Crested Butte Wildflowers, Wildlife, and Community Identity

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Research Primer

Background

The high-elevation watersheds of the Gunnison Basin act as biogeochemical reactors, where snow, soil, bedrock, and microbes interact to shape the chemistry of water flowing downstream. Understanding how water moves through these landscapes — and what dissolves, precipitates, or transforms along the way — is central to predicting water quality, carbon cycling, and the fate of contaminants like uranium left behind from a century of mining and milling on the Colorado Plateau. Research in this area links mountain hydrology (how water travels through snowpack, soils, and fractured bedrock) with biogeochemistry (the chemical reactions that occur as water contacts rocks, organic matter, and microbes).

A few core concepts anchor this work. Weathering is the chemical breakdown of rocks by water and gases, releasing dissolved ions such as calcium, sulfate, and trace metals into streams. Reactive transport refers to the coupled movement and chemical transformation of these dissolved substances as water flows underground; geochemists describe sorption (the sticking of dissolved species to mineral or organic surfaces, often summarized as a distribution coefficient Kd) and cation exchange (swapping of dissolved ions for ions held on mineral surfaces) as key processes that slow contaminant migration. Concentration-discharge relationships describe how solute concentrations in streams change as flow rises and falls; when concentrations stay roughly constant, the system is called chemostatic, while hysteresis (different concentrations on the rising versus falling limb of a flood) reveals different sources contributing to streamflow.

Groundwater–surface water interactions matter especially in mountain catchments, because much of a stream's flow during dry periods comes from subsurface storage. Wetlands and riparian zones often function as biogeochemical hot spots, where low-oxygen conditions slow decomposition and produce elevated dissolved organic matter. Together, these processes determine how a watershed exports carbon, nutrients, and metals — and how human disturbances such as grazing, mining, or climate change reshape that export.

Foundational work

Early watershed-scale work in western Colorado focused on how land use altered the basic water and sediment balance of dryland catchments. A 14-year paired-watershed study near Grand Junction showed that grazed watersheds produced about 30% more runoff and 45% more sediment than ungrazed watersheds, with bare soil cover strongly correlated to runoff (r = 0.81) (Lusby, 1970). That study established the paired-watershed approach and the principle that surface cover, not just precipitation, governs how much water and material leaves a basin — a foundation for later, more chemically detailed studies in the region.

A second foundation came from process-based studies of solute sources in the East River, the RMBL-adjacent watershed that has become a community observatory for mountain biogeochemistry. Column experiments on Mancos shale, the dominant bedrock in much of the Gunnison Basin, showed that contact-metamorphosed shale releases calcium an order of magnitude faster than unaltered shale, with metamorphosed samples containing roughly 42% more calcite (Sams, 2018). Complementary stream chemistry work documented that wetland-bearing tributaries such as Rock Creek and Gothic Creek deliver dissolved organic carbon at concentrations 2.5 to 8.9 times higher than the main East River, identifying alpine wetlands as outsized carbon sources in the basin (Rainaldi, 2016).

Key findings

A central theme across studies is that the underlying geology sets the chemical fingerprint of mountain streams, but biology and hydrology modulate it. Mancos shale weathering experiments demonstrated that calcium release scales with calcite content and is sensitive to flow rate, with order-of-magnitude differences between 1 and 2 mL min⁻¹ flow conditions, indicating that residence time of water in contact with rock is as important as rock chemistry itself (Sams, 2018). In the Copper Creek sub-catchment of the Upper East River, paired concentration-discharge and tracer measurements identified sites with strong groundwater contributions — recognizable by cold temperatures, high total dissolved solids, and low pH — and quantified discharge gains downstream, showing that small alpine catchments are not uniform but are stitched together from distinct groundwater sources (Ruckhaus, 2017).

Wetlands emerge repeatedly as biogeochemical hot spots. Detailed sampling along East River tributaries showed dissolved organic carbon concentrations rising from below 1 mg/L at wetland inlets to over 3 mg/L at outlets within a single growing season, and Rock Creek Wetland alone was estimated to hold between 3.3 and 5.2 million kilograms of soil organic carbon (Rainaldi, 2016). Notably, wetland presence rather than vegetation cover, elevation, or hillslope explained tributary carbon export, pointing to saturation and low oxygen — not landscape position alone — as the master controls.

A parallel body of work addresses uranium reactive transport at former mill sites on the Colorado Plateau, where residual uranium below excavated tailings continues to release into groundwater. Pairing fission-track radiography with electron microscopy revealed that uranium occurs in three distinct solid-phase forms: coatings of aluminum-silicon gel and gypsum, evaporite salts in the unsaturated zone, and uranium sorbed to organic carbon (Johnson et al., 2021). Column experiments showed that high-alkalinity river water mobilizes uranium from unsaturated sediments far more efficiently than rain-like deionized water, implying that floods, not storms, drive long-term uranium release; organic-carbon-rich sediments retained uranium more strongly, consistent with a higher sorption coefficient (Johnson et al., 2022). Field-scale push-pull tests then quantified hydraulic conductivity, dispersion, cation exchange, and gypsum dissolution parameters needed for sitewide reactive transport models, moving the field beyond a single fixed Kd toward chemistry-aware predictions (Johnson et al., 2023).

Current frontier

Early work in the 1970s established the basic land-use controls on runoff and erosion in western Colorado (Lusby, 1970). Studies in the mid-2010s shifted attention to solute sources within mountain catchments, identifying wetlands and metamorphosed bedrock as disproportionate contributors of carbon and major ions in the East River (Rainaldi, 2016; Sams, 2018; Ruckhaus, 2017) (Sams, 2018) (Ruckhaus, 2017). Since 2020, the frontier has moved in two directions. First, uranium research has progressed from identifying solid-phase mineral hosts (Johnson et al., 2021), to characterizing release behavior in laboratory columns (Johnson et al., 2022), to deriving aquifer-scale transport parameters via field tracer tests calibrated with reactive transport models (Johnson et al., 2023). Second, the discovery of enormous extrachromosomal DNA elements called Borgs in archaea — including from Colorado wetland sites, with 19 distinct types identified across western U.S. wetlands and lengths up to a third of the host chromosome — hints that microbial communities mediating methane and metal cycling may be far more genetically dynamic than previously assumed (Dance, 2021).

Methodologically, the field is converging on multiscale, multi-method approaches: pairing column experiments with field tracer tests, coupling geochemical analyses with microbial genomics, and integrating these into reactive transport models that can simulate variable sorption under changing remediation or climate scenarios.

Open questions

Key questions remain about how mountain watersheds will respond to a warming, drying climate. How will earlier snowmelt and longer dry seasons reshape groundwater contributions to streams, and will wetland carbon stocks remain stable as water tables drop? At contaminated sites, can reactive transport models built from current tracer tests reliably forecast uranium release decades into the future, particularly under increased flooding or shifts in groundwater alkalinity? How do the newly discovered Borg elements alter the metabolic potential of wetland microbes that govern methane and metal cycling? And how transferable are findings from the East River to other Gunnison Basin catchments with different bedrock, glacial history, and land-use legacies? Addressing these questions will require sustained, basin-wide observatories that link hydrology, geochemistry, and microbiology across scales.

References

Dance, A. (2021). Massive DNA 'BORG' Structures Perplex Scientists. Nature. →

Johnson, R. H., Hall, S. M., Tigar, A. D. (2021). Using Fission-Track Radiography Coupled with Scanning Electron Microscopy for Efficient Identification of Solid-Phase Uranium Mineralogy at a Former Uranium Pilot Mill (Grand Junction, Colorado). Geosciences. →

Johnson, R. H., Paradis, C. J., Kent, R. D., Tigar, A. D., Reimus, P. W. (2023). Single-Well Push–Pull Tracer Test Analyses to Determine Aquifer Reactive Transport Parameters at a Former Uranium Mill Site (Grand Junction, Colorado). Minerals. →

Johnson, R. H., Tigar, A. D., Richardson, C. D. (2022). Column-Test Data Analyses and Geochemical Modeling to Determine Uranium Reactive Transport Parameters at a Former Uranium Mill Site (Grand Junction, Colorado). Minerals. →

Lusby, G. C. (1970). Hydrologic and Biotic Effects of Grazing vs. Non-Grazing near Grand Junction, Colorado. Journal of Range Management. →

Rainaldi, E. (2016). The Role of Alpine Wetlands as Hot Spots of Dissolved Organic Carbon in the East River, Colorado. →

Ruckhaus, M. (2017). Concentration-discharge behavior as an indication of groundwater contribution in Copper Creek sub-catchment of the Upper East River Basin. →

Sams, A. (2018). Contact Metamorphism of the Mancos Shale: Impacts on Solute Release and Weatherability in the East River Valley, Gothic, CO. →

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