Paolo Benettin’s paper was just accepted, which was the result of his study abroad visit here in the lab during the fall 2013 and spring 2014. The manuscript explores water age-dependent transport in estimating we
athering-derived solute export. The model predicts water travel time dynamics from water stable isotope data and represents geochemical dissolution at the catchment-scale as a simple first-order kinetic relationship based explicitly on the dynamic water travel time distributions. Paolo completed his dissertation last year at the University of Padova and is now a postdoc at EPFL (École polytechnique fédérale de Lausanne).
Abstract: We combine experimental and modeling results from a headwater catchment at the Hubbard Brook Experimental Forest (HBEF), New Hampshire, USA, to explore the link between stream solute dynamics and water age. A theoretical framework based on water age dynamics, which represents a general basis for characterizing solute transport at the catchment scale, is here applied to conservative and weathering-derived solutes. Based on the available information about the hydrology of the site, an integrated transport model was developed and used to compute hydrochemical fluxes. The model was designed to reproduce the deuterium content of streamflow and allowed for the estimate of catchment water storage and dynamic travel time distributions (TTDs). The innovative contribution of this paper is the simulation of dissolved silicon and sodium concentration in streamflow, achieved by implementing first-order chemical kinetics based explicitly on dynamic TTD, thus upscaling local geochemical processes to catchment scale. Our results highlight the key-role of water stored within the sub-soil glacial material in both the short- and long-term solute circulation. The travel time analysis provided an estimate of streamflow age distributions and their evolution in time related to catchment wetness conditions. The use of age information to reproduce a 14-year dataset of silicon and sodium stream concentration shows that, at catchment scales, the dynamics of such geogenic solutes are mostly controlled by hydrologic drivers, which determine the contact times between the water and mineral interfaces. Justifications and limitations toward a general theory of reactive solute circulation at catchment scales are discussed.