The influence of mixing on seasonal carbon dioxide and methane fluxes in ponds
Joseph S. Rabaey, James B. Cotner
Abstract
Inland waters are important sources of the greenhouse gases carbon dioxide (CO 2 ) and methane (CH 4 ). Ponds have amongst the highest CO 2 and CH 4 fluxes of all aquatic ecosystems, yet seasonal variation in fluxes remain poorly characterized, creating challenges for accurately estimating annual emissions. Further, ponds can exhibit a range of mixing regimes, yet the impact of mixing regimes on gas emissions remains unclear. Here, we assessed annual dynamics of CO 2 and CH 4 in four temperate ponds (Minnesota, USA) that varied in mixing regimes. The ponds ranged from annual sinks to sources of CO 2 (−1 to 15 mol m −2 yr −1 ) and were all significant sources of CH 4 (4.3–8.2 mol m −2 yr −1 ), with annual fluxes in CO 2 equivalents of 1.8–4.1 kg CO 2 -eq. m −2 yr −1 . Mixing regimes impacted CO 2 and CH 4 dynamics, as stratified periods were associated with more anoxia, greater accumulation of gases in the bottom waters, higher emissions of CH 4 , and lower fluxes of CO 2 . Ponds with stronger summer stratification also had increased CO 2 and CH 4 fluxes associated with fall turnover. Overall, the two ponds with the strongest stratification had higher annual fluxes (2.6, 4.1 kg CO 2 -eq. m −2 yr −1 ) compared to the two ponds that more frequently mixed (1.8, 2.2 kg CO 2 -eq. m −2 yr −1 ).