Adsorption as a methane storage process in natural lake sediment

Abstract

Methane stored in a natural lake sediment was investigated. Fresh sediment (8–25 cm in sediment depth) taken from Lake Biwa, Japan, contains 2.6 μmol/g d.s. (dry sediment) of CH 4 on average. The sediment retained 0.31 μmol/g d.s. of CH 4 even after air drying, which is 12% of the total CH 4 in the fresh sediment. The higher the temperature for drying of the sediment, the smaller the amount of CH 4 retained. The result of an adsorption experiment indicated that dried and completely degassed lake sediment adsorbs CH 4 . Clay particles in the sediment are possibly responsible for the adsorption of CH 4 . Methane observed in the fresh lake sediment was probably produced by bacteria in the past, then adsorbed on the sediment particles. Adsorption is another form of storage of CH 4 in lake and ocean sediments, in addition to the well known forms of dissolved, bubble, and hydrate CH 4 .