Importance of Soil and Fractured Bedrock Storage in Sustaining Vegetation Productivity and Streamflow for Sub-Humid Mountainous Catchments

Ravindra Dwived1, T. Meixner1, J. McIntosh1, T. Ferré1, C. Eastoe2, C. Castro1, GY Niu1, R. Minor3, J. Knowles3, GA Barron-Gafford3, N. Abramson4, B. Mitra, M. Stanley, J. Chorover5

1Department of Hydrology and Atmospheric Sciences, 2Department of Geosciences (retired), 3School of Geography and Development, 4Biosphere-2, 5Department of Soil, Water and Environmental Science, The University of Arizona

6University of Texas, College Station,

7Mt. Lemmon Water District, Tucson, AZ

Mountainous catchments provide critical water and ecosystem services for adjacent lowlands in xeric regions, yet a better understanding of the role of catchment water storage in provisioning these services remains a grand challenge for hydro-ecologists. Here, we performed catchment-scale water balance and baseflow recession analyses for understanding the role of ecohydrologic and hydraulic storages on ecosystem and streamflow sustainability within the high-elevation Marshall Gulch catchment in the Santa Catalina Critical Zone Observatory. Using long-term (2009-2017) observations of hydraulic fluxes and shallow water stores, results indicate that the ecosystem is not in a steady-state and is still responding to recent fire, i.e. Aspen fire in 2003. During the dry season, following spring snowmelt and before the summer monsoons, most of the vegetation productivity is maintained by shallow water storage providing water at a rate of 0.9 (±0.23) mm/day. A comparison of ecohydrologic and hydraulic storage estimates further shows a strong relationship (r2=0.70) between the two reservoirs, with ecohydrologic storage being greater by a factor of 2.5. Finally, the results indicate groundwater storage available for vegetation productivity in this mountainous catchment is larger than the storage available for sustaining streamflow, which suggests greater resiliency of the terrestrial ecosystem to climate-induced water stresses.