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Volume 65, Issue 4
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Masahito UEYAMA, Ken HAMOTANI, Wataru NISHIMURA2009 Volume 65 Issue 4 Pages 315-325
Published: March 10, 2009
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSContinuous observation of carbon dioxide (CO2) flux is an important issue to understand the global carbon cycle. Although the eddy covariance (EC) method is a promising means of measuring the fluxes, its high cost is often constraint. We therefore developed a technique for a high accuracy measurement system using a relaxed eddy accumulation (REA) method with an inexpensive gas analyzer, and tested the measurement system compared with the EC measurement at a cypress forest. Since spectral analysis revealed that the gas analyzer had both high and low frequency noise, we eliminated the former by using a moving average, and then calculated mean concentration with a shorter averaging period to avoid the low frequency noise, whereby the accuracy of the gas analyzer was improved at least 10-fold beyond the specification. The measured diurnal variation and the magnitude of CO2 fluxes by the EC and REA methods were almost identical, suggesting that our REA system was highly accurate as well as the EC system. The estimated root mean square error (RMSE) of the CO2 flux between the EC and the REA methods was 0.17 mg CO2 m-2 s-1. Although the open-path EC method could not be used to measure the flux during the rain event, spectral analysis suggested that the measured flux by the REA method was reliable during rainfall. The proposed measurement system will be applicable to the backup of the EC measurement as well as other trace gas flux measurements.View full abstractDownload PDF (1142K) -
Masashi OKADA, Toshichika IIZUMI, Yousay HAYASHI, Masayuki YOKOZAWA2009 Volume 65 Issue 4 Pages 327-337
Published: March 10, 2009
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSA remarkable declining trend in rice quality has already been observed in western Japan and the future global warming associated with climate change is likely to exacerbate such risk. In this study, a simple statistical model was constructed to estimate the rice quality, which is defined as the proportion of white immature grains on a prefectural scale, in terms of two major climate variables during the grain-filling stage: the cumulative weighted effective temperature δ and the cumulative solar radiation SR. In order to account for the uncertainties included in the processes involved, Bayesian inference was used to estimate the model parameters. The modeled time changes in rice quality correlated well to those observed. Specifically, the reproducibility of rice quality since 2000 was particularly high. These results suggested that a combination of the two climate factors was responsible for the recent variability in rice quality on a prefectural scale. Subsequently, the elasticity of rice quality relative to δ and SR was examined based on the model. The elasticity represents the relative change in rice quality in response to a change in δ or SR, with a positive (negative) sign indicating increased (decreased) quality. Consequently, the mean elasticity of the rice quality relative to SR was larger than that to δ in Kyushu. Moreover, the time changes of rice quality in Kyushu synchronized with that of SR under high temperature conditions, suggesting that rice plants become more sensitive to conditions of insufficient radiation if exposed to high temperatures. Consequently, it was concluded that the contribution of the radiation condition to the variation in rice quality become relatively larger along with the recent increase in temperature.View full abstractDownload PDF (874K) -
Shinjiro OHKUBO, Naoto YOKOYAMA, Yoshiko KOSUGI, Satoru TAKANASHI, Nao ...2009 Volume 65 Issue 4 Pages 339-348
Published: March 10, 2009
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSWe estimated the vertical distribution of CO2 effluxes from trunks, branches, and leaves in a temperate cypress forest by estimating the spatial distribution of biomass. To quantify the distribution of the CO2 source per unit biomass of each organ, we measured the respiration rate of 47 trunk, 26 branch, and 30 leaf samples from one representative tree. To quantify the distribution of biomass per unit height, we measured the positions of all of the branches and leaves, and then collected them to estimate branch volume and leaf area from their dry weight.
Trunk respiration rate per sapwood volume increased with height within the canopy, but no clear difference was apparent below the canopy. The respiration rate per unit volume of lower branches was less than that of higher branches. Small-diameter branches had a higher respiration rate per unit volume than did large-diameter branches. The respiration rate per leaf surface area of leaves higher on the tree was greater than that of lower leaves, as was also the case of leaves farther from the trunk compared with those nearer the trunk. The cumulative trunk, branch, and leaf respiration per ground area at 25°C was estimated to be 1.36, 0.62, and 2.19 μmol m-2 s-1, respectively. CO2 efflux from the trunk per unit height did not differ significantly throughout the tree. The peak CO2 efflux per unit height was greater for leaves than branches. CO2 efflux from the canopy level (>11.5 m) accounted for 75% of cumulative above ground CO2 efflux, excluding soil respiration, and 38% of total ecosystem respiration including soil respiration.View full abstractDownload PDF (789K) -
Parinaz RAHIMZADEH BAJGIRAN, Yo SHIMIZU, Fumiki HOSOI, Kenji OMASA2009 Volume 65 Issue 4 Pages 349-355
Published: March 10, 2009
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSIn order to evaluate how vegetation indices are affected by climatic patterns and to assess the relationships between them in semi-arid ecosystems of Iran, a six year (2000-2005) time series Moderate Resolution Image Spectrometer (MODIS) data over a six month growing season was used for retrieving Normalized Difference Vegetation Index (NDVI) and two Normalized Difference Infrared Indices (NDII6 and NDII7 using band 6 and 7 MODIS data, respectively) used as Vegetation Water Index (VWI). The study was carried out in dry farming and rangeland areas located in northwestern part of the country. Vegetation indices dynamics and relationships as well as their response to precipitation were studied. The results revealed the high dependence of temporal dynamics of MODIS vegetation indices on precipitation, promising the capability to differentiate drought and normal conditions in different land cover types. Among all indices, NDVI was found to be the best index to be used for drought detection for it had better relationship with precipitation and close relationship with the VWIs. The results of this research can be used as the basis to develop a region-specific drought index for semi-arid regions of Iran.View full abstractDownload PDF (821K) -
Masana YOKOYA, Takayoshi AOYAMA2009 Volume 65 Issue 4 Pages 357-363
Published: March 10, 2009
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThornthwaite's climatic division system based on potential evapotranspiration (PE) and climatic water balance is well known. In this study, a climatic division of the rice-producing district in the Chubu region of Japan is proposed based on Thornthwaite's system. The PE and climatic water balance were calculated using 1-km mesh units on mesh climate charts derived from data acquired by the AMeDAS system. From published sources, data was gathered on the rice yields of all the municipalities in the Chubu region from 1979 to 2001, and related to the PE and climatic water balance data calculated using Thornthwaite's method. It emerged that the rice yields were optimal for an August mean PE of 140 mm and enhanced in dry conditions. Moreover, to make the climatic division, a cluster analysis was performed for each municipality using PE, the moisture index (degree of humidity derived from a water balance calculation), and rice yield data. Consequently, the Chubu region was divided into 5 categories: Wetland, Nagano basin, Mountain, Hokuriku plain, and Tokai plain. This division expresses the basic climatic features that are important to rice production. Our climatic division differs from others in that our division is based both on climatic elements, which are an origin, and on rice yields, which are agricultural outputs.View full abstractDownload PDF (1026K) -
Yoshinobu HARAZONO, Kazuhiro CHIKAMOTO, Shunsaku KIKKAWA, Toru IWATA, ...2009 Volume 65 Issue 4 Pages 365-374
Published: March 10, 2009
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSNDVI (Normalized Difference of Vegetation Index) was employed to estimate the carbon budget remotely with satellite data. However, NDVI has some difficulties in application to agricultural crops, boreal forest, and tundra ecosystems. We proposed a new vegetation index GR (greenery ratio) to detect the vegetation change remotely, and we applied it to estimate CO2 budget of Japanese rice paddy with MODIS satellite data. GR was ratio of green (G) to the trichromatic visible bands (R+G+B) of MODIS, and an empirical GR-CO2 budget model was developed as functions of MODIS-data and observed micrometeorology and fluxes at the rice paddy of Mase-site. The daily PAR (photosynthetically active radiation) was also estimated by MODIS. The parameterized model provided good performance to estimate daily magnitudes and seasonal trends of GPP (gross primary productivity), however, RE (ecosystem respiration) showed a little under-estimation, especially differed in late growing season. In contradiction to the observed CO2 budget, the estimated budgets were 2% greater of GPP and 5% less of RE and 9% greater of NEE (net ecosystem exchange). The large discrepancy in NEE was owing to the poor estimation of RE after drainage. Further study to improve RE estimation was needed.View full abstractDownload PDF (945K) -
Tomoyoshi HIROTA, Masato FUKUMOTO2009 Volume 65 Issue 4 Pages 375-386
Published: March 10, 2009
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSSurface moisture availability is the most important parameter for estimating evaporation from bare soil using the bulk transfer method. In this study, we developed a simple method for the estimation and parameterization of surface moisture availability over a period ranging from 10 days to several months on bare soil using only routine meteorological data without using sensible and latent heat flux and soil moisture data. If the daily mean soil temperature is observed with other routine meteorological data of daily values (air temperature, solar radiation, precipitation, wind speed, humidity, etc.), surface moisture availability can be estimated by using a simple soil temperature model without using the sensible and latent heat flux observation data. The simple soil temperature model is composed of the heat balance equation at the ground surface, bulk transfer method and modified version of the force-restore model for estimating daily mean soil temperature. The estimation period of surface moisture availability ranges from 10 days to several months according to precipitation conditions that reflect soil wetness. The antecedent precipitation index (API) is an effective indicator by which the soil wetness condition can be judged without using soil moisture. This enables classification of proper estimation periods of surface moisture availability. The surface moisture availability is estimated by minimizing the sum of the squares of the residual between the observed value of the daily mean soil temperature and the calculated value under the estimation period as classified by API. Furthermore, for the purpose of estimating daily mean soil temperature and cumulative evaporation on bare soil using only routine meteorological data, we propose that the surface moisture availability can be parameterized using the ratio of precipitation to potential evaporation with estimation periods ranging from 10 days to several months.View full abstractDownload PDF (874K)
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