Quantitative interpretation of specific conductance frequency distributions in karst

Area of Science:

• Hydrogeology
• Environmental Science
• Geochemistry

Background:

• Traditional methods using the coefficient of variation (CV) for classifying karst aquifers based on specific conductance frequency distributions (CFDs) are often inaccurate.
• Multimodal CFDs and the CV approach can lead to erroneous classifications of dominant flow or recharge types.

Purpose of the Study:

• To develop and demonstrate a more rigorous method for analyzing CFDs to understand water types contributing to spring flow.
• To provide a quantitative approach for comparing hydrogeochemical populations within karst aquifers across different water years.

Main Methods:

• Analyzing specific conductance frequency distributions (CFDs) by separating them into additive normal distributions representing distinct hydrogeochemical populations.
• Quantifying the mean, variance, and contribution of each water type to the overall CFD.
• Applying the method to four years of data from Barton Springs, Austin, Texas.

Main Results:

• The CFD consistently separated into the same normally distributed populations each year, despite year-to-year variations in overall shape.
• Each population was suggested to represent a distinct water type linked to specific aquifer functioning modes.
• Changes in population parameters correlated with aquifer responses to climatic variations.

Conclusions:

• No single specific conductance parameter adequately describes karst aquifer behavior.
• The degree of karst behavior is dynamic and varies annually based on hydrologic conditions.
• The developed method offers deeper insights into aquifer functioning and water source contributions.