Monday, February 25, 2013, 12:00PM - 1:00PM
U.S. Geological Survey
Full title: Using calcium and alkalinity as surrogates for dust in snow: Implications for snowmelt timing
Dave Clow with Mark Williams (CU) and G.P. Ingersoll (USGS)
Abstract: Widespread dust deposition events occur with regularity in the Rocky Mountains, and there is concern that dust deposited on snow may contribute to earlier melting of the snowpack by decreasing snowpack albedo. However, direct measurements of dust in snow are difficult and rarely made. A proxy for dust content would allow us to easily estimate current deposition rates of dust and whether dust deposition rates have changed over time. In this study, calcium and alkalinity concentrations in snow were tested as indicators for dust deposition, based on the hypothesis that these solutes are derived primarily from dissolution of eolian carbonate dust blown onto, and subsequently incorporated into the snowpack. Samples were collected from a dust-rich layer of snow after a major dust event in February 2006 at 13 sites in Colorado. The samples were analyzed for calcium, alkalinity, and dust concentrations; results indicated strong positive correlations among these analytes (r2 ≥ 0.95), supporting the hypothesis that calcium and alkalinity can be used as surrogates for dust.
Depth-integrated snowpack samples have been collected annually just prior to maximum snow accumulation at 57 sites in the Rocky Mountains since 1993 as part of a regional snow chemistry survey program. Data from these samples show strong upward trends in calcium and alkalinity concentrations (p < 0.03), with trend magnitude increasing from north to south; these results suggest an increase in deposition of dust to snow in the southern Rockies over the past two decades.
The influence of dust deposition on snowmelt timing at the regional survey sites was investigated by regressing climate variables and snowpack chemistry against snowmelt timing indices derived from SNOTEL data. Results indicated that maximum SWE was positively related to snowmelt timing (inducing later melt); and calcium concentrations and April and May air temperature were negatively related to snowmelt timing (promoting earlier melt). The regression model explained 77% of the variance in snowmelt timing, and the influence of dust (as inferred from calcium concentrations) was significant, although smaller than the effects of SWE and air temperature on snowmelt timing.
- Started career in mountain hydrology in 1984 while doing a Masters in geochemistry at Emerald Lake, in Sequoia National Park.
- Learned to telemark while skiing breakable crust at Emerald with Mark Williams, who was also a grad student at the time.
- Began working for the USGS as a research hydrologist in 1990.
- Graduated from University of Wyoming with a PhD in Geochemistry in 1992.
- Research focuses on watershed biogeochemistry and the effects of climate change on mountain hydrology.
Free and open to the public