Wendy S. Brown - Publications with AbstractsBugs Unlimited, LLCPO Box 1451 Crested Butte, CO 81224 wshbrown ª icloud. com affiliated with The Rocky Mountain Biological Laboratory (RMBL) Lawrence Berkeley National Laboratory (LBL) Berkelhammer,M; Page,GF; Zurek,F; Still,C; Carbone,MS; Talavera,W; Hildebrand,L; Byron,J; Inthabandith,K; Kucinski,A; Carter,M; Fossa,K; Brown,W; Carroll,RWH; Simonpietri,A; Worsham,M; Breckheimer,I; Ryken,A; Maxwell,R; Gochis,D; Raleigh,M; Small,E and Williams,KH 2025 Canopy structure modulates the sensitivity of subalpine forest stands to interannual snowpack and precipitation variability. Hydrology and Earth System Sciences 29 pp.701-718. https://doi.org/10.5194/hess-29-701-2025 PDF Abstract: "Declining spring snowpack is expected to have widespread effects on montane and subalpine forests in western North America and across the globe. However, the effect of this forcing at the species and hillslope scale are difficult to predict from remote sensing or eddy covariance. Here, we present data from a network of sap velocity sensors and xylem water isotope measurements from three common subalpine tree species (Picea engelmannii, Abies lasiocarpa, Populus tremuloides) across a hillslope transect in a subalpine watershed in the Upper Colorado River Basin. We use these data to compare tree- and stand-level responses to the historically high spring snowpack but low summer rainfall of 2019 against the low spring snowpacks but high summer rains of 2021 and 2022. From the sap velocity data, we found that only 40 % of the trees showed an increase in cumulative transpiration in response to the large snowpack year (2019), illustrating the absence of a common response to a major decline in snowpack. The trees that benefited from the large snow year were all found in dense canopy stands - irrespective of species - while trees in open canopy stands were more active during the years with modest snow and higher summer rains. This pattern reflects how persistent access to soil moisture recharged by snowmelt in topographically-mediated convergence zones shapes stand density. These locally dense canopies also experience high levels of summer rainfall interception that reduce summer precipitation inputs to the soil perpetuating their greater sensitivity to snowmelt inputs. The results illustrate that the progression towards a low snowpack future will manifest at the sub-hillslope scale in dense stands with significant rainfall interception and high water demands reflecting their historical reliance on snowmelt water." Bouskill,NJ; Newcomer,M; Carroll,RWH; Beutler,C; Bill,M; Brown,WS; Conrad,M; Dong,WS; Falco,N; Maavara,T and Newman,A 2024 A Tale of two catchments: Causality analysis and isotope systematics reveal mountainous watershed traits that regulate the retention and release of nitrogen. Journal of Geophysical Research: Biogeosciences, 129(3), p.e2023JG007532. PDF Abstract: "Mountainous watersheds are characterized by variability in functional traits, including vegetation, topography, geology, and geomorphology, which determine nitrogen (N) retention, and release. Coal Creek and East River are two contrasting catchments within the Upper Colorado River Basin that differ markedly in total nitrate (NO3-) export. The East River has a diverse vegetation cover, and sinuous floodplains, and is underlain by N-rich marine shale. At 0.21 ± 0.14 kg ha-1 yr-1, the East River exports ∼3.5 times more NO3- relative to the conifer-dominated Coal Creek (0.06 ± 0.02 kg ha-1 yr-1). While this can partly be explained by the larger size of the East River, the distinct watershed traits of these two catchments imply different mechanisms controlling the aggregate N-export signal. A causality analysis shows physical and biogenic processes were critical in determining NO3- export from the East River catchment. Stable isotope ratios of NO3- (δ15NNO3 and δ18ONO3) show the East River catchment is a strong hotspot for biogeochemical processing of NO3- at the hillslope soil-saprolite. By contrast, the conifer-dominated Coal Creek retained nearly all atmospherically deposited NO3-, and its export was controlled by catchment hydrological traits (i.e., snowmelt periods and water table depth). The conservative N-cycle within Coal Creek is likely due to the abundance of conifer trees, and smaller riparian regions, retaining more NO3- overall and reduced processing prior to export. This study highlights the value of integrating isotope systematics to link watershed functional traits to mechanisms of watershed element retention and release." Plain Language Summary: "The role different functional traits play in the retention and release of nitrogen remains uncertain. Here we describe how two neighboring catchments in the Upper Colorado River Basin, characterized by contrasting vegetation, geology, and geomorphology, cycle and export nitrogen. The East River catchment, which is underlain by nitrogen-rich shale, and has a diverse vegetation cover, releases over three times as much nitrate (NO3-) than the conifer-dominated Coal Creek, which is underlain by granitic rock. However, a suite of analyses show that the distinct watershed traits of these two catchments lead to diverse pathways of nitrogen cycling. Biogenic processes, critical to determining NO3- export in East River, impart strong biogeochemical processing prior to export. By contrast, Coal Creek retains almost all of the atmospherically deposited NO3-, likely due to uptake by conifers, and a small riparian region. This study highlights the use of nitrate isotope systematics to parse different mechanisms leading to NO3- export." Key Points: • Comparing and contrasting neighboring catchments identifies watershed traits regulating the cycling, retention and release of nitrogen • Conifer forest-dominated catchments show a conservative nitrogen cycling, retaining ∼97% of atmospherically dominated nitrate • By contrast, meadow-dominated catchments underlain Mancos shale are biogeochemical hotspots for N-cycling, and export higher nitrate loads Carroll,RWH; Bearup,LA; Brown,W; Dong,W; Bill,M and Willlams,KH 2018 Factors controlling seasonal groundwater and solute flux from snow-dominated basins. Hydrological Processes. 1-16. PDF Abstract: "Critical zone influences on hydrologic partitioning, subsurface flow paths and reactions along these flow paths dictate the timing and magnitude of groundwater and solute flux to streams. To isolate first-order controls on seasonal streamflow generation within highly heterogeneous, snow-dominated basins of the Colorado River, we employ a multivariate statistical approach of end-member mixing analysis using a suite of daily chemical and isotopic observations. Mixing models are developed across 11 nested basins (0.4 to 85 km2) spanning a gradient of climatological, physical, and geological characteristics. Hydrograph separation using rain, snow, and groundwater as end-members indicates that seasonal contributions of groundwater to streams is significant. Mean annual groundwater flux ranges from 12% to 33% whereas maximum groundwater contributions of 17% to 50% occur during baseflow. The direct relationship between snow water equivalent and groundwater flux to streams is scale dependent with a trend toward self-similarity when basins exceed 5.5 km2. We find groundwater recharge increases in basins of high relief and within the upper subalpine where maximum snow accumulation is coincident with reduced conifer cover and lower canopy densities. The mixing model developed for the furthest downstream site did not transfer to upstream basins. The resulting error in predicted stream concentrations points toward weathering reactions as a function of source rock and seasonal shifts in flow path. Additionally, the potential for microbial sulfate reduction in floodplain sediments along a low-gradient, meandering portion of the river is sufficient to modify hillslope contributions and alter mixing ratios in the analysis. Soil flushing in response to snowmelt is not included as an end-member but is identified as an important mechanism for release of solutes from these mountainous watersheds. End-member mixing analysis used in combination with high-frequency observations reveals important aspects of catchment hydrodynamics across scale." Carroll,RW; Deems,J; Sprenger,M; Maxwell,R; Brown,W; Newman,A; Beutler,C and Williams,KH 2022 Modeling snow dynamics and stable water isotopes across mountain landscapes. Geophysical Research Letters, p.e2022GL098780. html Abstract: "A coupled hydrologic and snowpack stable water isotope model assesses controls on isotopic inputs across a mountainous basin. Annually, the most depleted isotope conditions occur in the upper subalpine where snow accumulation is high, and rainfall is low. Snowmelt isotopic evolution over time indicates fractionation processes account for <25% snowmelt enrichment. Meltwater isotopic inputs are largely determined by controls on the amount, phase and isotopic mass of precipitation coincident with the ablation period. Effect of vapor loss from the snowpack on d-excess in snowmelt is a balance between energy and snow-availability. It is highest above treeline, and in the grass and aspen-dominated portions of the upper montane where vegetation shading is low. Deep snowpack in conifer forests limit the influence of vapor loss in the subalpine. Wet years reduce the effects of vapor loss on snowmelt across the basin, except in the lower montane where added snowfall bolsters snow-limited conditions." Key Points: • Precipitation timing, phase, and isotopic value dominate meltwater inputs. Fractionation accounts for less than 25% total enrichment • The most depleted isotopic water inputs occur in the upper subalpine where snow accumulation is high and rainfall is low • Deep snowpack and shading of conifer forests limit the influence of vapor loss on snowmelt Plain Language Summary: "Stable water isotopes are used in hydrology to track vegetation water use and stream water source. Watersheds reliant on snow alter the timing of water inputs through snow storage and melt and may produce a different isotopic input signal due to evaporation of the snowpack prior to melt. We combine a hydrologic and snowpack isotope model to understand how landscape position and climate may affect isotopic water inputs in a large mountain basin with nearly 2 km in vertical relief. The lightest isotopes occur in the upper subalpine where snow accumulation is highest and rain inputs are low. The temporal evolution of isotopes in snowmelt is largely controlled by elevation and its influence on the amount, phase (rain or snow) and isotopic mass of spring precipitation coincident with the snowmelt period. Snowpack alterations account for <25% total snowmelt enrichment. Changes to the snowpack isotopic signature by vapor loss are most important where vegetation does not shade the snow, where moderate snowfall occurs and evaporation potential is relatively high. Changes are highest above treeline and in areas with meadows and aspen forests. Vapor loss effects on snowpack are lowest in the deep snow found in conifer forests, and in snow-limited lower elevations." Fox,PM; Carrero,S; Anderson,C; Dewey,C; Keiluweit,M; Conrad,M; Naughton,HR; Fendorf,S; Carroll,R; Dafflon,B; and Malenda-Lawrence,H; Dwivedi,D; Gilbert,B; Christensen,JN; Boye,K; Beutler,C; Brown,W; Newman,A; Versteeg,R; Williams,KH and Nico,PS 2022 Sulfur biogeochemical cycling and redox dynamics in a shale-dominated mountainous watershed. Journal of Geophysical Research: Biogeosciences, 127(6), p.e2021JG006769. PDF Abstract: "Sulfur (S) is an essential macronutrient and important component of the earth's crust, and its cycling has critical impacts on trace metal mobility, water quality, and human health. Pyrite weathering is the primary pathway by which sulfur enters surface waters. However, biogeochemical cycling of sulfur in soils and the river corridor mediates sulfate exports. In this study, we identified the major forms of sulfur across multiple compartments and scales in a pristine mountainous watershed, including shale bedrock weathering profiles, hillslope soils, and alluvial floodplain sediments, in order to provide insight into biogeochemical sulfur cycling in a hydrologically variable alpine system. X-ray absorption near-edge spectroscopy (XANES) analysis of shale weathering profiles showed clear evidence of pyrite oxidation to sulfate, with large accumulations of intermediate S(0) (20%-53%). Micro-scale XANES showed evidence of reprecipitation of pyrite at fracture surfaces within the permanently saturated zone. Organic sulfur dominated S speciation in shallow hillslope soil and floodplain sediment, with little evidence of reduced inorganic S. However, mackinawite formation, representing active sulfate reduction, was observed in saturated oxbow sediments and saturated weathered shale underlying floodplain sediments. Further evidence of sulfate reduction from aqueous sulfur isotopic analysis was observed in shallow groundwater transects across an Fe-reducing meander, whereas increases in pore water sulfate concentrations implied sulfur oxidation at other locations. The data present an integrated picture of sulfur cycling in a shale-dominated watershed, where riverine sulfate exports are mediated by biological cycling, particularly in redox-stratified and temporally dynamic hyporheic zone sediments." Plain Language Summary: "Sulfur is an essential macronutrient and biologically important component of the earth's crust, and its cycling has critical impacts on water quality and human health. Weathering of the mineral pyrite from rock is the primary pathway by which sulfur enters surface waters, and alterations to the hydrologic cycle due to climate change may affect pyrite weathering rates. However, biological cycling of sulfur in soils and the river corridor mediates the release of sulfur to rivers and the ocean. In this study, we identified the major forms of sulfur across a pristine mountainous watershed, including shale bedrock weathering profiles, hillslope soils, and alluvial floodplain sediments. Shale weathering profiles showed pyrite conversion to sulfate, with large accumulations of intermediate elemental sulfur. In the river corridor, precipitation of the mineral mackinawite was observed in water-saturated sediments. By contrast, organic sulfur compounds were the primary forms of sulfur in shallow, unsaturated hillslope soil and floodplain sediment, demonstrating the importance of biological sulfur cycling in these zones. The data present an integrated picture of sulfur cycling in a shale-dominated watershed, where riverine sulfate exports are controlled by a balance of rock weathering and biological cycling, particularly in the hydrologically and biologically dynamic river corridor." Key Points: • Bedrock shale weathering profiles show pyrite oxidation to elemental Sulfur (S) and sulfate, with reprecipitation of pyrite at fracture surfaces • Organic-S compounds dominate S speciation in unsaturated hillslope soil and floodplain sediment • River corridor processes, such as biological uptake and reduction may attenuate sulfate releases from oxidative pyrite weathering Johnson,K; Christensen,J; Gardner,WP; Sprenger,M; Li,L; Williams,KH; Carroll,RW; Thiros,N; Brown,W; Beutler,C and Newman,A 2024 Shifting groundwater fluxes in bedrock fractures: Evidence from stream water radon and water isotopes. Journal of Hydrology, p.131202. Highlights: • Hydrologic connectivity shifts from high to low throughout the summer. • Shallow flow paths are important for late summer streamflow generation. • Spatial origin of groundwater discharge varies with hydrologic connectivity. • Dynamic storage explains variability in groundwater flux and stream water origin. Abstract: "Geologic features (e.g., fractures and alluvial fans) can play an important role in the locations and volumes of groundwater discharge and degree of groundwater-surface water (GW-SW) interactions. However, the role of these features in controlling GW-SW dynamics and streamflow generation processes are not well constrained. GW-SW interactions and streamflow generation processes are further complicated by variability in precipitation inputs from summer and fall monsoon rains, as well as declines in snowpack and changing melt dynamics driven by warming temperatures. Using high spatial and temporal resolution radon and water stable isotope sampling and a 1D groundwater flux model, we evaluated how groundwater contributions and GW-SW interactions varied along a stream reach impacted by fractures (fractured-zone) and below the fractured hillslope (non-fractured zone) in Coal Creek, a Colorado River headwater stream affected by summer monsoons. During early summer, groundwater contributions from the fractured zone dominated, but declined throughout the summer. Groundwater contributions from the non-fractured zone were constant throughout the summer and became proportionally more important later in the summer. We hypothesize that groundwater in the non-fractured zone is dominantly sourced from a high-storage alluvial fan at the base of a tributary that is connected to Coal Creek throughout the summer and provides consistent groundwater influx. Water isotope data revealed that Coal Creek responds quickly to incoming precipitation early in the summer, and summer precipitation becomes more important for streamflow generation later in the summer. We quantified the change in catchment dynamic storage and found it negatively related to stream water isotope values, and positively related to modeled groundwater discharge and the ratio of fractured zone to non-fractured zone groundwater. We interpret these relationships as declining hydrologic connectivity throughout the summer leading to late summer streamflow supported predominantly by shallow flow paths, with variable response to drying from geologic features based on their storage. As groundwater becomes more important for sustaining summer flows, quantifying local geologic controls on groundwater inputs and their response to variable moisture conditions may become critical for accurate predictions of streamflow." Peckarsky,BL; McIntosh,AR; Horn,SC; McHugh,K; Booker,DJ; Wilcox,AC; Brown,W and Alvarez,M 2014 Characterizing disturbance regimes of mountain streams. Freshwater Science 33(3) 716-730. PDF Abstract: "Characterizing biologically relevant stream disturbance regimes is challenging, but necessary to answer questions about disturbance effects on ecological processes. No universally accepted approach exists for characterizing stream disturbance regimes. Our goal was to evaluate approaches that can be applied to test effects of disturbance on benthic organisms. We defined disturbance as events or environmental conditions caused by changes in stream discharge that affect the stability or habitability of the stream bed. We used several metrics to describe disturbance regimes of mountain streams that were not permanently gauged in 1 catchment, and considered the trade-off between effort required to obtain the data and the quality of information gained. We used an innovative photographic method to assess substrate particle movement empirically as a benchmark for comparison to other indicators of channel stability and to metrics describing hydrologic variability relevant to streambed stability. We used a model selection procedure to choose the best combination of individual variables to explain variation in substrate particle movement and included those variables in a multivariate axis of disturbance that can be applied to evaluate effects of disturbance on benthic organisms. Individual variables with the highest explanatory power were maximum daily increase in discharge and the Pfankuch index of channel stability. Substrate particle size and stream size (drainage basin area) were related to the multivariate index of disturbance, but channel gradient was not. Protocols used to measure substrate stability and to obtain the multivariate index of disturbance were labor intensive, but our analyses indicate it may be reasonable to use more easily measured variables (e.g., Pfankuch index) to estimate disturbance to benthic organisms at local scales, although explanatory power may be reduced. Our analyses provide a menu of options to estimate variation in local disturbance regimes of ungauged mountain streams that may not be adequately explained by extrapolation from hydrographs of gauged streams." Sprenger,M; Carroll,RW; Dennedy-Frank,J; Siirila-Woodburn,ER; Newcomer,ME; Brown,W; Newman,A; Beutler,C; Bill,M; Hubbard,SS; and Williams,KH 2022 Variability of snow and rainfall partitioning into evapotranspiration and summer runoff across nine mountainous catchments. Geophysical Research Letters, p.e2022GL099324. html Abstract: "Understanding the partitioning of snow and rain contributing to either catchment streamflow or evapotranspiration (ET) is of critical relevance for water management in response to climate change. To investigate this partitioning, we use endmember splitting and mixing analyses based on stable isotope (18O) data from nine headwater catchments in the East River, Colorado. Our results show that one third of the snow partitions to ET and 13% of the snowmelt sustains summer streamflow. Only 8% of the rainfall contributes to the summer streamflow, because most of the rain (67%) partitions to ET. The spatial variability of precipitation partitioning is mainly driven by aspect and tree cover across the sub-catchments. Catchments with higher tree cover have a higher share of snow becoming ET, resulting in less snow in summer streamflow. Summer streamflow did not contain more rain with higher rainfall sums, but more rain was taken up in ET." Plain Language Summary: "Snowmelt from the Rocky Mountains is crucial for the water supply in the Upper Colorado River Basin (UCRB). With reduced snowpack and earlier snowmelt due to climate change, it is important to understand how much of the snow directly contributes to streamflow and how much returns directly to the atmosphere via evaporation and vegetation use, called evapotranspiration (ET). We applied a stable isotope mass balance approach to investigate this for nine catchments in the UCRB. We found that snow sustains not only most the streamflow but also ¾ of the ET. Rainfall was mostly (2/3) lost to the atmosphere through ET. The variation of the snow and rain contributions to streamflow and ET were mainly driven by the catchment aspect and tree cover. The findings show that the timing of snowmelt (influenced by aspect) and plant water use (influenced by tree cover) determined how much snow became streamflow and ET." Key Points: • For the mountainous catchments in the Upper Colorado River, the fate of snow (rain) is 33% (67%) evapotranspiration (ET) and 13% (8%) summer streamflow • In catchments with relatively higher tree cover, snow was more likely to evapotranspire with less rain and snow sustaining streamflow • Increased rainfall led to greater share of rain in ET rather than streamflow, while snowfall variation had little effect Sprenger,M; Carroll,RW; Marchetti,D; Bern,C; Beria,H; Brown,W; Newman,A; Beutler,C and Williams,KH 2024 Stream water sourcing from high-elevation snowpack inferred from stable isotopes of water: a novel application of d-excess values. Hydrology and Earth System Sciences, 28(7), pp.1711-1723. PDF Abstract: "About 80% of the precipitation at the Colorado River's headwaters is snow, and the resulting snowmelt-driven hydrograph is a crucial water source for about 40 million people. Snowmelt from alpine and subalpine snowpack contributes substantially to groundwater recharge and river flow. However, the dynamics of snowmelt progression are not well understood because observations of the high-elevation snowpack are difficult due to challenging access in complex mountainous terrain as well as the cost and labor intensity of currently available methods. We present a novel approach to infer the processes and dynamics of high-elevation snowmelt contributions predicated upon stable hydrogen and oxygen isotope ratios observed in streamflow. We show that deuterium-excess (d-excess) values of stream water could serve as a comparatively cost-effective proxy for a catchment-integrated signal of high-elevation snowmelt contributions to catchment runoff. We sampled stable hydrogen and oxygen isotope ratios of the precipitation, snowpack, and stream water in the East River, a headwater catchment of the Colorado River, and the stream water of larger catchments at sites on the Gunnison River and Colorado River. The d-excess of snowpack increased with elevation; the upper subalpine and alpine snowpack (>3200m) had substantially higher d-excess compared to lower elevations (<3200m) in the study area. The d-excess values of stream water reflected this because d-excess values increased as the higher-elevation snowpack contributed more to stream water generation later in the snowmelt/runoff season. End-member mixing analyses based on the d-excess data showed that the share of high-elevation snowmelt contributions within the snowmelt hydrograph was on average 44% and generally increased during melt period progression, up to 70%. The observed pattern was consistent during 6 years for the East River, and a similar relation was found for the larger catchments on the Gunnison and Colorado rivers. High-elevation snowpack contributions were found to be higher for years with lower snowpack and warmer spring temperatures. Thus, we conclude that the d-excess of stream water is a viable proxy to observe changes in high-elevation snowmelt contributions in catchments at various scales. Inter-catchment comparisons and temporal trends of the d-excess of stream water could therefore serve as a catchment-integrated measure to monitor if mountain systems rely on high-elevation water inputs more during snow drought compared to years of average snowpack depths." Sprenger,M; Seeger,S; Berkelhammer,M; Bogie,NA; Hess,RJ; Brown,WS; Kuppel,S and Knighton,J 2025 Opportunistic short-term water uptake dynamics by subalpine trees observed via in situ water isotope measurements. Water Resources Research, 61(8), p.e2024WR039171. PDF Abstract: "Variations in tree water sources are important to understand in semi-arid ecosystems because climatic shifts towards lower snowpack and increased drought affect water availability in subalpine forests of the western US. Here, we use daily in situ measurements of stable isotopes (2H & 18O) in soil and tree stem water, soil matric potential and sap flow to study tree water uptake dynamics. We instrumented three soil profiles down to 90 cm, as well as three aspen and engelmann spruce trees near Gothic, Colorado, in the East River watershed. We observed the fate of natural isotopic variations in rainfall, soil, and plants from June to October 2022, and in August 2023 we conducted a 2H labeled irrigation experiment. Our observations showed that all studied aspen trees compensated for water scarcity in the shallow soil by shifting the dominant water source at 60(±20) cm to ⅔ of uptake from 90 cm within a few days of a dry period. Both species relied on snowmelt stored in the subsoil to sustain transpiration. Intense rainfall caused the plant water uptake to shift partially to top soil layers within 2 days. Spruce transpiration was lower and relied more on snowmelt, because rainfall infiltration was low in the spruce stand due to high canopy interception. Our findings highlight the important role of snowmelt stored in the deep soil layers for subalpine forest drought response and the dominant fate of monsoonal rainfall to become transpiration rather than recharging groundwater and streams in the Upper Colorado River." Tokunaga,TK; Tran,AP; Wan,J; Dong,W; Newman,AW; Beutler,CA; Brown,WS; Henderson,AN and Williams,KH 2022 Quantifying subsurface flow and solute transport in a snowmelt-recharged hillslope with multiyear water balance. Water Resources Research, p.e2022WR032902. http://doi.org/10.1029/2022WR032902 PDF Abstract: "Quantifying flow and transport from hillslopes is vital for understanding water quantity and quality in rivers, but remains obscure because of limited subsurface measurements. Using measured hydraulic conductivity K profiles and water balance over a single year to calibrate a transmissivity feedback model for a hillslope in the East River watershed (Colorado) proved unsatisfactory for predicting flow over the subsequent years. Well-constrained field-scale K were obtained by optimizing subsurface flux predictions over years having large differences in recharge, and by including estimates of interannual transfer of excess snowmelt recharge. Water and solute exports during high snowmelt recharge occur predominantly via shallow groundwater flow through weathered rock and soil because of their enlarged transmissivities under saturated conditions. Conversely, these shallow pathways are less active in snow drought years when the water table remains deeper within the weathering zone. Hillslope soil water monitoring showed that rainfall does not infiltrate deeply during summer and fall months, and revealed water losses consistent with model ET predictions. By combining water table-dependent fluxes with pore water chemistry in different zones, time-dependent rates of solute exports become predictable. As an example, calibrated K were combined with dissolved nitrogen concentrations in pore waters to show the snowmelt-dependence of reactive nitrogen exported from the hillslope, further supporting the recent finding that the weathering zone is the dominant source of reactive nitrogen at this site. Subsurface export predictions can now be obtained for wide ranges of recharge based on measurements of water table elevation and profiles of pore water chemistry." Key Points: • Large contrasts in annual precipitation are essential for constraining hydraulic conductivity profiles estimated by transmissivity feedback • Flow and transport during snowmelt occur predominantly within shallow depths because water table rise amplifies transmissivities • A framework is presented for estimating subsurface flow and transport on hillslopes based on sparsely distributed measurements Tokunaga,TK; Wan,J; Williams,KH; Brown,W; Henderson,A; Kim,Y; Tran,AP; Conrad,ME; Bill,M; Carroll,RW; and Dong,W 2019 Depth-and time-resolved distributions of snowmelt-driven hillslope subsurface flow and transport, and their contributions to surface waters. Water Resources Research. PDF Abstract: "Major components of hydrologic and elemental cycles reside underground, where their complex dynamics and linkages to surface waters are obscure. We delineated seasonal subsurface flow and transport dynamics along a hillslope in the Rocky Mountains (USA), where precipitation occurs primarily as winter snow and drainage discharges into the East River, a tributary of the Gunnison River. Hydraulic and geochemical measurements down to 10 m below ground surface supported application of transmissivity feedback of snowmelt to describe subsurface flow and transport through three zones: soil, weathering shale, and saturated fractured shale. Groundwater flow is predicted to depths of at least 176 m, although a shallower limit exists if hillslope-scale hydraulic conductivities are higher than our local measurements. Snowmelt during the high snowpack water year 2017 sustained flow along the weathering zone and downslope within the soil, while negligible downslope flow occurred along the soil during the low snowpack water year 2018. We introduce subsurface concentration-discharge (C-Q) relations for explaining hillslope contributions to C-Q observed in rivers and demonstrate their calculations based on transmissivity fluxes and measured pore water specific conductance and dissolved organic carbon. The specific conductance data show that major ions in the hillslope pore waters, primarily from the weathering and fractured shale, are about six times more concentrated than in the river, indicating hillslope solute loads are disproportionately high, while flow from this site and similar regions are relatively smaller. This methodology is applicable in different representative environments within snow-dominated watersheds for linking their subsurface exports to surface waters." Key Points: • Hillslope groundwater flow depth and water mass balance are reconciled using transmissivity feedback • Solute concentrations are diminished during low snowpack years because of limited transmissive fluxes along the soil and weathering zones • Subsurface concentration-discharge relations were developed to explain time-dependent hillslope exports of solutes to surface waters Varadharajan,C; Agarwal,DA; Brown,W; Burrus,M; Carroll,RW; Dafflon,B; Dwivedi,D; Enquist,BJ; Faybishenko,B; Henderson,A; Henderson,M; Hendrix,V; Hubbard,S; Kakalia,Z; Newman,A; Potter,B; Steltzer,H; Versteeg,R;Williams,K; Wilmer,C; Wu,Y 2019 Challenges in building an end-to-end system for acquisition, management, and integration of diverse data from sensor networks in watersheds: lessons from a mountainous community observatory in East River, Colorado. Abstract: "The U.S. Department of Energy's Watershed Function Scientific Focus Area (SFA), centered in the East River, Colorado, generates diverse datasets including hydrological, geological, geochemical, geophysical, ecological, microbiological and remote sensing data. The project has deployed extensive field infrastructure involving hundreds of sensors that measure highly diverse phenomena (e.g. stream and groundwater hydrology, water quality, soil moisture, weather) across the watershed. Data from the sensor network are telemetered and automatically ingested into a queryable database. The data are subsequently quality checked, integrated with the United States Geological Survey's stream monitoring network using a custom data integration broker, and published to a portal with interactive visualizations. The resulting data products are used in a variety of scientific modeling and analytical efforts. This paper describes the SFA's end-to-end infrastructure and services that support the generation of integrated datasets from a watershed sensor network. The development and maintenance of this infrastructure, presents a suite of challenges from practical field logistics to complex data processing, which are addressed through various solutions. In particular, the SFA adopts a holistic view for data collection, assessment and integration, which dramatically improves the products generated, and enables a co-design approach wherein data collection is informed by model results and vice-versa." 
Wan,J; Tokunaga,T; Brown,W; Newman,AM; Dong,W; Bill,M; Beutler,CA; Henderson,AN; Harvey-Costello,N; Conrad,ME; Bouskill,NJ; Hubbard,SS and Williams,KH 2021 Bedrock weathering contributes to subsurface reactive nitrogen and nitrous oxide emissions. Nature Geoscience 14(4)217-224. https://doi.org/10.1038/s41561-021-00717-0 Data
Abstract: "Atmospheric nitrous oxide contributes directly to global warming, yet models of the nitrogen cycle do not account for bedrock, the largest pool of terrestrial nitrogen, as a source of nitrous oxide. Although it is known that release rates of nitrogen from bedrock are large, there is an incomplete understanding of the connection between bedrock-hosted nitrogen and atmospheric nitrous oxide. Here, we quantify nitrogen fluxes and mass balances at a hillslope underlain by marine shale. We found that, at this site, bedrock weathering contributes 78% of the subsurface reactive nitrogen, while atmospheric sources (commonly regarded as the sole sources of reactive nitrogen in pristine environments) account for only the remaining 22%. About 56% of the total subsurface reactive nitrogen denitrifies, including 14% emitted as nitrous oxide. The remaining reactive nitrogen discharges in porewaters to a floodplain where additional denitrification probably occurs. We also found that the release of bedrock nitrogen occurs primarily within the zone of the seasonally fluctuating water table and suggest that the accumulation of nitrate in the vadose zone, often attributed to fertilization and soil leaching, may also include contributions from weathered nitrogen-rich bedrock. Our hillslope study suggests that, under oxygenated and moisture-rich conditions, weathering of deep, nitrogen-rich bedrock makes an important contribution to the nitrogen cycle." Wan,J; Tokunaga,TK; Beutler,CA; Newman,AW; Dong,W; Bill,M; Brown,WS; Henderson,AN; Tran,AP and Williams,KH 2024 Hydrological control of rock carbon fluxes from shale weathering. Nature Water, pp.1-15. PDF Abstract: "Shale bedrocks hold Earth's largest carbon inventory. Although water is recognized for cycling elements through terrestrial environments, understanding how hydrology controls ancient rock carbon (Crock) release is limited. Here we measured depth- and season-dependent subsurface water fluxes and pore-water and pore-gas geochemistry (including radiocarbon) over five vastly different water years along a hillslope. The data reveal that the maximum depth of annual water table oscillations determines the weathering depth. Seasonally varying subsurface water fluxes determine the export forms and rates of weathered Crock. Eighty percent of released Crock is emitted as CO2 to the atmosphere primarily during warmer and lower water table seasons and 20% of released Crock as bicarbonate exports mostly during months of snowmelt to the hydrosphere. Thus, the rates and forms of Crock weathering and export are clearly controlled by climate via hydrologic regulation of oxygen availability and subsurface flow. The approaches developed here can be applied to other environments." Wan,J; Tokunaga,TK; Williams,KH; Dong,W; Brown,W; Henderson,AN; Newman,AW and Hubbard,SS 2019 Predicting sedimentary bedrock subsurface weathering fronts and weathering rates. Scientific Reports (9) 17198 doi:10.1038/s41598-019-53205-2" PDF Abstract: "Although bedrock weathering strongly influences water quality and global carbon and nitrogen budgets, the weathering depths and rates within subsurface are not well understood nor predictable. Determination of both porewater chemistry and subsurface water flow are needed in order to develop more complete understanding and obtain weathering rates. In a long-term field study, we applied a multiphase approach along a mountainous watershed hillslope transect underlain by marine shale. Here we report three findings. First, the deepest extent of the water table determines the weathering front, and the range of annually water table oscillations determines the thickness of the weathering zone. Below the lowest water table, permanently water-saturated bedrock remains reducing, preventing deeper pyrite oxidation. Secondly, carbonate minerals and potentially rock organic matter share the same weathering front depth with pyrite, contrary to models where weathering fronts are stratified. Thirdly, the measurements-based weathering rates from subsurface shale are high, amounting to base cation exports of about 70 kmolc ha-1 y-1, yet consistent with weathering of marine shale. Finally, by integrating geochemical and hydrological data we present a new conceptual model that can be applied in other settings to predict weathering and water quality responses to climate change." Whiteman,HH; Wissinger,SA and Brown,WS 1996 Growth and foraging consequences of facultative paedomorphosis in the tiger salamander, Ambystoma tigrinum nebulosum. Evolutionary Ecology (10) 433-446. PDF (190 KB) Summary: "Facultative paedomorphosis in salamanders occurs when larvae respond to varying environmental conditions by either metamorphosing into terrestrial metamorphic adults or retaining their larval morphology to become sexually mature paedomorphic adults. Several hypotheses have been proposed for the evolutionary maintenance of this environmentally induced dimorphism, but few data are available to assess them adequately. We studied a montane population of the tiger salamander,Ambystoma tigrinum nebulosum, and measured the adult growth rate and body condition across three growing seasons to assess the relative costs and benefits of each morph. Metamorphic adults grew more than paedomorphic adults in terms of snout-vent length across years and in weight within years. Dietary analyses and foraging experiments revealed some of the proximate factors that may underlie these differential growth patterns. Across all prey, metamorphs had significantly higher biomass and calories per stomach sample than paedomorphs. Metamorphic diets primarily consisted of the fairy shrimpBranchinecta coloradensis, whereas paedomorphic diets contained a variety of benthic and terrestrial invertebrates. Foraging experiments revealed that both morphs are more successful at capturing fairy shrimp relative to other prey types and both show high electivity toward this prey. However, fairy shrimp occurred only in non-permanent ponds and thus are inaccessible to paedomorphs, which can survive only in permanent ponds. Paedomorphs also experience higher levels of intraspecific competition with large larvae in permanent ponds than metamorphs do in non-permanent ponds. Thus, metamorphs obtain a growth advantage over paedomorphs by foraging in non-permanent ponds that contain fairy shrimp and have reduced intraspecific competition. These results suggest that paedomorphs should have decreased fitness relative to metamorphs, primarily because metamorphs can move into the best habitats for growth. The net fitness effect of morph-specific differences in dispersal depend on whether there are trade-offs with other life history traits. Nonetheless, because the relative benefit of metamorph dispersal will change with environmental conditions in permanent ponds and the surrounding habitat, the relative fitness payoff to each morph should track changes in the environment. Thus, facultative paedomorphosis may be maintained in part by variable, environmentally-specific fitness payoffs to each morph." Wissinger,SA; Brown,WS and Jannot,JE 2003 Caddisfly life histories along permanence gradients in high altitude wetlands in Colorado (U.S.A.). Freshwater Biology 48(2) PDF (427 KB) Abstract: "1. Larvae of cased caddisflies (Limnephilidae and Phryganeidae) are among the most abundant and conspicuous invertebrates in northern wetlands. Although species replacements are often observed along permanence gradients, the underlying causal mechanisms are poorly understood. In this paper, we report on the distributional patterns of caddisflies in permanent and temporary high-altitude ponds, and how those patterns reflect differences in life history characteristics that affect desiccation tolerance (fundamental niches) versus constraints related to biotic interactions (realised niches). 2. Species (Hesperophylax occidentalis and Agrypnia deflata) that were encountered only in permanent ponds are restricted in distribution by life history (no ovarian diapause, aquatic oviposition, and/or inability to tolerate desiccation). Although the egg masses of H. occidentalis tolerate desiccation, the larvae leave the protective gelatinous matrix of the egg mass because adults oviposit in water. 3. Three species (Asynarchus nigriculus, Limnephilus externus and L. picturatus) have life history characteristics (rapid larval growth, ovarian diapause and terrestrial oviposition of desiccation-tolerant eggs) that should facilitate the use of both permanent and temporary habitats. However, A. nigriculus is rare or absent in most permanent ponds, and L. externus and L. picturatus are rare or absent in most temporary ponds. Experimental data from a previous study on the combined effects of salamander predation and interspecific interactions among caddisflies (e.g. intraguild predation) suggest that biotic interactions limit each species to a subset of potentially exploitable habitats. 4. Many wetland invertebrates exhibit species replacements along permanence gradients, but few studies have separated the relative importance of the effects of drying per se from the effects of biotic interactions. Our results emphasise the complementary roles of comparative data on life histories and experimental data on competition and predation for understanding invertebrate distributions along permanence gradients." Wissinger,SA; Bohonak,A; Whiteman,HH and Brown,WS 1999 Subalpine Wetlands in Colorado. In: Invertebrates in Freshwater Wetlands of North America: Ecology and Management. (Eds: Batzer,D; Rader,R; Wissinger,S) John Wiley & Sons,, 757-790. PDF (3407 KB) Abstract: "Wetlands are abundant in wet subalpine and montane valleys on the western slopes of the Rocky Mountains. Although geological and vegetational characteristics are well studied for a diversity of wetland types and incorporated into a regional classification, there is a paucity of information about the invertebrates in these habitats and the factors that affect their distribution and abundance. In this chapter we report on work at a subalpine wetland complex in the Elk Mountains of central Colorado composed of numerous adjacent basins that vary considerably in size, depth, water chemistry, and hydroperiod. We identified over 100 planktonic and benthic invertebrates at the site and found that different basins have quite different species assemblages. We used comparative data on the abiotic environment (area, depth, hydroperiod, chemistry) in 40 basins and information about the density of tiger salamanders, the only vertebrate predator, to construct a path analytic model to explore hypotheses about the relative importance of these factors on invertebrate community composition. Basin area, hydroperiod, and salamander densities have significant and collinear effects on species diversity and community composition. Large, permanent basins with multiple year-classes of salamander larvae are most diverse and are dominated by small-bodied zooplankton, chironomid midges, small dytiscid beetles, and cased caddisflies. Semipermanent, autumnal basins are less diverse thatn permanent basins and dominated by species that are absent or rare in permanent basins (large-bodied cladocerans and copepods, fairy shrimp, large dytscid beetles). In semipermanent basins beetles replace salamander larvae as the top predators on benthic invertebrates, although salamander adults and hatchlings remain top predators on large-bodied zooplankton. Small, vernal basins lack salamanders and are dominated by a subset of autumnal-basin species (several zooplankton, mosquitoes, a beetle, a caddisfly, a corixid water boatman) that are able to complete development before they dry in the early summer. Although a few species are restricted to permanent habitats because they cannot tolerate drying, most of the invertebrates in these wetlands are physiologically capable of, and have life cycle amenable for, exploiting both permanent and nonpermanent basins. Thus, biotic interactions, especially the direct and indirect effects of salamander predation, are viable hypotheses for explaining patterns of invertebrate distribution and abundance along the permanence gradient from vernal to semipermanent to permanent wetland basins. Human activities that threaten salamander populations should have cascading effects on the invertebrate communities in permanent subalpine wetlands." Wissinger,SA; Sparks,GB; Rouse,GL; Brown,WS and Steltzer,H 1996 Intraguild predation and cannibalism among larvae of detritivorous caddisflies in subalpine wetlands. Ecology 77(8) 2421-2430. Abstract PDF (1372 KB) Abstract: "Comparative data from subalpine wetlands in Colorado indicate that larvae of the limnephilid caddisflies, Asynarchus nigriculus and Limnephilus externus, are reciprocally abundant among habitats-Limnephilus larvae dominate in permanent waters, whereas Asynarchus larvae dominate in temporary basins. The purpose of this paper is to report on field and laboratory experiments that link this pattern of abundance to biotic interactions among larvae. In the first field experiment, growth and survival were compared in single and mixed species treatments in littoral enclosures. Larvae, which eat mainly vascular plant detritus, grew at similar rates among treatments in both temporary and permanent habitats suggesting that exploitative competition is not important under natural food levels and caddisfly densities. However, the survival of Limnephilus larvae was reduced in the presence of Asynarchus larvae. Subsequent behavioral studies in laboratory arenas revealed that Asynarchus larvae are extremely aggressive predators on Limnephilus larvae. In a second field experiment we manipulated the relative sizes of larvae and found that Limnephilus larvae were preyed on only when Asynarchus larvae had the same size advantage observed in natural populations. Our data suggest that the dominance of Asynarchus larvae in temporary habitats is due to asymmetric intraguild predation (IGP) facilitated by a phenological head start in development. These data do not explain the dominance of Limnephilus larvae in permanent basins, which we show elsewhere to be an indirect effect of salamander predation. Behavioral observations also revealed that Asynarchus larvae are cannibalistic. In contrast to the IGP on Limnephilus larvae, Asynarchus cannibalism occurs among same-sized larvae and often involves the mobbing of one victim by several conspecifics. In a third field experiment, we found that Asynarchus cannibalism was not density-dependent and occurred even at low larval densities. We hypothesize that Asynarchus IGP and cannibalism provide a dietary supplement to detritus that may be necessary for the timely completion of development in these nutrient-poor, high-elevation wetlands." Wissinger,SA; Steinmetz,J; Alexander,JS and Brown,WS. 2004 Larval cannibalism, time constraints, and adult fitness in caddisflies that inhabitat temporary wetlands. Oecologia 138: 39-47. PDF (198 KB) Abstract: "The fitness of non-feeding adult insects depends on energy accumulated during the larval stage. Larvae of the caddisfly Asynarchus nigriculus primarily feed on plant detritus, but supplement their diet with animal material obtained through cannibalism. Habitat drying constrains development in many populations of this species, and we hypothesized that cannibalism should accelerate development to facilitate timely metamorphosis. We manipulated larval diets in a field experiment by supplementing detritus with animal material, and in a laboratory experiment by varying animal material and detritus quality (conditioned vs unconditioned). We measured the effects of dietary manipulation on larval and pupal growth and development, the timing of metamorphosis, and adult fitness correlates. The results of the laboratory experiment suggest that this species can metamorphose with a detritus-only diet, but development is extremely protracted. In the field experiment, individuals with animal material in their diet had higher larval survival, shorter larval and pupal development times, and earlier emergence dates (7-10 days), than those without a supplement. This delay in emergence should have important effects on survival in natural populations where the difference between desiccation and successful emergence can be only a few days. Dietary supplementation also affected adult body mass (30-40% increase), female fecundity (30% more eggs), and proportional allocation to different adult body parts. Our results are consistent with recent growth-development models that predict coupled (earlier emergence and larger adults) rather than tradeoff responses (earlier emergence and smaller adults) to pre-threshold manipulation of larval diets. Many detritivorous aquatic insects supplement their diets with animal material, and our data provide evidence that this supplementation can have strong effects on fitness. This type of dietary supplementation should be especially important for taxa that do not feed as adults, and in temporary habitats that impose time constraints on larval development." Wissinger,SA; Whiteman,HH; Sparks,GB; Rouse,GL and Brown,WS 1999 Foraging trade-offs along a predator-permanence gradient in subalpine wetlands. Ecology 80(6) 2102-2116. Abstract PDF (2543 KB) Abstract: "We conducted a series of field and laboratory experiments to determine the direct and indirect effects of a top predator, the tiger salamander (Ambystoma tigrinum nebulosum), on larvae of two species of limnephilid caddisflies (Limnephilus externus and Asynarchus nigriculus) in subalpine wetlands in central Colorado. Asynarchus larvae predominate in temporary wetlands and are aggressive intraguild predators on Limnephilus larvae, which only predominate in permanent basins with salamanders. We first conducted a field experiment in mesocosms (cattle tanks) to quantify the predatory effects of different life stages of salamanders on the two caddisfly species. Two life stages of the salamanders (larvae and paedomorphs) preferentially preyed on Asynarchus relative to Limnephilus. Subsequent laboratory experiments revealed that high Asynarchus activity rates and relatively ineffective antipredatory behaviors led to higher salamander detection and attack rates compared to Limnephilus. In a second field experiment (full factorial for presence and absence of each of the three species), we found that salamander predation on Asynarchus had an indirect positive effect on Limnephilus: survival was higher in the presence of salamanders + Asynarchus than with just Asynarchus. In the laboratory we compared the predatory effects of salamanders with and without their mouths sewn shut and found the observed indirect positive effect on Limnephilus survival to be mainly the result of reduced numbers of Asynarchus rather than salamander-induced changes in Asynarchus behavior. We argue that indirect effects of predator-predator interactions on shared prey will be mainly density-mediated and not trait-mediated when one of the predators (in this case, Asynarchus) is under strong selection for rapid growth and therefore does not modify foraging behaviors in response to the other predator. The reciprocal dominance of Limnephilus and Asynarchus in habitats with and without salamanders probably reflects a trade-off between competitive superiority and vulnerability to predation. The high activity levels and aggressiveness that enable Asynarchus to complete development in temporary habitats result in strong asymmetric competition (via intraguild predation) with Limnephilus. In permanent habitats these same behaviors increase Asynarchus vulnerability to salamander predation, which indirectly benefits Limnephilus. This and previous work implicate salamanders as keystone predators that exert a major influence on the composition of benthic and planktonic assemblages in subalpine wetlands." Wissinger,SA; Whissel,J; Eldermire,C and Brown,W 2006 Predator defense along a permanence gradient: roles of case structure, behavior, and developmental phenology in caddisflies, Oecologia, Pages 1 - 12. PDF (311 KB) Abstract: "Species replacements along freshwater permanence gradients are well documented, but underlying mechanisms are poorly understood for most taxa. In subalpine wetlands in Colorado, the relative abundance of caddisfly larvae shifts from temporary to permanent basins. Predators on caddisflies also shift along this gradient; salamanders (Ambystoma tigrinum nebulosum) in permanent ponds are replaced by predaceous diving beetles (Dytiscus dauricus) in temporary habitats. We conducted laboratory and field experiments to determine the effectiveness of caddisfly cases in reducing vulnerability to these predators. We found that larvae of a temporary-habitat caddisfly (Asynarchus nigriculus) were the most vulnerable to salamanders. Two relatively invulnerable species (Limnephilus externus, L. picturatus) exhibited behaviors that reduced the likelihood of detection and attack, whereas the least vulnerable species (Agrypnia deflata) was frequently detected and attacked, but rarely captured because cases provided an effective refuge. Vulnerability to beetle predation was also affected by cases. The stout cases of L. externus larvae frequently deterred beetle larvae, whereas the tubular cases of the other species were relatively ineffective. Two of these vulnerable species (A. nigriculus and L. picturatus) often co-occur with beetles; thus, case construction alone is insufficient to explain patterns of caddisfly coexistence along the permanence gradient. One explanation for the coexistence of these two species with beetles is that they develop rapidly during early summer and pupate before beetle larvae become abundant. One species (L. picturatus) pupates by burying into soft substrates that serve as a refuge. The other (A. nigriculus) builds stone pupal cases, which in field experiments, more than doubles survival compared to organic pupal cases. The combined results of these experiments suggest that caddisfly distributions along permanence gradients depend on a suite of primary and secondary predator defenses that include larval and pupal case structure, predator-specific escape behaviors, and the phenology of larval development." Zhi,W; Li,L; Dong,W; Brown,W; Kaye,J; Steefel,C; and Williams,KH 2019 Distinct source water chemistry shapes contrasting concentration-discharge patterns. Water Resources Research. https://doi.org/10.1029/2018WR024257 Abstract: "Understanding concentration-discharge (C-Q) relationships are essential for predicting chemical weathering and biogeochemical cycling under changing climate and anthropogenic conditions. Contrasting C-Q relationships have been observed widely, yet a mechanistic framework that can interpret diverse patterns remains elusive. This work hypothesizes that seemingly disparate C-Q patterns are driven by switching dominance of end-member source waters and their chemical contrasts arising from subsurface biogeochemical heterogeneity. We use data from Coal Creek, a high-elevation mountainous catchment in Colorado, and a recently developed watershed reactive transport model (BioRT-Flux-PIHM). Sensitivity analysis and Monte-Carlo simulations (500 cases) show that reaction kinetics and thermodynamics and distribution of source materials across depths govern the chemistry gradients of shallow soil water and deeper groundwater entering the stream. The alternating dominance of organic-poor yet geo-solute-rich groundwater under dry conditions and organic-rich yet geo-solute-poor soil water during spring melt leads to the flushing pattern of dissolved organic carbon and the dilution pattern of geogenic solutes (e.g., Na, Ca, and Mg). In addition, the extent of concentration contrasts regulates the power law slopes (b) of C-Q patterns via a general equation urn:x-wiley:00431397:media:wrcr23907:wrcr23907-math-0001. At low ratios of soil water versus groundwater concentrations (Cratio = Csw/Cgw < 0.6), dilution occurs; at high ratios (Cratio > 1.8), flushing arises; chemostasis occurs in between. This equation quantitatively interprets b values of 11 solutes (dissolved organic carbon, dissolved P, NO3-, K, Si, Ca, Mg, Na, Al, Mn, and Fe) from three catchments (Coal Creek, Shale Hills, and Plynlimon) of differing climate, geologic, and land cover conditions. This indicates potentially broad regulation of subsurface biogeochemical heterogeneity in determining C-Q patterns and wide applications of this equation in quantifying b values, which can have broad implications for predicting chemical weathering and biogeochemical transformation at the watershed scale." Zhi,W; Williams,KH; Carroll,RW; Brown,W; Dong,W; Kerins,D. and Li,L 2020 Significant stream chemistry response to temperature variations in a high-elevation mountain watershed. Communications Earth & Environment, 1(1) 1-10. Html Abstract: "High-elevation mountain regions, central to global freshwater supply, are experiencing more rapid warming than low-elevation locations. High-elevation streams are therefore potentially critical indicators for earth system and water chemistry response to warming. Here we present concerted hydroclimatic and biogeochemical data from Coal Creek, Colorado in the central Rocky Mountains at elevations of 2700 to 3700m, where air temperatures have increased by about 2°C since 1980. We analyzed water chemistry every other day from 2016 to 2019. Water chemistry data indicate distinct responses of different solutes to inter-annual hydroclimatic variations. Specifically, the concentrations of solutes from rock weathering are stable inter-annually. Solutes that are active in soils, including dissolved organic carbon, vary dramatically, with double to triple peak concentrations occurring during snowmelt and in warm years. We advocate for consistent and persistent monitoring of high elevation streams to record early glimpse of earth surface response to warming." |