Alkalinity generation in snowmelt and rain runoff during short distance flow over rock

Abstract

High-elevation ecosystems in the western United States typically have patchy, discontinuous areas of surficial soils surrounded by large areas of rock outcrop, talus, and scree. Snowmelt and precipitation that percolate through soil increase in alkalinity, principally by increasing base cation concentration through cation exchange, and by decreasing acid anion concentration by adsorption or uptake of sulfate and nitrate. While it is widely believed that changes in chemistry during runoff over rock outcrop and through saprolite contribute to increases in alkalinity, there have been few studies that document the magnitude of this change. In the Wind River Mountains, WY, snowmelt and rain samples increased in alkalinity approximately 35 meq L^-1 during 15 to 50 meter transport over rock, lichens, and thin pockets of saprolite and soil. Alkalinity increases were principally due to increased base cation concentration. Nitrate concentrations in snow melt decreased from approximately 8 meq L^-1 to <1 meq L^-1; however, nitrate increased following rock transport of rainfall. There were significantly increasing trends in alkalinity generation with increased path length; however, the relationship with path length was not strong.

Citation

Clayton, James L. 1998. Alkalinity generation in snowmelt and rain runoff during short distance flow over rock. Res. Pap. RMRS-RP-12. Ogden, UT: U.S. Department of Agriculture, Rocky Mountain Research Station. 7 p.