Hydrologic functioning of the deep critical zone and contributions to streamflow in a high‐elevation catchment: Testing of multiple conceptual models

Abstract

High-elevation mountain catchments are often subject to large climatic and topographic gradients. Therefore, high-density hydrogeochemical observations are needed to understand water sources to streamflow and the temporal and spatial behaviour of flow paths. These sources and flow paths vary seasonally, which dictates short-term storage and the flux of water in the critical zone (CZ) and affect long-term CZ evolution. This study utilizes multiyear observations of chemical compositions and water residence times from the Santa Catalina Mountains Critical Zone Observatory, Tucson, Arizona to develop and evaluate competing conceptual models of seasonal streamflow generation. These models were tested using endmember mixing analysis, baseflow recession analysis, and tritium model "ages" of various catchment water sources. A conceptual model involving four endmembers (precipitation, soil water, shallow, and deep groundwater) provided the best match to observations. On average, precipitation contributes 39-69% (55 ± 16%), soil water contributes 25-56% (41 ± 16%), shallow groundwater contributes 1-5% (3 ± 2%), and deep groundwater contributes~0-3% (1 ± 1%) towards annual streamflow. The mixing space comprised two principal planes formed by (a) precipitation-soil water-deep groundwater (dry and summer monsoon season samples) and (b) precipitation-soil water-shallow groundwater (winter season samples). Groundwater contribution was most important during the wet winter season. During periods of high dynamic groundwater storage and increased hydrologic connectivity (i.e., spring snowmelt), stream water was more geochemically heterogeneous, that is, geochemical heterogeneity of stream water is storage-dependent. Endmember mixing analysis and 3 H model age results indicate that only 1.4 ± 0.3% of the long-term annual precipitation becomes deep CZ groundwater flux that influences long-term deep CZ development through both intercatchment and intracatchment deep groundwater flows.

Mountain‐Block Recharge: A Review of Current Understanding

“…Voeckler et al () calibrated a specified head outlet in a numerical coupled surface water and groundwater model of the Upper Penticton Creek, BC, and estimated that only 7% of recharge leaves the catchment in the subsurface and becomes interbasin flow. Two studies in Marshall Gulch, AZ, obtained very small estimates (1–2% of precipitation) for bedrock groundwater recharge in this headwater catchment based on a storage‐discharge function (Ajami et al, ) and baseflow recession analysis (Dwivedi et al, ), though neither studies had access to bedrock wells for their analysis. Sandoval et al () applied a similar approach as Ajami et al () and estimated bedrock recharge to be 1–4% of precipitation in the Punitaqui Basin of northern Chile.…”

Hydrology of Mountain Blocks in Arizona and New Mexico as Revealed by Isotopes in Groundwater and Precipitation

“…Previous stable isotope studies in the SCM addressed the origin of spring water [26], the origin of groundwater associated with the detachment fault [27], the nature of precipitation at a station at 2420 masl [28] and relationships among precipitation, critical zone groundwater, soil water and stream flow [6,8,29,30].…”

Magnetic resonance sounding measurements as posterior information to condition hydrological model parameters: Application to a hard-rock headwater catchment

“…The evolution of groundwater storage in such systems in response to climatic forcing is also of great importance as it controls the amount of water and elements released to the downstream part of rivers, supports ecosystem services, and strongly impacts the amplitude of streamflow during low-flow and high-flow periods (Rinderer et al, 2014;Blumstock et al, 2016). Water circulation in such environments is complex as it is shaped by the strong heterogeneity of the subsurface medium and lacks homogenization usually brought by large-scale systems (Beven et al, 1988;Ameli et al, 2016;Chorover et al, 2017;Kim et al, 2017;Riebe et al, 2017;Dwivedi et al, 2019). In the context of hardrock geology, the spatial variability of the hydraulic properties from the superficial soils to the deeper bedrock substantially impacts the hydrological catchment response to rainfall (Banks et al, 2009;Gannon et al, 2014;Diek et al, 2014;McMillan and Srinivasan, 2015;Welch et al, 2014;Singh et al, 2018).…”