Tracer-based characterization of hyporheic exchange and benthic biolayers in streams

Water Resources Research
By: , and 

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Abstract

Shallow benthic biolayers at the top of the streambed are believed to be places of enhanced biogeochemical turnover within the hyporheic zone. They can be investigated by reactive stream tracer tests with tracer recordings in the streambed and in the stream channel. Common in-stream measurements of such reactive tracers cannot localize where the processing primarily takes place, whereas isolated vertical depth profiles of solutes within the hyporheic zone are usually not representative of the entire stream. We present results of a tracer test where we injected the conservative tracer bromide together with the reactive tracer resazurin into a third-order stream and combined the recording of in-stream breakthrough curves with multidepth sampling of the hyporheic zone at several locations. The transformation of resazurin was used as an indicator of metabolism, and high-reactivity zones were identified from depth profiles. The results from our subsurface analysis indicate that the potential for tracer transformation (i.e., the reaction rate constant) varied with depth in the hyporheic zone. This highlights the importance of the benthic biolayer, which we found to be on average 2 cm thick in this study, ranging from one third to one half of the full depth of the hyporheic zone. The reach-scale approach integrated the effects of processes along the reach length, isolating hyporheic processes relevant for whole-stream chemistry and estimating effective reaction rates.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Tracer-based characterization of hyporheic exchange and benthic biolayers in streams
Series title Water Resources Research
DOI 10.1002/2016WR019393
Volume 53
Issue 2
Year Published 2017
Language English
Publisher American Geophysical Union
Contributing office(s) National Research Program - Eastern Branch
Description 20 p.
First page 1575
Last page 1594