Connection between concentration-discharge relations and near-stream groundwater residence times
Abstract
Headwater streams are subject to changes in water quantity and quality as climate change continues to impact recharge patterns by decreasing the mean snow water equivalent in the western U.S. Concentration-discharge (C-Q) relations are commonly used to discern hydrochemical processes that control stream chemistry, but C-Q data alone does not provide information about the source of groundwater sourcing streamflow. Here, we combine C-Q relations with groundwater residence times to explore the connection between the age of groundwater sourcing streams and stream C-Q patterns. We instrumented the Hotel Gulch watershed, a small, high-elevation, granitic catchment in the Manitou Experimental Forest, CO (area = 3.5 km2, mean elevation = 2700 m) with paired stilling and groundwater wells. We measured major cations and anions (n = 30) and stream discharge from April to November in 2021 & 2022 to create eight unique C-Q relations. In addition, we collected 3H and CFC-12 samples in June and September of 2021 that were used to model groundwater residence times with binary mixing between young and old piston flow in TracerLPM. We observe near-chemostatic behavior at all eight sites, but find that as the C-Q slope of silica and calcium approaches zero, near-stream groundwater residence time increases. This conclusion suggests a correlation between the age of groundwater sourcing streamflow and the in-stream geochemical and hydrologic response. Groundwater with longer residence times has a larger buffering capacity to perturbations, and thus we hypothesize that in areas where groundwater residence time is long, the relation between stream discharge and solute concentrations will remain more stable as climate change continues to impact recharge inputs in headwater catchments.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.H32S1152W