Shohei Murayama

Gross primary production and net ecosystem exchange of a cool-temperate deciduous forest estimated by the eddy covariance method

Abstract An eddy covariance measurement system was installed to measure long-term turbulent fluxes of heat, water vapor, and CO2 over a cool-temperate deciduous forest in the central part of Japan. Previous to a long-term measurement, a comparison of flux measurements using open- and closed-path type infrared gas analyzers was conducted for CO2 and water vapor. The closure of the energy budget over the forest was also examined to test the validity of the flux measurements. Using a whole year data from 25 July 1998 to 24 July 1999, the relation between the night-time air temperature and the night-time CO2 flux over the forest (ecosystem respiration) was investigated. The results suggest that the night-time CO2 flux was significantly influenced by the vertical air temperature gradient over the canopy. The night-time CO2 flux increased exponentially with the temperature when the stability was nearly neutral, while it was insensitive to the temperature under stable conditions. Daily values of the net ecosystem exchange (NEE) and the gross primary production (GPP) of the forest were estimated, and they were parameterized as a function of the air temperature and the absorbed photosynthetic active radiation (APAR). The results show a clear seasonal change in GPP caused by changes in the light-use efficiency and the maximum rate of carbon fixation of the canopy with LAI. The estimated NEE based on the parameterization agrees well with the observed NEE during the observational period.

High concentrations of black carbon over middle latitudes in the North Pacific Ocean

During 4 years of research cruises over the central Pacific Ocean from 1993 through 1996, a region of extremely high concentration of black carbon aerosol (>150 ng C m -3 ) was routinely observed in the middle-latitude zone (27°-48°N) along the 175°E line of longitude (near the International Date Line). In the cruises along the latitude lines of 30°N and 35°N, a strong west-to-east gradient of black carbon was also observed. Backward trajectory analysis shows that the air parcels containing high concentration of black carbon had passed over the Asian continent during the previous 10 days. The concentration of black carbon was relatively well correlated with non-sea-salt (nss.) SO 4 2- in the aerosols. This indicates that the high concentration of black carbon observed originated from the combustion of sulfur-containing materials, presumably coal, on the Asian continent. Mass size distributions of the black carbon exhibit a mode at 0.5-0.7 μm in aerodynamic diameter, which is unexpectedly large and coincides with the mode of SO 4 2- aerosol. This suggests that black carbon and SO 4 2- were internally mixed, and additional growth in particle size occurred through cloud processing. This study shows that anthropogenic aerosols are transported over greater distances than previously indicated by global dispersion models. The trajectory analysis indicates that this is due to the high-altitude transport of materials which reduces the possibility of encountering precipitating clouds; the aerosols are lofted over the continent initially, transported at relatively high altitudes over the ocean, and then brought to the surface in the central part of the North Pacific Ocean by mesoscale weather systems. The measured mixing ratio of black carbon/nss.SO 4 2- and the state of the mixture (internal) suggest that the aerosols transported from Asia over the North Pacific Ocean have a low single-scattering albedo.

Temporal variations of atmospheric CO2 concentration in a temperate deciduous forest in central Japan

In order to examine the temporal variation of the atmospheric CO2 concentration in a temperate deciduous forest, and its relationship with meteorological conditions, continuous measurements of CO2 and meteorological parameters have been made since 1993 on a tower at Takayama in the central part of Japan. In addition to an average secular increase in atmospheric CO2 of 1.8 ppm yr−1, diurnal variation with a maximum during the night-time to early morning and a minimum in the afternoon is observed from late spring to early fall; the diurnal cycle is not so clearly observed in the remaining seasons of the year. A concentration difference between above and below the canopy, and its diurnal variation, can also be seen clearly in summer. Daily mean concentration data show a prominent seasonal cycle. The maximum and the minimum of the seasonal cycle occur in April and from mid August to mid September, respectively. Day-to-day changes in the diurnal cycle of CO2 are highly dependent on the day-to-day variations in meteorological conditions. However, CO2 variations on longer time scales (>10 d) appear to be linearly related to changes in respiration. At Takayama, variations in the 10-d standard deviation of daily mean CO2 data and 10-d averaged respiration show distinct relationships with soil temperature during spring and fall seasons. In spring, respiration has a stronger exponential dependence on soil temperature than in fall. Interestingly, in summer when soil temperature becomes greater than about 15 °C, biological respiration becomes more variable and independent of the soil temperature. Thus, at the Takayama site, the Q10 relationship is seasonally dependent, and does not represent well the biological respiration process when the soil temperature rises above 15 °C.

Examination of model‐estimated ecosystem respiration using flux measurements from a cool‐temperate deciduous broad‐leaved forest in central Japan

Reducing uncertainty in the emission of carbon dioxide (CO2) from plants and microbes is critically important in determining carbon budgets. We examined properties of net ecosystem CO2 exchange (NEE) derived from a processbased model that simulates an ecosystem carbon cycle, focusing on nighttime flux determined from ecosystem respiration and soil efflux. The model simulated autotrophic and heterotrophic respiration using semi-empirical ecophysiological parameterizations. In a cool-temperate deciduous broad-leaved forest in central Japan, simulation results from 1998 to 2005 were compared with measurement of the forest made using eddy-covariance and chamber methods. The model estimated annual ecosystem respiration as 1397 g Cm-2 yr-1, of which 67% was from the soil surface, with a clear seasonal cycle. Compared to flux observations, the model appropriately captured daytime NEE, but produced substantial differences from the observed nighttime NEE. The differences were evident under stable atmospheric conditions (at low friction velocity), implying a problem with the observations. With regard to soil-surface CO2 efflux (soil respiration), the model estimation was consistent with chamber observations, except in winter periods with thick snow cover. We discuss whether the model is applicable for estimating ecosystem respiration rates, and what is required to improve the predictability of the model.

Aircraft Observation of CO2, CO, O3 and H2 over the North Pacific during the PACE‐7 Campaign

Aircraft observation under the Pacific Atmospheric Chemistry Experiment (PACE) program was performed from February 13 to 21, 2000 to examine in detail the distributions of CO2 in the free troposphere between 5 and 11 km. Continuous measurements of CO2mixing ratios were made using an on-board measuring system over the northern North Pacific between Nagoya, Japan and Anchorage, Alaska, and the western North Pacific between Nagoya and Saipan. Other trace gases, such as CO and O3, were also observed using continuous measuring systems at the same time. CO2 over the northern Pacific (35¼N and higher) showed highly variable mixing ratios, ranging from 374 ppm in the upper troposphere to 366 ppm in the lowermost stratosphere. This highly variable distribution of CO2 was quite similar to that of CO, but the relationship between CO2 and O3 showed a strong negative correlation. These results indicated that the exchange process between the stratosphere and the troposphere significantly influences the large CO2variation. On the other hand, the CO2 over the western North Pacific to the south of Japan showed no significant variation in the upper troposphere at 11 km but a relatively larger variability at 5 km. The CO2 enhancement at lower altitudes coincided with the CO elevation due to the intrusion of a polluted air mass. Trajectory analysis indicated that the Asian continental outflow perturbed the CO2 distributions over the western Pacific. Very low mixing ratios of O3 of less than 20 ppb were distributed in the latitude band of 15–30¼N at 11 km, reflecting the effects of transport from the equatorial region.

Dataset of CarboEastAsia and uncertainties in the CO2 budget evaluation caused by different data processing

The datasets of net ecosystem CO2 exchange (NEE) were acquired from 21 forests, 3 grasslands, and 3 croplands in the eastern part of Asia based on the eddy covariance measurements of the international joint program, CarboEastAsia. The program was conducted by three networks in Asia, ChinaFLUX, JapanFlux, and KoFlux, to quantify, synthesize, and understand the carbon budget of the eastern part of Asia. An intercomparison was conducted for NEE estimated by three gap-filling procedures adopted by ChinaFLUX, JapanFlux, and KoFlux to test the range of uncertainty in the estimation of NEE. The overall comparison indicated good agreement among the procedures in the seasonal patterns of NEE, although a bias was observed in dormant seasons depending on the different criteria of data screening. Based on the gap-filled datasets, the magnitude and seasonality of the carbon budget were compared among various biome types, phenology, and stress conditions throughout Asia. The annual values of gross primary production and ecosystem respiration were almost proportional to the annual air temperature. Forest management, including clear-cutting, plantation, and artificial drainage, was significant and obviously affected the annual carbon uptake within the forests. Agricultural management resulted in notable seasonal patterns in the crop sites. The dataset obtained from a variety of biome types would be an essential source of knowledge for ecosystem science as well as a valuable validation dataset for modeling and remote sensing to upscale the carbon budget estimations in Asia.

Interannual variation in the atmospheric CO2 growth rate: Role of atmospheric transport in the Northern Hemisphere

In this study, we examine the role of the atmospheric circulation variability in reproducing the interannual variability of the observed atmospheric CO 2 growth rate in the Northern Hemisphere. Results from a series of numerical experiments performed with a three-dimensional atmospheric transport model driven by European Centre for Medium-Range Weather Forecasts winds from 1979 to 1999 and forced at the bottom with an annually balanced, seasonally distributed (i.e., no interannual variations) terrestrial CO 2 flux calculated by the Camegie-Ames-Stanford Approach (CASA) ecosystem model show changes in atmospheric CO 2 growth rates that are significantly correlated with those observed at many stations located in midlatitude to high-latitude regions in the Northern Hemisphere. Particularly, we find that the North Atlantic Oscillation (NAO) and the Pacific-North America (PNA) indices are correlated with the observed growth rates at Alert and Point Barrow. This suggests that where there is large variability in atmospheric circulation, it needs to be taken into account when changes in observed atmospheric CO 2 at various stations are to be understood in terms of changes in CO 2 sources. In numerical experiments in which biospheric CO 2 fluxes from the CASA model are perturbed in a known arbitrary way, we find that the Northern Hemisphere observational sites do not appear to be sensitive to changes in the CO 2 seasonal flux cycle except at close proximity and thus would not be useful for inferring a Northern Hemisphere biospheric sink. Results suggest sensitivity of the locations of some monitoring stations, with respect to atmospheric circulation patterns, in detecting major changes in the biospheric CO 2 flux from certain regions in the Northern Hemisphere.

O 2 :CO 2 exchange ratios observed in a cool temperate deciduous forest ecosystem of central Japan

Detailed observations of O2:CO2 exchange ratios were conducted in a cool temperate deciduous forest located in central Japan. The exchange ratios of soil respiration and net assimilation were found to be 1.11±0.01 and 1.02±0.03 from soil chamber and branch bag measurements, respectively. Continuous measurements of the atmospheric O2/N2 ratio and the CO2 concentration, made inside the canopy during a summer season, indicated that the average exchange ratio was lower in the daytime (0.87±0.02) than in the nighttime (1.03±0.02) with a daily mean value of 0.94±0.01. The observed average daytime and nighttime exchange ratios were nearly consistent with the corresponding values obtained from a one-box canopy O2/CO2 budget model simulation of net turbulent O2 and CO2 fluxes between the atmosphere and the forest ecosystem. Our results suggest that the daily mean exchange ratios of the net turbulent O2 and CO2 fluxes depend sensitively on the forest ecosystem processes.

Quantification of emission estimates of CO 2 , CH 4 and CO for East Asia derived from atmospheric radon-222 measurements over the western North Pacific

ABSTRACT Emissions of CO, CH4 and CO2 in East Asia were estimated using the atmospheric concentration of 222Rn measured at Minamitorishima (MNM) and Yonagunijima (YON) with a high-precision 222Rn measuring system. The 222Rn measurements showed a distinct seasonal variation, as well as enhanced 222Rn (ERN) events associated with high-frequency synoptic variations. The enhancements of CO, CH4 and CO2 coincided with the ERN events at MNM and YON. The enhancement ratios ΔCH4/ΔRn, ΔCO2/ΔRn and ΔCO/ΔRn calculated for the ERN events and corrected for the radioactive decay of 222Rn during the transport were used to estimate the emissions of CO, CH4 and CO2 by multiplying a constant 222Rn exhalation rate of 1.0 atom cm−2 s−1 and the associated catchment area estimated by a 3D transport model. By modifying the categorisation of the sources, the 222Rn-derived emissions of CO2 and CH4 were found to be in agreement with the published emission databases. As for the CO emission, results of our study were consistent with the REAS CO emission database but showed that the EDGAR database underestimates the CO emission over East Asia by about 44%. It is demonstrated that the 222Rn tracer method used in this study could provide a useful and independent tool to verify the trace gas emissions in East Asia.

Observation of O2:CO2 exchange ratio for net turbulent fluxes and its application to forest carbon cycles

An average O2:CO2 exchange ratio for net turbulent O2 and CO2 fluxes in a cool temperate deciduous forest in central Japan was obtained based on an aerodynamic method using continuous measurements of atmospheric O2/N2 ratio and CO2 concentration. The average daily mean O2:CO2 exchange ratio was 0.86 during summer, 2013, a value significantly lower than the 1.1 used as a globally averaged terrestrial biospheric O2:CO2 exchange ratio in a CO2 budget analysis. Using the value of 0.86, along with the O2:CO2 exchange ratio of 1.11 for the ecosystem respiration (RE) and 1.00 for the gross primary production (GPP), the net ecosystem production (NEP) measured with an eddy covariance method was separated into GPP and RE using a one-box canopy O2/CO2 budget model. The estimated average daily-mean GPP and RE values were consistent, within estimation errors, with those estimated from an empirical function of air temperature; the RE values were also comparable to the soil CO2 efflux observed using an open-flow soil chamber method. These results suggest that the simultaneous observation of O2 and CO2 concentrations in a forest has potential as a new tool to evaluate the forest CO2 budget.