ABSTRACT

From measurements of the concentrations of Ca⁺², Mg⁺², Na⁺¹ and K⁺¹, pH and carbon isotope (¹³C/¹²C) ratios, the chemical history of an Alpine "lake-spring" complex is determined. Water, percolating through the upper lake's substrate, is charged with CO₂ by bacterial oxidation of organic matter in the sediment or by microbial and root respiration in the poorly developed soil zones of the upper lake's basin. The water is transported along faults and fractures, through quartz latite basement rock, dissolving calcium carbonate and leaching Ca² and Na¹ from andesine feldspar. Calcite is more rapidly weathered, exceeding andesine at a mole ratio between 2 and 3 to 1. Saturation of the water w th respect to calcite is approached before discharge as perennial springs at 10,200-ft elevation. During subsequent surface flowage, the spring water re-equilibrates, both isotopically and chemically, with atmospheric CO₂.