Macroalgal metabolism and lateral carbon flows can create significant carbon sinks
<p>Macroalgal beds have drawn attention as one of the vegetated coastal ecosystems that act as atmospheric <span class="inline-formula">CO<sub>2</sub></span> sinks. Although macroalgal metabolism as well as inorganic and organic carbon flows are important path...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-05-01
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| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/17/2425/2020/bg-17-2425-2020.pdf |
| Summary: | <p>Macroalgal beds have drawn attention as one of the
vegetated coastal ecosystems that act as atmospheric <span class="inline-formula">CO<sub>2</sub></span> sinks.
Although macroalgal metabolism as well as inorganic and organic carbon flows
are important pathways for <span class="inline-formula">CO<sub>2</sub></span> uptake by macroalgal beds, the
relationships between macroalgal metabolism and associated carbon flows are
still poorly understood. In the present study, we investigated carbon flows,
including air–water <span class="inline-formula">CO<sub>2</sub></span> exchange and budgets of dissolved inorganic
carbon, total alkalinity, and dissolved organic carbon (DOC), in a temperate
macroalgal bed during the productive months of the year. To assess the key
mechanisms responsible for atmospheric <span class="inline-formula">CO<sub>2</sub></span> uptake by the macroalgal
bed, we estimated macroalgal metabolism and lateral carbon flows (i.e.,
carbon exchanges between the macroalgal bed and the offshore area) by using field
measurements of carbon species, a field-bag method, a degradation
experiment, and mass-balance modeling in a temperate <i>Sargassum</i> bed over a diurnal
cycle. Our results showed that macroalgal metabolism and lateral carbon
flows driven by water exchange affected air–water <span class="inline-formula">CO<sub>2</sub></span> exchange in the
macroalgal bed and the surrounding waters. Macroalgal metabolism caused
overlying waters to contain low concentrations of <span class="inline-formula">CO<sub>2</sub></span> and high
concentrations of DOC that were efficiently exported offshore from the
macroalgal bed. These results indicate that the exported water can
potentially lower <span class="inline-formula">CO<sub>2</sub></span> concentrations in the offshore surface water and
enhance atmospheric <span class="inline-formula">CO<sub>2</sub></span> uptake. Furthermore, the <i>Sargassum</i> bed exported 6 %–35 % of the macroalgal net community production (NCP; 302–1378 mmol C m<span class="inline-formula"><sup>−2</sup></span> d<span class="inline-formula"><sup>−1</sup></span>) as DOC to the offshore area. The results of degradation
experiments showed that 56 %–78 % of macroalgal DOC was refractory DOC
(RDOC) that persisted for 150 d; thus, the <i>Sargassum</i> bed exported 5 %–20 % of
the macroalgal NCP as RDOC. Our findings suggest that macroalgal beds in
habitats associated with high water exchange rates can create significant
<span class="inline-formula">CO<sub>2</sub></span> sinks around them and export a substantial amount of DOC to
offshore areas.</p> |
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| ISSN: | 1726-4170 1726-4189 |