School of Environment, Nanjing Normal University, Nanjing, 210023, China; State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, 430072, China; Department of Chemical Engineering, Tokyo University of Agriculture and Technology, Tokyo, 184-8588, Japan.
State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, 430072, China.
Environ Pollut. 2020 Oct;265(Pt B):114919. doi: 10.1016/j.envpol.2020.114919. Epub 2020 Jun 4.
Shallow lakes are a crucial source of methane (CH), a potent greenhouse gas, to the atmosphere. However, large uncertainties still exist regarding the response of CH emissions to the increasing trophic levels of lakes as well as the underlying mechanisms. Here, we investigate the CH emission flux from lakes with different trophic states in the middle and lower reaches of the Yangtze River basin, China to evaluate the effect of the trophic lake index (TLI) on CH emissions. The mean CH emission fluxes from mesotrophic, eutrophic, middle-eutrophic, and hyper-eutrophic lakes were 0.1, 4.4, 12.0, and 130.4 mg m h, respectively. Thus, the CH emission flux ranged widely and was positively correlated with the degree of eutrophication. The relative abundance of methanogens with respect to the total population for the mesotrophic, eutrophic, mid-eutrophic, and hyper-eutrophic states was 0.03%, 0.35%, 0.94%, and 1.17%, respectively. The biogeographic-scale pattern of lakes classified as each of these four trophic states indicated that CH emissions could be well-predicted by the NH-N concentration in the water column, as both NH-N and CH were produced during mineralisation of labile organic matter in lake sediment. In addition, the shift from clear to turbid water, which is an unhealthy evolution for lakes, was associated with a nonlinear increase in the CH emissions from the studied lakes. In particular, the hypereutrophic lakes functioned as CH emission hotspots. Our findings highlight that nutrient levels, as a potential facilitator of CH emissions, should be considered in future research to accurately evaluate the greenhouse gas emissions from shallow lakes.
浅水湖泊是大气中甲烷（CH）的重要来源，甲烷是一种强效温室气体。然而，对于湖泊富营养化水平增加对 CH 排放的响应以及潜在机制，仍存在较大不确定性。在这里，我们研究了中国长江中下游不同营养状态湖泊的 CH 排放通量，以评估营养状态指数（TLI）对 CH 排放的影响。中营养、富营养、中富营养和过富营养湖泊的平均 CH 排放通量分别为 0.1、4.4、12.0 和 130.4 mg m h。因此，CH 排放通量范围很广，与富营养化程度呈正相关。甲烷菌相对于总种群的相对丰度分别为中营养、富营养、中富营养和过富营养状态的 0.03%、0.35%、0.94%和 1.17%。这些营养状态下的湖泊生物地理尺度模式表明，CH 排放可以通过水柱中的 NH-N 浓度很好地预测，因为 NH-N 和 CH 都是在湖泊沉积物中易分解有机物的矿化过程中产生的。此外，从清澈到浑浊水的转变（这是湖泊不健康的演变）与研究湖泊中 CH 排放量的非线性增加有关。特别是过富营养湖泊成为 CH 排放的热点。我们的研究结果表明，氮素水平作为 CH 排放的潜在促进因素，在未来的研究中应加以考虑，以准确评估浅水湖泊的温室气体排放。
