Dissolved CH<sub>4</sub> coupled to photosynthetic picoeukaryotes in oxic waters and to cumulative chlorophyll <i>a</i> in anoxic waters of reservoirs
<p>Methane (<span class="inline-formula">CH<sub>4</sub></span>) emissions from reservoirs are responsible for most of the atmospheric climatic forcing of these aquatic ecosystems, comparable to emissions from paddies or biomass burning. Primarily, <span cla...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-06-01
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| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/17/3223/2020/bg-17-3223-2020.pdf |
| Summary: | <p>Methane (<span class="inline-formula">CH<sub>4</sub></span>) emissions from reservoirs are
responsible for most of the atmospheric climatic forcing of these aquatic
ecosystems, comparable to emissions from paddies or biomass burning.
Primarily, <span class="inline-formula">CH<sub>4</sub></span> is produced during the anaerobic mineralization of
organic carbon in anoxic sediments by methanogenic archaea. However, the
origin of the recurrent and ubiquitous <span class="inline-formula">CH<sub>4</sub></span> supersaturation in oxic
waters (i.e., the methane paradox) is still controversial. Here, we
determined the dissolved <span class="inline-formula">CH<sub>4</sub></span> concentration in the water column of
12 reservoirs during summer stratification and winter mixing to explore
<span class="inline-formula">CH<sub>4</sub></span> sources in oxic waters. Reservoir sizes ranged from 1.18 to 26.13 km<span class="inline-formula"><sup>2</sup></span>. We found that dissolved <span class="inline-formula">CH<sub>4</sub></span> in the water column varied
by up to 4 orders of magnitude (0.02–213.64 <span class="inline-formula">µ</span>mol L<span class="inline-formula"><sup>−1</sup></span>), and all oxic depths
were consistently supersaturated in both periods. Phytoplanktonic sources
appear to determine the concentration of <span class="inline-formula">CH<sub>4</sub></span> in these reservoirs
primarily. In anoxic waters, the depth-cumulative chlorophyll <span class="inline-formula"><i>a</i></span>
concentration, a proxy for the phytoplanktonic biomass exported to
sediments, was correlated to <span class="inline-formula">CH<sub>4</sub></span> concentration. In oxic waters, the
photosynthetic picoeukaryotes' abundance was significantly correlated to the
dissolved <span class="inline-formula">CH<sub>4</sub></span> concentration during both the stratification and the
mixing. The mean depth of the reservoirs, as a surrogate of the vertical
<span class="inline-formula">CH<sub>4</sub></span> transport from sediment to the oxic waters, also contributed
notably to the <span class="inline-formula">CH<sub>4</sub></span> concentration in oxic waters. Our findings suggest
that photosynthetic picoeukaryotes can play a significant role in
determining <span class="inline-formula">CH<sub>4</sub></span> concentration in oxic waters, although their role as
<span class="inline-formula">CH<sub>4</sub></span> sources to explain the methane paradox has been poorly explored.</p> |
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| ISSN: | 1726-4170 1726-4189 |