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Abstract. The isotopic composition of dioxygen in the atmosphere is a global tracer which depends on the biosphere flux of dioxygen toward and from the atmosphere (photosynthesis and respiration) as well as exchanges with the stratosphere. When measured in fossil air trapped in ice cores, the relative concentration of 16O, 17O and 18O of O2 can be used for several applications such as ice core dating and past global productivity reconstruction. However, there are still uncertainties about the accuracy of these tracers as they depend on the integrated isotopic fractionation of different biological processes of dioxygen production and uptake, for which we currently have very few independent estimates. Here we determined the respiration and photosynthesis fractionation coefficients for atmospheric dioxygen from experiments carried out in a replicated vegetation-soil-atmosphere analog of the terrestrial biosphere in closed chambers with growing Festuca arundinacea. The values for 18O discrimination during soil respiration and dark respiration in leave are equal to −12.3 ± 1.7 ‰ and −19.1 ± 2.4 ‰, respectively. We also found a value for terrestrial photosynthetic fractionation equal to +3.7 ± 1.3 ‰. This last estimate suggests that the contribution of terrestrial productivity in the Dole effect may have been underestimated in previous studies.

Data-poor tropical wetlands constitute an important source of atmospheric CH 4 in the world. We studied CH 4 fluxes using closed chambers along a soil moisture gradient in a tropical seasonal swamp in the Okavango Delta, Botswana, the sixth largest tropical wetland in the world. The objective of the study was to assess net CH 4 fluxes and controlling environmental factors in the Delta's seasonal floodplains. Net CH 4 emissions from seasonal floodplains in the wetland were estimated at 0.072 ± 0.016 Tg a −1 . Microbial CH 4 oxidation of approximately 2.817 × 10 −3  ± 0.307 × 10 −3  Tg a −1 in adjacent dry soils of the occasional floodplains accounted for the sink of 4% of the total soil CH 4 emissions from seasonal floodplains. The observed microbial CH 4 sink in the Delta's dry soils is, therefore, comparable to the global average sink of 4–6%. Soil water content (SWC) and soil organic matter were the main environmental factors controlling CH 4 fluxes in both the seasonal and occasional floodplains. The optimum SWC for soil CH 4 emissions and oxidation in the Delta were estimated at 50% and 15%, respectively. Electrical conductivity and pH were poorly correlated ( r 2  ≤ 0.11, p  < 0.05) with CH 4 fluxes in the seasonal floodplain at Nxaraga. This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part1)'.

&lt;p&gt;Tree stems can be a source of the greenhouse gas methane (CH&lt;sub&gt;4&lt;/sub&gt;) and locally as regionally important to the overall GHG budget. Stem emissions even hold the potential of narrowing down knowledge gap in the global methane budget. However, assessments of the global importance of stem CH&lt;sub&gt;4&lt;/sub&gt;&amp;#160;emissions are complicated by a lack of research and high variability between individual ecosystems. Here, we determined the contribution of emissions from stems of mature black alder (&lt;em&gt;Alnus glutinosa&lt;/em&gt;&amp;#160;(L.) Gaertn.) to overall CH&lt;sub&gt;4&lt;/sub&gt; exchange in two temperate peatlands. We measured emissions from stems and soils using closed chambers in a drained and an undrained alder forest over 2 years. Furthermore, we studied the importance of alder leaves as substrate for methanogenesis in an incubation experiment. Stem CH&lt;sub&gt;4&lt;/sub&gt; emissions at the undrained alder forest were very variable in time and only persisted for a few weeks during the year. Generally the drained alder forest did not soil nor stem CH&lt;sub&gt;4&lt;/sub&gt; emissions. Different upscaling approaches were assessed and all approaches showed that stem CH&lt;sub&gt;4&lt;/sub&gt; emissions contributed less than 0.3 % to the total ecosystem CH&lt;sub&gt;4&lt;/sub&gt; budget. However, stem CH&lt;sub&gt;4&lt;/sub&gt; seem to depend strongly on the hydrological regime and therefore vary strongly between ecosystems. Hence, every ecosystem must be consdidered attentively with respect to their stem CH&lt;sub&gt;4&lt;/sub&gt; emissions.&lt;/p&gt;

AbstractSeveral approaches exist for measuring greenhouse gases (GHGs), mainly CO2, N2O, and CH4, from soil surfaces. The principle methods that are used to measure GHG from agricultural sites are chamber-based techniques. Both open and closed chamber techniques are in use; however, the majority of field applications use closed chambers. The advantages and disadvantages of different chamber techniques and the principal steps of operation are described. An important part of determining the quality of the flux measurements is the storage and the transportation of the gas samples from the field to the laboratory where the analyses are carried out. Traditionally, analyses of GHGs are carried out via gas chromatographs (GCs). In recent years, optical analysers are becoming increasingly available; these are user-friendly machines and they provide a cost-effective alternative to GCs. Another technique which is still under development, but provides a potentially superior method, is Raman spectroscopy. Not only the GHGs, but also N2, can potentially be analysed if the precision of these techniques is increased in future development. An important part of this chapter deals with the analyses of the gas concentrations, the calculation of fluxes, and the required safety measures. Since non-upland agricultural lands (i.e. flooded paddy soils) are steadily increasing, a section is devoted to the specificities of GHG measurements in these ecosystems. Specialised techniques are also required for GHG measurements in aquatic systems (i.e. rivers), which are often affected by the transfer of nutrients from agricultural fields and therefore are an important indirect source of emission of GHGs. A simple, robust, and more precise methodof ammonia (NH3) emission measurement is also described.

SummaryTree stems can be a source of the greenhouse gas methane (CH4). However, assessments of the global importance are complicated by a lack of research and a high variability between ecosystems. Here, we determined the contribution of emissions from tree stems of mature black alder (Alnus glutinosa (L.) Gaertn.) to overall CH4 exchange in two temperate peatlands.We measured emissions from stems and soils using closed chambers in a drained and a wet alder forest over two years. Further, we studied the importance of alder leaves as substrate for methanogenesis in an incubation experiment.Stem CH4 emissions were shortlived and occurred only during times of inundation at the wet site. The drained site did not show stem emissions and the soil acted as a small CH4 sink. The contribution of stem emissions to the overall CH4 budget was below 0.3% in both sites.Our results show that also mature black alders intermittently can be a source of CH4. However, the low share of stem-mediated CH4 emissions in both forests may indicate that this pathway is only of minor relative importance in temperate peatlands.

&lt;p&gt;Carbon dioxide (CO&lt;sub&gt;2&lt;/sub&gt;) is one of the first gases to escape from the magmatic environment due to its low solubility in basaltic magmas at low pressures. Monitoring of volcanic gases in Tenerife Island (2,304 km&lt;sup&gt;2&lt;/sup&gt;) has been focused mainly on diffuse CO&lt;sub&gt;2&lt;/sub&gt; degassing and other volatiles due to the absence of visible gas manifestations except fumaroles at the summit of Teide volcano. An inexpensive method to determine CO&lt;sub&gt;2&lt;/sub&gt; fluxes based in the absorption of CO&lt;sub&gt;2&lt;/sub&gt; through an alkaline medium followed by titration analysis has been used with the aim of contributing to the volcanic surveillance of Tenerife. During summer 2016, a network of 31 closed alkaline traps was deployed along the three volcanic rifts of Tenerife (NE, NW and NS) and at Ca&amp;#241;adas Caldera. To do so, an aliquot of 50 mL of 0.1N KOH solution is placed inside the chamber at each station to absorb the CO&lt;sub&gt;2&lt;/sub&gt; released from the soil. The solution is replaced in a weekly basis and the trapped CO&lt;sub&gt;2&lt;/sub&gt; is later analyzed at the laboratory by titration. Values are expressed as weekly integrated CO&lt;sub&gt;2 &lt;/sub&gt;efflux. We present herein the results of one year CO&lt;sub&gt;2 &lt;/sub&gt;efflux estimated by closed alkaline traps. The CO&lt;sub&gt;2&lt;/sub&gt; efflux values ranged from 1.0 to 14.5 g&amp;#183;m&lt;sup&gt;-2&lt;/sup&gt;&amp;#183;d&lt;sup&gt;-1&lt;/sup&gt;, with average values of 8.5 g&amp;#183;m&lt;sup&gt;-2&lt;/sup&gt;&amp;#183;d&lt;sup&gt;-1&lt;/sup&gt; for the NE rift-zone, 5.2 g&amp;#183;m&lt;sup&gt;-2&lt;/sup&gt;&amp;#183;d&lt;sup&gt;-1 &lt;/sup&gt;for Ca&amp;#241;adas Caldera, 6.4 g&amp;#183;m&lt;sup&gt;-2&lt;/sup&gt;&amp;#183;d&lt;sup&gt;-1&lt;/sup&gt; for NW rift-zone and 6.1 g&amp;#183;m&lt;sup&gt;-2&lt;/sup&gt;&amp;#183;d&lt;sup&gt;-1&lt;/sup&gt; for NS rift-zone. The estimated CO&lt;sub&gt;2 &lt;/sub&gt;efflux values were of the same order than the observed ones in 2016. Relatively high CO&lt;sub&gt;2&lt;/sub&gt; efflux values were observed at the NE rift-zone, where maximum values were measured. The temporal evolution of CO&lt;sub&gt;2 &lt;/sub&gt;efflux estimated by closed alkaline traps did not show significant variations during 2019. However, small seasonal variations are observed during the period 2016 &amp;#8211; 2019. To investigate the origin of the soil CO&lt;sub&gt;2&lt;/sub&gt;, soil gas samples were weekly sampled on the head space of the closed chambers. Chemical and isotopic composition of C in the CO&lt;sub&gt;2&lt;/sub&gt; were analysed in the gas samples. The concentration of CO&lt;sub&gt;2&lt;/sub&gt; on the head space of the closed chambers showed a range of 355-50,464 ppm, with an average value of 1,850 ppmV, while the isotopic composition expressed as d&lt;sup&gt;13&lt;/sup&gt;C-CO&lt;sub&gt;2&lt;/sub&gt; showed a range from -5.03 to -30.44 &amp;#8240;, with an average value of -15.9 &amp;#8240;. The heaviest values of d&lt;sup&gt;13&lt;/sup&gt;C-CO&lt;sub&gt;2&lt;/sub&gt; are in the NW rift-zone. The systematics of closed static chambers alkaline traps can be a simple and economical tool with volcanic surveillance purposes in system where visible volcanic gases manifestations are absence.&lt;/p&gt;

This study was conducted to examine the CH4 emission in the core zone and the effects of water and soil physical and chemical characteristics and water depth on CH4 emission in U Minh Thuong National Park, Kien Giang Province. The study was carried out from September, 2016 to November, 2016. The CH4 was collected by closed chambers. The results showed that the soil had a low pH (3.89 - 5.12), a high total phosphorus (0.1 % P2O5) and lower potential redox (from -186 to -145 mV). The organic matter (54.6 %) and total nitrogen (1.15 %) were high in thick peat layers. The organic matter (2.15 - 3.93 %) and total nitrogen (0.1 %) were low in thin or no peat layer. The surface water was polluted by organic matter and was not suitable for domestic use (QCVN 08-MT: 2015/BTNMT column A2). CH4 emission in clay based and peat land based Melaleuca forest areas were 106 mg.m-2.h-1 and 135 mg.m-2.h-1, respectively. The CH4 emission was not correlated with either water and soil physical and chemical characteristics or water depth, but might be correlated microbial factors. We need to study water, soil characteristics, CH4 emission of months in years.