Kenzo Kitamura

Energy balance above a boreal coniferous forest: a difference in turbulent fluxes between snow-covered and snow-free canopies

To evaluate the interactive effects of snow and forest on turbulent fluxes between the forest surface and the atmosphere, the surface energy balance above a forest was measured by the eddy correlation method during the winter of 1995–1996. The forest was a young coniferous plantation comprised of spruce and fir. The study site, in Sapporo, northern Japan, had heavy and frequent snowfalls and the canopy was frequently covered with snow during the study period. A comparison of the observed energy balance above the forest for periods with and without a snow-covered canopy and an analysis using a single-source model gave the following results: during daytime when the canopy was covered with snow, the upward latent heat flux was large, about 80% of the net radiation, and the sensible heat flux was positive but small. On the other hand, during daytime when the canopy was dry and free from snow, the sensible heat flux was dominant and the latent heat flux was minor, about 10% of the net radiation. To explain this difference of energy partition between snow-covered and snow-free conditions, not only differences in temperature but also differences in the bulk transfer coefficients for latent heat flux were necessary in the model. Therefore, the high evaporation rate from the snow-covered canopy can be attributed largely to the high moisture availability of the canopy surface. Evaporation from the forest during a 60-day period in midwinter was estimated on a daily basis as net radiation minus sensible heat flux. The overall average evaporation during the 60-day period was 0·6 mm day−1, which is larger than that from open snow fields. Copyright

The effect of canopy-snow on the energy balance above a coniferous forest

To evaluate an interactive effect of snow on energy exchange between the forest and atmosphere, the energy balance above a forest was measured continuously between February and April of 1997 in the Hitsujigaoka Experimental Forest, Sapporo, northern Japan. The forest was a dense. 23-year-old, coniferous plantation. The study site had frequent snowfalls and the canopy was frequently covered with snow during the study period. Snow-cover on the canopy was monitored daily using a photo-camera mounted above the canopy, and the fraction of the snow-covered area on the canopy was determined as an index of the canopy-snow condition. Turbulent energy fluxes above the canopy were measured using the eddy and band-pass covariance method. The diurnal courses of the measurements showed that turbulent fluxes were sensitive to the snow on the canopy. Latent heat fluxes dominated above the snow-covered canopy and sensible heat flux prevailed above the snowfree canopy. The effect of the canopy-snow on turbulent energy exchange was examined using the evaporative efficiency for the canopy-layer in an energy balance model composed of two sources of vapor fluxes. The evaporative efficiency changed dynamically according to the canopy-snow condition in the short terms and could be positively related to the extension of the snow-covered area on the canopy. A quantitative relationship was empirically determined between the evaporative efficiency and the fraction of the canopy-snow area. The snowcover season in the study site can be classified into the following two types of turbulent flux composition: (1) in mid-winter, when the canopy was snow-covered, latent heat flux dominated and the Bowen ratio was positive and low; (2) during the snowmelt season, sensible heat flux from the dry canopy prevailed and the Bowen ratio was much larger than in mid-winter.

Continuous estimation of winter carbon dioxide efflux from the snow surface in a deciduous broadleaf forest

The objective of our study was to estimate CO 2 efflux from the snow surface in a deciduous broadleaf forest throughout the duration of winter on the basis of a continuous measurement of CO 2 concentration at the soil-snow interfaces. Continuous CO 2 efflux was estimated from the CO 2 concentration gradient across the snow cover. We examined the accuracy of the values obtained from the CO 2 concentration gradient across the snow cover by comparing them with the values observed by the closed static chambers. Although each couple of the values from both methods had relatively large differences, the amounts of the values were consistent. The average CO 2 efflux ± 1 SD was 1.4 ± 1.0 gCO 2 m -2 d -1 throughout the duration of winter. The estimated CO 2 efflux in winter is considered to be reasonable, compared with the value obtained by a relationship between soil temperature and soil respiration in the same forest and with the values reported in forest ecosystems in middle latitudes. Our value is, however, smaller than the value obtained by the eddy covariance technique at a tower in the same forest. We attempted to estimate the hypothetical CO 2 efflux, minimizing the impact of pressure pumping. The average CO 2 efflux was estimated at 2.0 gCO 2 m -2 d -1 .

Suspended sediment discharge in subsurface flow from the head hollow of a small forested watershed, northern Japan

Surface flow and suspended sediment discharge from the head hollow of the Jozankei Experimental Watershed in Hokkaido, northern Japan, were measured to clarify the implications of subsurface hydrology for soil movement. Subsurface discharges during the extremely large storms of 1993 to 1994 were measured in a V-notch weir installed at a natural spring near the bottom of the head hollow, and shallow groundwater levels were observed in the wells excavated in the hollow. Sediment samples whose particle size range from 0·001 to 0·1 mm were manually and automatically collected at 15 to 60 min intervals, by use of 1 or 21 polyethylene bottles. Maximum concentration and flux of suspended sediment during the storms preceded the peak discharge of subsurface flow by several hours. Neither the changes in concentration (mg l−1) nor flux (mg s−1) of suspended sediment coincided with those in subsurface discharge (l s−1). Furthermore, sediment concentration was poorly correlated with the rate of change in subsurface discharge (l s−2) during the rising limb of the hydrograph. Suspended sediment flux during the acceleratory limb, however, was closely correlated with the rate of change in subsurface discharge. The relationship between suspended sediment flux and rate of change in subsurface discharge were in inverse proportion to initial subsurface discharge before the storm runoff and they represented rare seasonal variation. Subsurface hydraulic erosion and transport of suspended sediment resulting from changes in rate of change in subsurface discharge actively occur during the acceleratory rising limb of the hydrograph. Accordingly, subsurface hydraulic erosion during the acceleratory rising limb of the hydrograph can be physically understood by analysing suspended sediment flux associated with rate of change in subsurface discharge and initial subsurface discharge.

New data-driven estimation of terrestrial CO2 fluxes in Asia using a standardized database of eddy covariance measurements, remote sensing data, and support vector regression

The lack of a standardized database of eddy covariance observations has been an obstacle for data-driven estimation of terrestrial CO2 fluxes in Asia. In this study, we developed such a standardized database using 54 sites from various databases by applying consistent postprocessing for data-driven estimation of gross primary productivity (GPP) and net ecosystem CO2 exchange (NEE). Data-driven estimation was conducted by using a machine learning algorithm: support vector regression (SVR), with remote sensing data for 2000 to 2015 period. Site-level evaluation of the estimated CO2 fluxes shows that although performance varies in different vegetation and climate classifications, GPP and NEE at 8days are reproduced (e.g., r2=0.73 and 0.42 for 8day GPP and NEE). Evaluation of spatially estimated GPP with Global Ozone Monitoring Experiment 2 sensor-based Sun-induced chlorophyll fluorescence shows that monthly GPP variations at subcontinental scale were reproduced by SVR (r2=1.00, 0.94, 0.91, and 0.89 for Siberia, East Asia, South Asia, and Southeast Asia, respectively). Evaluation of spatially estimated NEE with net atmosphere-land CO2 fluxes of Greenhouse Gases Observing Satellite (GOSAT) Level 4A product shows that monthly variations of these data were consistent in Siberia and East Asia; meanwhile, inconsistency was found in South Asia and Southeast Asia. Furthermore, differences in the land CO2 fluxes from SVR-NEE and GOSAT Level 4A were partially explained by accounting for the differences in the definition of land CO2 fluxes. These data-driven estimates can provide a new opportunity to assess CO2 fluxes in Asia and evaluate and constrain terrestrial ecosystem models. (Less)

Subsurface discharge and suspended sediment yield interactions in a valley head of a small forested watershed

Sediment hield caused by hydraulic agents is believed to be one of the most important geomorphic processes in headwaters. Observations of shallow groundwater levels and suspended sediment yield were used to develop relationships between subsurface discharge and sediment movement in a valley head of a small forested watershed in Hokkaido, northern Japan. Drainage capacity of the soil was closely correlated with subsurface soil movement in the valley head. An increase in subsurface discharge associated with an increase in the drainage capacity of the soil depended heavily on the discharge of fine-grained particles originating from the soil. Clogging created by the fine-grained particles in the soil caused a decrease in subsurface discharge associated with the decline in the drainage capacity. In addition, neither the drainage capacity of the soil nor subsurface discharge changed because of the sediment unavailability within the subsurface flow system. Accordingly, as shown by the changes in the drainage capacity of the sedimentary soil, subsurface discharge and suspended sediment yield from the valley head showed strong interactions.

Evaporation of snow intercepted by a todo-fir forest (I) Water balance measurements

In spring 1972, serious needle cast damage caused by a hitherto unknown species of Lophodermium occurred on Japanese red pine seedlings in many nurseries in Iwate Prefecture, northern Honshu, Japan. From 1972 to 1974, 6 to 7 million 2-year-old seedlings were affected by this fungus. The causal fungus was named Lophodermium iwatense Sakuyama after etiological and biological studies. The first symptoms of the disease are yellow spots on the current year s needles which usually appear in November. The affected needles turn brown in April of the following year, and begin to drop in May to June. Spermogonia and spermatia of the fungus are formed on the diseased needles from May to June. Mature apothecia and ascospores of the fungus are abundant on the diseased needles from July to September. In the field, ascospores are discharged from early July to early October, with a vigorous dispersal period from late July to early September. No black zone lines are usually observed on diseased needles, but brown zone lines are formed frequently. L. iwatense showed strong pathogenicity to Japanese red pine seedlings in inoculation tests using ascospores. Ascospores germinate betweem 5 and 30~ with an optimum at 20~ The mycelia of the fungus grow between 10 and 25~ with an optimum at 20-25~ Three other Lophodermium species, L. conigenum, L. nitens and L. staleyi were recorded for the first time in Japan. A satisfactory method of disease control is to spray Maneb as 1/500 dilution at the rate of 300 ml/m 2, four times at 2-weeks intervals from late July to early September.