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Stream solute tracer timescales changing with discharge and reach length confound process interpretation
Author(s) -
Schmadel Noah M.,
Ward Adam S.,
Kurz Marie J.,
Fleckenstein Jan H.,
Zarnetske Jay P.,
Hannah David M.,
Blume Theresa,
Vieweg Michael,
Blaen Phillip J.,
Schmidt Christian,
Knapp Julia L.A.,
Klaar Megan J.,
Romeijn Paul,
Datry Thibault,
Keller Toralf,
Folegot Silvia,
Arricibita Amaia I. Marruedo,
Krause Stefan
Publication year - 2016
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1002/2015wr018062
Subject(s) - tracer , advection , dispersion (optics) , discharge , diffusion , environmental science , hydrology (agriculture) , mechanics , geology , physics , geography , thermodynamics , drainage basin , cartography , geotechnical engineering , nuclear physics , optics
Improved understanding of stream solute transport requires meaningful comparison of processes across a wide range of discharge conditions and spatial scales. At reach scales where solute tracer tests are commonly used to assess transport behavior, such comparison is still confounded due to the challenge of separating dispersive and transient storage processes from the influence of the advective timescale that varies with discharge and reach length. To better resolve interpretation of these processes from field‐based tracer observations, we conducted recurrent conservative solute tracer tests along a 1 km study reach during a storm discharge period and further discretized the study reach into six segments of similar length but different channel morphologies. The resulting suite of data, spanning an order of magnitude in advective timescales, enabled us to (1) characterize relationships between tracer response and discharge in individual segments and (2) determine how combining the segments into longer reaches influences interpretation of dispersion and transient storage from tracer tests. We found that the advective timescale was the primary control on the shape of the observed tracer response. Most segments responded similarly to discharge, implying that the influence of morphologic heterogeneity was muted relative to advection. Comparison of tracer data across combined segments demonstrated that increased advective timescales could be misinterpreted as a change in dispersion or transient storage. Taken together, our results stress the importance of characterizing the influence of changing advective timescales on solute tracer responses before such reach‐scale observations can be used to infer solute transport at larger network scales.