内蒙古草原CH4 通量的DNDC 模型模拟

甲烷（CH4）是增温效应仅次于二氧化碳（CO2）的重要温室气体。内蒙古草原是欧亚温带草原的重要类型，具有典型的生态地域代表性。如何理解该区域CH4 交换的时空格局与环境控制、不同土地利用类型的源汇特征以及CH4 通量对气候变化的响应、对于我们进一步理解全球变化与陆地生态系统关系具有十分重要的意义。本研究以内蒙古草原锡林河流域为对象，首次在国内应用DNDC 生物地球化学模型模拟干草原和河漫滩湿地的CH4 通量，预测CH4 循环对未来气候变化的响应，并对该区域干草原的CH4 吸收进行了区域模拟估算。结果表明： 1.在模型中添加植被生长节律与土壤CH4 吸收的关系函数后，DNDC 模型能够准确地模拟锡林河流域干草原CH4 吸收的大小及其年变化。土壤温度、土壤水分和植被生长状况是影响干草原大气CH4 吸收的主要因素。 2.水位，土壤温度，质地和植被生长节律是控制河漫滩湿地CH4 通量的主要因子。根据有限水位测定值估算模拟周期内全部水位数据的方法能够应用于模拟水位相对比较稳定区域的未知时期水位。经过该修正的DNDC 模型能够较为准确的捕获锡林河流域河边湿地的CH4 排放通量的大小及年变化。 3.干草原和湿地年CH4 通量对温度变化敏感，而对降水量变化不敏感，其中湿地比干草原对温度变化的响应更加敏感。 4.温度升高可显著地促进干草原和湿地的日CH4 吸收和排放能力，其CH4 通量的增加均表现出明显的季节性差异。干草原日CH4 通量对降水量增加20% 的响应并不显著，而河漫滩湿地的响应虽显著，变幅却很小且增减程度不同。 5.与2005 年相比，2050 年干草原河漫滩湿地的CH4 吸收和排放量将分别增加10%和77%。锡林河流域CH4 通量对未来气候变化产生正反馈作用，并且湿地CH4 排放对未来气候变化的响应大于干草原CH4 吸收的响应。未来气候变化将增加锡林河流域CH4 源强度。 6. 锡林河流域干草原CH4 吸收量达2.42Gg C•yr-1。干草原CH4 吸收量的空间异质性较大，各栅格单元（0.01 ×0.01 度）的CH4 吸收量变化为0-404.6 kg C，其中大部分区域CH4 吸收量变化在150-250 kg C•yr-1 之间。草甸草原的大气CH4 吸收能力显著高于典型草原。干草原CH4 吸收率平均为2.59 kg C• ha-1 •yr-1。干草原CH4 吸收量的空间异质性是土壤有机质含量、土壤质地、土壤温度湿度，植被类型等因素共同作用的结果，与单一变量的关系并不明显。

The change of gaseous carbon fluxes following the switch of dominant producers from macrophytes to algae in a shallow subtropical lake of China

Successions of lake ecosystems from clear-water, macrophyte-rich conditions into turbid states with abundant phytoplankton have taken place in many shallow lakes in China. However, little is know about the change of carbon fluxes in lakes during such processes. We conducted a case study in Lake Biandantang to investigate the change of carbon fluxes during such a regime shift. Dissolved aquatic carbon and gaseous carbon (methane (CH4) and carbon dioxide (CO2)) across air-water interface in three sites with different vegetation covers and compositions were studied and compared. CH4 emissions from three sites were 0.62 +/- 0.36, 0.70 +/- 0.36, and 1.31 +/- 0.57 mg m(-2) h(-1), respectively. Correlation analysis showed that macrophytes, rather than phytoplankton, directly positively affected CH4 emission. CO2 fluxes of three sites in Lake Biandantang were significantly different, and the average values were 77.8 +/- 20.4, 52.2 +/- 14.1 and 3.6 +/- 26.8 mg m(-2) h(-1), respectively. There were an evident trend that the larger macrophyte biomass, the lower CO2 emissions. Correlation analysis showed that in different sites, dominant plant controlled CO2 flux across air-water interface. In a year cycle, the percents of gaseous carbon release from lake accounting for net primary production were significantly different (from 39.3% to 2.8%), indicating that with the decline of macrophytes and regime shift, the lake will be a larger carbon source to the atmosphere. (c) 2006 Elsevier Ltd. All rights reserved.

Methane and carbon dioxide fluxes from a shallow hypereutrophic subtropical Lake in China

Up to now, there have been few studies in the annual fluxes of greenhouse gases in lakes of subtropical regions. The fluxes of methane (CH4) and carbon dioxide (CO2) across air-water interface were measured in a shallow, hypereutrophic, subtropical Lake Donghu (China) over a year cycle, using a static chamber technique. During the year, Lake Donghu emitted CH4 and CO2; the average flux of CH4 and CO2 was 23.3 +/- 18.6 and 332.3 +/- 160.1 mg m(-2) d(-1), respectively. The fluxes of CH4 and CO2 showed strong seasonal dynamics: CH4 emission rate was highest in summer, remaining low in other seasons, whereas CO2 was adsorbed from the atmosphere in spring and summer, but exhibited a large emission in winter. Annual carbon (C) budget across air-water interface in Lake Donghu was estimated to be 7.52 +/- 4.07 x 10(8) g. CH4 emission was correlated positively with net primary production (NPP) and temperature, whereas CO2 flux correlated negatively with NPP and temperature; however, there were no significant relationships between the fluxes of CH4 and CO2 and dissolved organic carbon, a significant difference from boreal lakes, indicating that phytoplankton rather than allochthonous matter regulated C dynamics across air-water interface of subtropical lake enriched nutrient content. (c) 2005 Elsevier Ltd. All rights reserved.

Diel variation of methane fluxes in summer in a eutrophic subtropical lake in China

The summer diel variation of methane (CH4) flux was investigated in a eutrophic, subtropical lake in China. The CH4 concentration was always supersaturated, and the emission rate ranged from 0.24 to 45.51 mg m(-2) h(-1). The diel variations of CH4 flux in June and August showed a single peak in early afternoon and a minimum in the morning, while the pattern varied irregularly in May. There was a moderate relationship between water and sediment temperature and CH4 emission rate in some months.

N2O fluxes from the native and grazed semi-arid steppes and their driving factors in Inner Mongolia, China

This paper presents results of 2 years (from January 2005 to December 2006) of measurement of N2O fluxes from the native and grazed Leymus chinensis (LC) steppes in Inner Mongolia, China using the static opaque chamber method. The measurement was at a frequency of twice per month in the growing season and once per month in the non-growing season. In addition, the possible effect of water-heat factors on N2O fluxes was statistically analyzed. The results indicated that there were distinct seasonal patterns in N2O fluxes with large fluxes in spring, summer, and autumn but negative fluxes in winter. The annual net emission of N2O ranging from 0.24 to 0.30 kg N2O-N ha(-1) and from 0.06 to 0.26 kg N2O-N ha(-1) from the native and grazed LC steppe, respectively. Grazing activities suppressed N2O production. In the growing season, soil moisture was the primary driving factor of N2O fluxes. The high seasonal variation of N2O fluxes was regulated by the distribution of effective rainfall, rather than precipitation intensity. Air temperature or soil temperature at 0, 5, and 10 cm depth was the most restricting factor of N2O fluxes in the non-growing season.

Short-term effects of sheep excrement on carbon dioxide, nitrous oxide and methane fluxes in typical grassland of Inner Mongolia

Excrement patches of grazing animals play an important role in greenhouse gas (GHG) fluxes due to the high nitrogen (N) and available carbon (C) deposited in small areas, but little information is available for the effect of excrement in the Inner Mongolian grassland (43 26 degrees N, 116 degrees 40'E). To elucidate the effect of grazing sheep urine, fresh dung and compost on fluxes of methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O), a short-term field study (65 days) was carried out in the typical grassland of Inner Mongolia with the optimised closed chamber/GC technique. Compared with the control, cumulative net CH4 consumption decreased 36, 31, and 18% from urine, fresh dung, and compost plots, respectively; net CO2-C output increased by 6.5, 1.5, and 1.2% from urine, fresh dung, and compost treated soil, respectively; about three times as much N2O-N was emitted from urine and the fresh dung treatments during 65 days. Nitrous oxide emission was positively correlated with CO, emission (R = 0.691, P < 0.01) and water-filled pore space (R = 0.698, P < 0.01). The percentages of N2O-N loss of applied-N were 0.44 and 1.05% for urine and fresh dung, respectively. Our results suggest that in autumn in the degraded grassland of Inner Mongolia, the effect of sheep excrement may be ignored when evaluating the total GHG emissions.

Estimating surface CO2 fluxes from space-borne dry air mole fraction observations using an Ensemble Kalman filter

We have developed an ensemble Kalman Filter (EnKF) to estimate 8-day regional surface fluxes of CO2 from space-borne CO2 dry-air mole fraction observations (XCO2) and evaluate the approach using a series of synthetic experiments, in preparation for data from the NASA Orbiting Carbon Observatory (OCO). The 32-day duty cycle of OCO alternates every 16 days between nadir and glint measurements of backscattered solar radiation at short-wave infrared wavelengths. The EnKF uses an ensemble of states to represent the error covariances to estimate 8-day CO2 surface fluxes over 144 geographical regions. We use a 12×8-day lag window, recognising that XCO2 measurements include surface flux information from prior time windows. The observation operator that relates surface CO2 fluxes to atmospheric distributions of XCO2 includes: a) the GEOS-Chem transport model that relates surface fluxes to global 3-D distributions of CO2 concentrations, which are sampled at the time and location of OCO measurements that are cloud-free and have aerosol optical depths <0.3; and b) scene-dependent averaging kernels that relate the CO2 profiles to XCO2, accounting for differences between nadir and glint measurements, and the associated scene-dependent observation errors. We show that OCO XCO2 measurements significantly reduce the uncertainties of surface CO2 flux estimates. Glint measurements are generally better at constraining ocean CO2 flux estimates. Nadir XCO2 measurements over the terrestrial tropics are sparse throughout the year because of either clouds or smoke. Glint measurements provide the most effective constraint for estimating tropical terrestrial CO2 fluxes by accurately sampling fresh continental outflow over neighbouring oceans. We also present results from sensitivity experiments that investigate how flux estimates change with 1) bias and unbiased errors, 2) alternative duty cycles, 3) measurement density and correlations, 4) the spatial resolution of estimated flux estimates, and 5) reducing the length of the lag window and the size of the ensemble. At the revision stage of this manuscript, the OCO instrument failed to reach its orbit after it was launched on 24 February 2009. The EnKF formulation presented here is also applicable to GOSAT measurements of CO2 and CH4.

Surface Deformations as Indicators of Deep Ebullition Fluxes in a Large Northern Peatland

Peatlands deform elastically during precipitation cycles by small (+/- 3 cm) oscillations in surface elevation. In contrast, we used a Global Positioning System network to measure larger oscillations that exceeded 20 cm over periods of 4 - 12 hours during two seasonal droughts at a bog and fen site in northern Minnesota. The second summer drought also triggered 19 depressuring cycles in an overpressured stratum under the bog site. The synchronicity between the largest surface deformations and the depressuring cycles indicates that both phenomena are produced by the episodic release of large volumes of gas from deep semi-elastic compartments confined by dense wood layers. We calculate that the three largest surface deformations were associated with the release of 136 g CH4 m(-2), which exceeds by an order of magnitude the annual average chamber fluxes measured at this site. Ebullition of gas from the deep peat may therefore be a large and previously unrecognized source of radiocarbon depleted methane emissions from northern peatlands.

(Supplemental Table 2) Plant characteristics, GHG fluxes, and soil chemical and microbial properties in experimental treatments in Alexandra Fiord

We evaluated above- and belowground ecosystem changes in a 16 year, combined fertilization and warming experiment in a High Arctic tundra deciduous shrub heath (Alexandra Fiord, Ellesmere Island, NU, Canada). Soil emissions of the three key greenhouse gases (GHGs) (carbon dioxide, methane, and nitrous oxide) were measured in mid-July 2009 using soil respiration chambers attached to a FTIR system. Soil chemical and biochemical properties including Q10 values for CO2, CH4, and N2O, Bacteria and Archaea assemblage composition, and the diversity and prevalence of key nitrogen cycling genes including bacterial amoA, crenarchaeal amoA, and nosZ were measured. Warming and fertilization caused strong increases in plant community cover and height but had limited effects on GHG fluxes and no substantial effect on soil chemistry or biochemistry. Similarly, there was a surprising lack of directional shifts in the soil microbial community as a whole or any change at all in microbial functional groups associated with CH4 consumption or N2O cycling in any treatment. Thus, it appears that while warming and increased nutrient availability have strongly affected the plant community over the last 16 years, the belowground ecosystem has not yet responded. This resistance of the soil ecosystem has resulted in limited changes in GHG fluxes in response to the experimental treatments.

Methane and sulfide fluxes in permanent anoxia: in situ studies at the Dvurechenskii mud volcano (Sorokin Trough, Black Sea)

The Dvurechenskii mud volcano (DMV), located in permanently anoxic waters at 2060 m depth (Sorokin Trough, Black Sea), was visited during the M72/2 cruise with the RV Meteor to investigate the methane and sulfide release from mud volcanoes into the Black Sea hydrosphere. We studied benthic fluxes of methane and sulfide, and the factors controlling transport, consumption and production of both compounds within the sediment. The pie shaped mud volcano showed temperature anomalies as well as solute and gas fluxes indicating high fluid flow at a small elevation north of the geographical center. The anaerobic oxidation of methane (AOM) coupled to sulfate reduction (SR) was excluded from this zone due to fluid-flow induced sulfate limitation and a fresh mud flow and consequently methane escaped into the water column with a rate of 0.46 mol/m**2/d. In the outer center of the mud volcano fluid flow and total methane flux were decreased, correlating with an increase in sulfate penetration into the sediment, and with higher SR and AOM rates. Here between 50-70% of the methane flux (0.07-0.1 mol/m**2/d) was consumed within the upper 10 cm of the sediment. Also at the edge of the mud volcano fluid flow and rates of methane and sulfate turnover were substantial. The overall amount of dissolved methane released from the mud volcano into the water column was significant with a discharge of 1.4x10**7 mol/yr. The DMV maintains also high areal rates of methane-fueled sulfide production of on average 0.05 mol/m**2/d. However, we concluded that sulfide and methane emission into the hydrosphere from deep water mud volcanoes does not significantly contribute to the sulfide and methane inventory of the Black Sea.

Continuous CO2/CH4/CO measurements (2012–2014) at Beromünster tall tower station in Switzerland

The understanding of the continental carbon budget is essential to predict future climate change. In order to quantify CO₂ and CH₄ fluxes at the regional scale, a measurement system was installed at the former radio tower in Beromünster as part of the Swiss greenhouse gas monitoring network (CarboCount CH). We have been measuring the mixing ratios of CO₂, CH₄ and CO on this tower with sample inlets at 12.5, 44.6, 71.5, 131.6 and 212.5 m above ground level using a cavity ring down spectroscopy (CRDS) analyzer. The first 2-year (December 2012–December 2014) continuous atmospheric record was analyzed for seasonal and diurnal variations and interspecies correlations. In addition, storage fluxes were calculated from the hourly profiles along the tower. The atmospheric growth rates from 2013 to 2014 determined from this 2-year data set were 1.78 ppm yr⁻¹, 9.66 ppb yr⁻¹ and and -1.27 ppb yr⁻¹ for CO₂, CH₄ and CO, respectively. After detrending, clear seasonal cycles were detected for CO₂ and CO, whereas CH₄ showed a stable baseline suggesting a net balance between sources and sinks over the course of the year. CO and CO₂ were strongly correlated (r² > 0.75) in winter (DJF), but almost uncorrelated in summer. In winter, anthropogenic emissions dominate the biospheric CO₂ fluxes and the variations in mixing ratios are large due to reduced vertical mixing. The diurnal variations of all species showed distinct cycles in spring and summer, with the lowest sampling level showing the most pronounced diurnal amplitudes. The storage flux estimates exhibited reasonable diurnal shapes for CO₂, but underestimated the strength of the surface sinks during daytime. This seems plausible, keeping in mind that we were only able to calculate the storage fluxes along the profile of the tower but not the flux into or out of this profile, since no Eddy covariance flux measurements were taken at the top of the tower.

Field data on methane fluxes, temperature, soil gas profiles and microbial activities in ponds of the northeast Siberian polygonal tundra

The data files give the basic field and laboratory data on five ponds in the northeast Siberian Arctic tundra on Samoylov. The files contain water and soil temperature data of the ponds, methane fluxes, measured with closed chambers in the centres without vascular plants and the margins with vascular plants, the contribution of plant mediated fluxes on total methane fluxes, the gas concentrations (methane and dissolved inorganic carbon, oxygen) in the soil and the water column of the ponds, microbial activities (methane production, methane oxidation, aerobic and anaerobic carbon dioxide production), total carbon pools in the different horizons of the bottom soils, soil bulk density, soil substance density, and soil porosity.

Methane fluxes and carbonate deposits at eastern Mediterranean cold seeps

High acoustic seafloor-backscatter signals characterize hundreds of patches of methane-derived authigenic carbonates and chemosynthetic communities associated with hydrocarbon seepage on the Nile Deep Sea Fan (NDSF) in the Eastern Mediterranean Sea. During a high-resolution ship-based multibeam survey covering a ~ 225 km**2 large seafloor area in the Central Province of the NDSF we identified 163 high-backscatter patches at water depths between 1500 and 1800 m, and investigated the source, composition, turnover, flux and fate of emitted hydrocarbons. Systematic Parasound single beam echosounder surveys of the water column showed hydroacoustic anomalies (flares), indicative of gas bubble streams, above 8% of the high-backscatter patches. In echosounder records flares disappeared in the water column close to the upper limit of the gas hydrate stability zone located at about 1350 m water depth due to decomposition of gas hydrate skins and subsequent gas dissolution. Visual inspection of three high-backscatter patches demonstrated that sediment cementation has led to the formation of continuous flat pavements of authigenic carbonates typically 100 to 300 m in diameter. Volume estimates, considering results from high-resolution autonomous underwater vehicle (AUV)-based multibeam mapping, were used to calculate the amount of carbonate-bound carbon stored in these slabs. Additionally, the flux of methane bubbles emitted at one high-backscatter patch was estimated (0.23 to 2.3 × 10**6 mol a**-1) by combined AUV flare mapping with visual observations by remotely operated vehicle (ROV). Another high-backscatter patch characterized by single carbonate pieces, which were widely distributed and interspaced with sediments inhabited by thiotrophic, chemosynthetic organisms, was investigated using in situ measurements with a benthic chamber and ex situ sediment core incubation and allowed for estimates of the methane consumption (0.1 to 1 × 10**6 mol a**-1) and dissolved methane flux (2 to 48 × 10**6 mol a**-1). Our comparison of dissolved and gaseous methane fluxes as well as methane-derived carbonate reservoirs demonstrates the need for quantitative assessment of these different methane escape routes and their interaction with the geo-, bio-, and hydrosphere at cold seeps.