Impacts of damming and climate change on the ecosystem structure of headwater streams: a case study from the Pyrenees

ABSTRACT Climate change, damming, and metal pollution are among the main anthropogenic threats to headwater streams. We designed a case study to assess how these stressors impact the ecosystem structure of headwater streams by using the biofilm and macroinvertebrate communities of a Pyrenean stream. We observed a strong seasonal pattern in the stream that interacted with the analysed stressors by having synergistic, but also antagonistic, responses on the ecosystem structural parameters. Both damming and a decrease in precipitation reduced the water flow of the stream and increased its temperature, which promoted an increase in algal and macroinvertebrate biomass at the expense of the biodiversity of their communities, a situation expected to worsen in a climate change context. The decrease in precipitation also increased the concentration of metals and metalloids in the water column and in biofilms, but the water diversion from damming reduced their contributions downstream. The maintenance of an adequate ecological flow in dam-impounded streams is encouraged to overcome these impacts in the current climate change context. More field studies are needed to assess how multiple anthropogenic stressors interact and threaten the ecosystem integrity in a realistic and applied context.