Hourly methane and carbon dioxide fluxes from temperate ponds

• Published in: Biogeochemistry 2024-02, Vol.167 (2), p.177-195
• Main Authors: Sø, Jonas Stage, Martinsen, Kenneth Thorø, Kragh, Theis, Sand-Jensen, Kaj
• Format: Article
• Language: English
• Subjects: Biogeosciences; Carbon dioxide; Carbon dioxide emissions; Climate change; Earth and Environmental Science; Earth Sciences; Ecosystems; Emissions; Environmental Chemistry; Fluxes; Global warming; Grasslands; Greenhouse effect; Greenhouse gases; Headspace; Life Sciences; Methane; Organic carbon; Photosynthesis; Ponds; Summer; Water temperature; Wind speed; Winter
• ISSN: 1573-515X; 0168-2563; 1573-515X
• DOI: 10.1007/s10533-024-01124-4

Ponds are regarded as greenhouse gas (GHG) emission hot spots, but how hot are they? We examined this question by measuring methane (CH 4 ) and carbon dioxide (CO 2 ) fluxes in six forest and open land ponds on grasslands in Denmark during summer and winter. We used floating chambers with do-it-yourself sensors and automated headspace venting, allowing for 7404 hourly measurements. We found highly variable gas fluxes within ponds and between seasons and pond types. Ebullitive CH 4 fluxes were more variable than diffusive CH 4 fluxes. Ebullition was absent when total CH 4 fluxes were lowest (15 µmol m −2  h −1 ), dominant (> 90%) at the highest fluxes (> 400 µmol m −2  h −1 ), and increased with water temperature. In summer, a minor daily increase in diffusive fluxes was found on days with high wind speed, while CH 4 ebullition remained constant. CO 2 fluxes paralleled the day-night balance of photosynthesis and respiration. Mean CH 4 ebullition in open and forest ponds exceeded CH 4 diffusive fluxes 4.1 and 7.1-fold in summer (avg. 22.5 °C) and 2.3 and 2.5-fold in winter (9.6 °C), respectively. CO 2 emissions were higher on a molar basis than CH 4 emissions, both in summer and winter, while their annual global warming potentials were similar. Mean annual gas emissions from open and forest ponds (1092 and 2527 g CO 2 e m −2  y −1 ) are naturally high due to extensive external input of dissolved CO 2 and organic carbon relative to pond area and volume.