Language：English   Publishing type：Research paper (scientific journal)   Publisher：Society of Agricultural Meteorology of Japan  

Year-round eddy covariance flux measurements were made in a semiarid grassland in Mongolia during 2009-2014 to examine the interannual variability in net ecosystem CO2 exchange (NEE) and its climatic controls. Annual cumulative NEE ranged from －20.9 to 8.1 g C m－2 yr－1, indicating that the semiarid grassland ecosystem can be a carbon source or a carbon sink, depending on climatic conditions. A correlation analysis showed that interannual variability in NEE was significantly related to precipitation and soil water content at 10 cm depth (SWC10) in June and to the vapor pressure deficit (VPD) in July. In addition, the variation in gross primary production (GPP) in July contributed most to the interannual variation in NEE
and GPP in July was significantly related to June precipitation, June SWC10, and July VPD. From these results, we concluded that precipitation during the early growing season and air dryness during the middle growing season were essential climatic factors regulating the interannual variation in NEE in this semiarid grassland.

DOI： 10.2480/agrmet.D-17-00035

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japanese Society of Soil Science and Plant Nutrition  

We constructed an empirical model in which the rates of gross primary production (GPP) and ecosystem respiration (R_<eco>) were calculated using meteorological, soil and plant variables, based on our previous measurements of carbon dioxide (CO_2) fluxes using a closed-chamber technique in Mongolian grasslands. In the previous studies, we determined GPP and R_<eco> using transparent and opaque chambers and simultaneously measured the environmental variables inside and beside the chambers. These measurements allowed us to quantify direct and accurate relationships between the rates of GPP and R_<eco> and their controlling factors. The GPP, R_<eco> and their difference net ecosystem CO_2 exchange (NEE) were computed in a semiarid grassland site of Mongolia for the growing seasons of 2010 and 2011 using observed values of photo-synthetically active radiation, air and soil temperatures, vapor pressure deficit, soil water content and estimated values of aboveground biomass from a remotely sensed vegetation index. Model performance was validated by comparing the modeled and observed NEE values using an eddy covariance technique. Results showed that the model successfully reproduced the magnitude and seasonal variations of the observed NEE, and regression analysis showed reasonable agreement in both years. Cumulative rates of GPP and R_<eco> during the plant-growing season (May - September) were 200.3 and 210.5 g carbon (C) m^<-2> in the dry year (2010) and 342.3 and 300.1 g C m^<-2> in the wet year (2011), respectively. This result indicates that drought was more effective in reducing CO_2 uptake by the plant than in reducing ecosystem respiration. Consequently, the grassland ecosystem was a net carbon source during the growing season in 2010 and a net carbon sink in 2011.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SOC AGRICULTURAL METEOROLOGY JAPAN  

Grassland ecosystems cover a large area of the land surface and play an important role in the global carbon cycle. The objectives of this study were to examine the spatial variability of gross primary production (GPP) and ecosystem respiration (R-eco) within a semiarid grassland ecosystem and to evaluate the environmental factors that control the spatial patterns of carbon exchanges. We determined GPP and R-eco using transparent and opaque closed chambers at nine grassland sites in central Mongolia during the summers from 2009 through 2011. To remove effects of temporal changes in radiation and temperature, GPP and R-eco were fitted to light- and temperature-response curves. The fitting parameters (light-saturated GPP [P-max], apparent quantum yield [alpha], standardized R-eco at 20 degrees C [R-20], and the temperature sensitivity [Q(10)] of R-eco) were compared among the sites. The GPP and R-eco parameters differed significantly among the sites. Spatial patterns of P-max and R-20 were highly correlated with plant aboveground green biomass (A GB) and number of plant species. The Q(10) of R-eco was significantly related to soil moisture. The light-saturated GPP normalized to the amount of AGB did not differ significantly among the sites, whereas the R-20 residuals of the linear biomass model were correlated with soil water content and carbon/nitrogen ratios. The results suggest that, within this semiarid grassland, spatial variations of GPP are strongly controlled by AGB and that variations in R-eco are associated mainly with AGB and secondarily with soil water content and soil nutrient condition.

DOI： 10.2480/agrmet.D-13-00026

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SOC AGRICULTURAL METEOROLOGY JAPAN  

In the present study, we calculated seven vegetation indices (simple ratio [SR], normalized difference vegetation index [NDVI], enhanced vegetation index [EVI], soil-adjusted vegetation index [SAVI], optimized soil-adjusted vegetation index [OSAVI], land surface water index [LSWI], and greenery ratio [GR]) based on MODIS surface reflectance data and analyzed the relationships between these indices and the aboveground biomass in semiarid grasslands in Mongolia. The measured values of the biomass for the study area ranged from 7.5 to 137.0 g dry weight (dw) m(-2). The results revealed that NDVI, SR, and OSAVI were strongly correlated with the biomass. Among these, NDVI showed the best performance as a proxy of the plant biomass of Mongolian grasslands. The relationships of NDVI and OSAVI with the temporal variation and spatial pattern of biomass were statistically similar, suggesting that a single linear equation was appropriate to derive aboveground biomass values from NDVI or OSAVI.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SOC AGRICULTURAL METEOROLOGY JAPAN  

We investigated the temporal and spatial variability of nighttime temperatures in a complex of small valleys in the western Kanto Plain, Saitama Prefecture, Japan, by conducting horizontal and vertical temperature measurements throughout one winter season. The magnitude of nocturnal cooling in the valley was greater in March than during the mid-winter period. The horizontal distribution of mean nighttime temperatures and nocturnal cooling under clear and calm conditions indicated that temperatures in the middle or lower areas of the valleys tended to be lower than those in the upper areas even though the elevation differences were small. Vertical profiles of air temperature measured by a kytoon system on clear nights revealed the development of a temperature inversion above the valley floor at night; the top of the inversion exceeded the height of the ridge adjacent to the valley. Under these conditions, down-valley flows of cold air were a significant phenomenon below the inversion layer. Our results suggest that local nocturnal drainage flow below the temperature inversion could contribute to nocturnal cooling in these valleys.

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本農業気象学会  

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Language：English   Publisher：InTech  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Part of collection (book)   Publisher：Springer International Publishing  

Wetlands are one of the most important ecosystems in the world. The West Siberian Lowland (WSL) is the world’s largest high-latitude wetland covering nearly two-thirds of western Siberia
thus, remote sensing techniques play an important role in monitoring them. At least half of this area consists of peatlands, which sequester atmospheric carbon in the form of slightly decomposed plant matter. WSL is considered a net source of methane gas, which is one of the most important greenhouse gases. High spatial resolution satellite data are effective for monitoring land cover type changes, but cannot cover a wide area because of a narrow swath width. On the other hand, global scale data are indispensable in covering large areas, but are too coarse to acquire detailed information because of their low spatial resolution. We need to devise a method for data fusion with different spatial resolutions for monitoring such scale-variant phenomena. In this chapter, a Terra ASTER image near Noyabrsk mire is used to map six wetland ecosystems (bare soil, birch forest, conifer forest, open bog, open water, and palsa) supplemented by field observation. Spectral mixture analysis is then performed between Terra MODIS and ASTER data acquired on the same day. Field observations of CH4 flux are subsequently scaled up with these different spatial resolution satellite data. Each of the wetland ecosystem coverage fraction at the subpixel level is provided by spectral mixture analysis. Field observation shows that the mean rate of CH4 emission from open bog and open water averaged 123.1 and 24.6 mg C/m2/day, respectively. The methane emission from the area is estimated by multiplying these average methane emission rates and the fraction coverage in each MODIS pixel. Finally, the total methane emission over MODIS coverage is estimated at 1.86 × 109 g CH4/day and the mean methane emission over MODIS coverage was calculated as 43.1 mg C/m2/day. We conclude that this mean value is within the probabilistic variability when compared with the other research results.

DOI： 10.1007/978-1-4419-6749-7_18

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

The Mongolian steppe zone constitutes a major part of East Asian grasslands. The objective of this study was to evaluate the quantitative dependence of ecosystem respiration (R-eco) on the environmental variables of soil water and plant biomass in a semiarid grassland ecosystem. We determined R-eco using opaque, closed chambers in a Mongolian grassland dominated by graminaceous perennial grasses during six periods: July 2004, May 2005, July 2005, September 2005, June 2006, and August 2009. Using the data collected when soil water content and aboveground biomass were relatively constant, values of R-eco were fitted to an exponential temperature function, and the standardized rate of R-eco at 20 degrees C (R-20) and temperature sensitivity (Q(10)) of R-eco were calculated for each measurement plot and period. The results indicate that aboveground biomass significantly affected the variation in R-20, and the relationship was expressed with a linear model. The R-20 residuals of the linear biomass model were highly correlated with soil water content by a quadratic function. The Q(10) values showed a weak positive relationship with soil water content. Temporal and spatial variations in R-eco were well predicted by the exponential temperature model with R-20, which relates to aboveground biomass and soil water content, and with Q(10), which relates to soil water content.

DOI： 10.1111/j.1747-0765.2010.00502.x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

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Language：English   Publishing type：Research paper (bulletin of university, research institution)   Publisher：首都大学東京都市環境学部地理環境コース  

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Language：English   Publishing type：Research paper (scientific journal)  

Nighttime water vapor transportation from the atmosphere to the ground surface, which involves dew formation and water vapor adsorption to the soil, is very small, yet its contribution to the water budget has been recognized as important, especially in arid and semiarid regions. We applied a closed-chamber (CC) technique to measure nighttime water vapor flux between the atmosphere and a grassland ecosystem and used a microlysimeter (ML) method to validate the results of the CC measurements. The CC measurements were conducted on nine nights in May, July, and September of 2005 and June of 2006 at a Mongolian semiarid grassland. The results of our study indicate that water vapor was transported upward during five nights and downward during four nights, and the magnitude of nighttime water vapor fluxes ranged between -0.011 mm h-1 and 0.011 mm h-1 (a positive value represents upward transportation). We also found that downward vapor transportations were involved in both dew formation and direct water vapor adsorption. The results of the CC and ML methods showed good agreement, suggesting that the CC method is appropriate for measuring small water vapor fluxes. © 2007, The Society of Agricultural Meteorology of Japan. All rights reserved.

DOI： 10.2480/agrmet.63.103

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本農業気象学会  

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Other Link： http://agriknowledge.affrc.go.jp/RN/2010741486

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)   Publisher：筑波大学陸域環境センター  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本リモートセンシング学会  

Recently, the number of forest fires in West Siberian Lowland (WSL) is increasing and they are considered as one of the main driving factors influencing carbon cycling in whole earth. Since many forest fires take place in large and hardly accessible areas, remote sensing seems to be the most appropriate tool for creating forest fire recovering history. In this paper, SPOT HRV and Landsat ETM images were used to highlight the damaged area by fire that occurred in the summer of 1998. The damaged area was extracted by using principal component analysis supplemented by ground truth data. The total burnt area was calculated to be 13.8 (km²). Then re-generation condition in burnt area from 1995 to 2002 was investigated using NOAA AVHRR data with sub-pixel land cover characterization. We demonstrate that the phenomena observed by remote sensing data is consistent with climatic data including daily precipitation and temperature. The method proposed in this study can be an effective way for forest recovering monitoring.

DOI： 10.11440/rssj.27.13

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Language：English   Publisher：北海道大学出版会  

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Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：国立環境研究所地球環境研究センター  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japanese Society of Soil Science and Plant Nutrition  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：BLACKWELL MUNKSGAARD  

Methane and carbon dioxide fluxes were measured in a birch forest soil in West Siberia, in August 1999, June 2000 and September 2000. The study site had a very thick organic horizon that was subject to drought during the observation periods. The soils always took up CH4, while CO2 was released from the surface to the atmosphere. CH4 consumption and CO emission rates ranged from 0.092 to 0.28 Mg C m(-2) h(-1) and from 110 to 400 mg C m(-2) h(-1) respectively. The CH4 consumption rate and soil temperatures showed significant relationships for individual measurements. The soil respiration rate was weakly correlated with individual soil temperatures. This study examined the effect of current and lagged soil temperatures at a depth of 5 cm on CH4 consumption and soil respiration. The variation in the correlation coefficient between CH4 consumption and lagged soil temperature was greatest at a 4-h lag, whereas that for soil respiration showed a gentle peak at lags from several hours to half a day. This difference in the temperature-related lag effect between CH4 consumption and soil respiration results from differences in the exchange processes. Neither flux showed any correlation with soil moisture. The limited variation in soil moisture during our observation period may account for the lack of correlation. However, the droughty soil conditions resulted in high gas diffusion and, consequently, high CH4 consumption.

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Language：English   Publisher：東京都立大学理学部地理学科  

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Language：Japanese   Publisher：東京大学生産技術研究所  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Continuous changes in methane (CH4) and carbon dioxide (CO2) concentrations inside a closed chamber were measured on the forest floor at three sites: a deciduous forest and a coniferous forest in Hokkaido, Japan, and a birch forest in West Siberia, Russian Federation. Flux estimations by three types of regression methods, exponential, nonlinear, and linear, were examined using field-collected concentration data. The pattern of change with time of the gas concentration in the headspace differed, mainly according to site but also, to a lesser extent, according to the gas. This was a function of both the chamber height and surface soil property relating to soil gas diffusion and the gas concentration profile. Flux estimations did not differ statistically between the exponential and nonlinear methods for either gas at any site, because both of those regression methods were based on diffusion theory. However, the flux values estimated by linear regression were significantly different from those estimated by the other two methods for both CH4 and CO2 at the deciduous forest site and for CO2 at the coniferous forest site. Shortening the chamber deployment period improved the linearity of the curve, but did not completely eliminate the error. Our results suggest that linear regression is not a good model of the change in headspace concentration with time. (C) 2003 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.soilbio.2003.07.005

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Language：English   Publisher：東京都立大学理学部地理学科  

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Language：Japanese   Publisher：古今書院  

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Language：Japanese   Publisher：東京大学生産技術研究所  

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Publishing type：Research paper (international conference proceedings)  

West Siberian Lowland (WSL) is the world's largest high-latitude wetland covering nearly 2/3 of western Siberia. At least half of this area consists of peatlands, which sequester atmospheric carbon in the form of unde-composed plant matter and it is presumed to be the source of methane gas. In this paper, firstly, an ASTER image near Noyabrsk mire was used to map 6 wetland ecosystem (red pine, white birch, bog, palsa, open water and bare soil) supplemented by field observation. Then spectral linear mixture analysis was performed between MODIS and ASTER data acquired on the same day. Secondly, field observations were scaled up with these different spatial resolution satellite data. Each of the wetland ecosystem coverage ratio in sub-pixel level was provided by the spectral linear mixture analysis. Field observation shows that the mean rate of CH4 emission from bog and open water averaged 5.246 and 1.081 (mg CH4 m-2h-1) respectively. The methane emission from the area was estimated by multiplying these average methane emission rate and the area percentage of bog and open water in each pixel. Finally, the mean methane emission over MODIS coverage was estimated 1.864 (109g CH4/day).

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本農業気象学会  

Diurnal variation in CO₂ flux from the soil was measured by a closed chamber technique at a developed land site in Tokyo from September to November in 1999. The measurements were made four times for 24-h periods at two fixed sites where there was no plant cover (A) and where Miscanthus sinensis was dominant (B). CO₂ fluxes averaged 98.2mg CO₂ m^-2h^-1 at the site A and 184.3mg CO₂ m^-2h^-1 at the site B. The fluxes from both sites showed a clear diurnal variation, which was high during the day and low at night. The temporal variation was highly correlated with the air and soil temperatures, especially at depths of 1 and 5cm. The relationship between CO₂ flux and temperature was exponential. The CO₂ flux increased exponentially 1.99 times when the soil temperature at 1cm deep increased by 10°C.

DOI： 10.2480/agrmet.57.155

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Language：Japanese   Publisher：東京大学生産技術研究所  

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Language：English   Publisher：東京都立大学理学部地理学科  

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Language：English   Publisher：Hokkaido University  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

The relationships between vegetation types and methane flux were evaluated in north-eastern Siberia in the summer of 1995. Based on 71 50 × 50-cm plots, the vegetation was divided into three types by TWINSPAN cluster analysis: (1) Eriophorum grassland where species richness was high and moss well-established (Eriophorum grassland), (2) horsetail grassland with moss cover and (3) Carex grassland without moss. Vascular plant cover in all vegetation types was less than 50%. The methane flux was measured by a static chamber method. Horsetail grassland emitted the highest amount of methane, 165.5 mg CH4/m2/d, while diverse-sedge grassland emitted less methane, i.e., -1.9 mg CH4/m2/d. Methane flux positively increased with electric conductivity (EC), water depth, thaw depth, and soil humidity. Of those, EC was strongly correlated to methane emission (Spearman's rank correlation, r2 = 0.630). The difference in methane flux between horsetail grassland and sedge-dominated grassland suggested that the morphological characteristics of vascular plants were important on methane transport, probably because vascular plants, such as horsetail, that developed aerenchyma and intercellular gas space promoted methane transport from soil to air while mosses do not. © 2001 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0038-0717(01)00058-X

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Language：English   Publisher：Hokkaido University  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Summer variations in net methane flux and environmental variables were investigated in a Siberian permafrost area during the summers of 1993 and 1995. In each region, the measurements were made at two fixed sites: waterlogged wetlands and relatively dry grasslands. Methane flux from the waterlogged site at Tiksi (71.5 degrees N, 130.0 degrees E) averaged 46.3 mg CH4 m(-2) d(-1). Flux from the waterlogged Site at Chersky (68.5 degrees N, 161.4 degrees E) was approximately one order of magnitude greater than that at Tiksi and averaged 281.1 mg CH4 m(-2) d(-1). Fluxes from the relatively dry sites were near zero and frequently negative in both regions. The emissions from the waterlogged sites showed diurnal and intraseasonal variation, while no significant variation in flux was observed at the dry sites. Our results suggest that temporal variation in methane flux From waterlogged sires in permafrost areas was controlled by the thermal regime of a seasonal thaw layer. The diurnal variation in the flux was correlated with ground temperature at a depth of 10-30 cm. For summer-season variation. the correlation between flux and centimeter-degrees, which is the product of ground temperature and thaw depth, was quite strong. The parameter, centimeter-degrees, is expected to be a good predictive indicator of methane emission from wetlands in permafrost areas. (C) 2000 Elsevier Science Ltd. All rights reserved.

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Language：English   Publisher：東京都立大学理学部地理学科  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Geographical Society of China  

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Language：English   Publisher：Hokkaido University  

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Language：English   Publisher：Hokkaido University  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本雪氷学会  

The objective of this study is to estimate the response of the permafrost at the Daisetsu Mountains, central Hokkaido to a continuous climatic change. A one-dimensional, nonsteady state, heat conduction model with phase change is used to calculate the change of permafrost thickness during the last 20, 000 years. The result of simulation shows that the permafrost responded quickly to the surface temperature change and it has remained without thaw since the Last Glacial Maximum. The minimum permafrost thickness is estimated at 11.5 m at about 5 kyr B. P. and reached to 30.1 m at present. The simulation also indicates that the permafrost thickness is sensitive to soil water content and ground heat flow.

DOI： 10.5331/seppyo.57.125

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Other Link： https://jlc.jst.go.jp/DN/JALC/00033967462?from=CiNii

Language：English   Publisher：Hokkaido University  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本気象学会  

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Other Link： http://dl.ndl.go.jp/info:ndljp/pid/10601550

Language：English   Publisher：Hokkaido University  

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Language：English   Publisher：Hokkaido University  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：International Society of Permafrost  

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Language：English   Publisher：北海道大学低温科学研究所  

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Language：Japanese   Publisher：北海道大学低温科学研究所  

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Language：Japanese   Publisher：北海道大学低温科学研究所  

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Language：Japanese   Publisher：北海道大学低温科学研究所  

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Language：English   Presentation type：Oral presentation (invited, special)  

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Language：Japanese   Presentation type：Poster presentation  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Poster presentation  

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Language：Japanese   Presentation type：Oral presentation (general)  

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