Groundwater - Surface Water Interactions and Geochemistry along a High-Sinuosity Meander in a Mountain Meadow

The 2008 Hydrogeology Field Camp of the University of Texas at Austin examined groundwater-surface water interactions and geochemical parameters throughout a meander bend of the Jaramillo Creek in the Valles Caldera National Preserve, northern New Mexico. The water from the Jaramillo Creek was derived from snow melt, and travels along a sinuous channel within the caldera primarily composed of weathering products of volcanic tuffs. Forty one piezometers were installed throughout eight transects of a point bar, from which water was sampled and analyzed for stable and unstable chemical parameters. A typical groundwater sample from the site was concentrated in sodium, bicarbonate, aluminum and iron and depleted in calcium. The pH of groundwater was found to decrease with distance from surface water interfaces. The average pH of the groundwater was approximately 6.2 and varied substantially throughout the transects. A general trend was found where pH was highest near the stream and lowest in the center of each transect. Humic acids are interpreted as the cause of the low pH, and are likely causing the dissolution of feldspars in the volcanic terrain allowing for the high aluminum content. Due to low pH, high concentrations of both ferric and ferrous iron were present. Recently infiltrated water from snow melt has likely been the transport mechanism for humic acids, derived from microbial decay of peaty soils.