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Quantifying the Effect of Aquatic Vegetation on Interfacial Gas Transfer in Streams
  • Chien-Yung Tseng,
  • Rafael Tinoco
Chien-Yung Tseng
University of Illinois at Urbana Champaign

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Rafael Tinoco
University of Illinois at Urbana Champaign
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Abstract

Turbulence generated by aquatic vegetation in rivers, lakes, and estuaries, can significantly alter the flow structure throughout the whole water column, affecting gas transfer mechanisms at the air-water interface, driving changes in indicators of water quality. We conducted a series of laboratory experiments with rigid cylinder arrays to mimic vegetation using a staggered configuration in a recirculating Odell-Kovasznay type race-track flume. 2D planar Particle Image Velocimetry (PIV) was used to characterize the mean flow field and turbulent flow statistics, to characterize the effect of emergent and submerged vegetation in terms of turbulent kinetic energy, Reynolds stresses, and turbulent shear production. The surface gas transfer rate was determined by measuring the dissolved oxygen (DO) concentration during the re-aeration process in water based on the methodology proposed by the American Society of Civil Engineers (ASCE). Our data provide new insight on how stem- and canopy- scale turbulence affect the surface gas transfer rate at different submergence ratios and array densities. The relation between mean flow velocity and turbulent shear production in these scenarios is used to develop a modified surface renewal (SR) model using turbulent shear production as an indicator of gas transfer efficiency, which allows us to more accurately predict surface gas transfer rates in vegetated flows.