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Assessment of methane and carbon dioxide emissions in two sub‐basins of a small acidic bog lake artificially divided 30 years ago

Sepulveda‐Jauregui, Armando, Martinez‐Cruz, Karla, Lau, Maximilian, Casper, Peter
Freshwater biology 2018 v.63 no.12 pp. 1534-1549
basins, bogs, carbon dioxide, carbon dioxide production, dissolved organic carbon, dissolved oxygen, global warming, greenhouse gas emissions, greenhouse gases, hydrochemistry, lakes, methane, oxygen, peatlands, seasonal variation, temperature
Although lakes are important sources of methane (CH₄) and carbon dioxide (CO₂) to the atmosphere contributing to global warming, their CH₄ and CO₂ emissions are rarely assessed. In particular, increasing inputs of terrestrial dissolved organic carbon (DOC) may affect gas dynamics and alter seasonal changes in gas production. Here, we analysed variations in CH₄ and CO₂ dynamics in sub‐basins of an acidic bog lake, which was artificially divided into four quarters three decades ago, leading to divergence in water chemistry and biology. In the divided lake, only the south‐west basin (SW) received DOC inputs from an adjacent peat bog, while the north‐east basin (NE) was hydrologically disconnected. A year‐long determination of CH₄ and CO₂ production and emission patterns in the two contrasting basins exposed the indirect mechanisms by which DOC supply exercised control on greenhouse gas dynamics in this shallow lake. In both basins, dissolved CH₄ was negatively correlated with dissolved oxygen (O₂) through the water column, suggesting that aerobic methanotrophy is an important regulator of CH₄ emissions in this lake. In contrast, the amount of CO₂ stored in oxic and anoxic layers was not significantly different between the basins, suggesting that O₂ is not the most important driver of dissolved CO₂. Estimated total CH₄ and CO₂ emissions were 2.1 and 1.7 times lower in the NE basin than in the SW basin, with major CH₄ and CO₂ emissions occurring during the fall turnover. The differences in CH₄ and CO₂ emissions suggest that the hydro‐physical properties, namely seasonal temperature, the duration of stratification and O₂ availability, are the main drivers of CH₄ and CO₂ emissions to the atmosphere from small shallow lakes under the influence of DOC inputs under global warming pressure.