Can trees along agricultural headwater streams improve the aquatic ecology and habitat quality? This question was asked by four scientists from Finnish and Canadian institutes. And their answer is: Yes, they can!

The authors set out to study the effects on ecology of riparian land use. To do this, they studied 11 paired forested and open agricultural headwater stream reaches. The word ‘paired’ means that each stream had a sibling stream reach with similar habitat characteristics: The reaches within a stream had similar water quality, but different extent of riparian forest cover.

The parameters they studied included stream habitat characteristics, water temperature, algal growth, macrophytes (water plants growing on the stream bed and riparian margin habitat), benthic macroinvertebrates (invertebrates living at the bottom of the stream) and fish communities. 

The authors found that riparean forests are important to reduce negative effects of climate change on biota. Photo: Jarno Turunen.

Interestingly, they found unmistakably evidence of the ecological benefits of forested riparian reaches in the agricultural headwater streams. This suggests that riparian forests in agricultural streams can partly mitigate the adverse impacts of agricultural diffuse pollution on biota.

Moreover, they found that riparian forests reduced the fluctuation of stream water temperature and maximum water temperatures. This is highly relevant, since climate change predictions include higher summer temperatures, which again may enhance algae growth and have negative impacts on species adapted to cold water temperatures. Hence, this study suggests that riparian forests may partly mitigate harmful effects on headwater stream biodiversity and ecosystem functions of predicted climate change.

There is a large difference in conditions for aquatic life in streams with and without bank vegetation. (Photo: Jarno Turunen).

Turunen, J, Elbrecht, V, Steinke, D, Aroviita, J. Riparian forests can mitigate warming and ecological degradation of agricultural headwater streams. Freshw Biol. 2021; 66: 785– 798.

Feature photo: Jarno Turunen.