Controlling factors and effects of chronic nitrogen and sulphur deposition on methane oxidation in a temperate forest soil

Soil CH4 flux rates were determined on 28 occasions between June 1996 and July 1997 in a temperate deciduous woodland in south-west England. The effects of environmental and edaphic factors on flux rates and the effects of chronic deposition of sulphuric acid, nitric acid and ammonium sulphate were investigated. The soil was a consistent net CH4 oxidiser, with mean (n = 10) oxidation rates for plots exposed to ambient throughfall ranging from 44.3 to 110.6 μg CH4 m-2 h-1 between samplings; net CH4 production was not observed. The annual mean uptake rate differed by only 6% from the annual mean flux calculated from the literature for other studies of >364 d duration in temperate and boreal deciduous woodlands. The CH4 uptake rates were correlated with soil water potential (square-root transformed), temperature and depth of organic horizon (r2 = 0.78, 0.30 and 0.41, respectively). Soil water potential was the best predictor of net CH4 oxidation rates and when temperature was added to the regression model no improvement in the r2 was observed. The chronic deposition of sulphuric acid stimulated net methane oxidation (