Present tropical peat deposits are the outcome of net carbon removal from the atmosphere and form one of the largest terrestrial organic carbon stores on the Earth. Reclamation of pristine tropical peatland areas in Southeast Asia increased strikingly during the last half of the 20th century. Drainage due to land-use change is one of the main driving factors accelerating carbon loss from the ecosystem. Dams were built in drainage-affected peatland area canals in Central Kalimantan, Indonesia, in order to evaluate major patterns in gaseous carbon dioxide and methane fluxes and in peat hydrology immediately before and after hydrologic restoration. The sites included peat swamp forest and deforested burned area, both affected by drainage for nearly 10 years. Higher annual minimum soil water table levels prevailed on both sites after restoration; the deforested site water table level prevailed considerably longer near the peat surface, and the forest water table level remained for a longer period in the topmost 30 cm peat profile after restoration. Forest soil gas fluxes were clearly higher in comparison to the deforested area. Cumulative forest floor CO2 emissions (7305-7444 g x m(-2) x yr(-1); 166.0-169.2 mol CO2 x m(-2) x yr(-1)) and the deforested site CO2 emissions (2781-2608 g x m(-2) x yr(-1); 63.2-59.3 mol CO2 x m(-2) x yr(-1)) did not markedly reflect the notably differing hydrological conditions the year before and after restoration. The forest floor was a weak CH4 sink (-0.208 to -0.368 g x m(-2) x yr(-1); -13.0 to -22.9 mmol CH4 x m(-2) x yr(-1)) and the deforested site a comparable CH4 source (0.197-0.275 g x m(-2) x yr(-1); 12.3-17.1 mmol CH4 x m(-2) x yr(-1)) in the study period. In general, higher soil water table levels had a relatively small effect on the annual CH4 emission budgets. In the two site types the gas flux response into hydrological conditions in degraded tropical peat can be attributed to differing CO2 and CH4 dynamics, peat physical characteristics, and vegetation.

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Chamber measurements of trace gas fluxes between the land surface and the atmosphere have been conducted for almost a century. Different chamber techniques, including static and dynamic, have been used with varying degrees of success in estimating greenhouse gases (CO2, CH4, N2O) fluxes. However, all of these have certain disadvantages which have either prevented them from providing an adequate estimate of greenhouse gas exchange or restricted them to be used under limited conditions. Generally, chamber methods are relatively low in cost and simple to operate. In combination with the appropriate sample allocations, chamber methods are adaptable for a wide variety of studies from local to global spatial scales, and they are particularly well suited for in situ and laboratory-based studies. Consequently, chamber measurements will play an important role in the portfolio of the Pan-European long-term research infrastructure Integrated Carbon Observation System. The respective working group of the Integrated Carbon Observation System Ecosystem Monitoring Station Assembly has decided to ascertain standards and quality checks for automated and manual chamber systems instead of defining one or several standard systems provided by commercial manufacturers in order to define minimum requirements for chamber measurements. The defined requirements and recommendations related to chamber measurements are described here.

We studied concentrations of carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) in the eutrophic Temmesjoki River and Estuary in the Liminganlahti Bay in 2003-2004 and evaluated the atmospheric fluxes of the gases based on measured concentrations, wind speeds and water current velocities. The Temmesjoki River was a source of CO 2 , CH 4 and N 2 O to the atmosphere, whereas the Liminganlahti Bay was a minor source of CH 4 and a minor source or a sink of CO 2 and N 2 O. The results show that the fluxes of greenhouse gases in river ecosystems are highly related to the land use in its catchment areas. The most upstream river site, surrounded by forests and drained peatlands, released significant amounts of CO 2 and CH 4 , with average fluxes of 5,400 mg CO 2 -C m -2 d -1 and 66 mg CH 4 -C m -2 d -1 , and concentrations of 210 lM and 345 nM, respectively, but N 2 O concentrations, at an average of 17 nM, were close to the atmospheric equilibrium concentration. The downstream river sites surrounded by agricultural soils released significant amounts of N 2 O (with an average emission of 650 lg N 2 O-N m -2 d -1 and concentration of 22 nM), whereas the CO 2 and CH 4 concentrations were low compared to the upstream site (55 lM and 350 nM). In boreal regions, rivers are partly icecovered in wintertime (approximately 5 months). A large part of the gases, i.e. 58% of CO 2 , 55% of CH 4 and 36% of N 2 O emissions, were found to be released during wintertime from unfrozen parts of the river.

Abstract. Tropical peatlands are one of the most important terrestrial ecosystems in terms of impact on the atmospheric greenhouse gas composition. Currently, greenhouse gas emissions from tropical peatlands following disturbances due to deforestation, drainage or wildfire are substantial. We quantified in situ nitrous oxide (N2O) fluxes during both dry and wet seasons using a closed chamber method at sites that represented differing land uses and land use change intensities in Central Kalimantan, Indonesia. Cumulative N2O fluxes were compared with carbon dioxide (CO2) and methane (CH4) fluxes. The mean N2O flux rates (N2O-N &plusmn: SD, mg m−2 h−1) varied as follows: drained forest (0.112 ± 0.293) > agricultural peat at the Kalampangan site (0.012 ± 0.026) > drained burned peat (0.011 ± 0.018) > agricultural peat at the Marang site (0.0072 ± 0.028) > undrained forest (0.0025 ± 0.053) > clear-felled, drained, recovering forest (0.0022 ± 0.021). The widest N2O flux range was detected in the drained forest (max. 2.312 and min. −0.043 mg N2O-N m−2 h−1). At the other flux monitoring sites the flux ranges remained at about one tenth that of the drained forest site. The highest N2O emission rates were observed at water tables close to the peat surface where also the flux range was widest. Annual cumulative peat surface N2O emissions (expressed in CO2 equivalents as a percentage of the total greenhouse gas (N2O, CO2 and CH4) emissions) were 9.2 % at highest, but typically ~1 %. Average N2O fluxes and also the total of monitored GHG emissions were highest in drainage-affected forest which is characterized by continuous labile nitrogen availability from vegetation, and water tables typically below the surface.

Research infrastructures play a key role in launching a new generation of integrated long-term, geographically distributed observation programmes designed to monitor climate change, better understand its impacts on global ecosystems, and evaluate possible mitigation and adaptation strategies. The pan-European Integrated Carbon Observation System combines carbon and greenhouse gas (GHG; CO2, CH4, N2O, H2O) observations within the atmosphere, terrestrial ecosystems and oceans. High-precision measurements are obtained using standardised methodologies, are centrally processed and openly available in a traceable and verifiable fashion in combination with detailed metadata. The Integrated Carbon Observation System ecosystem station network aims to sample climate and land-cover variability across Europe. In addition to GHG flux measurements, a large set of complementary data (including management practices, vegetation and soil characteristics) is collected to support the interpretation, spatial upscaling and modelling of observed ecosystem carbon and GHG dynamics. The applied sampling design was developed and formulated in protocols by the scientific community, representing a trade-off between an ideal dataset and practical feasibility. The use of open-access, high-quality and multi-level data products by different user communities is crucial for the Integrated Carbon Observation System in order to achieve its scientific potential and societal value.

Many of the world’s peatlands have been affected by water table drawdown and subsequent loss of organic matter. Rewetting has been proposed as a measure to restore peatland functioning and to halt carbon loss, but its effectiveness is subject to debate. An important prerequisite for peatland recovery is a return of typical microbial communities, which drive key processes. To evaluate the effect of rewetting, we investigated 13 fen peatland areas across a wide (>1500 km) longitudinal gradient in Europe, in which we compared microbial communities between drained, undrained, and rewetted sites. There was a clear difference in microbial communities between drained and undrained fens, regardless of location. Community recovery upon rewetting was substantial in the majority of sites, and predictive functional profiling suggested a concomitant recovery of biogeochemical peatland functioning. However, communities in rewetted sites were only similar to those of undrained sites when soil organic matter quality (as expressed by cellulose fractions) and quantity were still sufficiently high. We estimate that a minimum organic matter content of ca. 70% is required to enable microbial recovery. We conclude that peatland recovery after rewetting is conditional on the level of drainage-induced degradation: severely altered physicochemical peat properties may preclude complete recovery for decades.

Intact sediment cores from rivers of the Bothnian Bay (Baltic Sea) were studied for denitrification based on benthic fluxes of molecular nitrogen (N 2 ) and nitrous oxide (N 2 O) in a temperature controlled continuous water flow laboratory microcosm under 10, 30, 100, and 300 lM of 15 N enriched nitrate (NO 3 -, *98 at. %). Effluxes of both N 2 and N 2 O from sediment to the overlying water increased with increasing NO 3 -load. Although the ratio of N 2 O to N 2 increased with increasing NO 3 -load, it remained below 0.04, N 2 always being the main product. At the NO 3 -concentrations most frequently found in the studied river water (10-100 lM), up to 8% of the NO 3 -was removed in denitrification, whereas with the highest concentration (300 lM), the removal by denitrification was less than 2%. However, overall up to 42% of the NO 3 -was removed by mechanisms other than denitrification. As the microbial activity was simultaneously enhanced by the NO 3 -load, shown as increased oxygen consumption and dissolved inorganic carbom efflux, it is likely that a majority of the NO 3 -was assimilated by microbes during their growth. The 15 N content in ammonium (NH 4 ? ) in the efflux was low, suggesting that reduction of NO 3 -to NH 4 ? was not the reason for the NO 3 -removal. This study provides the first published information on denitrification and N 2 O fluxes and their regulation by NO 3 -load in eutrophic high latitude rivers.