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Sources and sinks of methane

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This paper presents tower-based measurements of methane (CH4) and nitrous oxide (N20) exchange between a boreal aspen stand and the atmosphere. Boreal ecosystems are a priority trace gas research area, and the work was conducted as part of the Boreal Ecosystem-Atmosphere Study (BOREAS). Methane and nitrous oxide fluxes were measured continuously between April 16 and September 16, 1994, in the Prince Albert National Park, Saskatchewan. The fluxes were determined using a high-resolution tunable diode laser Trace Gas Analysis System (TGAS) together with micrometeorological techniques. Both the CH 4 and the N20 fluxes were small and required long averaging times to be resolved. Over the full experiment, small emissions of both CH 4 and N O were measured above the aspen stand. The mean flux of N20 was 1.4 + 0.7 ng m ' s - or 1.9-2.5 ng m -2 s - when an enhancement factor to compensate for the breakdown of similarity theory just above forest canopies is included. Low rates of nitrification and denitrification throughout the growing season may explain the consistently small N20 fluxes. The CH 4 flux averaged 15.7 _+ 2.8 ng m -2 S -1, or 21-28 ng m -2 s -1, including the similarity theory enhancement factor. The CH 4 emissions were highest between late July and mid-September, and there was a strong correlation between the CH 4 flux and the soil temperature. Whereas CH 4 emission was measured from the above-canopy footprint, uptake was recorded close to the tower base. Overall, it appears that CH 4 emissions from anoxic wet patches located throughout the above-canopy footprint overwhelmed uptake from drier areas to produce a net emission of CH 4 from the aspen site.
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This chapter provides an overview of the linkages between hydrology and biogeochemistry in terrestrial and aquatic systems. Selected topics include hydrological pathways on drainage basin slopes, mountain environments, within-river (or in-stream) processes, wetlands, groundwater (and groundwater–surface water interactions), and lakes. Beginning from catchment headwaters, This chapter introduces mechanisms delivering water from hillslopes to stream channels, highlighting the relative importance of biogeochemical processes along hydrological pathways. It considers processes affecting components of the water budget, including snow formation and ablation processes, and interactions with the soil below snow cover and during snowmelt. It presents the concept of nutrient spiraling and the importance of temperature and stream flow variability on biogeochemistry, as well as groundwater–surface water interactions through hyporheic and riparian zones. This chapter contrasts important processes in hydrologically isolated wetlands with those temporally connected to streams and rivers. It addresses stream and groundwater inputs, stratification, and within-lake processes, interactions with sediments, and a discussion about limiting nutrients. This chapter presents information about typical reactions controlled by hydrological pathways, lithology (mineralogy) and biota, the importance of residence time in biogeochemical evolution, and linkages between groundwater and surface water. An example is given of the effects of human activities on these linkages, focusing on acidic atmospheric deposition.
Article
Diurnal variation in the rate of methane emission and its relation to water table depth and macro climate was studied in several plant communities within an acid,Sphagnum dominated, mixed mire in Northern Sweden. Provided that diurnal variation in solar radiation and air temperature occurred, methane fluxes differed during day and night. Diurnal patterns in methane emission rates were found to differ among mire plant communities. In relatively dry plant communities (ridges, minerotrophic lawn), the average nighttime emission rates were 2–3 times higher than the daytime rates during the two periods with high diurnal variation in solar radiation and air temperature. Methane emission was significantly (p < 0.05) related to solar radiation and soil temperature at depths of 5 and 10 cm at all sampling points in the dry plant communities. In the wetter plant communities, no significant difference between daytime and nighttime average methane emission rates were found even though methane emissions were significantly related with radiation and soil temperature at approximately 70% of the sampling points. The increased emission rate for methane at night in the comparatively dry plant communities was probably caused by an inhibition of methane oxidation, owing to the lower nighttime temperatures or to a delay in the supply of root-exuded substrate for the anaerobic bacteria, or by both. The pattern observed in the wet plant communities indicated that methane production were positively related either to soil temperature or light-regulated root exudation.
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