New insights on river health

Leaf litter build up in a German stream. Credit: M.O. Gessner

Leaf litter build up in a German stream. Credit: M.O. Gessner

A continent-wide survey of Europe's waterways has recommended better ways to monitor how rivers are responding to organic pollution and other pressures arising from human activity.

Published today in Science, the large-scale collaboration between several researchers included Dr Sally Hladyz from Monash University's School of Biological Sciences. The researchers looked at leaf litter breakdown rates as an indicator of river health.

Leaf litter breakdown rates give important insights into how the river ecosystem is functioning, which cannot be achieved by looking only at water quality or fish communities.

The teams deployed 2400 mesh litter bags to monitor the breakdown rates in 100 European streams across streams with varying levels of organic pollution.

Results indicated that water quality measured from nutrient concentrations was a good predictor of breakdown rates at the extremes of very polluted, and relatively unpolluted, waterways. However, in streams with moderate levels of nutrient concentration or pollution, leaf litter analysis provided critical data that could not be obtained by assessing water quality only.

Dr Hladyz said the study showed that monitoring leaf litter breakdown was a reliable assessment of river health that could be more widely adopted to complement established measures of river health.

"Leaf litter breakdown rates are really a sign of changes in ecosystem function. It's a useful indicator of river health because the rates alter in response to a variety of stressors related to human activity, such as land use and exotic plant invasions," Dr Hladyz said.

"It's also relatively cheap and easy to measure, meaning it wouldn't be overly difficult to include in current bioassessments of water ways."

Dr Hladyz is currently trialing the technique in response to river regulation in the southern Murray-Darling Basin.

"Australian and European environments are clearly different; however, streams are facing similar pressures from agriculture, industry and other human activities the world over. If we find better ways of assessing the health of river systems, they should be more widely implemented," Dr Hladyz said.