TY - JOUR

T1 - Hourly methane and carbon dioxide fluxes from temperate ponds

AU - Sø, Jonas Stage

AU - Martinsen, Kenneth Thorø

AU - Kragh, Theis

AU - Sand-Jensen, Kaj

N1 - Publisher Copyright: © The Author(s) 2024.

PY - 2024

Y1 - 2024

N2 - Ponds are regarded as greenhouse gas (GHG) emission hot spots, but how hot are they? We examined this question by measuring methane (CH4) and carbon dioxide (CO2) 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 CH4 fluxes were more variable than diffusive CH4 fluxes. Ebullition was absent when total CH4 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 CH4 ebullition remained constant. CO2 fluxes paralleled the day-night balance of photosynthesis and respiration. Mean CH4 ebullition in open and forest ponds exceeded CH4 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. CO2 emissions were higher on a molar basis than CH4 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 CO2e m−2 y−1) are naturally high due to extensive external input of dissolved CO2 and organic carbon relative to pond area and volume.

AB - Ponds are regarded as greenhouse gas (GHG) emission hot spots, but how hot are they? We examined this question by measuring methane (CH4) and carbon dioxide (CO2) 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 CH4 fluxes were more variable than diffusive CH4 fluxes. Ebullition was absent when total CH4 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 CH4 ebullition remained constant. CO2 fluxes paralleled the day-night balance of photosynthesis and respiration. Mean CH4 ebullition in open and forest ponds exceeded CH4 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. CO2 emissions were higher on a molar basis than CH4 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 CO2e m−2 y−1) are naturally high due to extensive external input of dissolved CO2 and organic carbon relative to pond area and volume.

KW - Carbon dioxide-CO

KW - Diffusive flux

KW - Ebullitive methane

KW - Greenhouse gasses

KW - Methane-CH

KW - Ponds

U2 - 10.1007/s10533-024-01124-4

DO - 10.1007/s10533-024-01124-4

M3 - Journal article

AN - SCOPUS:85186906591

VL - 167

SP - 177

EP - 195

JO - Biogeochemistry

JF - Biogeochemistry

SN - 0168-2563

ER -