Decadal trends in solute concentrations, mass flux, and discharge reveal variable hydrologic and geochemical response to climate change in two alpine watersheds

Heil, E.; Warix, Sara R.; Singha, Kamini; Navarre‐Sitchler, Alexis

doi:10.1016/j.apgeochem.2022.105402

Cited by 3 publications

(5 citation statements)

References 62 publications

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“…At the time of writing, the USGS hosts 72,485 hydrologic data sets with a mean data range of 14 years, with no constraints on continuous data collection. While many studies have focused on long-term changes in hydrologic and geochemical fluxes in headwater environments (Foks et al, 2018;Heil et al, 2022), the range of residence times we observe here and seen in other similar headwater environments (Georgek et al, 2017;Manning et al, 2012;Warix et al, 2021) exceeds the length of most long-term hydrologic and geochemical data sets. To observe how changes in climate are impacting how groundwater is stored and transported, the hydrologic community must continue to prioritize long-term data sets (Singha & Navarre-Sitchler, 2021), regardless of the age of groundwater.…”

Section: Implications For Stream Drying and Groundwater Age In Future...mentioning

confidence: 50%

Local Topography and Streambed Hydraulic Conductivity Influence Riparian Groundwater Age and Groundwater‐Surface Water Connection

Warix,

Navarre‐Sitchler,

Manning

et al. 2023

Water Resources Research

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The western U.S. is experiencing increasing rain to snow ratios due to climate change, and scientists are uncertain how changing recharge patterns will affect future groundwater‐surface water connection. We examined how watershed topography and streambed hydraulic conductivity impact groundwater age and stream discharge at eight sites along a headwater stream within the Manitou Experimental Forest, CO USA. To do so, we measured: (a) continuous stream and groundwater discharge/level and specific conductivity from April to November 2021; (b) biweekly stream and groundwater chemistry; (c) groundwater chlorofluorocarbons and tritium in spring and fall; (d) streambed hydraulic conductivity; and (e) local slope. We used the chemistry data to calculate fluorite saturation states that were used to inform end‐member mixing analysis of streamflow source. We then combined chlorofluorocarbon and tritium data to estimate the age composition of riparian groundwater. Our data suggest that future stream drying is more probable where local slope is steep and streambed hydraulic conductivity is high. In these areas, groundwater source shifted seasonally, as indicated by age increases, and we observed a high fraction of groundwater in streamflow, primarily interflow from adjacent hillslopes. In contrast, where local slope is flat and streambed hydraulic conductivity is low, streamflow is more likely to persist as groundwater age was seasonally constant and buffered by storage in alluvial sediments. Groundwater age and streamflow paired with characterization of watershed topography and subsurface characteristics enabled identification of likely controls on future stream drying patterns.

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Section: Implications For Stream Drying and Groundwater Age In Future...mentioning

confidence: 50%

Local Topography and Streambed Hydraulic Conductivity Influence Riparian Groundwater Age and Groundwater‐Surface Water Connection

Warix,

Navarre‐Sitchler,

Manning

et al. 2023

Water Resources Research

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“…As watershed aridity increases in many systems due to climate change, reaction rates have been hypothesized to increase, leading to higher mean stream‐solute concentrations (Li et al, 2022). Stream‐solute concentrations have been observed to increase over the last 30 years in catchments throughout the United States (Heil et al, 2022; Li et al, 2022). However, despite these increases in solute concentrations, we do not expect a proportional change in C – Q slope as increasing solute concentrations (C) will be buffered by decreases in stream discharge ( Q ) as a result of increasing aridity.…”

Section: Resultsmentioning

confidence: 99%

“…As watershed aridity increases in many systems due to climate change, reaction rates have been hypothesized to increase, leading to higher mean stream-solute concentrations (Li et al, 2022). Streamsolute concentrations have been observed to increase over the last 30 years in catchments throughout the United States (Heil et al, 2022;Li et al, 2022). However, despite these increases in solute…”

Section: Coupled Geochemical Reactions Drive Chemostasis Rather Than ...mentioning

confidence: 99%

Water‐rock interactions drive chemostasis

Warix,

Navarre‐Sitchler,

Singha

2024

Hydrological Processes

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The western U.S. is experiencing shifts in recharge due to climate change, and it is currently unclear how hydrologic shifts will impact geochemical weathering and stream concentration–discharge (C–Q) patterns. Hydrologists often use C–Q analyses to assess feedbacks between stream discharge and geochemistry, given abundant stream discharge and chemistry data. Chemostasis is commonly observed, indicating that geochemical controls, rather than changes in discharge, are shaping stream C–Q patterns. However, few C–Q studies investigate how geochemical reactions evolve along groundwater flowpaths before groundwater contributes to streamflow, resulting in potential omission of important C–Q controls such as coupled mineral dissolution and clay precipitation and subsequent cation exchange. Here, we use field observations—including groundwater age, stream discharge, and stream and groundwater chemistry—to analyse C–Q relations in the Manitou Experimental Forest in the Colorado Front Range, USA, a site where chemostasis is observed. We combine field data with laboratory analyses of whole rock and clay x‐ray diffraction and soil cation‐extraction experiments to investigate the role that clays play in influencing stream chemistry. We use Geochemist's Workbench to identify geochemical reactions driving stream chemistry and subsequently suggest how climate change will impact stream C–Q trends. We show that as groundwater age increases, C–Q slope and stream solute response are not impacted. Instead, primary mineral dissolution and subsequent clay precipitation drive strong chemostasis for silica and aluminium and enable cation exchange that buffers calcium and magnesium concentrations, leading to weak chemostatic behaviour for divalent cations. The influence of clays on stream C–Q highlights the importance of delineating geochemical controls along flowpaths, as upgradient mineral dissolution and clay precipitation enable downgradient cation exchange. Our results suggest that geochemical reactions will not be impacted by future decreasing flows, and thus where chemostasis currently exists, it will continue to persist despite changes in recharge.

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“…The second approach involved computing and evaluating trends in flow‐adjusted concentrations, a method employed in previous water quality trend studies (e.g., Hirsch et al., 1991; Mast, 2013). Concentrations of relatively non‐reactive solutes produced by mineral weathering, such as SO 4 and Zn (and likely Cu at pH < 5), generally increase with decreasing discharge in mountain streams (Heil et al., 2022; Li et al., 2022; Petach et al., 2021; Winnick et al., 2017). For each sample site, a relationship between concentration and streamflow was estimated for SO 4 , Zn, and Cu by a regression line fit to data on a C‐Q plot of the log of the measured concentration ( C m ) versus the log of the “index flow” ( Q I ).…”

Section: Methodsmentioning

confidence: 99%

“…A key unanswered question linked to causal mechanisms is whether stream solute loads (mass flux, equal to streamflow multiplied by concentration) are increasing in addition to concentrations; if loads are not increasing, the observed concentration increases may be primarily attributable to the dilution effect (mechanism 3), with mechanisms 1 and 2 having little or no influence. A few studies have reported increasing solute loads in unmineralized mountain watersheds and invoked increasing sulfide weathering rates (e.g., Crawford et al, 2019;Heil et al, 2022;Mast, 2013), but studies in ARD-affected mountain streams have not directly evaluated temporal trends in load. Crouch et al (2013) present both streamflow and Zn concentration data from the upper Snake River and identify increasing Zn concentrations under similar low-flow conditions from 1971 to 2011, implying increasing Zn loads, but temporal load trends are not quantitatively examined.…”

Section: Introductionmentioning

confidence: 99%

Climate‐Driven Increases in Stream Metal Concentrations in Mineralized Watersheds Throughout the Colorado Rocky Mountains, USA

Manning,

Petach,

Runkel

et al. 2024

Water Resources Research

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Increasing stream metal concentrations apparently caused by climate warming have been reported for a small number of mountain watersheds containing hydrothermally altered bedrock with abundant sulfide minerals (mineralized watersheds). Such increases are concerning and could negatively impact downstream ecosystem health, water resources, and mine‐site remediation efforts. However, the pervasiveness and typical magnitude of these trends remain uncertain. We aggregated available streamwater chemistry data collected from late summer and fall over the past 40 years for 22 mineralized watersheds throughout the Colorado Rocky Mountains. Temporal trend analysis performed using the Regional Kendall Test indicates significant regional upward trends of ∼2% of the site median per year for sulfate, zinc, and copper concentrations in the 17 streams affected by acid rock drainage (ARD; median pH ≤ 5.5), equivalent to concentrations roughly doubling over the past 30 years. An examination of potential load trends utilizing streamflow data from eight “index gages” located near the sample sites provides strong support for regionally increasing sulfate and metal loads in ARD‐affected streams, particularly at higher elevations. Declining streamflows are likely contributing to regionally increasing concentrations, but increasing loads appear to be on average an equal or greater contributor. Comparison of selected site characteristics with site concentration trend magnitudes shows the highest correlation for mean annual air temperature and mean elevation (R2 of 0.42 and 0.35, respectively, with all others being ≤0.14). Future research on climate‐driven controlling mechanisms should therefore focus on processes such as melting of frozen ground directly linked to site mean temperature and elevation.

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Decadal trends in solute concentrations, mass flux, and discharge reveal variable hydrologic and geochemical response to climate change in two alpine watersheds

Cited by 3 publications

References 62 publications

Local Topography and Streambed Hydraulic Conductivity Influence Riparian Groundwater Age and Groundwater‐Surface Water Connection

Local Topography and Streambed Hydraulic Conductivity Influence Riparian Groundwater Age and Groundwater‐Surface Water Connection

Water‐rock interactions drive chemostasis

Climate‐Driven Increases in Stream Metal Concentrations in Mineralized Watersheds Throughout the Colorado Rocky Mountains, USA

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