Elevation and Geological Influences on Alpine Surface-Water Chemistry: Implications for Backcountry Water Treatment in Colorado

Alpine waters are influenced by both elevation and the geological characteristics of their respective regions, yet these factors may individually affect different components of water chemistry in their own ways. This study investigated relationships among elevation, geological setting, and water chemistry across three major Colorado mountain regions: the San Juan Mountains, Elk Mountains, and Front Range. Nine alpine stream sites were sampled, with three sites in each region representing approximately 9,000-10,000, 10,000-11,000, and 11,000-12,000 ft in elevation above sea level. Measurements on-site included pH, electrical conductivity, total dissolved solids, and dissolved oxygen, while alkalinity, hardness, and nitrate were analyzed shortly after sample collection. Alkalinity, a measure of buffering capacity, decreased consistently with increasing elevation across all three regions, representing the strongest elevation-related pattern observed. In contrast, conductivity, total dissolved solids, and hardness differed substantially among regions but did not exhibit a consistent relationship with elevation. Front Range waters had substantially lower dissolved mineral concentrations than waters that were sampled in the Elk and San Juan mountains. Dissolved oxygen also decreased with elevation, representing another correlation with elevation although the mechanism responsible could not be determined from the available measurements. Conductivity and hardness were strongly associated within the sampled dataset (R2 = 0.997). These chemical differences have implications for backcountry water treatment. Although portable mechanical filters can target bacteria and other microbes, they leave most dissolved ions---including those contributing to hardness and total dissolved solids---largely unchanged. Consequently, the differences in dissolved water chemistry observed among the three regions would likely persist following mechanical filtration. These findings indicate that the geological and elevational characteristics of an alpine water source can influence the chemical conditions of the water during treatment in the backcountry. Understanding these differences may help inform the selection and usage of backcountry treatment methods based on the chemistry of water sources.