Signatures of hydrologic function across the critical zone observatory network

Wlostowski A. N., N. Molotch, S. P. Anderson, S. L. Brantley, J. Chorover, D. Dralle, P. Kumar, L. Li, K. A. Lohse, J. M. Mallard, J. C. McIntosh, S. F. Murphy, E. Parrish, M. Safeeq, M. Seyfried, Y. Shi, and C. Harman

Published in Water Resources Research, 2021

Despite a multitude of small catchment studies, we lack a deep understanding of how variations in critical zone architecture lead to variations in hydrologic states and fluxes. This study characterizes hydrologic dynamics of fifteen catchments of the US Critical Zone Observatory (CZO) Network where we hypothesized that our understanding of subsurface structure would illuminate patterns of hydrologic partitioning. The CZOs collect datasets that characterize the physical, chemical, and biological architecture of the subsurface, while also monitoring hydrologic fluxes such as streamflow, precipitation, and evapotranspiration. For the first time, we collate time series of hydrologic variables across the CZO network and begin the process of examining hydrologic signatures across sites. We find catchments with low baseflow indices and high runoff sensitivity to storage receive most of their precipitation as rain and contain clay-rich regolith profiles, prominent argillic horizons, and/or anthropogenic modifications. In contrast, sites with high baseflow indices and low runoff sensitivity to storage receive the majority of precipitation as snow and have more permeable regolith profiles. The seasonal variability of water balance components is a key control on the dynamic range of hydraulically-connected water in the critical zone. These findings lead us to posit that water balance partitioning and streamflow hydraulics are linked through the co-evolution of critical zone architecture but that much work remains to parse these controls out quantitatively.