QUANTITATIVE EVALUATION OF DATA QUALITY IN ELECTRONIC DATA LOGGING OF KARST FLOW SYSTEMS

Authors: GROVES, CHRIS - WESTERN KENTUCKY UNIVERSI; Bolster, Carl; MEIMAN, JOE - NATIONAL PARK SERVICE

Submitted to: National Speleological Society Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 7/7/2005
Publication Date: 7/7/2005
Citation: Groves, C., Bolster, C.H., Meiman, J. 2005. Quantitative evaluation of data quality in electronic data logging of karst flow systems. National Speleological Society Annual Meeting.

Interpretive Summary: A fundamental characteristic of many well-developed karst flow systems is rapid variation in the flow and water chemistry conditions that govern system eolution and function. Since it is the distribution, movement, and chemical characteristics of these fluids that control both long-term system evolution and contemporary aquifer behavior, understanding these processes is a key goal in the quantitative evaluation of karst systems. Recently, progress has been made in understanding the details of these processes with the use of electronic probes and digital data loggers. The importance for karst comes not as much for the convenience provided by remote, automatic data collection, as for the ability to collect high temporal resolution data. The fact that data loggers can record data with resolution as fine as minutes (or seconds for that matter, limited only by the data storage room) essentially solves a long standing, thorny problem in karst hydrology--the evaluation of continuously, and often rapidly, changing conditions. In this paper we describe an effort underway within Cave Spring Caverns, Kentucky to rigorously define the practical limits of reported precision (associated with the reproducibility of a result) and accuracy (conformity with the true value of the measured parameter) in karst water monitoring by working under essentially ideal conditions of easy access, equipment security, and available electricity. Early results show that the continuous monitoring of specific conductance, pH, and water temperature allow much more accurate and precise estimates of four parameters controlling background carbonate water chemistry: carbon dioxide pressure, total inorganic carbon, the saturation index with respect to calcite, and the limestone dissolution rate.

Technical Abstract: A characteristic of many karst flow systems is rapid variation in the flow and water chemistry conditions that govern system evolution and function. Recently, progress has been made in understanding the details of these processes with the use of electronic probes and digital data loggers. Some parameters can be measured directly while others can be statistically related to direct observations, and from these a variety of usefull quantities can be derived. A challenge in this work, however, lies in the quantitative evaluation of data quality. We report here on an ongoing effort underway within Cave Spring Caverns, Kentucky to rigorously define the practical limits of reported precision (associated with the reproducibility of a result) and accuracy (conformity with the true value of the measured parameter) in karst water monitoring by working under essentially ideal conditions of easy access, equipment security and available electricity. After measuring flow through a tipping bucket rain gauge to develop a rating curve, water from an underground waterfall is monitored for temperature, pH, and spC by three independent probe/data logger (Campbell CR10X)systems with two-minute resolution. This redundancy reduces the probability for data loss by equipment malfunction and allows calculation of a standard deviation to quantify measurement precision. Early results show that data can be obtained within one standard deviation of <0.2 degrees C for temperature, <4S/cm@25 degrees C for specific conductance, and <0.01 unit for pH. We continue to evaluate accuracy issues, especially for pH with highly precise measurements complicated by instrument differences and carbon dioxide degassing.