PeriCarb-EFA · Effects of extreme flow changes on periphyton biofilm and carbon cycling in Alpine streams

Effects of extreme flow changes on periphyton biofilm and carbon cycling in Alpine streams

Climate change is increasingly altering the frequency and intensity of extreme hydrological events, such as droughts and floods, with profound consequences for freshwater ecosystems. In mountain regions, these changes are occurring faster than in most other biomes. Alpine catchments are experiencing reduced snow accumulation, earlier snowmelt, shifts in the timing of peak discharge, and longer periods of low flow. These transformations directly affect streams and rivers, which play a central but still underestimated role in the global carbon cycle by retaining, transforming and releasing large amounts of carbon before it reaches coastal oceans. Despite growing evidence that inland waters are major sources of carbon dioxide to the atmosphere, a key knowledge gap remains: how climate-driven changes in flow regimes modify the biological processes that control carbon cycling in streams. In particular, the response of benthic biofilms — complex microbial communities that dominate ecosystem metabolism in running waters — to extreme and recurrent flow disturbances is still poorly understood. The PeriCarb project was designed to address this gap by investigating how extreme hydrological events and their increasing frequency reshape microbial communities and carbon processing in Alpine headwater streams and springs. By combining controlled experiments, long-term field observations and modelling approaches, the project aimed to identify the mechanisms linking flow variability, biodiversity and ecosystem metabolism across spatial scales, from biofilms to individual stream reaches and entire headwater networks. The overall objective of PeriCarb was to improve the predictability of how climate-driven hydrological change will alter carbon fluxes from headwater systems, with a specific focus on Alpine regions that are highly sensitive to warming and hydrological shifts. The project sought to determine how droughts and floods affect the structure and functioning of microbial communities, how these biological changes translate into altered carbon uptake and release, and how these effects propagate downstream to influence catchment-scale carbon processing. By providing quantitative and process-based estimates of how extreme events modify carbon cycling, PeriCarb contributes to a more accurate representation of inland waters in climate models and carbon budgets. In the broader political and strategic context of the European Green Deal and international climate mitigation efforts, the project supports the need for science-based assessments of climate feedbacks and for identifying critical thresholds beyond which freshwater ecosystems may shift towards stronger carbon sources.

Data: CORDIS, © European Union