Cyanobacteria blooms: A neglected facilitator of CH₄ production in eutrophic lakes

Lakes are regarded as one of the important sources of atmospheric CH₄. However, the role of cyanobacteria blooms (CBBs) play in the CH₄ production in eutrophic lakes is not fully clear. In this study, the spatial distribution characteristics of CH₄ concentrations in surface water and sediment columns were investigated in Zhushan Bay of Taihu lake, China. Results showed that CH₄ concentrations in CBBs accumulated zones were much higher than that in the open lake areas, with the highest values of 3.79 μmol·L^-1 and 2261.88 μmol·L^-1 in surface water and sediment columns, respectively. CH₄ concentrations were strongly influenced by various factors. In surface water, the occurrence of CBBs greatly contributed to CH₄ productions, as evidenced by the well-predicting for CH₄ concentrations using Chl-a and NH₄⁺ concentrations. In the sediments, the Ignition Loss and C:N ratio values were two indicators of CH₄ contents, suggesting that the methanogenesis processes were influenced by not only the quantities, but also the qualities of organic matter. The labile substrates produced during the CBBs decomposition processes promoted the CH₄ production and migration from sediments to the water column, resulting in the coherence in CH₄ concentrations between the sediments and the surface water. The high-resolution determinations of CH₄ concentrations in surface water and sediments clarified that the CBBs were a neglected facilitator of CH₄ productions, which should be considered in the future estimation of CH₄ emissions in eutrophic lakes.