Methane production and consumption in loess soil at different slope position.

Methane (CH(4)) production and consumption and soil respiration in loess soils collected from summit (Top), back slope (Middle), and slope bottom (Bottom) positions were assessed in laboratory incubations. The CH(4) production potential was determined under conditions which can occur in the field (relatively short-term flooding periods with initially ambient O(2) concentrations), and the CH(4) oxidation potential was estimated in wet soils enriched with CH(4). None of the soils tested in this study emitted a significant amount of CH(4). In fact, the Middle and Bottom soils, especially at the depth of 20-40 cm, were a consistent sink of methane. Soils collected at different slope positions significantly differed in their methanogenic, methanotrophic, and respiration activities. In comparison with the Top position (as reference soil), methane production and both CO(2) production and O(2) consumption under flooding were significantly stimulated in the soil from the Middle slope position (P < 0.001), while they were reduced in the Bottom soil (not significantly, by 6 to 57%). All upper soils (0-20 cm) completely oxidized the added methane (5 kPa) during 9-11 days of incubation. Soils collected from the 20-40 cm at the Middle and Bottom slope positions, however, consumed significantly more CH(4) than the Top soil (P < 0.001).