Hydrochemistry of snowmelt at Rabbit Ears Pass, Rocky Mountains, Colorado

TitleHydrochemistry of snowmelt at Rabbit Ears Pass, Rocky Mountains, Colorado
Publication TypeConference Proceedings
Year of Conference1993
AuthorsPeters, N. E., and Leavesley G. H.
Conference Name61st Annual Western Snow Conference
Series TitleProceedings of the 61st Annual Western Snow Conference
Date PublishedJune 1993
PublisherWestern Snow Conference
Conference LocationQuebec City, Quebec
KeywordsChemistry, Groundwater, Snowmelt, Water quality

The chemical composition of snowmelt from ridge-top lysimeters, groundwater along a hillslope transect, and streamwater at the basin outlet was monitored during the spring of 1991 and 1992 in a 2-km² subalpine catchment on the western flank of the Rocky Mountains near Steamboat Springs, Colorado. Most of the snowmelt occurred during two-month periods that began in mid May 1991 and mid April 1992. The solutes in the meltwater were differentially eluted from the snowpack in each year and the meltwater was dominated by Ca(2+) and Mg(2+) and the acid anions, SO4(2-) and NO3(-); the concentration sum of Ca(2+) and Mg(2+) was equal to the sum of SO4(2-) and NO3(-).The composition of groundwater and streamwater was dominated by weathering products, such as Ca(2+), HCO3(-) (measured as alkalinity), and dissolved SiO2, and their concentrations decreased as snowmelt progressed. The SO4(2-) and NO3(-) concentrations of groundwater generally were higher than those of meltwater. In particular, groundwater from one well in the mid-slope position, which was at the highest elevation sampled, had extremely high NO3(-) concentrations during snowmelt in both years. These high NO3(-) concentrations were balanced by Ca(2+) concentrations. As snowmelt progressed, NO3(-) and Ca(2+) concentrations in groundwater decreased, consistent with dilution by meltwater from the snowpack.Solute concentrations in streamwater also decreased as snowmelt progressed. The NO3(-) concentrations decreased more rapidly than did SO4(2-) concentrations. These results indicate that some of the SO4(2-) and NO3(-) in streamwater was derived from sources other than the snowpack, or that the meltwater composition on other drainages was more concentrated with respect to other constituents. Also, the relative changes in the SO4(2-) and NO3(-) concentrations of streamwater indicate that different processes control their mobility.