Methane Emission from Flooded Soils of Rice Paddies in Rostov Oblast

Abstract

The methane fluxes to the atmosphere from the rice fields in the Rostov oblast (south of the European Russia) are analyzed using the results of field chamber measurements. In addition to the measurements of methane fluxes at the stages of rice seedlings and full ripeness, the concentrations of methane and hydrogen sulfide, Eh, pH, density, and moisture content are determined in water and different horizons of flooded paddy soils. The methane flux to the atmosphere from a rice paddy varies in the range of 0.195–0.531 mg CH4/(m2 h) and is on the average 2.1-fold higher at the stage of full ripeness as compared with the stage of seedlings. The rate of the methane flux to the atmosphere from the surface of dry soils separating rice paddies is on the average 4.9–12.1-fold lower as compared with the flux from the paddies, varying from 0.034 to 0.045 mg CH4/(m2 h). After flooding the rice paddies, the Eh values decrease in the soils isolated by a water layer and, as a consequence, the methane concentration in soils increases as well as its fluxes to the atmosphere. According to our assessment, the total methane emission from the rice fields in the Rostov oblast approximately reaches 1.253 t/day of 150 t/year, which accounts for 0.4–1.5% of the total methane emission from the soils of the Rostov oblast.