Change in snowpack, soil water, and streamwater chemistry with elevation during 1990, Fraser Experimental Forest, Colorado

Abstract

Every 7–10 days during the winter of 1989–1990, we measured precipitation ion input, snowpack water equivalent (SWE) and ion content, soil water and streamwater chemistry along a subalpine to alpine elevation gradient in the Fraser Experimental Forest (FEF), Colorado. The objective was to quantify the effect of elevation and aspect on snowpack ion accumulation and loss, and relate these processes to subsequent change in soil water and first-order stream chemistry during snowmelt. SWE increased with elevation ( P < 0.001) and was greatest on NE aspects ( P < 0.001). Snowpack ion concentration increased with elevation, with NH 4 + and NO 3 − showing the most consistent ( P < 0.05) increase throughout winter. Snowpack base cation (C B) and S0 4 2− concentrations were significantly higher on NE aspect transects. In most weeks, the snowpack NH 4 + and NO 3 − content was highest ( P < 0.05) in the alpine zone. Peak snowpack NH 4 + and NO 3 − content totalled more than 1 kg inorganic N ha −1. Alpine soil water NO 3 − concentration during and after snowmelt was greater ( P < 0.001) than at lower elevations. However, there was no significant correlation between weekly snowpack ion loss and soil water chemistry. At the FEF, it seems that most snowmelt is routed through the watershed as subsurface flow. Soil processes such as ion exchange, biological uptake, overwinter nitrification and mineralization are probably major factors modifying melt water chemistry. There was no correlation between soil water chemistry and streamwater chemistry, which probably reflected the high variation in distance and time required for soil water to reach the stream.