3.8
CO₂ BUDGET OF INLAND ARCTIC TUNDRA ECOSYSTEMS IN ALASKA, MICROMETEOROLOGICAL MEASUREMENTS AND EMPIRICAL MODEL EVALUATIONS

Recent chamber measurements showed net CO₂ sources of terrestrial tussock tundra during the growing season. The objectives of this study are to assess the temporal variance in CO₂ exchange and to provide good estimation of whole-ecosystem CO₂ budget in response to temporal variations in meteorology and phenology. At first, we summarize the measured net CO₂ flux at wet sedge tundra ecosystem. Then the ecosystem functions were examined by a tundra CO₂ budget model (TCBM) applying the measured net CO₂ flux and micrometeorological data. The parameters determined by TCBM were applied to the simulation model for Tundra Ecosystem CO₂ Exchange (SIMTEC) to estimate the CO₂ budget during whole growing periods in 1995 & 1996. Finally we assess annual CO₂ budget of Arctic tundra ecosystem under the present climate.

The measurements were carried out at wet sedge and moist tussock tundra in North Slope, Alaska from late May to early September in 1995 & 1996, and mid October in 1997. Water and energy fluxes were determined by the eddy covariance technique with an open path IRGA (E-009A, Advanet) and a 3D sonic anemometer (DA-600, Kaijo).

TCBM is consisted with three parts, in which the measured net CO₂ flux is the budget of the photosynthesis and the ecosystem respiration. The first is calculating potential CO₂ assimilation of the tundra ecosystem, the second is calculating photosynthesis suppression caused by unsuitable meteorological conditions, and the third is determination the ecosystem respiration. The potential CO₂ assimilation was defined as a rectangular hyperbola function of solar radiation. The parameters of TCBM were applied to SIMTEC.

The measured net CO₂ flux during the vegetative period showed strong sink (320 gCO₂ m-2) at wet sedge tundra and the ideal homogeneous vegetation (no water surface) accumulates 353 gCO₂ m-2 in 1995. The sum of efflux of sedge tundra during cold season was estimated 226-323 gCO₂ m-2, so yearly CO₂ budget ranged from 94 gCO₂ m-2 sink to 3 gCO₂ m-2 source in 1995, while that ranged 43-140 gCO₂ m-2 source for the moist tussock tundra. Net CO₂ fluxes at both sites in 1996 were strong sink than in 1995 because of low summer temperature and warm spring (earlier start of growing season), and the annual budgets were sink. The CO2CO₂ budget at Arctic tundra ecosystem is a consist of delicate balance among vegetation assimilation, ecosystem respiration and spatial distribution of vegetation. These are affected directly by temperature, thus the Arctic warming will change the CO2 budget of tundra to source. Although there are a vegetation adaptation to the climate change and are many differences in soil and vegetation types, further analysis should be needed to evaluate the land scale carbon budget of the Arctic tundra ecosystems.

The 23rd Conference on Agricultural and Forest Meteorology