A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

FOREST CANOPY-TROPOSPHERE CO 2 AND TRACE GAS EXCHANGERATES IN THE FLONA TAPAJOS, PARA, BRAZIL, DETERMINED BYRADON-222 CANOPY AND SOIL FLUX MEASUREMENTSC.S. Martens 1 , H.P. Mendlovitz 1 , T.J. Shay 1 , M.C. Menton 1 , J.M.S. Moura 1 , O.L.L.Moraes 2 , R.L. Lima 1 and P.M. Crill 31 University of North Carolina at Chapel Hill, 2 Universidade Federal de Santa Maria,3 University of New HampshirePrimary author address: Department of Marine Sciences, University of North Carolina,Chapel Hill, NC 27599-3300 USAEmail addresses: cmartens@email.unc.edu, Mendlovitz@unc.edu, tshay@email.unc.edu,Patrick_Crill@unh.edu, mary@tap.com.br, jmauro@tap.com.br, moraes@mail1.ufsm.br,ABSTRACTContinuous canopy air and soil-air flux measurements of radon-222 have beencombined to quantify canopy air exchange rate coefficients, eddy diffusivities, and CO 2plus trace gas fluxes with the troposphere in old growth and selectively logged forests inthe Amazonian terre firme forest and pasture sites near Santarém, Pará, Brazil. The radoncanopy air and soil flux measurements, when fully integrated with LBA-ECO tower eddycovariance flux, forest canopy gas inventory and soil gas flux studies led by other teamsincluding Keller et al, (TG-07), Goulden and Rocha (CD-04), and Wofsy et al., (CD-10)can provide quantification of gas production, consumption and net fluxes that isindependent of eddy covariance measurements. Arrays of custom designed flow-throughradon detectors have been deployed since April, 2000 at 65 meter tower sites at bothprimary forest (km 67) and selectively logged (km 83) sites in the Tapajos NationalForest. A solar powered array has been utilized at the km 77 pasture site to help quantifythe development of nocturnal and convective boundary layers in collaboration withFitzjarrald and Moraes (CD-03). The detectors can accurately resolve 0.01 pCi/l/m radonactivity gradients within the forest canopy using 15 minute counting intervals. Canopyand above-canopy air radon activities at up to ten tower elevations at both sites decreasesystematically with height above the soil surface and range from over 1.0 pCi/l (0.3 meterelevation) to less than 0.05 pCi/l (64 meter elevation). Diel radon activity variations inthe Tapajos forest canopy at both sites are characterized by dual maxima peaking nearapproximately 0900 and 1730 local time that occur respectively as a result of nocturnalstratification and late afternoon stratification during the early evening transition. Radoninventories within the lower 10m of the forest canopy typically range by over 200 percentover a diel cycle. Soil-air radon fluxes have been determined using portable radonfluxometers capable of repeated thirty-minute flux measurements on soil collars installedaround the tower sites. Changes in the canopy air radon inventory combined with radonsoil flux measurements have been utilized to determine forest canopy-troposphereexchange rates that are combined with CO 2 and other trace gas concentration data todetermine their net forest canopy-troposphere fluxes.