Analaysis of Breakthrough Curve Behavior Of Rhodamine-wt and Sodium Chloride Tracers in a 4th Order Arctic River
Open Access
- Author:
- Smull, Erika M
- Area of Honors:
- Civil Engineering
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Dr. Michael Gooseff, Thesis Supervisor
Eric Todd Donnell, Thesis Honors Advisor
Patrick Reed, Faculty Reader - Keywords:
- Tracer Experiments
Solute Transport
Transient Storage
Rhodamine-WT - Abstract:
- Sodium chloride (NaCl) and Rhodamine-WT (RWT) are two common stream tracers, yet only NaCl is considered to be completely conservative. RWT is known to not behave conservatively due to sorption and desorption in the presence of organic material. This study seeks to better understand advantages and limitations of the two tracers on a larger scale river in a unique stream network. On the Kuparuk River, a 4th-order river located in the northern foothills of Alaska’s Brooks Range, a set of four tracer injections were performed in the summer of 2012 at a wide range of discharge values (454 L/s to 4442 L/s). Dual slug injections of RWT and NaCl were performed on the upstream end of a ~1.5 km reach, located in a watershed underlain by continuous permafrost. The normalized breakthrough curve (BTC) analyses indicate that the window of detection (time of tracer arrival to time of tracer non-detection) ranges from ~0.8-1.9 times the advective timescale for RWT, and from ~0.8-1.7 for NaCl. The BTC tail shapes are generally similar, with NaCl having a slighter steeper tail shape as fit to an exponential residence time distribution (RTD). With increasing discharge, the ratio of RWT:NaCl generally remains close to 1 through late-time tailing. Temporal moment analyses show smaller mean, variance, and skew values with increasing discharge for both RWT and NaCl, and very similar temporal moment magnitudes for the three higher discharges when comparing NaCl to RWT. Through a simple breakthrough decomposition method to determine transient storage, RWT does not display a significantly larger amount of transient storage as a percentage of the zeroth temporal moment for this experimental timescale (~2-4 hours). These results suggest that in a larger river system with similar dynamics, sorption is less evident, or that subsequent desorption is not seen on such a timescale. Therefore RWT appears to be a viable choice for tracer experiments in larger rivers, but more work needs to be done in other systems with a similar range of discharges before any set conclusions.