Gas transfer velocities of CO<sub>2</sub> in subtropical monsoonal climate streams and small rivers
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Published:2019-02-04
Issue:3
Volume:16
Page:681-693
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ISSN:1726-4189
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Container-title:Biogeosciences
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language:en
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Short-container-title:Biogeosciences
Author:
Li SiyueORCID, Mao Rong, Ma Yongmei, Sarma Vedula V. S. S.
Abstract
Abstract. CO2 outgassing from rivers is a critical component for evaluating
riverine carbon cycle, but it is poorly quantified largely due to limited
measurements and modeling of gas transfer velocity in subtropical streams and
rivers. We measured CO2 flux rates and calculated k and partial
pressure (pCO2) in 60 river networks of the Three Gorges
Reservoir (TGR) region, a typical area in the upper Yangtze River with
monsoonal climate and mountainous terrain. The determined k600 (gas
transfer velocity normalized to a Schmidt number of 600 (k600) at a
temperature of 20 ∘C) value (48.4±53.2 cm h−1) showed large variability
due to spatial variations in physical processes related to surface water turbulence.
Our flux-derived k values using chambers were comparable
with k values using the model derived from
flow velocities based on a subset of data. Unlike in open waters, e.g.,
lakes, k600 is more pertinent to flow velocity and water depth in the
studied river systems. Our results show that TGR river networks emitted
approx. 0.69 to 0.71 Tg CO2 (1 Tg =1012 g) during the monsoon
period using varying approaches such as chambers, derived k600 values
and models. This study suggests that incorporating scale-appropriate k
measurements into extensive pCO2 investigations is
required to refine basin-wide carbon budgets in subtropical streams and
small rivers. We concluded that the simple parameterization of k600 as a
function of morphological characteristics is site specific for
regions and watersheds and hence highly variable in rivers of the upper Yangtze.
k600 models should be developed for stream studies to evaluate the
contribution of these regions to atmospheric CO2.
Funder
National Natural Science Foundation of China
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Ecology, Evolution, Behavior and Systematics
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