PowerPoint Presentation

Seasonal and Inter-Annual Variability in Net EcosystemCO2 Exchange at Six Forest Flux Sites in Japan

Y. Ohtani*1, Y. Yasuda*1, Y. Mizoguchi*1, T. Watanabe*1, Y. Nakai*2, K. Kitamura*2,

S. Suzuki *1, K. Yamanoi*2, T. Saito*3, T. Morisawa*3, Y. Kominami*4, T. Miyama*4,

Y. Goto*4, T. Shimizu*5 and K. Tamai*5

*1 Forestry and Forest Products Research Institute (FFPRI);

*2 Hokkaido Research Center, FFPRI; *3 Tohoku Research Center, FFPRI;

*4 Kansai Research Center, FFPRI; *5 Kyushu Research Center, FFPRI, Japan

LU-209 / ICDC7 Land Use and the Terrestrial Carbon Cycle / September 28, 2005

Contents:

• Sites, Measurements and Data Processing

• Seasonal Changes in Observed Net EcosystemProduction (NEP) and Meteorological Factors

• Inter-Annual Variation in NEP

• Concluding Remarks

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Observation Sites

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LU-209 / Seasonal and Inter-Annual Variability of NEP in Japan / Y.Ohtani et al.

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Deciduous forest

Coniferous forest

Mixed forest

Measurement

CO2 Flux:

SAT: DA-600-3T / KAIJO

(20cm span)

IRGA: Li-6262 / Li-Cor

(closed-path)

Low-pass filter (24Hz cut off)

5~10Hz Sampling,

Recorded in MO

Tubing: 30~50m (6mm, teflon)

Air sampling rate:

Approx. 10Lmin-1

Water vapor removed

CO2 Storage Change:

IRGA: Li-6262 / Li-Cor

5 Levels below SAT

CO2 flux measurement system usingclosed-path gas analyzer

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LU-209 / Seasonal and Inter-Annual Variability of NEP in Japan / Y.Ohtani et al.

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LU-209 / Seasonal and Inter-Annual Variability of NEP in Japan / Y.Ohtani et al.

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Data Processing

Calculation of Fc: Eddy covariance method (every 30 min)

Lateral wind and vapor effects (Kimal et al, 1968) ; Wind rotation

(McMillen,1988) ; WPL correction (Webb et al, 1980)

Compensation of CO2 delay ; Correction of CO2 flux dumping

NEE = Fc + Sc

Quality Control: Visual inspection for raw data

QC for raw data (Vickers & Mahrt, 1997)

u* selection for Fc

Parameterization for Gap-Filling:

Semi-empirical parameterization (30 min)

Nighttime Re: Exponential to Ta or Ts

Re = a Q10 (Ta/10)

Daytime: Ag = NEP + Re

LU-209 / Seasonal and Inter-Annual Variability of NEP in Japan / Y.Ohtani et al.

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Observed NEP and Estimated Ag and Re

Observed NEP and estimated gross assimilation (Ag) and ecosystemrespiration (Re). Ag and Re are calculated by the parameterization used forgap-filling at every 30 minutes. Daily sums are plotted.

LU-209 / Seasonal and Inter-Annual Variability of NEP in Japan / Y.Ohtani et al.

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NEP and Meteorological Factors

Observed NEP (2002) indicated with air temperature, short wave radiationand precipitation (averaged over 5 days).

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Soil: andosol

LU-209 / Seasonal and Inter-Annual Variability of NEP in Japan / Y.Ohtani et al.

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Monthly NEP and Its Inter-Annual variations

Observed monthly NEP for 4 years indicated with air temperature, short waveradiation and precipitation.

LU-209 / Seasonal and Inter-Annual Variability of NEP in Japan / Y.Ohtani et al.

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Annual NEP and Its Inter-Annual variations

Annual NEP, annual mean air temperature and annual mean of daily shortwave radiation. Red and blue background colors indicate the maximum andminimum NEP among the years.

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Our results

ranged:

NEE (gC m-2 y-1)

Deciduous (NEE)

Coniferous (NEE)

Mixed (NEE)

Ronald (1998)

Added to Ronald (1998)

Latitude (North)

LU-209 / Seasonal and Inter-Annual Variability of NEP in Japan / Y.Ohtani et al.

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Observed Annual NEE to Latitude

LU-209 / Seasonal and Inter-Annual Variability of NEP in Japan / Y.Ohtani et al.

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Concluding Remarks

Tower flux measurement of CO2 was conducted in six forest sites in Japan.

In the seasonal change, the maximum NEP was about 1.5 ~ 2 times largerin the deciduous sites, although the growing period was about 2 ~ 2.5 timeslonger in coniferous sites.

The monthly NEP in the coniferous sites had inter-annual variationthroughout the season, but the variation was only appeared from April toOctober in the deciduous sites.

In the coniferous forests, the balance of assimilation and respirationinduced by seasonal changes in solar radiation and air temperature seemedto be an important factor.

In the deciduous broadleaved forest, solar radiation and the duration of thegrowing season are important factors with regards to annual NEP.

The annual NEP had no clear relationships to annual mean Ta and Sd.

NEP was obtained in six forest sites from 33 °to 43 °N, ranged from 250to 650 gCm-2y-1 .