Soil CO_2 flux in relation to dissolved organic carbon,soil temperature and moisture in a subtropical arable soil of China

Soil CO 2 emission from an arable soil was measured by closed chamber method to quantify year round soil flux and to develop an equation to predict flux using soil temperature, dissolved organic carbon(DOC) and soil moisture content. Soil CO 2 flux, soil temperature, DOC and soil moisture content were determined on selected days during the experiment from August 1999 to July 2000, at the Ecological Station of Red Soil, the Chinese Academy of Sciences, in a subtropical region of China. Soil CO 2 fluxes were generally higher in summer and autumn than in winter and spring, and had a seasonal pattern more similar to soil temperature and DOC than soil moisture. The estimation was 2 23 kgCO 2/(m 2·a) for average annual soil CO 2 flux. Regressed separately, the reasons for soil flux variability were 86 6% from soil temperature, 58 8% from DOC, and 26 3% from soil moisture, respectively. Regressed jointly, a multiple equation was developed by the above three variables that explained approximately 85 2% of the flux variance, however by stepwise regression, soil temperature was the dominant affecting soil flux. Based on the exponential equation developed from soil temperature, the predicted annual flux was 2 49 kgCO 2/(m 2·a), and essentially equal to the measured one. It is suggested the exponential relationship between soil flux and soil temperature could be used for accurately predicting soil CO 2 flux from arable soil in subtropical regions of China.

Seasonal and Annual Variations of CO_2 Fluxes in Rain-Fed Winter Wheat Agro-Ecosystem of Loess Plateau, China

To accurately evaluate the carbon sequestration potential and better elucidate the relationship between the carbon cycle and regional climate change, using eddy covariance system, we conducted a long-term measurement of CO 2 fluxes in the rain-fed winter wheat field of the Chinese Loess Plateau. The results showed that the annual net ecosystem CO 2 exchange （NEE） was （-71.6±5.7） and （-65.3±5.3） g C m-2 y-1 for 2008-2009 and 2009-2010 crop years, respectively, suggesting that the agro-ecosystem was a carbon sink （117.4-126.2 g C m-2 yr-1）. However, after considering the harvested grain, the agro- ecosystem turned into a moderate carbon source. The variations in NEE and ecosystem respiration （R eco ） were sensitive to changes in soil water content （SWC）. When SWC ranged form 0.15 to 0.21 m3 m-3, we found a highly significant relationship between NEE and photosynthetically active radiation （PAR）, and a highly significant relationship between R eco and soil temperature （T s ）. However, the highly significant relationships were not observed when SWC was outside the range of 0.15-0.21 m3 m-3. Further, in spring, the R eco instantly responded to a rapid increase in SWC after effective rainfall events, which could induce 2 to 4-fold increase in daily R eco , whereas the R eco was also inhibited by heavy summer rainfall when soils were saturated. Accumulated R eco in summer fallow period decreased carbon fixed in growing season by 16- 25%, indicating that the period imposed negative impacts on annual carbon sequestration.

Air–water CO2 flux in an algae bloom year for Lake Hongfeng,Southwest China:implications for the carbon cycle of global inland waters

The carbon cycle of global inland waters is quantitatively comparable to other components in the global carbon budget. Among inland waters, a significant part is man-made lakes formed by damming rivers. Manmade lakes are undergoing a rapid increase in number and size. Human impacts and frequent algae blooms lead to it necessary to make a better constraint on their carbon cycles. Here, we make a primary estimation on the air–water CO_2 transfer flux through an algae bloom year for a subtropical man-made lake—Hongfeng Lake, Southwest China. To do this a new type of glass bottles was designed for content and isotopic analysis of DIC and other environmental parameters. At the early stage of algae bloom,CO_2 was transferred from the atmosphere to the lake with a net flux of 1.770 g·C·m^(-2). Later, the partial pressure(pCO_2) of the aqueous CO_2 increased rapidly and the lake outgassed to the atmosphere with a net flux of 95.727 g·C·m^(-2). In the remaining days, the lake again took up CO_2 from the atmosphere with a net flux of 14.804 g·C·m^(-2). As a whole, Lake Hongfeng released 4527 t C to the atmosphere, accounting for one-third of the atmosphere/soil CO_2 sequestered by chemical weathering in the whole drainage. With an empirical mode decomposition method, we found air temperature plays a major role in controlling water temperature, aqueous pCO_2 and hence CO_2 flux. This work indicates a necessity to make detailed and comprehensive carbon budgets in man-made lakes.

Abiotic contribution to total soil CO_2 flux across a broad range of land-cover types in a desert region

As an important component of ecosystem carbon（C） budgets, soil carbon dioxide（CO2） flux is determined by a combination of a series of biotic and abiotic processes. Although there is evidence showing that the abiotic component can be important in total soil CO2 flux（R（total））, its relative importance has never been systematically assessed. In this study, after comparative measurements of CO2 fluxes on sterilized and natural soils, the R（total） was partitioned into biotic flux（R（biotic）） and abiotic flux（R（abiotic）） across a broad range of land-cover types（including eight sampling sites： cotton field, hops field, halophyte garden, alkaline land, reservoir edge, native saline desert, dune crest and interdune lowland） in Gurbantunggut Desert, Xinjiang, China. The relative contribution of R（abiotic） to R（total）, as well as the temperature dependency and predominant factors for R（total）, R（biotic） and R（abiotic）, were analyzed. Results showed that R（abiotic） always contributed to R（total） for all of the eight sampling sites, but the degree or magnitude of contribution varied greatly. Specifically, the ratio of R（abiotic） to R（total） was very low in cotton field and hops field and very high in alkaline land and dune crest. Statistically, the ratio of R（abiotic） to R（total） logarithmically increased with decreasing R（biotic）, suggesting that R（abiotic） strongly affected R（total） when R（biotic） was low. This pattern confirms that soil CO2 flux is predominated by biotic processes in most soils, but abiotic processes can also be dominant when biotic processes are weak. On a diurnal basis, R（abiotic） cannot result in net gain or net loss of CO2, but its effect on transient CO2 flux was significant. Temperature dependency of R（total） varied among the eight sampling sites and was determined by the predominant processes（abiotic or biotic） of CO2 flux. Specifically, R（biotic） was driven by soil temperature while R（abiotic） was regulated by the change in soil temperature（ΔT）. Namely, declining temperature（ΔT0） resulted in positive R（abiotic）（i.e., CO2 released from soil）. Without recognition of R（abiotic）, R（biotic） would be overestimated for the daytime and underestimated for the nighttime. Although R（abiotic） may not change the sum or the net value of daily soil CO2 exchange and may not directly constitute a C sink, it can significantly alter the transient apparent soil CO2 flux, either in magnitude or in temperature dependency. Thus, recognizing the fact that abiotic component in R（total） exists widely in soils has widespread consequences for the understanding of C cycling.

Monitoring and simulation of water,heat,and CO_2 fluxes in terrestrial ecosystems based on the APEIS-FLUX system

The Integrated Environmental Monitoring (IEM) project, part of the Asia-Pacific Environmental Innovation Strategy (APEIS) project, developed an integrated environmental monitoring system that can be used to detect, monitor, and assess environmental disasters, degradation, and their impacts in the Asia-Pacific region. The system primarily employs data from the moderate resolution imaging spectrometer (MODIS) sensor on the Earth Observation System-(EOS-) Terra/Aqua satellite, as well as those from ground observations at five sites in different ecological systems in China. From the preliminary data analysis on both annual and daily variations of water, heat and CO2 fluxes, we can confirm that this system basically has been working well. The results show that both latent flux and CO2 flux are much greater in the crop field than those in the grassland and the saline desert, whereas the sensible heat flux shows the opposite trend. Different data products from MODIS have very different correspondence, e.g. MODIS-derived land surface temperature has a close correlation with measured ones, but LAI and NPP are quite different from ground measurements, which suggests that the algorithms used to process MODIS data need to be revised by using the local dataset. We are now using the APEIS-FLUX data to develop an integrated model, which can simulate the regional water, heat, and carbon fluxes. Finally, we are expected to use this model to develop more precise high-order MODIS products in Asia-Pacific region.

Distributions and air-sea fluxes of CO_2 in the summer Bering Sea

The 3rd Chinese National Arctic Research Expedition （CHINARE-Arctic III） was carried out from July to September in 2008. The partial pressure of CO2 （pCO2） in the atmosphere and in surface seawater were determined in the Bering Sea during luly 11-27, 2008, and a large number of seawater samples were taken for total alkalinity （TA） and total dissolved inorganic carbon （DIC） analysis. The distributions of CO2 parameters in the Bering Sea and their controlling factors were discussed. The pCO2 values in surface seawater presented a drastic variation from 148 to 563 laatm （1 μatm = 1.013 25× 10-1Pa）. The lowest pCOz values were observed near the Bering Sea shelf break while the highest pCO2 existed at the western Bering Strait. The Bering Sea generally acts as a net sink for atmospheric CO2 in summer. The air-sea CO2 fluxes in the Bering Sea shelf, slope, and basin were estimated at -9.4, -16.3, and -5.1 mmol/（m2.d）, respectively. The annual uptake of CO2 was about 34 Tg C in the Bering Sea.

Summertime CO_2 fluxes from tundra of Ny-?lesund in the High Arctic

The Arctic ecosystem, especially High Arctic tundra, plays a unique role in the global carbon cycle because of amplified warming in the region. However, relatively little research has been conducted in High Arctic tundra compared with other global ecosystems. In the present work, summertime net ecosystem exchange （NEE）, ecosystem respiration （ER）, and photosynthesis were investigated at six tundra sites （DM1-DM6） on Ny-A.lesund in the High Arctic. NEE at the tundra sites varied between a weak sink and strong source （-3.3 to 19.0 mg CO2·m-2.h-1）. ER and gross photosynthesis were 42.8 to 92.9 mg CO2·m-2·h-1 and 54.7 to 108.7 mg CO2·m-2·h-1, respectively. The NEE variations showed a significant correlation with photosynthesis rates, whereas no significant correlation was found with ecosystem respiration, indicating that NEE variations across the region were controlled by differences in net uptake of CO2 owing to photosynthesis, rather than by variations in ER. A Qm value of 1.80 indicated weak temperature sensitivity of tundra ER and its response to future global warming. NEE and gross photosynthesis also showed relatively strong correlations with C/N ratio. The tundra ER, NEE, and gross photosynthesis showed variations over slightly waterlogged wetland tundra, mesic and dry tundra. Overall, soil temperature, nutrients and moisture can be key effects on CO2 fluxes, ecosystem respiration, and NEE in the High Arctic.

Characters of the P_(CO)_2 and CO_2 Flux in the East China Sea in Autumn

P CO 2 of air and seawater samples from the East China Sea (ECS) were measured in situ in autumn, 1994. Ocean currents, terrestrial fluviation, biological activities, etc.,P CO 2 characters in air and seawater were investigated. CO 2 flux and its character in the East China Sea are discussed on the basis of theP CO 2 profiles of air and seawater. It was clear that the nearshore was the source of CO 2; and that the outer sea area was the sink of CO 2; and that the shelf area of the ECS is a net sink for atmospheric CO 2 in autumn.

Fluxes of CO_2,CH_4 and N_2O from alpine grassland in the Tibetan Plateau

Using stat ic chamber technique, fluxes of CO 2 , CH 4 and N 2 O were measured in the alpine grassland area from July 2000 to July 2001, d eterminations of mean fluxes showed that CO 2 and N 2 O were gene rally released from the soil, while the alpine grassland accounted for a weak CH 4 sink. Fluxes of CO 2 , CH 4 and N 2 O ranged widely. The highest CO 2 emission occurred in August, whereas a lmost 90% of the whole year emission occurred in the growing season. But the variations of CH 4 and N 2 O fluxes did not show any clear patterns over the one-year-experim ent. During a daily variation, the maximum CO 2 emission occurred at 16:00, and then decreased to the minimum emi ssion in the early morning. Daily pattern analyses indicated that the variation in CO 2 fluxes was positively related to air temperatures (R 2 =0.73) and soil temperatures at a depth of 5 cm (R 2 =0.86), whereas daily variations in CH 4 and N 2 O fluxes were poorly explained by soil temperatures and climatic va riables. CO 2 emissions in this area were much lower than other grasslands in plain areas .

A Re-examination of Density Effects in Eddy Covariance Measurements of CO_2 Fluxes

Corrections of density effects resulting from air-parcel expansion/compression are important in interpreting eddy covariance fluxes of water vapor and CO2 when open-path systems are used. To account for these effects, mean vertical velocity and perturbation of the density of dry air are two critical parameters in treating those physical processes responsible for density variations. Based on various underlying assumptions, different studies have obtained different formulas for the mean vertical velocity and perturbation of the density of dry air, leading to a number of approaches to correct density effects. In this study, we re-examine physical processes related to different assumptions that are made to formulate the density effects. Specifically, we re-examine the assumptions of a zero dry air flux and a zero moist air flux in the surface layer, used for treating density variations, and their implications for correcting density effects. It is found that physical processes in relation to the assumption of a zero dry air flux account for the influence of dry air expansion/compression on density variations. Meanwhile, physical processes in relation to the assumption of a zero moist air flux account for the influence of moist air expansion/compression on density variations. In this study, we also re-examine mixing ratio issues. Our results indicate that the assumption of a zero dry air flux favors the use of the mixing ratio relative to dry air, while the assumption of a zero moist air flux favors the use of the mixing ratio relative to the total moist air. Additionally, we compare different formula for the mean vertical velocity, generated by air-parcel expansion/compression, and for density effect corrections using eddy covariance data measured over three boreal ecosystems.

Effects of amendments of paper mill sludge and nutrients on soil surface CO2 flux in northern hardwood forests

Safe and economical disposal of paper mill sludge is a key consideration for forest products industry. A study was conducted to examine the effects of amendments of sludge and nutrients on soil surface CO2 flux （Rs） in northern hardwood forests and to quantify the relationship among Rs, soil temperature, and moisture in these stands. The experiment was a randomized complete block design that included sludge-amended, fertilized, and control treatments in sugar maple （Acer saccharum Marsh） dominated hardwood forests in the Upper Peninsula of Michigan, USA. Results showed that Rs was positively correlated to soil temperature （R^2 = 0.80, p 〈 0.001）, but was poorly correlated to soil moisture. Soil moisture positively affected the Rs only in the sludge-amended treatment. The Rs was significantly greater in the sludge-amended treatment than in the fertilized （p = 0.033） and the control （p = 0.048） treatments. The maximum Rs in the sludge-amended treatment was 8.8 μmol CO2 · m^ 2. s^-1, 91% and 126% greater than those in the fertilized （4.6 μmol CO2 · m^-2· s^-1） and control （3.9 μmol CO2· m^- 2· s^-1） treatments, respectively. The Rs did not differ significantly between the fertilized and control treatments. The difference in Rs between sludge-amended and the other treatments decreased with time following treatment.

Microclimate and CO_2 fluxes on continuous fine days in the Xihu desert wetland,China

The Xihu desert wetland is located in an extremely arid area in Dunhuang,Gansu province of Northwest China.The area is home to an unusual geographic and ecological environment that is considered unique,both in China and the world.Microclimate is not only related to topography,but is also affected by the physical properties of underlying ground surfaces.Microclimate and CO2 flux have different characteristics under different underlying surface conditions.However,until now,few studies have investigated the microclimate characteristics and CO2 flux in this area.The eddy covariance technique（ECT） is a widely used and effective method for studying such factors in different ecosystems.Basing on data from continuous fine days obtained in the Dunhuang Xihu desert wetland between September 2012 and September 2013,this paper discussed and compared the characteristics of daily microclimate variations and CO2 fluxes between the two periods.Results from both years showed that there was a level of turbulent mixing and updraft in the area,and that the turbulent momentum flux was controlled by wind shear under good weather conditions.The horizontal wind velocity,friction wind velocity and vertical wind velocity were commendably consistent with each other.Air temperature in the surface layer followed an initial decreasing trend,followed by an increasing then decreasing trend under similar net radiation conditions.With changes in air temperature,the soil temperature in the surface layer follows a more obvious sinusoidal fluctuation than that in the subsoil.Components of ground surface radiation during the two study periods showed typical diurnal variations.The maximum diurnal absorption of CO2 occurred at around 11：00（Beijing time） in the Xihu desert wetland,and the concentrations of CO2 in both periods gradually decreased with time.This area was therefore considered to act as a carbon sink during the two observation periods.

Estimates and Variability of the Air-Sea CO2 Fluxes in the Gulf of Guinea during the 2005-2007 Period

Measurements of CO2 parameters (i.e. Total Alkalinity (TA) and Dissolved Inorganic Carbon (DIC)) were made from June 2005 to September 2007 in six EGEE (“Etude de la circulation océanique et de savariabilitédans le Golfe de GuinEE”) cruises to better assess air-sea CO2 fluxes in the Gulf of Guinea (6°N - 10°S, 10°E - 10°W). Two empirical relationships TA-Salinity and DIC-Salinity-Temperature were established. These relationships were then used to estimate the monthly fugacity of CO2 (fCO2) and air-sea CO2 fluxes. The monthly mean flux of CO2 reaches 1.76 ± 0.82 mmol·m-2·d-1 (resp. 2.90 ± 1.45 mmol·m-2·d-1) at the north of the Equator (resp. at the South). The north-south gradient observed as the patterns of the air-sea CO2 fluxes was mainly driven by the oceanic fCO2. This gradient was due to the low values of the CO2 parameters flowing by the Guinea Current (6°N - 0°) from the west to the east while the air-sea CO2 fluxes increased in the south (10°S - 0). In the north, the climatology of Takahashi underestimated the CO2 fluxes in the Gulf of Guinea when comparing to the estimated fluxes. This was due to the north-south gradient, which did not well reproduce by the climatology of Takahashi.

海南尖峰岭热带山地雨林近冠层CO_2及通量特征研究

采用梯度法及 CI-30 1 PS CO2 系统 ,实现了海南尖峰岭热带山地雨林近冠层 CO2 、微气象因子梯度观测研究 ,结果表明 :雨季晴、晴间少云及多云天气 ,9:0 0～ 1 8:0 0 CO2 浓度平均值分别在 34 9～ 35 0 ml/m3 (冠上 2 .8m)、34 6～ 34 8ml/m3(冠上 0 .8m)、34 5～ 34 9ml/m3 (林内 1 6 m)、35 2～ 35 7ml/m3 (林内 5 m) ,较旱季相应天气分别小 1 4～ 1 7.5、1 0 .1～ 2 3.7、1 6 .4～ 35 .7和 1 8.1～ 36 .1 ml/m3 ;1 :0 0～ 8:0 0 ,则雨季 CO2 浓度大于旱季 ;梯度浓度廓变量和实时动力计算反映出 ,8:0 0～ 1 8:0 0 CO2 通量由大气向林冠层 ,旱、雨季平均 CO2 通量分别为 ( 0 .6 1× 1 0 - 6kg/( m2· s)和 0 .71× 1 0 - 6kg/( m2· s) ,1 9:0 0通量甚微 ,2 0 :0 0～ 7:0 0 CO2 通量则由林冠向大气 ,平均 CO2 通量分别为 0 .36× 1 0 - 6kg/( m2 · s)和 0 .32× 1 0 - 6kg/( m2· s) ;雨季昼夜大气流向冠层的净 CO2 通量是相应旱季的 1 .5 6倍。总辐射、冠顶净辐射通量以 1 3:0 0～ 1 5 :0 0为最大时域 ,相对林内 2 1 m,80 %的辐射热能被冠层吸收 ,与 CO2 通量正相关 ;晴天冠上潜热、感热最高值分别在 1 3:0 0～1 4 :0 0和 9:0 0 ,反映热带山地雨林近冠层的汇、源即白昼光合固定 CO2

静态箱法原位观测草原CO_2通量的探讨

根据 IMGRASS研究计划 ,分析草原土壤 -植被系统 CO2 排放与吸收的生物机理和静态箱法在草地 CO2 通量原位观测实验中所遇到的难点问题 ,研究设计一套简单易行的静态箱实验方法 ,通过 1 999、2 0 0 0年连续两年在内蒙古半干旱草原的原位观测实验尝试 ,解决了利用静态箱法原位观测草原土壤 -植被系统与大气间 CO2 交换通量偏离实际的难题 ,校正了观测值的偏离 ,并实例分析校正了 1 998年内蒙古半干旱典型草原羊草草原土壤 -植被系统 CO2 通量 ,揭示了羊草草原 CO2 通量的变化规律特征。

森林生态系统CO_2通量研究方法与进展

介绍了森林生态系统CO2 通量研究的主要方法 :估算法、箱式法和微气象学法。其中微气象法包括空气动力学法、涡动相关法和涡动积聚法。着重介绍了涡动相关法的原理与应用 ,并对这几种研究方法分别进行了评价。最后概述了森林生态系统CO2

作物群体CO_2通量和水分利用效率的快速测定

In this paper,Eddy Correlation (EC) method was employed to measure the latent heat and CO 2 flux density and to calculate Water Use Efficiency (WUE) of winter wheat community in Yucheng district,Shandong Province in 1997.The results showed that the CO 2 flux density had an obvious diurnal change,with a maximum about1.5 mg·s -1 ·m -2 ,which appeared at about 9:00～10:00 am in general.The WUE of wheat community presented a fall trend from morning to afternoon,and the CO 2 flux density and WUE also had an obvious seasonal change,being lower in the early and late growth stages,and higher in the middle growth stage.The ranges of daily mean CO 2 flux density and WUE were 0.2～0.9 mg·s -1 ·m -2 and 5～20 gCO 2·kg -1 H 2O,respectively.

夏季东海西部表层海水中的pCO_2及海-气界面通量

根据 2 0 0 1年夏季长江口及东海西部海域表层海水pCO2 的实测数据 ,结合水文、化学和生物等要素的同步观测资料 ,对该海域pCO2 分布和变化的重要影响因素进行了探讨。结果表明 ,长江冲淡水是造成东海西部海域表层海水pCO2 分布不均匀的主要原因。利用Wan ninkhof( 1 992 )提出的通量模式计算 ,长江口口门附近海域和浙江近岸海域为CO2 的源区 ,1 2 3°E以东的调查海域表现为大气CO2 的汇 ,尤其是以 1 2 3°E ,32°N为中心 ,存在着一个极强的大气CO2 汇区。就整个东海西部海域而言 ,夏季可从大气净吸收 1 5 3× 1 0 4 tC。

湿地土壤CO_2通量研究进展

Wetland is considered as a special ecosystem which has some functions in the earth.Wetland’s carbon cycle is very important for global climate changes. The research on wetland soil CO-2 flux is a key of wetland carbon cycle. This paper analysed observation methods and influential factors of wetland soil CO-2 flux, introduced wetland soil CO-2 flux model, and discussed research emphases and direction on wetland soil CO-2 flux.

长白山四种林分土壤CO_2释放通量的研究

对长白山地区 4种典型林分下土壤释放CO2 通量的研究表明 ,在较短的时间尺度上 ,4种林型在CO2 释放通量上有显著的差别 ,各林型CO2 通量的释放表现出明显的空间异质性 ,其释放顺序为 :山杨白桦混交林 >原始阔叶红松林 >白桦林 >山杨林 ,其中山杨白桦混交林对CO2 释放的贡献最大 ,而山杨林最小。 4种林分土壤CO2 通量的全日变化过程并不一致 ,除山杨白桦混交林和气温有较一致性的规律 ,呈较明显的单峰型外 ,其余并无明显的变化规律。凋落物对林地CO2 释放通量的变化有显著的影响 ,有凋落物覆盖的林地土壤CO2 释放量明显大于无凋落物覆盖的林地 ,其平均通量为 2 6 2 86～ 5 5 6 5 5mgC·m-2 ·h-1,而无凋落物覆盖林地土壤CO2 的平均通量为 2 0 5 85～ 395 6 9mg·m-2 ·h-1。凋落物排放CO2 量占林地总排放量的14 %～ 30 % ,并且改变了林地CO2 释放通量大小的排序。