CHAMPAIGN, Ill., 9/16/19: Streambank forests that help to buffer streams from pollutants are particularly important for stream quality, even in areas such as east-central Illinois where cropland predominates and the river system has deteriorated, according to a University of Illinois study.
Forest buffers have long been known to improve stream environments in agricultural areas by filtering water runoff, stabilizing banks, and providing shade. But previous studies have found that these buffers are not adequate in rivers that are highly polluted with nutrients and sediment.
In a three-year study in the Embarras River region of Illinois, researchers studied fish communities in streams in the spring and summer, dividing the streams into three land-use categories. In the high buffer-high agriculture group, the percentage of forest buffer was the highest at greater than 75 percent, and field crops made up more than 73 percent of the land. The other two categories were high buffer-low agriculture and low buffer-high agriculture.
In the total region, row crops and small-grain agriculture made up 74 percent of the land.
“We were not sure if we would see a difference among the three land groups, given that all three groups are in a region that is greatly affected by agricultural practices,” said Eden Effert-Fanta, a research affiliate with the Illinois Natural History Survey (INHS). “But even in the two groups with the highest field crop areas, forest buffers were effective in limiting pollutants in streams.”
As expected, the highly buffered streams in areas with a lower percentage of agriculture had the best habitat, water quality, and fish diversity.
Fish populations were the greatest in streams where the vegetation buffer was minimal, but the species of fish differed from the other groups. The central stoneroller and the bluntnose minnow had large populations as they thrive in muddy streams polluted with high nutrient levels. Algae was also more abundant in these streams.
In the high buffer-low agriculture areas, fish considered to be less tolerant to pollution, such as longear sunfish and silverjaw minnows, proliferated. The presence of these species indicated that the water quality was better than that in the other two groups.
Identifying the types of fish in a stream gives a better indication of the water quality than testing the water for specific pollutants, Effert-Fanta said. Water tests give a one-time snapshot of water conditions, but fish have been living there for months or years.
“This study suggests that fish communities were influenced by stream conditions that were strongly controlled by the amount of riverbank forest buffer in the streams,” Effert-Fanta said.
Restoring forest buffers is key in maintaining higher-quality streams and protecting fish communities from adverse effects, especially in areas where the intensity of agricultural practices is high.
The study was published in the journal Hydrobiologia.
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