Karst aquifers, characterized by soluble rocks such as limestone and dolostone, provide drinking water to 20-25% of the world's population and are thus critical global water sources. However, recent work suggests that rapid alteration of karst aquifers due to the impact of climate change on precipitation patterns may affect recharge to these aquifers.
Much of the research on recharge in karst aquifers has relied on using patterns of spring discharge to quantify recharge. Spring outlets allow for continuous monitoring of discharge from karst aquifers, making them easily accessible monitoring sites. However, because springs can integrate multiple flow paths, it is difficult to rely on spring discharge patterns to get information on where and how karst aquifers are receiving recharge. Monitoring closer to the source of recharge through the measurement of cave drips allows for a more accurate analysis of recharge timing and mechanisms.
In this study, I conducted recession analyses on cave drip hydrographs from a 10-year record (2008-2018) of three drip monitoring stations within James Cave (Pulaski Co., VA) to: 1) examine differences in hydrologic characteristics of the epikarst (the zone of soil and weathered bedrock above a karst aquifer); 2) quantify the storage volume of the epikarst and 3) investigate seasonal, and annual trends in recharge.
Results of recession analysis show heterogeneity in epikarst hydrologic characteristics, reflected by calculations of the recession coefficient, , and storage volume. Calculations of the recession coefficient show subtle differences between the three drip sites, suggestive of spatial heterogeneity in permeability and storage in the overlying epikarst. The storage volume calculations show that during the recharge season (winter- spring), up to 95% of recharge through the unsaturated zone to the cave occurs through rapid pathways (i.e., fractures), and 5% through diffuse pathways (i.e., pores). However, during the recession period (spring-summer), when evapotranspiration is active, recharge through cave drips decreases and occurs predominantly through diffuse flow. Combined, these results underscore the importance of both spatial and temporal characterization of drip rates and other recharge inputs into karst aquifer systems. / Master of Science / Karst aquifers, characterized by soluble rocks such as limestone and dolostone, provide drinking water to 20-25% of the world's population and are thus critical global water sources. Recent work suggests that climate change may alter how karst aquifers are recharged; however, few studies have addressed this potential impact.
This study expands knowledge of recharge in karst aquifers through analysis of a 10-year record (2008-2018) of three cave drip measuring stations in James Cave (Pulaski Co., VA). I used recession analysis of the cave drip record to investigate temporal trends in recharge and to examine hydrologic characteristics of the epikarst, the zone of soil and weathered bedrock above the cave. Results of this analysis show seasonal patterns in cave drips, with the highest drip rates occurring in the winter and early spring. The analysis also shows spatial differences in hydrologic characteristics of the epikarst. Calculations of the storage volume show during the winter and early spring, up to 95% of recharge to the cave occurs through rapid pathways (i.e., fractures), and 5% occurs through diffuse pathways (pore spaces in the soil and rock).
Results of this study underscore the importance of both temporal and spatial characterization of cave drips and other recharge inputs into karst aquifer systems. The information gained from this study will add the body of knowledge on how karst aquifers receive recharge, which will aid in protection and management of these critical drinking water sources.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/104202 |
| Date | 16 July 2021 |
| Creators | Groce-Wright, Nigel C. |
| Contributors | Geosciences, Schreiber, Madeline E., Stewart, Ryan D., Pollyea, Ryan M. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf, application/pdf, application/pdf |
| Coverage | Virginia |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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