Snowpack chemistry at selected sites in Colorado and New Mexico during winter 1999-2000

Abstract

Abstract : Snowpacks at two high-elevation (> 3,000 m) sampling sites near McPhee and Sanchez Reservoirs in southern Colorado were selected to collect representative samples of atmospheric deposition to the surrounding watersheds during winter 1999-2000. In February 2000, annual snowpacks at two sites were sampled to determine concentrations of nitrate and sulfate; concentrations of the trace elements arsenic, mercury, and selenium; and the sulfur isotope ratios that result from atmospheric deposition to the area. Snowpack chemistry data at the two sites sampled in 1999-2000 are compared to 1993-99 averages at 10 other snow-sampling sites in Colorado and New Mexico that generally are downwind of the Four Corners area of the southwestern United States. Although concentrations of ammonium and nitrate in the 1999-2000 snowpacks were fairly typical compared to averages established at nearby sites in southern Colorado and northern New Mexico, chloride and sulfate concentrations were below the 1993-99 average, while arsenic, mercury, and selenium in snow were much below the 1993-99 average. However, very similar sulfur-isotope ratios (that are not a function of precipitation amounts) deposited in snowpacks at the nearby sites indicate the snowpack chemistries at the new sampling locations near McPhee and Sanchez reservoirs were affected by similar sources of sulfate.