Methane and nitrous oxide sources and emissions in a subtropical freshwater reservoir, South East Queensland, Australia
Reservoirs have been identified as an important source of non-carbon dioxide (CO<sub>2</sub>) greenhouse gases with wide ranging fluxes for reported methane (CH<sub>4</sub>); however, fluxes for nitrous oxide (N<sub>2</sub>O) are rarely quantified. This study inve...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2014-09-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/11/5245/2014/bg-11-5245-2014.pdf |
| Summary: | Reservoirs have been identified as an important source of non-carbon dioxide
(CO<sub>2</sub>) greenhouse gases with wide ranging fluxes for reported methane
(CH<sub>4</sub>); however, fluxes for nitrous oxide (N<sub>2</sub>O) are rarely
quantified. This study investigates CH<sub>4</sub> and N<sub>2</sub>O sources and
emissions in a subtropical freshwater Gold Creek Reservoir, Australia,
using a combination of water–air and sediment–water flux measurements and
water column and pore water analyses. The reservoir was clearly a source of
these gases as surface waters were supersaturated with CH<sub>4</sub> and N<sub>2</sub>O.
Atmospheric CH<sub>4</sub> fluxes were dominated by ebullition (60 to 99%)
relative to diffusive fluxes and ranged from 4.14 × 10<sup>2</sup> to
3.06 × 10<sup>5</sup> μmol CH<sub>4</sub> m<sup>−2</sup> day<sup>−1</sup> across
the sampling sites. Dissolved CH<sub>4</sub> concentrations were highest in the
anoxic water column and sediment pore waters (approximately 5 000 000%
supersaturated). CH<sub>4</sub> production rates of up to
3616 ± 395 μmol CH<sub>4</sub> m<sup>−2</sup> day<sup>−1</sup> were found
during sediment incubations in anoxic conditions. These findings are in
contrast to N<sub>2</sub>O where no production was detected during sediment
incubations and the highest dissolved N<sub>2</sub>O concentrations were found in
the oxic water column which was 110 to 220% supersaturated with
N<sub>2</sub>O. N<sub>2</sub>O fluxes to the atmosphere were primarily through the
diffusive pathway, mainly driven by diffusive fluxes from the water column
and by a minor contribution from sediment diffusion and ebullition. Results
suggest that future studies of subtropical reservoirs should monitor CH<sub>4</sub>
fluxes with an appropriate spatial resolution to ensure capture of ebullition
zones, whereas assessment of N<sub>2</sub>O fluxes should focus on the diffusive
pathway. |
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| ISSN: | 1726-4170 1726-4189 |