The effect of unsteady streamflow and stream-groundwater interactions on oxygen consumption in a sandy streambed

Jason Galloway,Aryeh Fox,Shai Arnon,Jörg Lewandowski

doi:10.1038/s41598-019-56289-y

Abstract

Streamflow dynamics are often ignored when studying biogeochemical processes in the hyporheic zone. We explored the interactive effects of unsteady streamflow and groundwater fluxes on the delivery and consumption of oxygen within the hyporheic zone using a recirculating flume packed with natural sandy sediments. The flume was equipped with a programmable streamflow control and drainage system that was used to impose losing and gaining fluxes. Tracer tests were used to measure hyporheic exchange flux and a planar optode was used to measure subsurface oxygen concentration patterns. It was found that the volume of the oxic zone decreased when the losing flux declined, and was drastically decreased when gaining conditions were applied. It was also found that unsteady streamflow led to a slight increase in the average volume of the oxic zone, compared to the average volume of the oxic zone under steady streamflow. However, the average oxygen consumption rates were significantly higher under unsteady streamflow compared to steady streamflow under all groundwater conditions with the exception of the highest losing flux. The present study provides the first insight into the interactions between streamflow unsteadiness and losing/gaining fluxes and improve understanding of their impact on microbial metabolism in the hyporheic zone.

Highlights

Streamflow dynamics are often ignored when studying biogeochemical processes in the hyporheic zone
Aerobic respiration in sandy streambeds is often concentrated in the upper section of the sediment and in the hyporheic zone (HZ), which is the area directly beneath and adjacent to a river where streamwater enters saturated sediments for a period of time before returning to the river[2]
This work has shown that the common practice of using steady streamflow as a basis for investigations of biogeochemical processes in natural systems can lead to a systematic misrepresentation of redox sensitive processes

Summary

Introduction

Streamflow dynamics are often ignored when studying biogeochemical processes in the hyporheic zone. We explored the interactive effects of unsteady streamflow and groundwater fluxes on the delivery and consumption of oxygen within the hyporheic zone using a recirculating flume packed with natural sandy sediments. The average oxygen consumption rates were significantly higher under unsteady streamflow compared to steady streamflow under all groundwater conditions with the exception of the highest losing flux. The present study provides the first insight into the interactions between streamflow unsteadiness and losing/gaining fluxes and improve understanding of their impact on microbial metabolism in the hyporheic zone. De Falco et al.[23] and Trauth et al.[24] revealed that increasing losing and gaining fluxes under steady streamflow resulted in nonlinear changes in oxygen consumption rates (OCRs) with OCRs being either enhanced or reduce depending on the specific set of conditions present. It is widely accepted today that HEF is determined by the competitive interaction between streamflow and groundwater losing and gaining conditions, to the best of our knowledge the impacts of unsteady streamflow and groundwater interactions on microbially mediated prsocess has never been studied

Objectives

Methods

Results

Discussion

Conclusion