The local scale system

Since the Japanese system started to provide data in March 1999, the missing data at the beginning of the year was filled using the empirical NEE-t function. During the growing period, the empirical NEE-PPFD function was used to patch the missing daytime data. Unfortunately, there were two months during 2000 when no data was measured at all due to data acquisition failure (June and July). During this period, the empirical NEE-PPFD and NEE-t relationships were used to fill data gaps.

Figure: Daily net CO exchange between the biosphere and the atmosphere as a function of time for the 3 m system during 1999 and 2000. The flat part is a consequence of the monthly average cycles used for data gap filling.

Figure shows the temporal variation of daily net CO exchange during 1999 and 2000 as a function of time. The figure is comparable with the measured net values of the 82 m system (fig. ).

Figure: Annual variation of carbon NEE, GPP and R for 1999 and 2000 measured by the local, 3 m system. Data are smoothed with boxcar average of 10 days for clarity. Solid line: carbon NEE: dashed line: R; dash dot line: GPP. Negative value indicate carbon uptake by the ecosystem.

Figure shows the temporal cycle of carbon NEE, R and GPP for the local, 3 m system. The most striking feature of the plot compared to fig. is the enhanced rates of photosynthesis and ecosystem respiration. Yearly cycles in 1999 (the only year when both measuring system was operative) are similar both in NEE, GPP and respiration. Maximum daily NEE sums were higher as measured by the 82 m system.

Other interesting feature is the negative NEE during November and December, 2000. This is caused by an unusual warm period which supported carbon sequestration by the small scale vegetation.

Finally, yearly sums of carbon NEE, GPP and R presented in table . There is a huge difference between carbon NEE calculated during 1999 and 2000. NEE measured in 1999 by the 82 m system and the 3 m system are very close. Since there are no more years available yet to compare yearly sums for the two systems, we may not conclude that the two systems measure the same NEE. Further data are needed to clarify the behaviour of the local scale during 2000.

Table: Annual sums of carbon NEE, GPP and R for 1999 and 2000 at 3 m.

	NEE [g C m year ]	GPP [g C m year ]	R [g C m year ]
1999	-86	-1555	1469
2000	-247	-1773	1526