Methane, carbon dioxide, and nitrous oxide emissions from two clear-water and two turbid-water urban ponds in Brussels (Belgium)
<p>Shallow ponds can occur either in a clear-water state dominated by macrophytes or a turbid-water state dominated by phytoplankton, but it is unclear if and how these two alternative states affect the emission of greenhouse gases (GHGs) such as carbon dioxide (CO<span class="inline-f...
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| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-08-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/22/3785/2025/bg-22-3785-2025.pdf |
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| Summary: | <p>Shallow ponds can occur either in a clear-water state dominated by macrophytes or a turbid-water state dominated by phytoplankton, but it is unclear if and how these two alternative states affect the emission of greenhouse gases (GHGs) such as carbon dioxide (CO<span class="inline-formula"><sub>2</sub></span>), methane (CH<span class="inline-formula"><sub>4</sub></span>), and nitrous oxide (N<span class="inline-formula"><sub>2</sub></span>O) to the atmosphere. We measured the dissolved concentration of CO<span class="inline-formula"><sub>2</sub></span>, CH<span class="inline-formula"><sub>4</sub></span>, and N<span class="inline-formula"><sub>2</sub></span>O from which the diffusive air–water fluxes were computed, in four urban ponds in the city of Brussels (Belgium): two clear-water macrophyte-dominated ponds (Silex and Tenreuken), and two turbid-water phytoplankton-dominated ponds (Leybeek and Pêcheries) on 46 occasions over 2.5 years (between June 2021 and December 2023). Ebullitive CH<span class="inline-formula"><sub>4</sub></span> fluxes were measured with bubble traps in the four ponds during deployments in spring, summer, and autumn, totalling 48 d of measurements. Measured ancillary variables included water temperature, oxygen saturation level ( %O<span class="inline-formula"><sub>2</sub></span>), concentrations of chlorophyll-<span class="inline-formula"><i>a</i></span> (Chl-<span class="inline-formula"><i>a</i>)</span>, total suspended matter (TSM), soluble reactive phosphorus (SRP), nitrite (NO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">2</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="cf5ab84666d459bfffb5030e23e4ac33"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-22-3785-2025-ie00001.svg" width="9pt" height="16pt" src="bg-22-3785-2025-ie00001.png"/></svg:svg></span></span>), nitrate (NO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M12" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="ee54bb0fff66afdafaf51bed1fde360d"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-22-3785-2025-ie00002.svg" width="9pt" height="16pt" src="bg-22-3785-2025-ie00002.png"/></svg:svg></span></span>), and ammonium (NH<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">4</mn><mo>+</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="f1ca5762abf079d28af10bf21d382d4c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-22-3785-2025-ie00003.svg" width="8pt" height="15pt" src="bg-22-3785-2025-ie00003.png"/></svg:svg></span></span>). The turbid-water and clear-water ponds did not differ significantly in terms of diffusive emissions of CO<span class="inline-formula"><sub>2</sub></span> and N<span class="inline-formula"><sub>2</sub></span>O. Clear-water ponds exhibited higher values of ebullitive CH<span class="inline-formula"><sub>4</sub></span> emissions compared to turbid-water ponds, most probably in relation to the delivery of organic matter from macrophytes to sediments, but the diffusive CH<span class="inline-formula"><sub>4</sub></span> emissions were not significantly different between clear- and turbid-water ponds. Across seasons, CH<span class="inline-formula"><sub>4</sub></span> emissions increased with water temperature in all four ponds, with ebullitive CH<span class="inline-formula"><sub>4</sub></span> fluxes having a stronger dependence on water temperature (<span class="inline-formula"><i>Q</i><sub>10</sub></span>) than diffusive CH<span class="inline-formula"><sub>4</sub></span> fluxes. The temperature sensitivity of ebullitive CH<span class="inline-formula"><sub>4</sub></span> fluxes decreased with increasing water depth, implying that shallow sediments would respond more strongly to warming (e.g. heat waves). Total annual CH<span class="inline-formula"><sub>4</sub></span> emissions (diffusive <span class="inline-formula">+</span> ebullitive) in CO<span class="inline-formula"><sub>2</sub></span> equivalents equalled those of CO<span class="inline-formula"><sub>2</sub></span> in turbid-water ponds and exceeded those of CO<span class="inline-formula"><sub>2</sub></span> in clear-water ponds, while N<span class="inline-formula"><sub>2</sub></span>O emissions were negligible compared to the other two GHGs. Total annual GHG emissions in CO<span class="inline-formula"><sub>2</sub></span> equivalents from all four ponds increased from 2022 to 2023 due to higher CO<span class="inline-formula"><sub>2</sub></span> diffusive fluxes, likely driven by higher annual precipitation in 2023 compared to 2022 (leading putatively to higher inputs for organic or inorganic carbon from run-off), possibly in response to the intense El Niño event of 2023. The findings of this work suggest that it might be necessary to account for the presence of submerged macrophytes when extrapolating ebullitive CH<span class="inline-formula"><sub>4</sub></span> fluxes in ponds at a larger scale (regional or global) (particularly if Chl-<span class="inline-formula"><i>a</i></span> is used as a descriptor), although it might be less critical for the extrapolation of diffusive CH<span class="inline-formula"><sub>4</sub></span>, CO<span class="inline-formula"><sub>2</sub></span>, and N<span class="inline-formula"><sub>2</sub></span>O fluxes.</p> |
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| ISSN: | 1726-4170 1726-4189 |