Dissolved organic matter is found in all river water, and can come from both a natural source such as the soil, as well as human sources such as organic pollutants. It can produce natural fluorescence which can be seen using high-tech equipment.

Researchers from Newcastle University took samples of the water in the River Ouseburn at Newcastle, and found that 70% could be correctly classified to the river's tributaries by measuring the natural fluorescence in the water.

Occasions when the scientists were unable to discriminate the tributary waters were due to either pollution or strong seasonal differences in dissolved organic matter.

Fluorescence is the process where molecules emit light after being energised. For example, glow in the dark toys fluoresce after being energised by ultra-violet daylight.

River waters fluoresce at wavelengths that the eye cannot see. They would also seem to glow in the dark if our eyes were sensitive to ultraviolet light.

However, the scientists used machines called spectrophotometers, which can see this fluorescence. Recent technological advances permit the rapid and precise measurement of river water fluorescence.

Dr Andy Baker, of the Centre for Land Use and Water Resources, Newcastle University, who led the research team, said: "Results suggest that spectrophotometric techniques have considerable potential in the fingerprinting of dissolved organic matter in rivers.

"This is very important as up until now it has not been possible to separate the dissolved organic matter fractions in river water. However, our results mean that it is now possible to use dissolved organic matter as a natural fingerprint of different water sources, and to monitor and detect organic pollutants."

Note: If no author is given, the source is cited instead.

• Nature of Water
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