Aerobic methane synthesis and dynamics in a river water environment

Reports of aerobic biogenic methane ([Formula: see text]) have generated new views about [Formula: see text] sources in nature. We examine this phenomenon in the free-flowing Yellowstone river wherein [Formula: see text] concentrations were tracked as a function of environmental conditions, phototrophic microorganisms (using chlorophyll [Formula: see text] , Chl [Formula: see text] , as proxy), as well as targeted methylated amines known to be associated with this process. [Formula: see text] was positively correlated with temperature and Chl [Formula: see text] , although diurnal measurements showed [Formula: see text] concentrations were greatest during the night and lowest during maximal solar irradiation. [Formula: see text] efflux from the river surface was greater in quiescent edge waters (71–94 μmol m(−2) d) than from open flowing current (~ 57 μmol m(−2) 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 [Formula: see text] , suggesting a lytic event led to their release; however, this did not correspond to increased [Formula: see text] concentrations. Spiking river water with GB or MMA yielded significantly greater [Formula: see text] than nonspiked controls, illustrating the metabolic potential of the river microbiome. In summary, this study provides evidence that: (1) phototrophic microorganisms are involved in [Formula: see text] synthesis in a river environment; (2) the river microbiome possesses the metabolic potential to convert methylated amines to [Formula: see text]; and (3) river [Formula: see text] concentrations are dynamic diurnally as well as during the summer active months.