PeriCarb implemented an integrated, multi-scale research strategy combining the analysis of controlled experiments, long-term field observations, targeted modelling and global data synthesis to investigate how extreme hydrological events alter carbon cycling in Alpine headwater streams and beyond. The scientific activities were structured around four tightly linked components: the analysis of existing mesocosm experiments at the biofilm scale, reach-scale field measurements in Alpine spring–stream systems, modelling of carbon processing in headwater networks, and the development of a global synthesis on carbon fluxes from springs.
At the biofilm scale, PeriCarb analysed a unique set of experimental stream mesocosms in which flow intensity and the frequency of extreme low-flow events had been manipulated prior to the start of the project. These experimental datasets were comprehensively analysed to address new scientific questions on the links between hydrological disturbance, biodiversity and carbon cycling. Detailed analyses of chlorophyll concentration, organic matter accumulation, primary production and ecosystem respiration were combined with taxonomic characterisation of microbial communities. This work led to the first peer-reviewed publication from the project, which demonstrated how flow variability and macroinvertebrates jointly regulate stream periphyton and ecosystem metabolism based on experimental stream mesocosms.
At the reach scale, PeriCarb carried out year-round monitoring in a network of four near-pristine Alpine spring–stream systems. High-frequency oxygen sensors, repeated carbon dioxide measurements and continuous discharge monitoring produced long-term metabolism time series spanning two full hydrological years. In two of these systems, data were collected also during winter under snow cover, generating rare observations of ecosystem functioning during periods that are typically inaccessible in mountain environments. The project combined high-frequency oxygen data with resazurin tracer experiments to quantify bacterial activity, systematic collection and taxonomic characterisation of periphyton biofilms, and repeated measurements of carbon dioxide concentrations. This integrated dataset enabled the development and application of new coupled oxygen–carbon dioxide modelling approaches, providing a mechanistic quantification of how seasonal hydrological dynamics regulate carbon processing in Alpine headwaters. These data are currently being analysed for publication.
At the headwater network scale, PeriCarb developed and applied modelling frameworks to upscale local biological responses to the scale of Alpine headwater streams. By coupling discharge dynamics, ecosystem metabolism and microbial biomass processes, the project quantified how changes in the frequency and intensity of extreme events propagate through headwater networks to modify organic carbon processing and downstream carbon exports.
During the project, field measurements revealed consistently high CO2 concentrations in several springs. This observation highlighted that groundwater-fed systems represent a previously underappreciated source of atmospheric carbon. It triggered the development of a strong global synthesis work focused on the role of springs in the global carbon budget. Through the creation of an international consortium involving partners from multiple continents, PeriCarb assembled one of the first worldwide databases of CO2 concentrations and fluxes from springs. An international high–impact-factor manuscript based on this global database is currently in preparation and represents a major expected outcome of the project.
Together, these activities delivered a coherent mechanistic and global understanding of how extreme flow events reshape microbial communities, ecosystem metabolism and carbon fluxes in running waters.
