Assessing the spatial and temporal variability of diffusive methane and nitrous oxide emissions from subtropical freshwater reservoirs

Ronald S. Musenze; Alistair Grinham; Ursula Werner; Deborah Gale; Katrin Sturm; James Udy; Zhiguo Yuan

doi:10.1021/es505324h

Assessing the spatial and temporal variability of diffusive methane and nitrous oxide emissions from subtropical freshwater reservoirs

Ronald S. Musenze^*
, Alistair Grinham
, Ursula Werner
, Deborah Gale
, Katrin Sturm
, James Udy
, Zhiguo Yuan

^*Corresponding author for this work

Research output: Journal Publications and Reviews › RGC 21 - Publication in refereed journal › peer-review

112 Citations (Scopus)

Abstract

Surface water-methane (CH₄) and nitrous oxide (N₂O) concentrations were measured and diffusive fluxes were estimated in three subtropical freshwater reservoirs (Little Nerang Dam (LND), Lake Wivenhoe (LW) and Lake Baroon (LB)) in southeast Queensland, Australia, during four seasons in 2011-2012. All reservoirs were strong sources of CH₄ in all seasons. Surface water CH₄ varied between 1350 and 524 000% saturation, and was overall highest in spring and summer, and lowest in winter, however, with no clear patterns common to all reservoirs. In contrast, all reservoirs switched from weak N₂O sinks in spring to strong N₂O sources for the rest of the year. N₂O saturation in all reservoirs varied between 70 and 1230%. There were significant differences for CH₄ concentrations and fluxes between the reservoirs. Within each reservoir, there was strong spatial CH₄ variability but minimal N₂O saturation variability. CH₄ saturation was higher in inflow zones than in the main body. Area-weighted average fluxes were estimated using six water-air gas transfer velocity estimation models and resulted in fluxes in the range 4.8-20.5, 2.3-5.4, and 2.3-7.5 mg CH₄ m^-2 d^-1, while N₂O was 0.07-0.41, 0.09-0.22, and 0.03-0.09 mg N₂O m^-2 d^-1 for LND, LW, and LB, respectively. Total emissions, in carbon dioxide equivalents, from all measurement campaigns were CH₄ dominated (67-86%). The measured degree of CH₄ saturation and fluxes are among the highest reported thus far indicating that subtropical freshwater reservoirs could be significant aquatic greenhouse gas sources. This paper provides a comprehensive assessment of the interplay between biogeochemical processes and the physical forcing driving the water-air gaseous emissions. The high variability coupled with the lack of consensus among estimation models calls for concerted efforts to address uncertainty of measurements for reliable emissions accounting. © 2014 American Chemical Society.

Original language	English
Pages (from-to)	14499-14507
Journal	Environmental Science and Technology
Volume	48
Issue number	24
DOIs	https://doi.org/10.1021/es505324h
Publication status	Published - 16 Dec 2014
Externally published	Yes

Bibliographical note

Publication details (e.g. title, author(s), publication statuses and dates) are captured on an “AS IS” and “AS AVAILABLE” basis at the time of record harvesting from the data source. Suggestions for further amendments or supplementary information can be sent to [email protected].

Funding

This work was funded by the Australian Research Council (ARC), Healthy Waterways, Ltd. and Seqwater through an industry linkage grant (ARC Linkage project # LP100100325). Seqwater also provided additional monthly TOC and DOC data. We are grateful for the discussions and support by Dr. Ava Simms and Dr. Michael Bartkow of Seqwater. We also thank Associate Prof. Charles Lemckert of Griffith University and Ms. Rikke Laursen for the assistance with wind data measurements in LND.

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title = "Assessing the spatial and temporal variability of diffusive methane and nitrous oxide emissions from subtropical freshwater reservoirs",

abstract = "Surface water-methane (CH4) and nitrous oxide (N2O) concentrations were measured and diffusive fluxes were estimated in three subtropical freshwater reservoirs (Little Nerang Dam (LND), Lake Wivenhoe (LW) and Lake Baroon (LB)) in southeast Queensland, Australia, during four seasons in 2011-2012. All reservoirs were strong sources of CH4 in all seasons. Surface water CH4 varied between 1350 and 524 000\% saturation, and was overall highest in spring and summer, and lowest in winter, however, with no clear patterns common to all reservoirs. In contrast, all reservoirs switched from weak N2O sinks in spring to strong N2O sources for the rest of the year. N2O saturation in all reservoirs varied between 70 and 1230\%. There were significant differences for CH4 concentrations and fluxes between the reservoirs. Within each reservoir, there was strong spatial CH4 variability but minimal N2O saturation variability. CH4 saturation was higher in inflow zones than in the main body. Area-weighted average fluxes were estimated using six water-air gas transfer velocity estimation models and resulted in fluxes in the range 4.8-20.5, 2.3-5.4, and 2.3-7.5 mg CH4 m-2 d-1, while N2O was 0.07-0.41, 0.09-0.22, and 0.03-0.09 mg N2O m-2 d-1 for LND, LW, and LB, respectively. Total emissions, in carbon dioxide equivalents, from all measurement campaigns were CH4 dominated (67-86\%). The measured degree of CH4 saturation and fluxes are among the highest reported thus far indicating that subtropical freshwater reservoirs could be significant aquatic greenhouse gas sources. This paper provides a comprehensive assessment of the interplay between biogeochemical processes and the physical forcing driving the water-air gaseous emissions. The high variability coupled with the lack of consensus among estimation models calls for concerted efforts to address uncertainty of measurements for reliable emissions accounting. {\textcopyright} 2014 American Chemical Society.",

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Assessing the spatial and temporal variability of diffusive methane and nitrous oxide emissions from subtropical freshwater reservoirs. / Musenze, Ronald S.; Grinham, Alistair; Werner, Ursula et al.
In: Environmental Science and Technology, Vol. 48, No. 24, 16.12.2014, p. 14499-14507.

Research output: Journal Publications and Reviews › RGC 21 - Publication in refereed journal › peer-review

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AU - Musenze, Ronald S.

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AU - Werner, Ursula

AU - Gale, Deborah

AU - Sturm, Katrin

AU - Udy, James

AU - Yuan, Zhiguo

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Assessing the spatial and temporal variability of diffusive methane and nitrous oxide emissions from subtropical freshwater reservoirs

Abstract

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