Chemical solute mass balance of Crater Lake, Oregon

Abstract

Crater Lake covers the floor of the caldera at the top of Mount Mazama. Surrounded by steep walls, the water surface of the lake occupies 78 percent of the catchment basin. No major rivers empty into the lake, and there is no surface outlet Based on a chemical solute mass balance model, mass inputs of major solute chemical components (Na, Ca, K, Mg, SO 4 , Cl, Si, and HCO 3 ) from atmospheric deposition and caldera springs do not equal the mass output in seepage from the lake. One or more previously unquantified sources must be present in the lake or watershed system to account for the calculated deficits of mass inputs which range from 50 to 90 percent of mass outputs. A hydrothermal source, with a flow rate of approximately 6 percent of me seepage rate and chemical composition similar to saline fluids found in isolated pockets on the bottom of Crater Lake and to hydrothermal springs in die Cascade Mountain Range, could account for the calculated input mass deficits for major solute chemical components. Atmospheric bulk deposition (wet plus dry) may account for up to 90 percent of nitrogen and 30 percent of phosphorus inputs to Crater Lake. A net removal of nutrients from the lake water column occurs through internal processes, most likely burial of cellular debris in sediments.