Overarching research question that guides CZO design

How does variability in climate, lithology and disturbance influence CZ structure and function over long (e.g., landscape evolution) and short (e.g., hydrologic event) time scales?

Goals of the Jemez-Catalina CZO

• Develop a cross-disciplinary, multi-scale, natural laboratory for collaborative observation and modeling.
• Measure the effects of climate, lithology, and disturbance variation on Critical Zone structure, function and evolution in the water-limited southwestern US.
• Focus on environmental gradients within regional watersheds.
• Develop a predictive-mechanistic understanding of how these systems affect environmental sustainability in a region of rapidly growing population growth and diminishing freshwater supplies.

Urban population growth throughout the southwestern US is sustained largely by water supplies that derive from upland catchments in nearby montane landscapes.  Southwestern mountain belts in Southern Arizona, for example, which vary widely in lithology, are sometimes termed “Sky Islands” because their higher elevations receive more annual precipitation, support greater vegetation biomass and have higher rates of net primary production than the surrounding “sea” of desert semi-arid to arid landscape. Ecosystems and soil development at high elevations in the Southwest also support domestic forestry, range and recreation industries.  Global climate models predict progressive warming and drying of the U.S. Southwest overall, and this is expected to affect the composition and health of ecosystems across the elevation range, e.g., through stress-induced disturbances such as insect outbreaks and wildfire.

Southwestern mountain systems are nonetheless expected to continue to serve as the water supply conduit to growing basin cities, in addition to supporting forestry, range and recreational activities.  The need to understand their capacity to do so in the context of changing climate motivates Jemez-Catalina CZO research.  The quantity and quality of water in upland catchments and receiving metropolitan areas depend on the processes that partition and transform it during its reactive transport through the CZ.  However, the present-day hydrologic, geomorphic and (bio)geochemical behavior of the CZ depends, in turn, on its structure, which has evolved over geological time scales in response to long-term climatic and tectonic forcing.  Therefore, a basic understanding of contemporary CZ behavior requires developing a conceptual model of how it has evolved to its current state, and how it will continue to evolve into the future.  Such evolution includes the formation of hydrologic flow paths, the geochemical differentiation of the weathering profile, and the production and erosion of soil-mantled hillslopes.