Impact of tropical forest cover changes on the spatio-temporal heterogeneities of water flow paths and water-rock interactions

International audiencePlants link the atmosphere to the Earth's crust, and much remains to be known about the hydrological and biogeochemical consequences of altering ecosystem distribution and functioning. This issue may be particularly pressing in highly seasonal hydroclimatic settings, where the intermittency of water flows and the transient storage of precipitation inputs are salient features to be considered for biogeochemical processes in the critical zone (CZ) and the general availability of water resources. Here we primarily focus on changing root water uptake profiles following land cover change, which heterogeneously alter water partitioning across landscape positions, and in turn impact the timing and spatial distribution of the reactive transport of nutrients within the CZ. We do so using simulations, under current conditions and hypothetical land cover scenarios, from a cascade of spatially-distributed numerical tools. Hydrological states are given by the process-based ecohydrological model EcH2O-iso, accounting for the coupling between energy balance, critical zone hydrology and vegetation dynamics. Water-rock interactions are described using the modular chemical weathering model WITCH3D, simulating dissolution/precipitation rates of mineral phases based on kinetics laws. This analysis is conducted at the long-term experimental catchment of Mule Hole in Peninsular India, where a pristine deciduous forest overlaying a deep unsaturated profile, under a monsoon climatic regime. This catchment is part of both the Indian Kabini CZ observatory and the French CZ observatory network OZCAR, with extensive hydrometric and chemical datasets available for model calibration and evaluation. We discuss the interplay between distinctively mobilized critical zone compartments from the hillslope scale to the whole catchment, distinguishing the respective controls of structural heterogeneity (in terms of hydrodynamic and chemical properties) and hydrological heterogeneities (in terms of changing flow paths)