MARTIN BOND / SCIENCE PHOTO LIBRARY MARTIN BOND / SCIENCE PHOTO LIBRARY
Stream analysis. Researcher checks a stream for pollution, acidity or low flow-rate by using a conductivity meter. The meter works by passing an electric current between the two electrodes in the water. Water conducts electricity more efficiently if it contains ions (dissolved chemicals). The source of these ions is pollution such as acid rain. Ions can be added artificially by dissolving salt further upstream. By measuring the time taken by the salt to move downstream, the flow-rate of the water can also be measured. If the flow-rate of the stream is low then the concentration of pollutants will tend to increase.
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