Loading...
Mapping the hyporheic zone in an acid-rock impacted stream with a salt tracer and electrical resistivity imaging under gaining and losing conditions
Arrue, Dayana A.
Arrue, Dayana A.
Citations
Altmetric:
Advisor
Editor
Date
Date Issued
2023
Date Submitted
Collections
Research Projects
Organizational Units
Journal Issue
Embargo Expires
Abstract
Acid-mine drainage (AMD) from legacy mining and acid-rock drainage (ARD) from sulfide-rich bedrock geology degrades water quality and aquatic habitat by sourcing low pH, metal-laden water to streams. The hyporheic zone serves as a biogeochemical hotspot in numerous streams impacted by acid mine drainage, where it helps regulate metal(loid) reactions and enhances water quality by causing the precipitation of metal oxides capable of adsorbing toxic metal(loid)s. Here, we used time-lapse electrical resistivity imaging and constant-rate sodium chloride tracer injections to assess the extent of the hyporheic zone in a high-alpine stream, Coal Creek, near Crested Butte, Colorado. This stream has been impacted by historic mining, AMD, and metal loads naturally originating from bedrock and fracture zones (i.e., ARD). Two tracer injection tests were performed during baseflow at similar flow rates, one during localized losing stream conditions and the other during localized gaining stream conditions. Electrical resistivity imaging, fluid (surface water), groundwater, and bulk electrical conductivities, and surface water and groundwater elevations and temperatures were analyzed to characterize surface water-groundwater interactions with the goal of delineating the hyporheic zone and its potential influence on metal fate and transport in Coal Creek, a snowmelt-dominated watershed. Results indicated that the hyporheic zone is constrained to ~2.5m below the stream and the immediate banks with a slight connectivity to an adjacent floodplain during the August baseflow tracer test under gaining stream conditions. In contrast, the hyporheic zone was constrained to ~2m below the stream and the immediate banks during the September baseflow tracer test under losing stream conditions. In general, the hyporheic zone had only minimal differences between tests and its overall impact to the stream system is similar during both conditions. The bulk conductivity revealed a diel cycle that mimicked groundwater temperature during both tracer tests. Based on the fluid and bulk breakthrough curves, the tracer’s transport was largely unhindered by transport through the hyporheic zone under both conditions, and there was no conclusive trend found between the stream condition (losing versus gaining) and the percent mass recovery, mean arrival time, variance, and skewness, which were calculated with temporal moments. Our results indicate metals in this system would therefore be driven largely by advection and dispersion with minimal retardation by transient storage through this stream system at baseflow. The hyporheic zone consequently has minimal capacity to attenuate metals along the studied reach during baseflow conditions, and metal loading into Coal Creek is expected to degrade downstream water quality.
Associated Publications
Rights
Copyright of the original work is retained by the author.