From microscale observation to macroscopic quantification: Linking microbial dynamics and carbon fluxes in inland waters

Inland waters are major players of the global carbon cycle. Despite their modest surface area on Earth, inland waters show a high biogeochemical reactivity across the land-ocean continuum and account for annual CO2 emissions equivalent to the ocean carbon sink. While such emissions are, for instance, commonly related to an overall prevalence of organic matter mineralization over production, our current understanding of the fine spatial and temporal dynamics of carbon cycling in aquatic systems remains limited. In this talk, we will discuss how continuous multi sensor monitoring networks enable characterizing the hydro-geochemical conditions and microbial communities driving the metabolic regimes of flowing waters, from small pristine alpine headwaters to larger human-impacted rivers. Moreover, in lentic ecosystems fueled by carbonate and silicate catchment weathering, we will present how calcite precipitation bound to autotrophic microbial metabolism represents a pivotal yet overlooked process of the carbon budget, whereby alkalinity inputs are translocated into CO2 emissions. These findings underline the relevance of fine scale mechanisms and inorganic equilibria to constrain carbon fluxes through inland waters and shape new research perspectives along the hydrological continuum.