摘要 :
Lake-atmosphere CO_2 flux was directly measured above a small, woodland lake using the eddy covariance technique and compared with fluxes deduced from changes in measured lake-water CO_2 storage and with flux predictions from boun...
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Lake-atmosphere CO_2 flux was directly measured above a small, woodland lake using the eddy covariance technique and compared with fluxes deduced from changes in measured lake-water CO_2 storage and with flux predictions from boundary-layer and surface-renewal models. Over a 3-yr period, lake-atmosphere exchanges of CO_2 were measured over 5 weeks in spring, summer, and fall. Observed springtime CO_2 efflux was large (2.3-2.7 mu mol m~2 s~1) immediately after lake-thaw. That efflux decreased exponentially with time to less than 0.2 mu mol m~2 s~1 within 2 weeks. Substantial interannual variability was found in the magnitudes of springtime efflux, surface water CO_2 concentrations, lake CO_2 storage, and meteorological conditions. Summertime measurements show a weak diunial trend with a small average downward flux (-0.17 mu mol m~2 s~1) to the lake's surface, while late fall flux was trendless and smaller (-0.0021 mu mol m~2 s~1). Large springtime efflux afforded an opportunity to malce direct measurement of lake-atmosphere fluxes well above the detection limits of eddy covariance instruments facilitating the testing of different gas flux methodologies and airwater gas-transfer models. Although there was an overall agreement in fluxes determined by eddy covariance and those calculated from lake-water storage change in CO_2, agreement was inconsistent between eddy covariance flux measurements and fluxes predicted by boundary- layer and surface-renewal models. Comparison of measured and modeled transfer velocities for CO_2, along with measured and modeled cumulative CO_2 flux,
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