Quantifying the Effects of Storm Track, Topography, and Vegetation on Chemical Loading to a Montane Snowpack, Valles Caldera National Preserve, NM

The spatial variability of chemicals deposited in seasonal snow cover creates difficulty in estimating input of potentially important sources of nutrients and pollutants into terrestrial and aquatic environments. This study quantifies how vegetation, aspect, storm track, and event characteristics control the spatial and temporal differences in snow chemistry and chemical load to a montane snowpack in the Valles Caldera National Preserve, northern New Mexico. This work was conducted in coordination with two simultaneous studies, the first addressing spatial differences in snow accumulation and ablation due to vegetation cover and the second examining the influence of aspect on the transit time of melt water through our study catchments. Building on this coordinated effort, this project will also link broader implications on the role of aspect and vegetation cover through chemical and isotopic analysis. Based on study design, we collected depth, density, stratigraphy and snow chemistry samples from six snow pit locations on approximate monthly intervals between January and April 2007. Snow chemistry samples were analyzed for major anions (Cl-, NO3-, SO42-), major cations (Ca2+, Na+, K+), water isotopes, and biogeochemical nutrients (DOC, DN). Initial analysis of anion data suggests that estimating anion loads with bulk snow samples versus layer distributed samples indicates bulk samples underestimate anion load at peak accumulation (p < 0.05). Coefficients of variation (CV) are used to analyze chemical load variability. CV's of anion loads vary spatially from 27% (Cl-) to 33% (NO3-) and for nutrient loads from 34% (DN) to 39% (DOC) at peak accumulation. Dense vegetation cover appears to strongly influence dissolved organic carbon but has no apparent affect on other solutes suggesting that the vegetation is the source of the increased DOC load rather than enhanced atmospheric deposition on trees. Preliminary storm track analysis indicates distinct NO3-/ SO42- ratios are dependant on depositional wind direction. Storm deposits with westerly components appear to yield higher SO42- concentrations producing lower ratios.