Radon fluxes in tropical forest ecosystems of Brazilian Amazonia: night-time CO2 net ecosystem exchange derived from radon and eddy covariance methods |
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| Authors: | Christopher S Martens Thomas J Shay† Howard P Mendlovitz Daniel M Matross‡ Scott R Saleska‡ Steven C Wofsy‡ W Stephen Woodward Mary C Menton §¶ José M S De Moura¶&#; Patrick M Crill Osvaldo L L De Moraes†† Risonaldo L Lima¶ |
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| Institution: | Department of Marine Sciences, CB-3300, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3300, USA,; Carolina Environmental Program, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA; Department of Earth and Planetary Sciences, Division of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA,; Department of Plant Sciences, Oxford University, UK,; ProjetoLBA-Ecologia, Rua 24 de Outubro, Santarém, Pará, Brazil,; CENA/USP, Piracicaba SP 13416-000, Brazil,; Complex Systems Research Center, University of New Hampshire, Durham, NH 03824-3525, USA,; Dept de Fisica, Universidade Federal de Santa Maria, Santa Maria RS 97119.900, Brazil |
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| Abstract: | Radon‐222 (Rn‐222) is used as a transport tracer of forest canopy–atmosphere CO2 exchange in an old‐growth, tropical rain forest site near km 67 of the Tapajós National Forest, Pará, Brazil. Initial results, from month‐long periods at the end of the wet season (June–July) and the end of the dry season (November–December) in 2001, demonstrate the potential of new Rn measurement instruments and methods to quantify mass transport processes between forest canopies and the atmosphere. Gas exchange rates yield mean canopy air residence times ranging from minutes during turbulent daytime hours to greater than 12 h during calm nights. Rn is an effective tracer for net ecosystem exchange of CO2 (CO2 NEE) during calm, night‐time hours when eddy covariance‐based NEE measurements are less certain because of low atmospheric turbulence. Rn‐derived night‐time CO2 NEE (9.00±0.99 μmol m?2 s?1 in the wet season, 6.39±0.59 in the dry season) was significantly higher than raw uncorrected, eddy covariance‐derived CO2 NEE (5.96±0.51 wet season, 5.57±0.53 dry season), but agrees with corrected eddy covariance results (8.65±1.07 wet season, 6.56±0.73 dry season) derived by filtering out lower NEE values obtained during calm periods using independent meteorological criteria. The Rn CO2 results suggest that uncorrected eddy covariance values underestimate night‐time CO2 loss at this site. If generalizable to other sites, these observations indicate that previous reports of strong net CO2 uptake in Amazonian terra firme forest may be overestimated. |
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| Keywords: | Amazon terra firme forest canopy gas exchange CO2 net ecosystem exchange (NEE) eddy covariance global carbon budget Radon-222 |
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