Conservation ecology of headwater streams: a case study from the Pyrenees

Pyrenean headwater streams are singular ecosystems with a particular seasonal pattern. They sustain a unique biodiversity especially sensitive to environmental change. Because of this, their ecosystem structure and function are highly threatened by many anthropogenic stressors such as the precipitation decrease and water warming promoted by climate change, damming, and metal pollution derived from mining and other human activities. This kind of streams are fundamental for the ecological integrity of whole river networks, but there is still a need of more knowledge to propose adequate management actions. Pyrenean headwater streams are a great example to appraise these topics as they are threatened by climate change and many of them are affected by damming and metal pollution. In this context, a practical research aim is needed in order to properly manage and conserve these threatened ecosystems. Considering these needs, this thesis has selected as a case study a Pyrenean headwater stream that presents a hydroelectric dam and that receives the runoff of other tributaries draining from an old antimony mine. The results obtained in this thesis provide, in a conservation context, new information about the interactive impacts of climate change, damming and metal pollution on the ecosystem structure and function of the aquatic communities in headwater streams. It was observed that a reduction in precipitations had a synergistic impact with damming through the reduction of the water flow, which promoted the autotrophy of the stream and reduced its biodiversity, altering its ecosystem functioning. These results provide scientific evidence for the proposal of effective management actions for these ecosystems, such as the maintenance of an environmental flow, especially when considering additional local threats to each headwater stream such as metal pollution. The consequences of these interactive threats are especially relevant for key headwater species. On one hand, the availability of basal resources such as algae and macroinvertebrates can be impaired, increasing the competition for certain preys on higher trophic levels, displacing species such as the endangered Pyrenean desman (Galemys pyrenaicus). On the other hand, the interaction of damming and metal pollution can severely affect the health and distribution of populations of sensitive species such as the Pyrenean brook newt (Calotriton asper). This thesis highlights the fact that integrative approaches, including trophic interactions, are useful to understand the effects of anthropogenic impacts on the biodiversity of headwater streams and to propose effective management and conservation actions. ​
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