Aerobic Methane Synthesis and Dynamics in a River Water Environment

Reports of aerobic biogenic methane () have generated new views about sources in nature. We examine this phenomenon in the free-flowing Yellowstone river wherein concentrations were tracked as a function of environmental conditions, phototrophic microorganisms (using chlorophyll , Chl , as proxy), as well as targeted methylated amines known to be associated with this process. was positively correlated with temperature and Chl , although diurnal measurements showed concentrations were greatest during the night and lowest during maximal solar irradiation. efflux from the river surface was greater in quiescent edge waters (71-94 mol m d) than from open flowing current (~ 57 mol m d). Attempts to increase flux by disturbing the benthic environment in the quiescent water directly below (~ 1.0 m deep) or at varying distances (0-5 m) upstream of the flux chamber failed to increase surface flux. Glycine betaine (GB), dimethylamine and methylamine (MMA) were observed throughout the summer-long study, increasing during a period coinciding with a marked decline in Chl , suggesting a lytic event led to their release; however, this did not correspond to increased concentrations. Spiking river water with GB or MMA yielded significantly greater than nonspiked controls, illustrating the metabolic potential of the river microbiome. In summary, this study provides evidence that: (1) phototrophic microorganisms are involved in synthesis in a river environment; (2) the river microbiome possesses the metabolic potential to convert methylated amines to ; and (3) river concentrations are dynamic diurnally as well as during the summer active months.