Modeling Snow Dynamics and Stable Water Isotopes Across Mountain Landscapes. Issue 20 (13th October 2022)

• Record Type: Journal Article
• Authors: Carroll, Rosemary W. H.; Deems, Jeffrey; Sprenger, Matthias; Maxwell, Reed; Brown, Wendy; Newman, Alexander; Beutler, Curtis; Williams, Kenneth H.
• Is Part Of: Geophysical research letters. Volume 49:Issue 20(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-10-13
• Subjects: stable water isotopes -- mountains -- snow -- Colorado -- hydrologic model -- isotope model; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2022GL098780
• Languages: English
• ISSNs: 0094-8276

Abstract

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. 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. 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