the sealed SCT loggers ameliorated some of these issues. Because sealed sensors/
loggers are generally not built for in-field calibration, raw data are softwarecorrected to values measured in the field with a calibrated conductivity meter at
the time of data download. The software applies a linear drift correction using a
two-point calibration with values measured in the field at the beginning and end of
each logging period.
Another challenge in karst is precipitation of calcite and other carbonate minerals on sensors, as dripwater is often saturated with respect to these minerals.
Calcite acts as an insulator and depresses the electrical conductivity measured by
the SCT logger. Maintenance procedures include gentle cleaning of the SCT
loggers with a soft brush prior to rinsing with a weak acid (acetic) and rinsed
with DI water to remove calcite buildup after download and prior to redeployment.
These cleaning procedures are effective at removing mineral buildup and biofilms
that may form on the sensor surface. All chemical solutions used in rinsing cave
equipment are collected and removed from the cave.
Another complication for in-cave monitoring is the development of biofilms on
instrument or collection-material surfaces, such as the collection tarp, and growth
of bacterial masses in the sample chamber. During each trip to the cave, sample
chambers are visually inspected for biofouling. If biofouling is identified, the
material is physically removed and the chamber disinfected with acetic acid.
3.5.2 Site Maintenance
Sediment buildup in the drip collection systems is a constant concern, especially
during the recharge season with high dripwater flows through the epikarst. Sediment can clog the systems, causing tarp sagging, which can result in tarp collapse.
Sediment buildup can also block flow to the sample collectors at the downstream
end of the system. Clearing the system of sediment is accomplished by
disconnecting the outfall hoses below the tarp funnel, the sample chamber, and
the rain gauge. Each of these is rinsed and back-flushed as appropriate to clear and
restore flow pathways and then reconnected and flushed with dripwater. The
interval for which such maintenance is required varies between sites and depends
on sediment yield from the epikarst over time.
4 Sample Collection and Analysis
In addition to the continuous measurements discussed above, samples of precipitation, soil water, dripwater, and stream water were collected monthly for geochemical analyses (anions, cations, alkalinity, dissolved organic carbon, water
isotopes, and carbon isotopes of organic and inorganic carbon) from July 2008 to
January 2012. Samples were brought back to the Virginia Tech laboratories for
processing and analysis. More details on sampling and analytical procedures,
as well as results, can be found in two graduate theses [21, 22].
Instrumenting Caves to Collect Hydrologic and Geochemical Data: Case Study. . .
221
loggers are generally not built for in-field calibration, raw data are softwarecorrected to values measured in the field with a calibrated conductivity meter at
the time of data download. The software applies a linear drift correction using a
two-point calibration with values measured in the field at the beginning and end of
each logging period.
Another challenge in karst is precipitation of calcite and other carbonate minerals on sensors, as dripwater is often saturated with respect to these minerals.
Calcite acts as an insulator and depresses the electrical conductivity measured by
the SCT logger. Maintenance procedures include gentle cleaning of the SCT
loggers with a soft brush prior to rinsing with a weak acid (acetic) and rinsed
with DI water to remove calcite buildup after download and prior to redeployment.
These cleaning procedures are effective at removing mineral buildup and biofilms
that may form on the sensor surface. All chemical solutions used in rinsing cave
equipment are collected and removed from the cave.
Another complication for in-cave monitoring is the development of biofilms on
instrument or collection-material surfaces, such as the collection tarp, and growth
of bacterial masses in the sample chamber. During each trip to the cave, sample
chambers are visually inspected for biofouling. If biofouling is identified, the
material is physically removed and the chamber disinfected with acetic acid.
3.5.2 Site Maintenance
Sediment buildup in the drip collection systems is a constant concern, especially
during the recharge season with high dripwater flows through the epikarst. Sediment can clog the systems, causing tarp sagging, which can result in tarp collapse.
Sediment buildup can also block flow to the sample collectors at the downstream
end of the system. Clearing the system of sediment is accomplished by
disconnecting the outfall hoses below the tarp funnel, the sample chamber, and
the rain gauge. Each of these is rinsed and back-flushed as appropriate to clear and
restore flow pathways and then reconnected and flushed with dripwater. The
interval for which such maintenance is required varies between sites and depends
on sediment yield from the epikarst over time.
4 Sample Collection and Analysis
In addition to the continuous measurements discussed above, samples of precipitation, soil water, dripwater, and stream water were collected monthly for geochemical analyses (anions, cations, alkalinity, dissolved organic carbon, water
isotopes, and carbon isotopes of organic and inorganic carbon) from July 2008 to
January 2012. Samples were brought back to the Virginia Tech laboratories for
processing and analysis. More details on sampling and analytical procedures,
as well as results, can be found in two graduate theses [21, 22].
Instrumenting Caves to Collect Hydrologic and Geochemical Data: Case Study. . .
221