CHARACTERIZATION OF GROUNDWATER FLOW PATHS THROUGH MEROKARST IN THE N04D SECTION OF THE KONZA PRAIRIE LONG-TERM ECOLOGICAL RESEARCH SITE IN NORTHEASTERN KANSAS, USA

Karst terrain covers approximately 10 % of earth’s surface. Flow paths through karst aquifers are often unpredictable because of solution-enlarged fractures, making prediction of contaminant movement difficult. Because fluorescent dye tracers behave similarly to some contaminants, dye tracing studies can reveal flow paths in karst. In this study, fluorescent dye tracers were used to determine the direction of groundwater flow. The field site, the Konza Prairie Long-Term Ecological Research Site, is located in northeastern Kansas, USA. Bedrock at Konza is Permian in age and consists of alternating limestones (1-2 meters) and mudstones (2-4 meters) that act as a merokarst terrain. Watershed N04d is 1.2 km² in area and is drained by a fourth-order, intermittent, losing stream. Potentiometric surface maps of the limestone aquifers show that, although stream water flows northward, groundwater appears to be flowing to the south in the Morrill Limestone aquifer. The Morrill aquifer is overlain by the Eiss Limestone aquifer, separated by the Stearns Shale. Potentiometric surface maps of the Eiss aquifer show groundwater flowing north. Although the regional dip of the strata is about 0.1° to the northwest, preliminary results suggest that there may be a local interruption to the regional trend, resulting in a southward dip.

To better characterize groundwater flow direction(s), fluorescent-dye tracing tests were conducted in some of the water wells in watershed N04d. In this study, fluorescein, eosine, and rhodamine were used as tracers to determine the direction of groundwater flow in the Morrill and Eiss limestone aquifers. Water grab samples and charcoal detection packets were deployed to concentrate dye in wells and along the stream where dye is expected to appear. Three tracer tests took place on July 29, 2017, during the dry season. After the first injection, with an increased head of 2.9 m from water used to flush the dye into the aquifer and a distance from the injection well to the stream of 7 meters, no dye was seen in the stream within 3 hours after the time of injection. This may indicate a relatively slow travel time, or that groundwater is moving away from the stream. The two other injections that occurred on this day were located farther from the stream and showed similar results.