Every Hillside Plays by Different Rules

The Critical Zone — from weathered bedrock through soil to the vegetation canopy — is where rock, water, air, and life interact to regulate water availability, soil formation, carbon cycling, and nutrient delivery to ecosystems. But we cannot predict how this zone will respond to accelerating change (climate shifts, land use intensification, wildfire, groundwater extraction). Hydrologic, geomorphic, and biogeochemical processes couple in nonlinear, site-specific ways that resist generalization. The result: we cannot reliably predict water quality changes from land use conversion, soil erosion rates under novel climate conditions, or contaminant transport through heterogeneous subsurface environments — all of which are essential for land management and water resource planning.

The Critical Zone provides nearly all terrestrial ecosystem services — freshwater supply, food production, carbon sequestration, flood buffering. Globally, 33% of soils are degraded. Groundwater, which supplies drinking water to ~2 billion people, is being extracted faster than recharged in many regions. Wildfire frequency and intensity are increasing, fundamentally altering Critical Zone processes (soil hydrophobicity, erosion rates, nutrient cycling) for years after burning. Land managers and water utilities need predictive tools but currently rely on empirical rules that break down under novel conditions.

Previous NSF Critical Zone Observatory (CZO) networks provided high-quality data from individual sites, but generalizing findings across lithologies, biomes, and climatic settings proved extremely difficult because the controlling processes differ fundamentally between granite, basalt, carbonate, and shale terrains. Hydrology, geomorphology, biogeochemistry, and soil science have historically been separate disciplines with different measurement techniques, different modeling traditions, and different vocabulary — creating persistent integration barriers. The interactions between microbial activity, bedrock composition, and climate on weathering rates are nonlinear and site-specific, resisting simple parameterization. Fate and transport of water, solutes, and contaminants through heterogeneous subsurface environments cannot be predicted from surface observations alone because subsurface heterogeneity is impossible to characterize at the relevant scales.

WaLCZ's $23.85M annual budget (60–80 awards) supports hypothesis-driven research on near-surface Earth systems. Integration of field, laboratory, and computational approaches at sites spanning diverse environmental gradients would enable comparative analysis. New sensor technologies for continuous monitoring of subsurface water chemistry and movement (soil moisture sensors, fiber-optic distributed temperature sensing, geophysical imaging). Process models that couple hydrologic, geomorphic, and biogeochemical cycles at catchment to regional scales. Cross-disciplinary proposals linking environmental biology, engineering, and social science to Earth science.

A student team could instrument a small local watershed with low-cost soil moisture sensors, rain gauges, and stream gauges to build a hydrologic response model, comparing their observations to predictions from a standard watershed model (e.g., SWAT, TOPMODEL) to quantify where the model fails. Alternatively, a team could analyze soil chemistry and water quality data from CZO or NEON sites across contrasting lithologies to test whether a single weathering model can predict both, identifying where site-specific factors dominate. Relevant skills: hydrology, soil science, sensor engineering, environmental chemistry, geospatial analysis.