Signatures of hydrologic function across the critical zone observatory network

Authors: WLOSTOWSKI, ADAM - University Of Colorado; MOLOTCH, NOAH - University Of Colorado; ANDERSON, SUZZANE - University Of Colorado; BRANTLEY, SUSAN - Pennsylvania State University; CHOROVER, JON - University Of Arizona; DRALLE, DAVID - University Of California; KUMAR, PRAVEEN - University Of Illinois; LI, LI - Pennsylvania State University; LOHSE, KATHLEEN - Idaho State University; MALLARD, JOHN - Duke University; MCINTOSH, JENNIFER - University Of Arizona; MURPHY, SHEILA - Us Geological Survey, Fort Collins Science Center; PARRISH, ERIC - University Of Colorado; SAFEEQ, MOHAMMAD - University Of California; Seyfried, Mark; SHI, YUNING - Pennsylvania State University; HARMAN, CIARAN - Johns Hopkins University

Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2020
Publication Date: 10/18/2020
Citation: Wlostowski, A., Molotch, N., Anderson, S., Brantley, S., Chorover, J., Dralle, D., Kumar, P., Li, L., Lohse, K., Mallard, J.M., McIntosh, J., Murphy, S.F., Parrish, E., Safeeq, M., Seyfried, M.S., Shi, Y., Harman, C. 2020. Signatures of hydrologic function across the critical zone observatory network. Water Resources Research. 57(3). Article e2019WR026635. https://doi.org/10.1029/2019WR026635.
DOI: https://doi.org/10.1029/2019WR026635

Interpretive Summary: The streamflow response of watersheds to inputs of snowmelt and rainfall varies greatly among different watersheds. We undertook this study to investigate the climatic and physical characteristics that control those responses. We evaluated runoff patterns from 15 different highly instrumented watersheds in the U.S Critical Zone Observatory network. We found that watersheds with low year-round flow and high sensitivity to input receive the majority of precipitation as rain and contain clay-rich regolith profiles, prominent argillic (soil clay) horizons, and/or anthropogenic modifications. In contrast, watersheds with the opposite properties receive a large portion of precipitation as snow, have sand-rich regolith profiles, and range from deeply to thinly weathered. The seasonal variability of water balance components appears to be a key control on the dynamic range of hydraulically-connected water in the critical zone. These findings collectively lead us to propose that water balance partitioning and streamflow hydraulics are linked through the co-evolution of critical zone architecture.

Technical Abstract: The capacity of the critical zone to store and transmit water is central to many landscape functions in the short term and to critical zone evolution over the long term. Despite a multitude of small catchment studies, we still lack a deep understanding of how variations in critical zone architecture lead to variations in hydrologic states and fluxes. As a path forward, this study characterizes the hydrologic dynamics of fifteen intensively monitored catchments of the US Critical Zone Observatory (CZO) Network. The US CZOs are collecting datasets that simultaneously characterize the physical, chemical, and biological architecture of the subsurface, while also monitoring common hydrologic fluxes such as streamflow, precipitation, and evapotranspiration. Here we 1) collate consistent daily timeseries of commonly observed hydrologic variables across the CZO network, 2) extract quantitative signatures of hydrologic function characterizing a) the partitioning of the water balance and b) the hydraulics controlling the release of water from storage as streamflow, and 3) examine the variability of these hydrologic signatures across the sites in the network. We then draw on the deep site-specific knowledge gained at the CZOs to consider the potential connections between these patterns of variability and the coevolution of the critical zones they arise in. We find catchments with low baseflow indices and high catchment runoff sensitivity to storage receive the majority of 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 catchment runoff sensitivity to storage receive a large portion of precipitation as snow, have sand-rich regolith profiles, and range from deeply to thinly weathered. The seasonal variability of water balance components appears to be a key control on the dynamic range of hydraulically-connected water in the critical zone. These findings collectively lead us to posit that water balance partitioning and streamflow hydraulics are linked through the co-evolution of critical zone architecture.