Inorganic And Organic Content Of Dust On Snow In The Colorado Front Range, USA
Parman, Jordan N 1 ; Williams, Mark W 2 ; Ingersoll, George P 3 ; Schuster, Paul F 4
1 Department of Geography and Institute of Arctic and Alpine Research, University of Colorado, Boulder
2 Department of Geography and Institute of Arctic and Alpine Research, University of Colorado, Boulder
3 US Geological Survey, Colorado Water Science Center, Denver Federal Center, Denver, CO
4 US Geological Survey, Boulder, CO
High-elevation environments are sensitive to atmospheric deposition of nitrogen and sulfur due to thin soils, sparse vegetation, dilute water bodies, and seasonal snowmelt patterns (Ingersoll et al., 2008). Past studies of dust and snow have focused on changes in the albedo of snow and the inorganic content of the dust, but little research has been conducted on how the organic and nutrient content of dust on snow may impact soil composition and snowpack chemistry (Psenner, 1999). This study quantifies and compares the inorganic and organic composition of snowpack following a red dust snowfall event that occurred on February 15, 2006 (Fig. 1). Southwest winds from the Four Corners region deposited a red dust layer of approximately 2-cm in thickness from the San Juan Mountains to the Front Range. The red dust was composed primarily of quartz and 2:1 clay, but also contained a calcite fraction, indicating exogenous sources of the dust (Fig. 2). This calcite component may have contributed to the high acid-neutralizing capacity of the red dust layer (940 ueq L-1), much higher than the 20 ueq L-1 common for this area. In addition, the nitrate concentrations in the red snow were approximately 90 ueq L-1, over eight times the average concentration at maximum accumulation for this site (Fig. 3). The red dust layer contained significantly higher values for inorganic (3232.8 mg) and organic (228.6 mg) mass compared to other snowpits in the sample region that did not contain a dust layer. The red snow was 7% organic, typical of the mineral-rich desert soils from which the dust layer was most likely derived. The carbon isotope ratio of the organic fraction showed the dust was slightly more enriched in 13C(-20.88%) than local soil (-26.1%), consistent with a far-travelled origin rather than a local source. These observations indicate that dust may be an important contributor of buffering capacity to snow, partially neutralizing the sulfuric and nitric acids that are also contained in atmospheric deposition (Clow and Ingersoll, 1993). These findings suggest that further research is needed to better understand the impact of dust on snow not only on melt rates and albedo changes, but also on how organic and nutrient concentrations contribute to biogeochemical cycling in high-elevation ecosystems.
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