Abstract: To understand the mechanism and affecting factors of CH₄ emission from freshwater marshes,we studied in situ the CH₄ emission in Sanjiang Plain of Northeast China,and its possible affecting factors.The results showed that from April to October 2003,the average CH₄ flux (3.30 mg·m^-2·h^-1) from Carex lasiocarpa marsh was lower than that (4.91 mg·m^-2·h^-1) from Deyeucia angustifolia marsh,but the difference was not significant.There were obvious changes in CH₄ flux from these marshes at different stages,and the controlling factor was not the same.In April,lower temperature limited CH₄ flux,but no significant difference was observed between the two marshes.From May to July,CH₄ flux from D.angustfolia marsh was significantly higher than that from C.lasiocarpa marsh (P<0.01),which mainly resulted from thawing-freezing action.In August,stem density and active organic carbon concentration in profiles became controlling factors,and the CH₄ flux from C.lasiocarpa marsh was higher than that from D.angustifolia marsh.

Key words: Tourmaline, Seawater, pH value, Salinity