DETERMINING SOLUTE INPUTS TO SOIL AND STREAM WATERS IN A SEASONALLY SNOW-COVERED MOUNTAIN CATCHMENT IN NORTHERN NEW MEXICO USING GE/SI AND 87SR/86SR RATIOS

The “critical zone” is an open system where interacting biological, chemical, and physical processes contribute to long-term evolution of the Earth’s surface and the structure of life on Earth. Mineral weathering is an important process in the “critical zone”, which produces base cations that are essential nutrients to support the biotic foundation of ecosystems. This study investigates how changes in hydrologic conditions affect subsurface flowpaths, thereby altering weathering influences on stream chemistry in a seasonally snow-covered headwater catchment in the Jemez Mountains in northern New Mexico. Germanium/silicon ratios, Sr isotope ratios, major ions and dissolved carbon species are utilized to trace base cation cycling in the catchment. Major cations display chemostatic behavior despite fluctuations in the hydrograph implying that subsurface flowpaths are the dominant influence on streamwater composition. Major ion concentrations in streamwaters are most comparable to groundwater. Silicon, calcium, and sodium are prevalent in streams, consistent with plagioclase weathering. Low ion concentrations in precipitation and direct runoff would result in a dilution trend that is not observed. Therefore, solute fluxes are governed by equilibrium with primary and secondary minerals, and the rate at which solutes are transported by water out of the system.