dc.description.abstract | Karst aquifers are a significant source of groundwater supply worldwide, yet are known for unpredictable flow paths and rapid groundwater velocity. Characterizing the complex nature of karst aquifers though dye tracing is essential to confronting problems, like contamination, that may threaten groundwater/drinking water supply. The aquifers this study focuses on are the Cottonwood, Morrill, and Eiss Limestones underlying the Konza Prairie Long-Term Ecological Research Site in Northeastern Kansas, USA. These aquifers are merokarst and consist of thin limestone beds that alternate with shales. Watershed N04d is drained by the northward flowing South Fork Branch of Kings Creek. Potentiometric surface maps of the Morrill Limestone indicate groundwater is flowing south in this unit. Overlying the Morrill, in the Eiss Limestone, potentiometric surface maps indicate groundwater flowing north. Here, the unusual contrasting groundwater flow directions of these units are investigated using dye-tracing to better understand the nature of merokarst aquifer systems. Fluorescein, eosine, and rhodamine WT were used as groundwater tracers to aid in the understanding of groundwater flow at Konza. Dyes were injected into monitoring wells on July 29th, 2017 and monitored via charcoal packets and water samples from wells and the South Fork Branch of Kings Creek. Low flow conditions dominated in this study period, both in the stream and in the aquifer. Groundwater velocity measurements from this tracer test suggest this is a diffuse flow system. The results of the tracer test show that groundwater is flowing north in the Eiss Limestone and Cottonwood Limestone, and south in the Morrill Limestone. The presence of dye in underlying limestone units suggests groundwater is leaking from the upper aquifers through shales that act as leaky aquitards. I propose that a collapse feature in the units at this site is causing groundwater to flow south in the Morrill Limestone, while springs in the Eiss Limestone and Cottonwood Limestone discharge groundwater in these units where groundwater flows northward. Trends in fractures also influence the direction of groundwater flow. The tracer-test revealed travel times comparable to those in epikarst, suggesting the results of this study may be widely applicable. | |