the lower fox river watershed monitoring program    
University of Wisconsin Green Bay
University of Wisconsin Milwaukee

Conductivity

Conductivity, or specific conductance, measures the ability of water to conduct an electrical current. A stream’s conductivity is directly proportional to the concentrations and types of positively and negatively charged ions present. Sources of ions are both naturally occurring and anthropogenic in origin, and include soil, bedrock, human and animal waste, fertilizers, pesticides, herbicides, and road salt. Specific conductance can also be used to approximate the Total Dissolved Solids (TDS) in the water.

A conductivity meter reads the conductivity directly from the stream. Conductivity is temperature-sensitive, but the meter automatically compensates for temperature differential by correcting values to a standard temperature of 25°C. The conductivity meter measures the flow of electrons over a specified distance, and is the reciprocal of resistance (ohms). Measurements are given in µS/cm (microSiemens per centimeter), which expresses the flow of electrons between two electrodes, each 1 square cm in surface area, that are 1 cm apart.

Streams in Northeast Wisconsin typically have conductivity values between 300 and 1800 µS/cm. During periods of snowmelt or in areas where there is barnyard runoff, the conductivity in a stream may exceed the detection limits for the Oakton ECTestr+ Low Conductivity Meter provided in the monitoring kits. In these situations, the conductivity should be reported as >1999 µS/cm. Although the State of Wisconsin has not established surface water quality standards for conductivity, it can be used as an indicator of excessive ion concentrations for further study.