CO 2, ADVANCES IN EAR TH SCIENCE , ) CO 2 ; :Q945 CO 2 CH 4. (eddy covariance technique) CO 2 H 2 O

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1 ADVANCES IN EAR TH SCIENCE Vol. 19 No. 4 Aug.,2004 : (2004) / Ξ CO 2, 3, (, ) :, CO 2, ( FL UXN ET) / CO 2, CO 2,, / CO 2,, : ; CO 2 ;CO 2 ; ; :Q945 :A CO 2 CH 4 [9,10 ],, CO 2, CO 2 (, ) [1 ] [11,12 ] (eddy covariance technique) CO 2 / [2 ], ( CO 2 ), CO 2 CO 2 [3,4 ], CO 2, CO 2 [4 7 ] [13, / CO 2 ] ( FL UXN ET) 100, [8 CO 2 H 2 O ] [14 ] Ξ : ; : : ( : KZCX12SW201201A). : (19752),,,,. E2mail : ac. cn : (19592),,,, 1 E2mail : ac. cn

2 4 : / CO 2 659, CO 2 : [15 ] F = w s g w c (4),, s CO 2, (CERN), w, w 0, (ChinaFL UX), CO 2 FL UXN ET,,, CO 2, / CO 2, WPL [18 ] 1, CO CO 2 0,,, CO 2 CO 2 CO 2 : [16 ] : 5 c + 5 u i c - D 52 N e = ( w c c ) r + Z r 5 c 5 t 5 x i 5 x 2 0 = S (1) 5 t d z (5) i c CO 2, t, u i x i ( i = 1,2,3), D CO 2 [9,10,19 ], FL UXN ET, S CO 2, (5) [3,6,19 ] CO 2, 1. 3, 1 [17 ], [16 ] 3 :, (5 c / 5 t = 0) ; ( S = 0) ;, 5 u i c / 5 x i = 0 D5 2 c / 5 x 2 i = 0 ( i = 1,2), (1) : 5 w c - D 52 c 5 z 5 z 2 = 0 (2) w = u 3, z = x 3, (5) CO 2,, z [17 ], (2), ( w = w + w, c = c + c ) : F 0 = D ( 5 1 c 5 z ) 0 = ( w c ) z = F z (3) Fig. 1 Schematic of the main processes and terms, which F 0 CO 2 have to be considered when assessing the validity of flux, F z z CO 2 measurement made by an eddy covariance system 1. 2,,, /

3 660 19,, ;,, ;,,,, 4 [14, ] :, ;,, [26 ] ; ; [16 ] :, ( ), ( ) ( ) [1,16 ] 2 ;, %, [19 ], 2. 3 [20 ] [27,28 ] [20 24 ] x, 0 (, Goulden [25 ] (low2 ), 0 ( pass filtering method) Massman [22,23 ] ), (analytical method), 0, [14 ] [19 ( ] ), [20 25 ] [19, ], 5 % 10 % [20 ] 0,, 0 [10 ] 2. 2 Paw [13 ] Wilczak [28 ], ( Planar fit) CO 2, ( CO 2 0 [28 ), CO 2 ],, CO 2, 4 % [19 ], [14 ] :,, CO 2 ;

4 4 : / CO , CO 2 10 % 40 % Lee [10 ] CO 2, [14 ], CO 2 [16 ], 2. 4 CO, 2,, 0, CO 2 [19 ],,,, 3. 2,, (1) :,, [30,31 ], 3. 3,,, (2) : [22,23 ] [32,33 ],, CO 2 [14 ], [34 ] [10,40 ] (3) :,,,, [35 ] [36 ] 3. 4, / CO 2 CO 2, / CO 2 ( ), / [37 ] CO 2 (4) :,, 0 ( ) CO 2 0, [1 ] Wofsy [3 ] Goulden [1 ] CO 2, u 3, ( References) : [38,39 ], 3 [1 ] Goulden M L, Munger J W, Fan S2M, et al. Measurements of

5 carbon sequestration by long2term eddy covariance : Methods and a critical evaluation of accuracy [ J ]. Global Change Biology, 1996,2 : [ 2 ] Baldocchi D D, Hicks B B, Meyers T P. Measuring biosphere2at2 mosphere exchange of biologically related gases with micrometeo2 rological methods[j ]. Ecology, 1988,69 : [ 3 ] Wofsy S C, Goulden M L, Munger J W, et al. Net exchange of CO 2 in a midlatitude forest [J ]. Science,1993,260 : [4 ] Berbigier P, Bonnefond J M, Mellmann P. CO 2 and water vapor fluxes for 2 years above Euroflux forest site [ J ]. A gricult ural and Forest Meteorology, 2001, 108 : [ 5 ] Grace J, Lloyd J, Mclntyre J, et al. Carbon dioxide uptake by an undisturbed tropical rain in southwest Amazonia, [J ]. Science,1995,270 : [ 6 ] Black T A, den Hartog G, Neumann H H, et al. Annual cycles of water vapor and carbon dioxide fluxes in and above a boreal as2 pen forest [J ]. Global Change Biology, 1996,2 : [ 7 ] Goulden M L, Munger J W, Fan S2M, et al. 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6 4 : / CO [ 34 ] Hu X, Lee X, Steven D E, et al. A numerical study of noctural wavelike motion in forest [ J ]. Boundary2L ayer Meteorology, 2002,102 : [ 35 ] Wyngaard J, Kosovic B. Similarity of structure2fuction parame2 ters in the stratified boundary2layer[j ]. Boundary2L ayer Meteo2 rology, 1994,71 : [ 36 ] Mahrt L. Momentum balance of gravity flow[j ]. Journal of the A t mospheric Sciences, 1982,39 : [ 37 ] Sun J, Desjardins R, Mahrt L, et al. Transport of carbon diox2 ide, water vapour, and ozone by turbulence and local circulations [J ]. Journal of Geophysical Reaearch, 1998, 103 : [38 ] Black T A, Chen W J, Barr A G, et al. Increased carbon se2 questration by s boreal deciduous forest in years with a warm spring[ J ]. Geophysical Research Letters, 2000, 27 : [ 39 ] Aubinet M, Grelle A, Ibrom A, et al. Estimates of the annual net carbon and water exchange of forest : The EUROFLUX methodology[j ]. A dvances in Ecological Research, 2000,30 : [ 40 ] Grace J, Malhi Y, Lloyd J, et al1the use of eddy covariance to infer the carbon dioxide uptake of Brazilian rain forest [J ]. Glob2 al Change Biology, 1996,2 : UNCERTAINTIES IN LONG2TERM STUDIES OF NET ECOSYSTEM CO 2 EXCHANGE WITH THE ATMOSPHERE BASED ON EDDY COVARIANCE TECHNIQUE WEN Xue2fa, YU Gui2rui, SUN Xiao2min ( Instit ute of Geographical Sciences and N at ural Resources Research, CA S, Beijing , China) Abstract : Direct and continuous long2term measurement s of canopy2scale carbon dioxide fluxes have only recently become possible due to t he improvement of eddy covariance technique. Now it has been widely used in long2term observation studies of CO 2 uptake and release by terrestrial ecosystem. A global network of microme2 teorological tower sites ( FL UXN ET) uses eddy covariance methods to measure the exchanges of CO 2 between terrestrial ecosystem and atmosphere, but a majority of the site are not in ideal conditions, which can not fully meet the basic assumption of eddy covariance technique for the CO 2 flux measurement, thus resulting in some uncertainties in t he flux measurement. Chinese Terrest rial Ecosystem Flux Observational Research Network ( ChinaFL U X) has been established, which relies on Chinese Ecosystem Research Network ( CERN) and applies eddy covariance of microclimatology as main research met hod to st udy fluxes of carbon dioxide between t he vege2 tation and soil of typical ecosystem and atmosphere. The objective of this paper is to introduce the basic assump2 tion of the eddy covariance technique, the basic theoretical equations, the types and characteristics of errors in long2term measurement s and to elucidate emp hatically t he uncertainties in t he flux measurement due to p hysical limitation of instrumentation, two and three dimensional air flow motion effects, methods of data processing, and underestimation of nighttime fluxes, etc. Where possible, t his paper makes recommendations concerning met hodologies and research priorities. Wit hout some understanding of and ability to compensate for t hese uncer2 tainties, cross2site comparisons and global scale synt hesis are difficult and uncertain at best. Thus, dada quality analysis and cont rol ( QA/ QC) and errors assessment s are necessary for cross2site comparisons and global scale synt hesis. Key words : Eddy covariance technique ; Net ecosystem CO 2 exchange ; CO 2 flux ; Non2ideal condition ; Un2 certainty1