The critical zone is the environment near the Earth’s surface in which biological, chemical, and physical processes interact and contribute to the evolution and structure of life on Earth. Mineral dissolution is an important process in the critical zone that supplies essential nutrients, to the biotic foundation of ecosystems. Stream chemical composition reflects the supply through mineral weathering and the loss of these elements through hydrologic transport. This study aims to determine the influence of mineral weathering on stream and soil water composition in a seasonally snow-covered headwater catchment in the Jemez Mountains in northern New Mexico by using a multi-tracer approach including major cations, strontium isotopes, germanium (Ge)/silica (Si) ratios and trace metals. Potential solute sources to stream waters include snowmelt, atmospheric wet and dry deposition, groundwaters and soil waters influenced by mineral weathering. Preliminary base cation, dissolved inorganic carbon (DIC), and dissolved organic carbon (DOC) results show that groundwater dominates stream water composition except during snowmelt in April and May. Furthermore, stream waters are enriched in base cations compared to snowmelt discharge and shallow soil waters suggesting contributions of solutes from mineral weathering along deeper subsurface flowpaths. Dilution trends of base cation concentrations are not observed during snowmelt, however high DOC and low DIC concentrations are present in stream waters indicating shallow soil flushing. Soil solid phase chemistry data shows soils are depleted in Ca, relative to Na, and K whereas stream waters are enriched in Ca, relative to Na, and K, which may be indicative of plagioclase or calcite weathering. Soils deeper in the soil profile are depleted in Ge relative to Si, whereas shallow soils are enriched in Ge. Therefore we hypothesize that shallow soil flushing during snowmelt periods will lead to elevated Ge/Si ratios in stream waters. In addition, strontium isotopes will be utilized to distinguish solute sources from bedrock weathering (relatively unradiogenic rhyolite) versus atmospheric inputs (e.g. relatively radiogenic dust). Together, the multiple tracers will provide insight into hydrologic flowpaths, solute sources, and stream water composition variability during the snowmelt, monsoon, and dry seasons.
Porter, C.M., McIntosh, J.C., Derry, L.A., Meixner, T., Chorover, J., Rasmussen, C., Brooks, P.D., Perdrial, J.N. (2011): 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. AGU Fall Meeting Presentations (Poster) Abstract B33G-0552..