Abstract Karst aquifers are productive groundwater systems, supplying approximately 25 % of the world’s drinking water. Sustainable use of this critical water
supply requires information about rates of recharge to karst aquifers. The overall
goal of this project is to collect long-term, high-resolution hydrologic and geochemical datasets at James Cave, Virginia, to evaluate the quantity and quality of
recharge to the karst system. To achieve this goal, the cave has been instrumented
for continuous (10-min interval) measurement of the (1) temperature and rate of
precipitation; (2) temperature, specific conductance, and rate of epikarst dripwater;
(3) temperature of the cave air; and (4) temperature, conductivity, and discharge of
the cave stream. Instrumentation has also been installed to collect both composite
and grab samples of precipitation, soil water, the cave stream, and dripwater for
geochemical analysis. This chapter provides detailed information about the instrumentation, data processing, and data management; shows examples of collected
datasets; and discusses recommendations for other researchers interested in hydrologic and geochemical monitoring of cave systems. Results from the research,
briefly described here and discussed in more detail in other publications, document
a strong seasonality of the start of the recharge season, the extent of the recharge
season, and the geochemistry of recharge.
Keywords Cave • Dripwater • Epikarst • Karst • Recharge • Subsurface monitoring
1 Introduction
Karst aquifers form from dissolution of soluble rock, including limestone and
dolostone, by groundwater. Dissolved carbon dioxide promotes dissolution of
these rocks, which enlarges fractures to form conduits and caves. Karst aquifers
are vital water resources, providing approximately 40 % of drinking water supplies
in the United States [1]. An estimated 25 % of the global population uses freshwater
derived in part or entirely from karst sources [2].
Characterizing how karst aquifers are recharged is crucial for sustaining this
critical groundwater resource. However, recharge processes in karst systems are
difficult to characterize due to heterogeneity of the epikarst. Epikarst is defined as
the interval of weathered and fractured bedrock that extends from the base of the
soil zone to less weathered bedrock below [2]. The epikarst is often called the
“skin” of karst aquifers [3], as it is a critical zone that significantly influences karst
hydrology, water quality, and ecosystems. The epikarst controls both the quantity
and quality of autogenic (internal) recharge to karst aquifers and, as a result, is a
particularly important component of the system.
Due to the highly variable flow velocities and residence times within the
epikarst, traditional methods to determine recharge generally do not work in
epikarst, thus requiring specialized techniques. Continuous monitoring of physical
and chemical characteristics of cave dripwater is one approach that can be used to
test hypotheses and answer a variety of scientific questions about the epikarst
system, including the biodiversity of epikarst communities (e.g., [4]), epikarst
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supply requires information about rates of recharge to karst aquifers. The overall
goal of this project is to collect long-term, high-resolution hydrologic and geochemical datasets at James Cave, Virginia, to evaluate the quantity and quality of
recharge to the karst system. To achieve this goal, the cave has been instrumented
for continuous (10-min interval) measurement of the (1) temperature and rate of
precipitation; (2) temperature, specific conductance, and rate of epikarst dripwater;
(3) temperature of the cave air; and (4) temperature, conductivity, and discharge of
the cave stream. Instrumentation has also been installed to collect both composite
and grab samples of precipitation, soil water, the cave stream, and dripwater for
geochemical analysis. This chapter provides detailed information about the instrumentation, data processing, and data management; shows examples of collected
datasets; and discusses recommendations for other researchers interested in hydrologic and geochemical monitoring of cave systems. Results from the research,
briefly described here and discussed in more detail in other publications, document
a strong seasonality of the start of the recharge season, the extent of the recharge
season, and the geochemistry of recharge.
Keywords Cave • Dripwater • Epikarst • Karst • Recharge • Subsurface monitoring
1 Introduction
Karst aquifers form from dissolution of soluble rock, including limestone and
dolostone, by groundwater. Dissolved carbon dioxide promotes dissolution of
these rocks, which enlarges fractures to form conduits and caves. Karst aquifers
are vital water resources, providing approximately 40 % of drinking water supplies
in the United States [1]. An estimated 25 % of the global population uses freshwater
derived in part or entirely from karst sources [2].
Characterizing how karst aquifers are recharged is crucial for sustaining this
critical groundwater resource. However, recharge processes in karst systems are
difficult to characterize due to heterogeneity of the epikarst. Epikarst is defined as
the interval of weathered and fractured bedrock that extends from the base of the
soil zone to less weathered bedrock below [2]. The epikarst is often called the
“skin” of karst aquifers [3], as it is a critical zone that significantly influences karst
hydrology, water quality, and ecosystems. The epikarst controls both the quantity
and quality of autogenic (internal) recharge to karst aquifers and, as a result, is a
particularly important component of the system.
Due to the highly variable flow velocities and residence times within the
epikarst, traditional methods to determine recharge generally do not work in
epikarst, thus requiring specialized techniques. Continuous monitoring of physical
and chemical characteristics of cave dripwater is one approach that can be used to
test hypotheses and answer a variety of scientific questions about the epikarst
system, including the biodiversity of epikarst communities (e.g., [4]), epikarst
206
M.E. Schreiber et al.