The Influence of an Extensive Dust Event on Snow Chemistry in the Southern Rocky Mountains

In mid-February 2006, windstorms in Arizona, Utah, and western Colorado generated a dust cloud that distributed a layer of dust across the surface of the snowpack throughout much of the Colorado Rockies; it remained visible throughout the winter. We compared the chemical composition of snowfall and snowpack collected during and after the dust deposition event with pre-event snow at 17 sites extending from central Colorado into southern Wyoming. The chemistry of dustevent snowfall and the post-event snowpack were compared to long-term wetfall precipitation and snowpack chemistry at the Fraser Experimental Forest (FEF). The pH of the snowpack formed during the dust event was 1.5 units higher, calcium was 10-fold higher, and acid neutralizing capacity (ANC) was 100-fold higher than levels measured in either early or late-season snow. Elevated ANC was attributable to dustderived increase in carbonate/bicarbonate ions, likely from soluble calcium carbonate inclusions in dust material. The single dust event contributed carbonate/ bicarbonate-derived ANC equivalent to the sum of strong acids deposited during the entire winter at FEF. Effects appeared more pronounced at upper elevations and in the sparse forest near treeline, compared to densely forested lower elevation sites. Monthly snowpack solute analysis at FEF has not documented an event of similar magnitude during its 17-year period of record. The solute composition of post-event snow is similar to average Fraser streamwater, however. To assess the effect of dust on the timing and composition of water exported from high-elevation ecosystems, future work should consider both the contributions of eolian deposition on soil development, plant communities, and nutrient and water relations plus the impact of individual deposition events on snowpack chemistry and duration.