Temperature-electrical conductivity relation of water for environmental monitoring and geophysical data inversion

Electrical conductivity (EC) is widely used for monitoring the mixing of fresh water and saline water, separating stream hydrographs, and geophysical mapping of contaminated groundwater. The measured EC values at various temperatures need to be reported as corresponding to a standard temperature because EC is dependent on temperature. An arbitrary constant is commonly used for temperature compensation assuming that EC-temperature relation is linear (for example 2% increase of EC per 1 degreesC). This paper examines the EC-temperature relation of natural waters having vastly different compositions and salinities. EC-temperature relation was slightly nonlinear in a temperature range 0-30 degreesC, but the linear equation approximated the relation reasonably well. The temperature compensation factor corresponding to 25 degreesC ranged between 0.0175 and 0.0198. When the mean value 0.0187 was used, the error of estimating EC at 25 degreesC from EC at 10 degreesC was less than about 2% for all samples tested. Temperature compensation factors vary substantially depending on the choice of standard temperature. Therefore, a care must be taken when standard temperatures different from 25 degreesC are used.