GROUNDWATER-SURFACE WATER INTERACTIONS IN A HEADWATER STREAM: EAST FORK, JEMEZ RIVER, NM

The hyporheic zone is a place of rapid water and solute exchange in which critical biogeochemical processes involving both groundwater and surface water take place. Water quality and solute fluxes are dynamic across a variety of time scales and respond to changes in temperature, precipitation, and ecosystem processes. The goal of this project is to investigate how biogeochemical processes vary across the annual hydrograph in New Mexico’s mountain sources of water. Of interest are both diel and seasonal variations in water chemistry and the chemical and hydrologic controls on these processes. Also of interest are natural events such as the Las Conchas fire that occurred in the summer of 2011.

As part of a Research Experience for Undergraduates (REU) funded by the National Science Foundation (NSF) and New Mexico EPSCoR, 34 shallow monitoring wells were installed in the hyporheic zone of the East Fork Jemez River in the Valles Caldera National Preserve during the summer of 2010. Water quality was sampled and analyzed in all wells and at two surface water locations. Continuous water quality sensors (T, pH, conductivity, dissolved oxygen (DO), depth) were deployed in selected wells and the adjacent stream. Field parameters and water levels were also measured multiple times through the summer of 2010. Additional sampling took place in the summer of 2011 before the Los Conchas fire and sampling has continued to take place after the fire. In general, pH is consistently lower in groundwater (GW) relative to surface water, and DO concentrations are consistently <1 mg/L in GW regardless of stream proximity. Specific conductance is either equal or higher than contemporaneous stream values. The significant diurnal variability observed in surface water DO, T, and pH is not observed in GW data. These data are important for understanding reactions in the hyporheic zone.