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

Soil CH4 flux rates were determined on 28 occasions between June 1996 and J uly 1997 in a temperate deciduous woodland in south-west England. The effec ts of environmental and edaphic factors on flux rates and the effects of ch ronic 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 mug CH4 m(-2) h(-1) between samplings; net CH4 production was no t 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 durat ion 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 (r(2) = 0.78, 0.30 and 0.41, respectively). S oil water potential was the best predictor of net CH4 oxidation rates and w hen temperature was added to the regression model no improvement in the r2 was observed. The chronic deposition of sulphuric acid stimulated net metha ne oxidation (P < 0.05), while the chronic deposition of nitric acid and am monium sulphate had no significant effect. (C) 2001 Elsevier Science Ltd. A ll rights reserved.