| Water level is supposed to affect methane emissions in wetlands. CH4 flux at different water levels together with environmental factors in the reed wetlands of Hangzhou Bay reclamation area was monitored. A water level gradient was set up: 0 cm(LW1), 10 cm( LW2), 20 cm(LW3) and 30 cm(LW4), From April 2014 to December 2014, temporal and spatial variation of CH4 emission fluxes were monitord using a static chamber–gas chromatographic technique. The spatial variation of soil methane production potential was also investigated. The effects of water level on seasonal variation and daily variation of methane emission flux was analyzed. The main results are as follows:1)The methane emission flux from the reed wetlands averaged 7.03 mg·m-2·h-1 during the observation period and the wetlands acted as sources of methane, irrespective of water level. Peak of methane emission was obeserved in the summer(June to August). The emission peak for LW1 and LW2 was 3.92 mg·m-2·h-1 and 18.21mg·m-2·h-1 respectively, in the middle of July, while for LW3 and LW4, the methane emission peak was 20.94 mg·m-2·h-1 and 22.06mg·m-2·h-1 respectively in late June. Methane emission increased with increasing water level in the reed growth peak period in late May to September. The average CH4 emission flux for the water levels was LW4(10.184 mg·m-2·h-1) > LW3(8.556 mg·m-2·h-1) > LW2(7.806 mg·m-2·h-1) > LW1(1.573 mg·m-2·h-1). During the whole observation period, the average CH4 emission flux exhibited a pattern of summer > autumn > spring > winter under the non-flooding conditions(LW1), and the average CH4 emission under flooding conditions(LW2、LW3、LW4) was Summer > Spring > Autumn > Winter. The Study showed that the methane emission rate increased with the water level in the reed middle to the end of growth period, but no significant difference of methane emission flux was observed at the beginning or at the end of the growth period. Temperature and reed biomass were two major factors that affect methane flux in the Hangzhou Bay reed wetlands under the flooding conditions. Methane emission at the shallow water levels was more affected by water level fluctuation than that at the deep water levels. Under the non-flooding conditions, temperature, soil organic carbon, reed biomass and soil water content all influenced methane emission flux change in these reed wetlands.2)The methane production potential of Hangzhou Bay reed wetland at different water levels was determined with an anaerobic incubation technique. The results showed that,(1) At the beginning of the reed growth(April), the average methane production potential at different water level water levels was 30 cm(0.167 μg·g-1·d-1) > 20 cm(0.121μg·g-1·d-1) > 10 cm(0.103μg·g-1·d-1) > 0 cm(0.011μg·g-1·d-1). In the later growth stage of the reed(September), the average methane production potential at different water level water level was 10 cm(2.158μg·g-1·d-1) >20 cm(2.118μg·g-1·d-1) > 0 cm(2.050μg·g-1·d-1) > 30 cm(1.462μg·g-1·d-1). Overall, the average methane production potential was significantly higher in the later growth stage than in the early growth stage.(2) The methane production potential increased with increasing water level in the early growth stage(April). In the later growth stage(September), the methane production potential did not exhibit a clear pattern with the change of water level.(3) The methane production potential in the early growth stage was significantly correlated with soil organic carbon content, soil p H and Eh, while in the late growth stage, the methane production potential was significantly correlated with soil organic carbon content, but not with soil p H, Eh and conductivity.3)CH4 flux at simulated different water levels(0, 5, 10 and 20 cm) of reed wetlands in the Hangzhou Bay area was investigated. The result showed that the methane emission flux acted as sources of methane at all the four water levels during the simulation period. Only one peak CH4 flux was observed for each selected water level during the period, but peak timing generally postponed with increasign water level. CH4 flux was lower in night and higher in day. The correlation analysis showed that air temperature and water temperature were the dominant factors to explain soil CH4 flux. CH4 flux was more influenced by soil temperature at the groundwater level(0 cm and 5 cm) than at deeper water levels. Meanwhile, soil p H was the dominant factor to explain soil CH4 flux under the non-flooding conditions. Soil Eh was the dominant factor to explain soil CH4 flux under the flooding conditions. |
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