Methane production in harmful algal blooms collapsed water: The contribution of non-toxic Microcystis aeruginosa outweighs that of the toxic variety

Cyanobacterial blooms can promote CH4 production. The proportions of toxic and non-toxic Microcystis aeruginosa spatiotemporally vary in algal water. However, the comparative contributions of decomposed toxic and non-toxic M. aeruginosa to methane (CH4) production are poorly understood. Here, a 61-day microcosm study was conducted to simulate the collapse processes of toxic and non-toxic M. aeruginosa. The results illustrated that the decomposition of M. aeruginosa induced anaerobic and nutrient-rich conditions in the water. However, the presence of non-toxic M. aeruginosa promoted the release of protein-like substances and aromatic proteins that are readily utilized by methanogens. In comparison, the release of microcystins by toxic M. aeruginosa resulted in a distinctive microorganism community structure. The relative abundance of dominant methanogens in the sediment of the system containing toxic M. aeruginosa was markedly lower than that of the system containing the non-toxic strain at the end of incubation. Despite the fact that almost equal amounts of total carbon were present in the two systems, the CH4 production per unit particulate total carbon (identified as carbon content vs. algal biomass) in the system containing non-toxic M. aeruginosa was 1.74-fold higher than that in the system containing the toxic strain. Considering these observations, it is likely that the currently predicted CH4 mass in algal waters is inaccurate, and should be considered when estimating CH4 emissions in eutrophic freshwater. (C) 2020 Elsevier Ltd. All rights reserved.