Organic Characteristics of High Sierra Nevada Snowfall during the Winter of 2014

Abstract:

During the winter of 2014 snow samples were collected from Tuolumne Meadows in Yosemite National Park (elevation 2600 m) for the determination of the organic constituents. Samples were collected from the middle of the snowpack during January - April (referred to as "snowpack" samples), from three depths in a cross-sectional pit dug in mid April ("snow pit" samples) and from fresh snow collected during two snowstorms ("snowstorm" samples). Samples were frozen immediately after collection in sealed glass containers and thawed just prior to analysis. The DOC concentration of snowpack samples varied from 0.9 - 1.7 mg C/L; the DOC of snowstorm samples had much lower values (0.3 - 0.4 mg C/L). DOC concentrations of snow taken from the top third of the snow pit in mid-April was much higher (6.6 mg C/L), but this sample had large amounts of "debris"; the snow samples from the middle and bottom of the snow pit had concentrations similar to the snowpack samples.

Snows were fractionated into hydrophobic, transphilic and hydrophilic acid fractions (HPOA, TPIA and HPIA, respectively); HPOA comprised between 30 and 44% of the total, TPIA ranged from 8-16% and HPIA ranged from 19-28%. Samples collected from the snow pit at the end of the winter always had lower percentages of TPIA and HPIA than those taken from the snowpack during the winter. All snow samples were also analyzed for low molecular weight organic acids (LMWOA) via ion chromatography, and all samples contained trace amounts of formate, acetate and oxalate, with acetate generally being predominant. A few of the samples showed evidence of trace amounts of propionate and butyrate, but no other organic acids could be positively identified. If it is assumed that the LMWOA fraction consisted of the three anions above (acetate, formate and oxalate), then the percentage of the HPIA which was LMWOA ranged from 5-15% with uniformly higher percentages occurring in the snowpack samples than in the snow pit samples taken at the end of the winter.

Understanding the composition and differences in the organic makeup of snow has implications ranging from atmospheric flow paths and sources of pollution through biologically-derived transformation reactions in the post-depositional hydrologic cycle to chemical weathering rates and geochemical reactions. Future work will focus on these aspects.