures minimized groundwater recharge. Contaminant load varied between high and low concentrations during the months of February and March reflecting the diurnal change between above and below freezing surface temperatures. Contaminant loads were highest during May through October when storm events are common. Contaminant load and transport are a function of the interaction of local hydrogeology and climate.

Disciplines

Agriculture | Environmental Health and Protection | Geology | Hydrology