Filamentous green algae Spirogyra regulates methane emissions from eutrophic rivers

Area of Science:

• Environmental Science
• Microbiology
• Biogeochemistry

Background:

• Filamentous green algae blooms impact river primary production and carbon cycling.
• Limited understanding exists on how these algae influence methane (CH4) emissions from river ecosystems.

Purpose of the Study:

• To investigate the factors regulating CH4 emissions from a eutrophic river with dense Spirogyra growth.
• To elucidate the dual role of Spirogyra in CH4 production and oxidation within river systems.

Main Methods:

• Incubation experiments combining biogeochemical, molecular biological, and stable carbon isotope analyses.
• Measurement of CH4 flux, dissolved oxygen, sediment CH4 oxidation potential, and methanotroph abundance.
• Analysis of water CH4 concentration, δ13C-CH4, and apparent fractionation factor (αapp).

Main Results:

• CH4 flux in algae+sediment incubations was nearly double that of sediment-only incubations.
• Increased sediment CH4 oxidation potential and methanotrophs were observed during Spirogyra blooms.
• Evidence suggests Spirogyra contributes to CH4 production in oxygenated river waters.

Conclusions:

• High dissolved oxygen during blooms enhances sediment CH4 consumption.
• Spirogyra-linked oxic water CH4 production is a significant factor in riverine CH4 emissions.
• Accurate estimation of CH4 emissions from algal-bloomed rivers requires considering these complex interactions.