Methane in surface waters of Oregon estuaries and rivers1

Abstract

Methane concentrations in surface waters of Oregon rivers and estuaries were measured over a 4‐yr period. Geographic variations in riverine CH4 were observed. Results from undisturbed forest streams indicate that rivers can contain high natural levels of CH4 not attributable to pollution. Lateral diffusion and runoff from saturated forest and fertilized agricultural soils may be important in determining methane levels in rivers. Methane concentrations in well‐flushed estuaries appear to be controlled mainly by mixing between high CH4‐containing river water and low CH4‐containing seawater endmembers. Rivers and estuaries were found to be sources of methane to the atmosphere. Calculated daily fluxes to the atmosphere ranged from 1.2 to 71 mg CH4 m−2 for rivers and from 0.04 to 21 mg CH4 m−2 for estuarine samples.