Filamentous green algae Spirogyra regulates methane emissions from eutrophic rivers

Excessive growth of filamentous green algae in rivers has attracted much attention due to their functional importance to primary production and carbon cycling. However, comprehensive knowledge of how filamentous green algae affect carbon cycling, especially the CH4 emissions from river ecosystems, remains limited. In this study, incubation experiments were conducted to examine the factors regulating CH4 emissions from a eutrophic river with dense growth of filamentous green algaeSpirogyrathrough combinations of biogeochemical, molecular biological, and stable carbon isotope analyses. Results showed that although water dissolved oxygen (DO) in the algae+sediment (A+S) incubation groups increased up to 19 mg L-1, average CH4 flux of the groups was 13.09 mu mol m(-2)day(-1), nearly up to two times higher than that from sediments without algae (S groups). The significant increase of sediment CH4 oxidation potential and methanotroph abundances identified the enhancing sediment CH4 oxidation during Spirogyrabloom. However, the increased water CH4 concentration was consistent with depleted water delta 13CCH4 and decreased apparent fractionation factor (alpha(app)), suggesting the important contribution ofSpirogyrato the oxic water CH4 production. It can thus be concluded that high DO concentration during the algal bloom promoted the CH4 consumption by enhancing sediment CH4 oxidation, while algal-linked oxic water CH4 production as a major component of water CH4 promoted the CH4 emissions from the river. Our study highlights the regulation ofSpirogyrain aquatic CH4 fluxes and will help to estimate accurately CH4 emissions from eutrophic rivers with dense blooms of filamentous green algae.

Automated summary

The excessive growth of filamentous green algae in rivers has raised significant concern due to their impact on primary production and carbon cycling. This study found that while Spirogyra algae blooms enhanced sediment CH4 oxidation and methanotroph abundances, they also contributed to the production of CH4 in oxygenated water, ultimately leading to increased CH4 emissions from the river.