Contribution of the decomposition of a macroalgal bloom to methane production in sea cucumber culture

CH4 is one of the most important greenhouse gases responsible for climate change. The effect of algal decomposition on CH4 emission fluxes in aquaculture environments is unknown. This study determined the relative abundance of methanogens in aquaculture in northern China. We determined various parameters in the water and sediment after the decomposition of Chaetomorpha valida. The results showed that the relative abundance of methanogens increased significantly during the decomposition of C. valida. The average CH4 emission flux was 50.64 mg m-2 h-1 when the density of C. valida was 25 mg cm-3, which was 11 times higher than that at a density of 0 mg cm-3. The concentrations of dissolved oxygen (DO), nitrite, nitrate and sulfate in the aquaculture pond significantly decreased during the decomposition of C. valida. The formation of a strong anaerobic reduction environment promoted the formation and release of CH4. Our results confirmed that the decomposition of C. valida enhanced the CH4 emission flux. The average CH4 emission fluxes ranged from 4.62 to 50.64 mg m-2 h-1. It is particularly important to remove decomposed algae in a timely manner and control greenhouse gas emissions from aquaculture ponds to mitigate climate change. •The relative abundance of methanogens increased significantly in the C. valida outbreak area.•The biomass of C. valida is a dominant driver that determines CH4 emission flux during the decomposition stage.•The decomposition of C. valida strengthens the degree of anaerobic reduction in the environment.•Dissolved organic carbon is the main contributor to CH4 emission flux in sea cucumber culture.