Waiting for the snow to melt…
Snowmelt is the primary source of streamflow generation and recharge in much of the southwestern United States, so the stable isotopic composition of snowmelt recharge is a critical endmember in the hydrograph separation of streamflow generation. However, the methodologies available to collect meltwater for stable isotope analysis are limited due to the remote and often seasonally inaccessible nature of the terrain where snowpacks develop. To address this problem, a robust methodology using passive capillary samplers (PCAPS) was developed. Lab results indicated that (1) the wicking process associated with PCAPS does not fractionate water, but precautions are necessary to prevent exchange between the wick and atmosphere, and (2) PCAPS effectively tracked the changing isotopic composition of a soil reservoir undergoing evaporation. To test this methodology in the field, twelve PCAPS were installed at remote sites within the Saguache Creek watershed, a large subwatershed of the Rio Grande in the San Juan Mountains of southern Colorado, during October 2007 prior to the onset of snow accumulation. Bulk and modified-bulk snow collectors were installed at each PCAPS installation site to quantify the isotopic evolution of the snow and snowmelt. Field results indicate that the stable isotopic composition of infiltrating meltwater collected via PCAPS had evolved relative to the isotopic compositions obtained via modified-bulk snow collectors. This outcome may be Frisbee is a Ph.D. Candidate in Hydrology at New
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