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Research progress on “methane paradox” phenomenon in lake surface waters.

YANG Le*   

  1. (Zhejiang Academy of Forestry, Hangzhou 310023, China).
  • Online:2020-04-10 Published:2020-04-10

Abstract: The traditional paradigm in aquatic sciences holds that microbial methanogenesis happens primarily in the anoxic conditions. The widely reported paradoxical supersaturation of CH4 in oxygenated surface waters challenges such traditional paradigm. Here, I summarized two new concepts in literature, i.e, external source hypothesis and insitu produced hypothesis, to explain the “methane paradox” phenomenon. The former supports that the lateral input of CH4 is from the surrounding littoral zone (FL), which could be important for small lakes with an organic-rich littoral zone. The latter believes in-situ production in the oxic surface waters (P), which accounts for large, deep lakes in the valleys. The external inputs from the upstream rivers (FR), turbulent diffusion from the sediments and metalimnion layers (FZ), the dissolution of bubbles (FD) are all contributed to the supersaturated CH4 concentrations in the oxic surface layers. CH4 emission flux at the airwater interface (E) and CH4 oxidation (O) can lead to CH4 loss in the oxic surface layers. The construction of CH4 mass balance model will be helpful for understanding the supersaturation of CH4 in oxygenated surface waters. Actually, the supersaturated CH4 concentration in the surface waters is related to environmental characteristics of lakes. However, differences in data analysis methods, sampling periods, and lake environments can result in the debates of two hypotheses.