Abstract: Effects of shading on stream water temperature and stenothermic macroinvertebrates; a synthesis of the findings along the trans-European latitudinal climate gradient
Our study showed that shaded reaches have a significant effect on the water temperature of lowland streams, both by cooling the water when it flows from an upstream open area into the forest and by having a downstream cooling effect when the water flows from the forest into an open area. Despite the fact a temperature effect was commonly detected, the magnitude of the effect differed considerably among streams. We showed that this was partly the result of the leaf area index of the riparian forest canopy and of the current velocity. Based on the presence of stenothermal macroinvertebrates, we detected an effect on soft-substrate inhabiting species, with more warm-stenothermic and potamal species in the open reaches and more crenal species in the shaded reaches of the streams, indicating that the cooling by the forest or warming in the open areas had consequences for the biota of the streams. We conclude that planting wooded riparian zones is a legitimate stream temperature mitigation measure which may benefit macroinvertebrates preferring relatively low stream water temperatures. Nonetheless, predicting the absolute temperature decrease initiated by a newly planted riparian zone is difficult, given the large differences detected among streams.
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