The role of filamentous algae Spirogyra spp. in methane production and emissions in streams

Periphyton is an important primary producer in freshwater ecosystems. However, their effects on methane (CH₄) production and emissions in streams and rivers are not fully understood. The purpose of this study was to investigate the effects of filamentous algae Spirogyra spp. on CH₄ flux and to characterize the factors responsible for these effects. Sediments cores were collected from a stream in the suburbs of Shanghai and either inoculated with Spirogyra spp. in the laboratory or left uninoculated. CH₄ flux, dissolved CH₄ concentration, potential CH₄ production rate and organic carbon in sediments and overlying water were measured for 2 months. Study results indicated that CH₄ fluxes in algal treatment columns were significantly higher than in unvegetated sediments during initial algal decomposition, while potential CH₄ production rates in algal treatment columns were significantly higher than in controls during both algal bloom and initial decomposition. The relationship between CH₄ flux and environmental parameters was assessed and CH₄ flux was found to exhibit a strongly positive relationship with dissolved organic carbon (DOC) concentration and potential CH₄ production rate during experimental periods. It was concluded that Spirogyra spp. increased CH₄ emissions in streams by providing algal carbon sources for methanogenesis and stimulating the CH₄ production in sediments. These findings may facilitate understanding the roles of periphyton in aquatic methane dynamics and global greenhouse gas emissions.