Correlating specific conductivity with total hardness in limestone and dolomite karst waters

Abstract

Under field conditions modern digital conductivity meters give standardized, rapid and reproducible measurements. Here we investigate the accuracy of their estimates of the composition of karst waters, as total hardness (TH, as mg/L CaCO 3 ) for limestone and dolomite. These are the fundamental measures of process in carbonate karst geomorphology. PHREEQC theoretical curves for the dissolution of pure calcite/aragonite and dolomite in water at 25°C are compared with water analyses from karst studies worldwide. Other principal ions encountered are sulphates, nitrates and chlorides (the 'SNC' group). From carbonate karsts, 2309 spring, well and stream samples were divided into uncontaminated (SNC < < < < < 10%), moderately contaminated (10 < < < < < SNC < < < < < 20%), and contaminated (SNC > > > > > 20%) classes. Where specific conductivity (SpC) is less than 600 µ µ µ µ µS/cm, a clear statistical distinction can be drawn between waters having little contamination and substantially contaminated waters with SNC > > > > > 20%. As sometimes claimed in manufacturers' literature, in 'clean' limestone waters TH is close to 1 /2SpC, with a standard error of 2-3 mg/L. The slope of the best-fit line for 1949 samples covering all SNC classes where SpC < < < < < 600 µ µ µ µ µS/cm is 1·86, very close to the 1·88 obtained for clean limestone waters; however, the value of the intercept is ten times higher. The regression line for clean limestone waters where SpC > > > > > 600 µ µ µ µ µS/cm helps to distinguish polluted waters from clean waters with possible endogenic sources of CO 2 . In the range 250 < < < < < SpC < < < < < 600 µ µ µ µ µS/cm, dolomite waters can be readily distinguished from limestone waters.

Infiltration processes and flow rates in developed karst vadose zone using tracers in cave drips

“…The higher electrical conductivity values (1130-1040 μS/ cm) in Location 3 is at the top of the range of natural waters in carbonate karst lands (Krawczyk and Ford, 2006), indicating saturation to calcite plus higher concentrations of Cl − , Na + , and SO 4 2− , as results of proximity to the sea and high evapotranspiration .…”

Water percolation process studies in a Mediterranean karst area

“…Climatic data and calculated potential evapotranspiration (ETp) during the experiment EC a non-conservative tracer, as also documented by the variability of natural EC measured at different drips (Table II). However, these values do not exceed 1000 µS/cm, and also natural water from carbonate karstlands rarely exceed this limit (Krawczyk and Ford, 2006). This means that the high EC of the sprinkling water (1460 µS/cm) could be regarded as a clear and strong signal for the high chloride concentration characterizing the local groundwater during summer, which was used for sprinkling.…”

“…Natural water from carbonate karstlands rarely exceed 1000 µS/cm (Krawczyk and Ford, 2006). However, in the wells of the Mount Carmel aquifer there is a tendency for salinity to increase during the period of main water extraction in summer, with chloride concentrations exceeding 400 mg/l in autumn (Guttman, 1998).…”

Interactions of diffuse and focused allogenic recharge in an eogenetic karst aquifer (Florida, USA)

“…Specific conductivity can be used in karst aquifers to distinguish between newly recharged precipitation and aquifer water that has reached chemical equilibrium with the carbonate rocks (e.g., Vesper and White 2004;Doctor et al 2006;Krawczyk and Ford 2006). Under low-flow conditions, River Rise shows higher specific conductivity than River Sink due to inflow of water from the UFA that has reacted with the aquifer matrix (Fig.…”