Headwater gas exchange quantified from O2 mass balances at the reach scale

Rovelli, Lorenzo and Attard, K.M. and Heppell, C.M. and Binley, Andrew Mark and Trimmer, M. and Glud, R.N. (2018) Headwater gas exchange quantified from O2 mass balances at the reach scale. Limnology and Oceanography: Methods, 16 (10). pp. 696-709. ISSN 1541-5856

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Abstract

Headwater streams are important in the carbon cycle and there is a need to better parametrize and quantify exchange of carbon-relevant gases. Thus, we characterized variability in the re-aeration coefficient (k2) and dissolved oxygen (O2) gas transfer velocity (k) in two lowland headwaters of the River Avon (UK). The traditional one-station open-water method was complemented by in situ quantification of riverine sources and sinks of O2 (i.e., groundwater inflow, photosynthesis and respiration in both the water column and benthic compartments - sediments) enabling direct hourly estimates of k2 at the reach–scale (~150 m) without relying on the nighttime regression method. Obtained k2 values ranged from 0.001 – 0.600 h-1. Average daytime k2 were a factor two higher than values at night, likely due to diel changes in water temperature and wind. Temperature contributed up to 46% of the variability in k on an hourly scale, but clustering temperature incrementally strengthened the statistical relationship. Our analysis suggested that k variability is aligned with dominant temperature trends rather than with short-term changes. Similarly, wind correlation with k increased when clustering wind speeds in increments correspondent with dominant variations (1 m s-1). Time scale is thus an important consideration when resolving physical drivers of re-aeration. Mean estimates of k from recent parametrizations proposed for upscaling, when applied to the settings of this study, were found to be in agreement with our independent O2 budget assessment (within <15%), adding further support to the validity of upscaling efforts aiming at quantifying large-scale riverine gas emissions.

Item Type:
Journal Article
Journal or Publication Title:
Limnology and Oceanography: Methods
Uncontrolled Keywords:
/dk/atira/pure/subjectarea/asjc/2200/2212
Subjects:
ID Code:
127094
Deposited By:
Deposited On:
28 Aug 2018 09:44
Refereed?:
Yes
Published?:
Published
Last Modified:
20 Sep 2020 05:00