Author(s)

R.J. Davies-Colley

Abstract

Optical water pollution: concepts, measurement and management R.J. Davies-Colley Water Quality Centre, National Institute of Water and Atmospheric Research, PO Box 11-115, Hamilton, New Zealand ABSTRACT Optical water pollution can be defined as the degradation of suitability-for-use of water by humans or aquatic life owing to a change in water colour or clarity. Water clarity has two related but distinct aspects: the penetration of (sun)light into waters, measured with submersible sensors, and the visual range (visibility), measured with standard targets (e.g. the Secchi disc). Water colour is linked to the upwelling light (spectral irradiance) as measured by a spectro- radiometer. Few criteria and guidelines are available internationally to prevent optical water pollution, but recent research is providing a scientific basis for such guidelines. The most constraining guideline is that visual clarity should not be reduced more than 20%, corresponding to a maximum 25% i

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