All issues
Volume 66, Issue 1
Displaying 1-7 of 7 articles from this issue
- |<
- <
- 1
- >
- >|
Full Papers
-
Takafumi MIYAMA, Taro HASHIMOTO, Yuji KOMINAMI, Kenta NAKAGAWA, Motono ...2010 Volume 66 Issue 1 Pages 1-9
Published: March 10, 2010
Released on J-STAGE: May 11, 2010
JOURNAL FREE ACCESSTo clarify the characteristics of the variation in methane (CH4) concentrations in a warm-temperate mixed forest in Japan, we measured vertical profiles and daily and seasonal variations in CH4 concentrations, and soil and foliage (Quercus serrata) CH4 fluxes. CH4 concentrations increased during rainy periods, and decreased in August. Almost constant CH4 uptake was observed at the forest floor throughout the year, but no CH4 flux was observed from the foliage. In the profile measurements, the CH4 concentration was slightly higher at canopy height when friction velocity (u*) was lower than 0.3 m s-1. These phenomena were observed on the same day at micrometeorological towers in ridge and valley positions. Variations in CH4 concentrations increased in summer, around ground level, and at canopy height. These results suggest that certain large scale factors govern variations in CH4 concentration around ground level and at canopy height. To understand the overall role of the forest in CH4 circulation, more continuous measurements as close as possible to sinks and sources will be needed.View full abstractDownload PDF (767K) -
Nguyen Duy KHANG, Akihiko KOTERA, Toshichika IIZUMI, Toshihiro SAKAMOT ...2010 Volume 66 Issue 1 Pages 11-21
Published: March 10, 2010
Released on J-STAGE: May 11, 2010
JOURNAL FREE ACCESSA numerical hydraulic model was developed and used to investigate the spread of salinity intrusion and the propagation of flooding in the Vietnamese Mekong Delta under two proposed scenarios: “baseline” (2000s) and “future” (2090s). The baseline scenario was based on observed hydrological and salinity intrusion data from 1998 to 2006. The changes in upstream flow discharge in the future scenario (increased for most of the year) were derived from previous research results obtained using the Japan Meteorological Agency atmospheric general circulation model output for the IPCC SRES A1B scenario. The sea level rise in the A1B scenario (a projected 53-cm increase) was also included in the future scenario. The resulting salinity intrusion and flood water levels were then used to roughly estimate possible rice cropping durations. We found that large adverse changes in duration of rice cultivation in the future scenario were caused mainly by floods with greater peaks, larger areal extents, and longer durations. The area potentially suitable for growing triple rice crops decreased from 31% of the total delta area currently to 5%, whereas that potentially suitable for a single rice crop increased from 21% currently to 62%. Using GIS techniques, we divided the delta into three areas with different levels of rice vulnerability levels. Areas of high and medium vulnerability covered approximately 31 and 36% of the total delta area, respectively.View full abstractDownload PDF (9129K) -
Osamu NAGATA, Tomotsugu YAZAKI, Yosuke YANAI2010 Volume 66 Issue 1 Pages 23-30
Published: March 10, 2010
Released on J-STAGE: May 11, 2010
JOURNAL FREE ACCESSNitrous oxide emissions from a drained peatland area (D site) and a drained and mineral soil-dressed (D-SD site) peatland area in central Hokkaido Island, northern Japan were measured. Nitrous oxide flux at the D-SD site was -0.01-1.15 mgN m-2 hr-1, showing a sudden increase during the period June-October. Nitrous oxide flux at the D site was -0.01-4.47 mgN m-2 hr-1, showing much higher fluxes (0.40-4.47 mgN m-2 hr-1) during July-October 2004 than other monitoring periods (0.30 mgN m-2 hr-1 maximum flux). The nitrous oxide concentration in the soil rose remarkably concomitantly with the nitrous oxide flux in 2004. These fluxes were much higher than those measured in an undeveloped mire near this study site. Annual nitrous oxide emissions at the D and D-SD site were 3.8-41.7 kgN ha-1 yr-1; which were far larger than in the above-described undeveloped mire (0.3 kgN ha-1 yr-1). The results of this study showed that the conversion of peatland into agricultural land with drainage and soil dressing changed their atmospheric impact dramatically. Nitrous oxide concentrations of soil gas were higher at the D site than at the D-SD site, particularly during 2004. High nitrous oxide concentrations in the soil gas corresponded to dramatically high nitrous oxide fluxes at the D site in 2004, while the precipitation surplus was also more than the other two years in 2004. Our results suggest that the peatland drainage contributes to increased nitrous oxide generation and that an interannual change of nitrous oxide emissions occurs with climate conditions.View full abstractDownload PDF (809K) -
Tserenpurev BAT-OYUN, Masato SHINODA, Mitsuru TSUBO2010 Volume 66 Issue 1 Pages 31-39
Published: March 10, 2010
Released on J-STAGE: May 11, 2010
JOURNAL FREE ACCESSThe Mongolian economy depends critically on products of range-fed livestock. Pasture is the major food source for livestock grazing, and its productivity is strongly affected by climatic variability. Direct measurement of pasture productivity is time-consuming and difficult, especially in remote areas of a large country like Mongolia with sparse spatial distribution of pasture monitoring. Therefore, modeling is a valuable tool to simulate pasture productivity. In this study, we used a remote sensing-based production efficiency model, that is, the Carnegie Ames Stanford Approach (CASA) model, to estimate pasture productivity in three main vegetation zones of Mongolia; desert steppe, steppe and forest steppe. The present study aimed to explore climatic and grazing effects on grassland productivity in Mongolian grasslands during 2005-2007, using ground-based measurements and simulation model outputs.
The ground measurements showed that grazing caused a significant decrease in measured aboveground phytomass and plant height. Simulation results demonstrated that the highest net primary productivity (NPP) of 83.2 gC/m2 and the lowest NPP of 12.6 gC/m2 over the growing season (April-September) occurred at Darkhan (steppe) and Mandalgovi (desert steppe), respectively. Moreover, the comparison of temperature and water stresses on pasture productivity indicated that water stress was stronger downregulator of NPP, verifying that drought is the major concern of pasture production. Based on the comparison between the measurements and simulation, the ratio of aboveground NPP to belowground NPP in the Mongolian perennial grasslands was estimated as 1:1.5.View full abstractDownload PDF (747K) -
Atsushi MARUYAMA, Yoshitaka KUROSE, Kazuhiko OHBA2010 Volume 66 Issue 1 Pages 41-50
Published: March 10, 2010
Released on J-STAGE: May 11, 2010
JOURNAL FREE ACCESSPrediction of phenological development of wheat (Triticum aestivum L.) is important for proper agronomic management and schedule planning. A model to calculate developmental rate (DVR) for short-day plant was applied for long-day plant to estimate the timing of heading and maturity of winter wheat using the concept of DVR. The DVR from emergence to heading was expressed using a function of daily mean air temperature and photoperiod. The DVR from heading to maturity was expressed using a function of daily mean air temperature only. The model was examined based on a field experiment in Kumamoto, Japan, in the 2003 and 2004 growing seasons. Three cultivars of winter wheat (Chikugoizumi, Saikai-185 and Iwainodaichi) were used to examine how the parameter values differ with cultivar. Calculated values for duration from emergence to heading and from heading to maturity showed good agreement with observed data over a wide range from 35-170 days and 30-55 days, respectively. Root mean square errors of the model estimation were 4.2-4.9 days for heading date and 1.7-2.8 days for maturity date, respectively. Phenological differences among the cultivars were mainly reflected in parameters expressing the DVR response to temperature. From emergence to heading, the temperature when the DVR is half of the maximum rate (Thv) differed with cultivar from 3 to 9°C. The Thv value was higher for a cultivar with a low degree of winter habit (Chikugoizumi), and lower for cultivars with a high degree of winter habit (Saikai-185 and Iwainodaichi). From heading to maturity, a parameter (Am) that expressed the DVR slope with change in temperature showed a higher value for Chikugoizumi, and lower values for Saikai-185 and Iwainodaichi. The model will be useful for predicting the phenological development of winter wheat and understanding the phenological response to climate change.View full abstractDownload PDF (820K)
Short Papers
-
Hisato ICHIKAWA, Hirakazu SEKI, Shinichi TAKAMI2010 Volume 66 Issue 1 Pages 51-56
Published: March 10, 2010
Released on J-STAGE: May 11, 2010
JOURNAL FREE ACCESSIn a previous study (Ichikawa et al., 2008), we found experimentally and confirmed theoretically that a porous column, the primary part of a solar pump, enhanced water evaporation. The evaporation rate from the surface of a sand column was higher than that from the water surface. Our previous study also showed that there was an optimum height of the sand column at which the rate of evaporation was the maximum. Experimental results for the water evaporation rate changed continuously with increasing water table depth and had a maximum at a particular depth value. The evaporation rates calculated from a mathematical model based on Philip and de Vries (1957), however, changed discontinuously at a particular value of water table depth at which maximum evaporation occurred. Assuming that the local evaporation rate on the column surface varies, following a statistical normal distribution, we computed its average over the column surface. The rates thus computed changed continuously with increasing water table depth, which agreed well with the experimental results. We therefore conclude that the discrepancy in the previous study arose because the experimental results are averages over the surface, while those theoretically calculated without considering the statistical distribution are merely local values on the surface.View full abstractDownload PDF (615K) -
Tomotsugu YAZAKI, Shin-ichi URANO, Kazuo YABE2010 Volume 66 Issue 1 Pages 57-61
Published: March 10, 2010
Released on J-STAGE: May 11, 2010
JOURNAL FREE ACCESSFog might play an important role in the water balance in foggy regions. We measured the amount of fog deposition (deposition of fog and dew waters) using lysimeters in a flatland mire on the Pacific coast of eastern Hokkaido Island. During five observed nights, summer fog was observed on four nights: one night had advection fog and three nights had radiation fog. The amount of advection-fog deposition per night was 0.6 mm on average, reaching 20% of the daily evapotranspirative water loss from this mire. This value suggests that the advection-fog water supply is not negligible. In contrast, the amount of radiation-fog water supply per night was much smaller than the other terms of water balance such as rainfall and evapotranspiration, indicating that the amount of radiation-fog deposition is negligibly small.View full abstractDownload PDF (933K)
- |<
- <
- 1
- >
- >|