Comparison of eddy covariance CO 2 and CH 4 fluxes from mined and recently rewetted sections in a northwestern German cutover bog

[摘要] With respect to their role in the global carbon cycle, natural peatlands are characterized by their ability to sequester atmospheric carbon. This trait is strongly connected to the water regime of these ecosystems. Large parts of the soil profile in natural peatlands are water saturated, leading to anoxic conditions and to a diminished decomposition of plant litter. In functioning peatlands, the rate of carbon fixation by plant photosynthesis is larger than the decomposition rate of dead organic material. Over time, the amount of carbon that remains in the soil and is not converted back to carbon dioxide grows. Land use of peatlands often goes along with water level manipulations and thereby with alterations of carbon flux dynamics. In this study, carbon dioxide ( CO 2 ) and methane ( CH 4 ) flux measurements from a bog site in northwestern Germany that has been heavily degraded by peat mining are presented. Two contrasting types of management have been implemented at the site: (1) drainage during ongoing peat harvesting on one half of the central bog area and (2) rewetting on the other half that had been taken out of use shortly before measurements commenced. The presented 2-year data set was collected with an eddy covariance (EC) system set up on a central railroad dam that divides the two halves of the (former) peat harvesting area. We used footprint analysis to split the obtained CO 2 and CH 4 flux time series into data characterizing the gas exchange dynamics of both contrasting land use types individually. The time series gaps resulting from data division were filled using the response of artificial neural networks (ANNs) to environmental variables, footprint variability, and fuzzy transformations of seasonal and diurnal cyclicity. We used the gap-filled gas flux time series from 2 consecutive years to evaluate the impact of rewetting on the annual vertical carbon balances of the cutover bog. Rewetting had a considerable effect on the annual carbon fluxes and led to increased CH 4 and decreased CO 2 release. The larger relative difference between cumulative CO 2 fluxes from the rewetted ( 13±6  mol m −2  a −1 ) and drained ( 22±7  mol m −2  a −1 ) section occurred in the second observed year when rewetting apparently reduced CO 2 emissions by 40 %. The absolute difference in annual CH 4 flux sums was more similar between both years, while the relative difference of CH 4 release between the rewetted ( 0.83±0.15  mol m −2  a −1 ) and drained ( 0.45±0.11  mol m −2  a −1 ) section was larger in the first observed year, indicating a maximum increase in annual CH 4 release of 84 % caused by rewetting at this particular site during the study period.

[学科分类] 大气科学