Significant changes in water pCO2 caused by turbulence from waterfalls

Leibowitz, Zachary William; Brito, Lorena Aparecida Fortes; Lima, Placiano Viana de; Eskinazi-Sant’Anna, Eneida Maria; Barros, Nathan

doi:10.1016/j.limno.2016.09.008

Cited by 16 publications

(17 citation statements)

References 17 publications

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“…This may in part reflect the shallower gradients of the streams and rivers in other studies which leads to less turbulent flow and lower evasion rates (Kokic et al, ; Schelker et al, ; Wallin et al, ). The steepest streams in our study included small waterfall sections which are known to increase turbulence and local evasion rates (Leibowitz et al, ; Natchimuthu et al, ).…”

Section: Discussionmentioning

confidence: 99%

The Influence of Flow and Bed Slope on Gas Transfer in Steep Streams and Their Implications for Evasion of CO₂

et al. 2017

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The evasion of greenhouse gases (including CO2, CH4, and N2O) from streams and rivers to the atmosphere is an important process in global biogeochemical cycles, but our understanding of gas transfer in steep (>10%) streams, and under varying flows, is limited. We investigated gas transfer using combined tracer injections of SF6 and salt. We used a novel experimental design in which we compared four very steep (18.4–29.4%) and four moderately steep (3.7–7.6%) streams and conducted tests in each stream under low flow conditions and during a high‐discharge event. Most dissolved gas evaded over short distances (~100 and ~200–400 m, respectively), so accurate estimates of evasion fluxes will require sampling of dissolved gases at these scales to account for local sources. We calculated CO2 gas transfer coefficients (KCO2) and found statistically significant differences between larger KCO2 values for steeper (mean 0.465 min−1) streams compared to those with shallower slopes (mean 0.109 min−1). Variations in flow had an even greater influence. KCO2 was substantially larger under high (mean 0.497 min−1) compared to low flow conditions (mean 0.077 min−1). We developed a statistical model to predict KCO2 using values of streambed slope × discharge which accounted for 94% of the variation. We show that two models using slope and velocity developed by Raymond et al. (2012) for streams and rivers with shallower slopes also provide reasonable estimates of our CO2 gas transfer velocities (kCO2; m d−1). We developed a robust field protocol which could be applied in future studies.

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Section: Discussionmentioning

confidence: 99%

The Influence of Flow and Bed Slope on Gas Transfer in Steep Streams and Their Implications for Evasion of CO₂

et al. 2017

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“…To estimate streamwater CO 2 , we collected data from Swiss Alpine streams, which we combined with stream data from Austria 16 , Kenya 64 , USA (A. Agerich, personal communication, Kuhn et al, 2017, C. Kuhn, personal communication; P. del Giorgio, personal communication; P. Raymond, personal communication), Brazil 65 , Tibet and China (refs. 15,66 , L. Ran personal communication), and New Zealand (V. De Staercke; M. Styllas; M. Tolsano, personal communication).…”

Section: Methodsmentioning

confidence: 99%

Unexpected large evasion fluxes of carbon dioxide from turbulent streams draining the world’s mountains

et al. 2019

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Inland waters, including streams and rivers, are active components of the global carbon cycle. Despite the large areal extent of the world’s mountains, the role of mountain streams for global carbon fluxes remains elusive. Using recent insights from gas exchange in turbulent streams, we found that areal CO2 evasion fluxes from mountain streams equal or exceed those reported from tropical and boreal streams, typically regarded as hotspots of aquatic carbon fluxes. At the regional scale of the Swiss Alps, we present evidence that emitted CO2 derives from lithogenic and biogenic sources within the catchment and delivered by the groundwater to the streams. At a global scale, we estimate the CO2 evasion from mountain streams to 167 ± 1.5 Tg C yr−1, which is high given their relatively low areal contribution to the global stream and river networks. Our findings shed new light on mountain streams for global carbon fluxes.

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“…Because of the rapids, gas exchange was spatially variable with k 600 in rapids up to 1,000× higher than the flat water segments in between. Waterfalls can also be hotspots of gas exchange, and can return CO 2 concentrations to equilibrium (Leibowitz, Brito, De Lima, Eskinazi-Sant'Anna, & Barros, 2017;Teodoru et al, 2015). Gas exchange velocity is unknown for waterfalls and because of the nearly instant and complete exchange, k 600 may not be knowable for large, steep drops such as Victoria Falls (Teodoru et al, 2015).…”

Section: River Discontinuitiesmentioning

confidence: 99%

Gas exchange in streams and rivers

Hall

Ulseth

2019

WIREs Water

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Gas exchange across the air–water boundary of streams and rivers is a globally large biogeochemical flux. Gas exchange depends on the solubility of the gas of interest, the gas concentrations of the air and water, and the gas exchange velocity (k), usually normalized to a Schmidt number of 600, referred to as k600. Gas exchange velocity is of intense research interest because it is problematic to estimate, is highly spatially variable, and has high prediction error. Theory dictates that molecular diffusivity and turbulence drives variation in k600 in flowing waters. We measure k600 via several methods from direct measures, gas tracer experiments, to modeling of diel changes in dissolved gas concentrations. Many estimates of k600 show that surface turbulence explains variation in k600 leading to predictive models based upon geomorphic and hydraulic variables. These variables include stream channel slope and stream flow velocity, the product of which, is proportional to the energy dissipation rate in streams and rivers. These empirical models provide understanding of the controls on k600, yet high residual variation in k600 show that these simple models are insufficient for predicting individual locations. The most appropriate method to estimate gas exchange depends on the scientific question along with the characteristics of the study sites. We provide a decision tree for selecting the best method to estimate k600 for individual river reaches to scaling to river networks. This article is categorized under: Water and Life > Nature of Freshwater Ecosystems Science of Water > Water Quality Water and Life > Methods

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Significant changes in water pCO2 caused by turbulence from waterfalls

Cited by 16 publications

References 17 publications

The Influence of Flow and Bed Slope on Gas Transfer in Steep Streams and Their Implications for Evasion of CO₂

The Influence of Flow and Bed Slope on Gas Transfer in Steep Streams and Their Implications for Evasion of CO₂

Unexpected large evasion fluxes of carbon dioxide from turbulent streams draining the world’s mountains

Gas exchange in streams and rivers

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Significant changes in water pCO2 caused by turbulence from waterfalls

Cited by 16 publications

References 17 publications

The Influence of Flow and Bed Slope on Gas Transfer in Steep Streams and Their Implications for Evasion of CO2

The Influence of Flow and Bed Slope on Gas Transfer in Steep Streams and Their Implications for Evasion of CO2

Unexpected large evasion fluxes of carbon dioxide from turbulent streams draining the world’s mountains

Gas exchange in streams and rivers

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Product

Resources

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The Influence of Flow and Bed Slope on Gas Transfer in Steep Streams and Their Implications for Evasion of CO₂

The Influence of Flow and Bed Slope on Gas Transfer in Steep Streams and Their Implications for Evasion of CO₂