QUANTIFYING TOPOGRAPHIC, VEGETATION, AND DISTURBANCE EFFECTS ON THE TRANSFER OF ENERGY AND MASS TO THE CRITICAL ZONE

Critical zone (CZ) evolution, structure, and function are driven by energy and mass fluxes into and through the terrestrial subsurface. Internal fluxes and spatial structure coevolve in response to the transfer and transformation of energy and mass through the CZ system. Quantifying these fluxes is central to understanding the CZ and predicting its ability to provide key services to society. Here we present an approach to quantifying the effective transfer of energy and mass (EEMT; MJ m^-2 yr^-1) to the subsurface that accounts for local variation in topography, water and energy balances, and primary production. The objectives of the current contribution were to quantify how (i) local topography controls coupled energy and water balances; (ii) vegetation effects local scale evapotranspiration and primary production; and (iii) disturbance effects energy and mass transfer to the critical zone, all at polypedon to hillslope scale resolution. The model was tested across a semiarid environmental gradient in southern Arizona, spanning desert to mixed conifer ecosystems as part of the Santa Catalina Mountain Critical Zone Observatory. Data indicated clear variation in EEMT by topography and with current vegetative cover. Key findings include: (i) greater values of EEMT were observed on north facing slopes in a given climate class and elevation zone, equivalent to a 300 m elevation gain; (ii) disturbance in the form of stand replacing wildfire substantially reduced estimates of EEMT as a result of a reduction in biomass and predicted primary productivity; (iii) we documented a power law relationship between aboveground biomass and EEMT.