Influence of landscape features on variation of δ2H and δ18O in seasonal mountain snowpack

Abstract:

Streamflow contributions from snowpack remain difficult to predict in snow dominated headwater catchments in the Rocky Mountains. There remains considerable uncertainty in how environmental change in mountain watersheds alter seasonal snowpack accumulation and development and how these relationships translate from gaged to ungaged catchments. Stable isotope analysis is a valuable tool for determining the contribution and changes of different source inputs to catchment water budgets. Stable isotope values in snowpack integrate source inputs and processes such as water vapor exchange, selective redistribution, and melt. For better understanding of how these physical processes vary at local and catchment scales, snowpack density, depth, snow water equivalence (SWE), δ²H and δ¹⁸O were examined at peak snowpack in spring 2013 and 2014 and at monthly time steps throughout the winter of 2013-2014. Distributed data and sample collection occurred between 2400 and 3300 m elevation across two pine beetle and spruce beetle impacted forest stands with variable canopy cover in the Libby Creek and Nash Fork Little Laramie River basins, Medicine Bow Range, Wyoming. Peak snowpack within these watersheds was 10% below historic average in 2013 and 50% above average in 2014 (NRCS Snotel data). Even with these contrasting peak snowpack patterns, elevation described less than 40% of the spatial variation of snow water equivalents (SWE) across the watersheds for both seasons. Hydrogen and oxygen isotope ratio values of snowpack sampled monthly in 2014 revealed early season separation from the local meteoric water line, suggesting some kinetic isotope effects. However, isotope ratio values at peak snowpack in 2013 reflected no such signal at any sampling location. The influence of landscape position and canopy cover will be modeled to detect and scale spatial and temporal changes in SWE and stable isotope composition of snowpack. Such an approach will provide increased understanding of how snowpack evolution varies across terrain features and how climate and land cover disturbances may affect snowpack development in Rocky Mountain watersheds.