Hydrochemical Characterization of Alpine and Alpine-Subalpine Stream Waters, Colorado Rocky Mountains, U.S.A.

Abstract

The hydrochemistry of stream waters in an alpine basin and alpine-subalpine basin were characterized after intensive chemical sampling from May 1986 to May 1987. The basins are within the Hourglass drainage basin which is tributary to the Cache la Poudre River in northern Colorado and are underlain by Silver Plume granite. The alpine basin had an annual water yield of 115 cm and was characterized as an ultra-oligotrophic sodium-bicarbonate type water. The alpine stream averaged 130 μeq L^-1 total dissolved solids. Concentrations for sodium, calcium, magnesium, potassium, and hydrogen were 27.3, 22.0, 7.7, 2.6, and 0.7 μeq L^-1, respectively. Concentrations in the alpine stream for bicarbonate, sulfate, nitrate, chloride, and orthophosphate were 31.7, 19.3, 11.0, and 0.7 μeq L^-1, respectively. The alpine-subalpine basin had an annual water yield of 72 cm and was typed as an oligotrophic calcium-bicarbonate water. The alpine-subalpine stream averaged approximately 300 μeq L^-1 total dissolved solids. Concentrations for sodium, calcium, magnesium, potassium, and hydrogen were 47.0, 64.1, 30.1, 3.1, and 0.4 μeq L^-1, respectively. Concentrations in the alpine-subalpine stream for bicarbonate, sulfate, nitrate, chloride, and orthophosphate were 110.2, 26.6, 5.3, 4.5, and 0.9 μeq L^-1, respectively. Denudation rates as measured by silica export were approximately equal for both waters at 6.8 × 10^-3 mm yr^-1.