Snowpack and precipitation chemistry at a high altitude site in the Canadian Rocky Mountains

SummaryThis study presents a first quantitative study of inorganic ion concentrations and loading in precipitation in the Canadian Rocky Mountains. The 2005/2006 winter snowpack and July 2006 rainfall are examined to define the magnitude, and altitudinal and seasonal variability of atmospheric deposition at high altitude sites. Little is currently known about the sources and concentrations of inorganic ions in watersheds in this region, and careful measurement of snowpack and rainfall chemistry are required to accurately assess the total annual deposition and the potential environmental effects of atmospheric pollution on high elevation ecosystems and snowmelt-dominated catchments on both sides of the continental divide.Snowpit profiles from three sites between 2100 and 2750 m above sea level (masl) show little variation in ion concentrations with altitude, but all sites show strong seasonal variations. Air-mass back trajectories and the identification of storms in snowpits using high-resolution oxygen isotope (δ18O) data show that the increases in acid anions in the surface (spring) layers and early-winter snow layers are associated with southwesterly storm systems that swept moisture across the northwestern US into western Canada. July rainfall ion concentrations were 1.5–3.0 times higher than winter snowpack concentrations and were also primarily associated with southwesterly storms. The chemical composition of precipitation in this region, and the relative contribution of snow and rain to annual precipitation, suggest that rates of nitrogen (N) deposition in the Canadian Rocky Mountains may be comparable to the US Rocky Mountains where N deposition is altering ecosystem function. These results lend support to increased monitoring of precipitation chemistry in this environmentally sensitive region.

► Atmospheric deposition of ions in snow and rain at high altitude.
► Identification of ion source areas using back trajectories to trace storm pathways.
► Elevated acid ion concentrations in snow are associated with southwesterly storms.
► On average ions in July rain are 1.5-3.0 times more concentrated than winter snow.
► Annual deposition will be sensitive to the amount of spring and summer precipitation.