EXPLORING CONTROLS ON UNSATURATED WATER MOVEMENT IN DRYLAND ENVIRONMENTS: INITIAL INSIGHTS FROM THE DRYLAND CRITICAL ZONE NETWORK CLUSTER

Chloride profiles from and flow modeling of deep dryland vadose zones in the western U.S. indicate that hydrologic processes in the root zone are largely independent of those occurring at depth (e.g. >10 m), and that water generally does not generally move across the lowermost extent of roots. However, more recent investigations of soil moisture at the Jornada Experimental Range (JER) near Las Cruces, New Mexico show deep (>3 m) vertical water movement during wetter than normal winters (Duniway et al., 2018) and hydrologic modeling calculations suggest aquifer recharge occurs below local playas (McKenna and Sala, 2018), indicating that interactions between shallow and deep dryland environments may be more dynamic (but episodic) than originally thought.

As part of new research carried out by the Dryland Critical Zone Network Cluster to identify carbon-water-nutrient connections in arid environments, controls and fluxes of water in the vadose zone at JER are being investigated at two sites (Piedmont and Playa). In the Piedmont site root zone, we hypothesize that caliche (pedogenic carbonate) layers inhibit vertical water movement and store water that may be accessible to plants during dryer periods. Vertical soil moisture sensor profiles have been installed to depths of up to 1m at sites with and without caliche (including sensors within the caliche), where present, to determine changes in water content in response to precipitation and evapotranspiration (determined from nearby meteorological tower data). The distribution and thickness of caliche layers are being mapped along transects across multiple surfaces at JER using ground penetrating radar. Results from preliminary 1-D HYDRUS soil moisture transport modeling using 8 years of meteorological data (2010-2019) largely fits observed patterns in soil moisture and suggests that the caliche layer is critical in controlling soil moisture content and distribution.

Hypothesizing that playas at JER may recharge local aquifers, a ~100m continuous core at the Playa site will be collected from the ground surface to the water table to document vertical variations in chloride and water content. Findings from this research will be linked to ongoing efforts to study nutrient and carbon cycling, leading to a more comprehensive understanding of dryland environments.