The overall aim of this project is to elucidate the biogeochemical processes that control the pH-alkalinity variation at fine scales in mountain aquatic sistems (e.g. microhabitats, interannual and decadal tendencies and fluctuations, changes across vegetation gradients), providing the reference to characterize the fluctuations that local diatoms communities may experience. This work is focused to address our general hypothesis that local diatom communities are responding to direct and catchment-mediated effects of the current atmospheric CO2 increase, by providing insight into the small scale mechanisms of alkalinity generation. Our specific working hypothesis in this subproject is that the aggregation of such fine scale mechanisms gives rise to mesoscale patterns/gradients of alkalinity (both in space and time), that are the ecological framework in which local communities evolve. The conceptual basis for this analysis is the Landscape Continuum Model (LCM) applied to high mountain catchments.