On the use of rhodamine WT for the characterization of stream hydrodynamics and transient storage

Water Resources Research
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Abstract

Recent advances in fluorometry have led to increased use of rhodamine WT as a tracer in streams and rivers. In light of this increased use, a review of the dye's behavior in freshwater systems is presented. Studies in the groundwater literature indicate that rhodamine WT is transported nonconservatively, with sorption removing substantial amounts of tracer mass. Column studies document a two-step breakthrough curve in which two structural isomers are chromatographically separated. Although the potential for nonconservative transport is acknowledged in the surface water literature, many studies assume that sorptive losses will not affect the characterization of physical transport processes. A literature review and modeling analysis indicates that this assumption is valid for quantification of physical properties that are based on the bulk of the tracer mass (traveltime), and invalid for the characterization of processes represented by the tracer tail (transient storage attributable to hyporheic exchange). Rhodamine WT should be considered nonconservative in the hyporheic zone due to nonconservative behavior demonstrated for similar conditions in groundwater. As such, rhodamine WT should not be used as a quantitative tracer in hyporheic zone investigations, including the study of long flow paths and the development of models describing hyporheic zone processes. Rhodamine WT may be used to qualitatively characterize storage in large systems, where there are few practical alternatives. Qualitative investigations should rely on early portions of the tracer profile, making use of the temporal resolution afforded by in situ fluorometry, while discarding later parts of the tracer profile that are adversely affected by sorption.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title On the use of rhodamine WT for the characterization of stream hydrodynamics and transient storage
Series title Water Resources Research
DOI 10.1002/2015WR017201
Volume 51
Issue 8
Year Published 2015
Language English
Publisher AGU Publications
Contributing office(s) Colorado Water Science Center, Toxic Substances Hydrology Program
Description 18 p.
First page 6125
Last page 6142
Online Only (Y/N) N
Additional Online Files (Y/N) N