Pilot Experiments on Air-Water Exchange of Carbon Dioxide in the Amazon Basin Simone Alin – University of Washington Scott Miller – University of California Irvine Alex Krusche – CENA, Universidade de São Paulo Jeff Richey – University of Washington Helber Freitas – Universidade de São Paulo

How much CO 2 is evaded from the rivers of the Amazon Basin? pCO 2 -> Outgassing JFMAMJJASOND pCO 2 (x 10 3  atm) Jt Jr Sol Ic Md Pr Ng Jp atm JFMAMJJASON D CO 2 Evasion (Tg C mo -1 ) T (>100m) S (<100 m) MF MC % 1.77 x 10 6 km 2 Inundation 1.2 ± 0.3 Mg C ha -1 y -1 or 0.5 Gt C y -1 for the whole Amazon Basin Richey et al., 2002

Estimating Air-Water CO 2 Exchange Floating “domes” –measure increase in CO 2 in enclosed space –smaller footprint –more easily deployed in various environments Eddy covariance –simultaneous measurements of air turbulence and CO 2 concentration –integrates flux measurements over larger footprint

Floating Dome

Scales of Sampling

Eddy Covariance Equipment

   4 3 2

CO 2 Accumulation in the Dome Time (minutes) CO 2 (ppm) Reserva Ducke

Evasion Rates vs. River pCO 2 pCO 2 (water) (ppm) CO 2 evasion (umol m -2 s -1 ) Low wind (fan: 2.0 m/s) r 2 =

Evasion Rates vs. River pCO 2 High wind (fan: 6.5 m/s) CO 2 evasion (umol m -2 s -1 ) r 2 = pCO 2 (water) (ppm)

Gas Transfer Velocity F CO2 = k s (pCO 2(water) – pCO 2 (air) ) where: k = gas transfer or piston velocity (cm hr -1 ) s = solubility of CO 2

Wind speed experiment – Rio Negro Wind (fan) speed (m s -1 ) k = wind speed r 2 = Wind speed <3 m/s >3 m/s Gas transfer velocity, k (cm hr -1 ) k values used by Richey et al., 2002

Wind speed experiment – Rio Solimões Gas transfer velocity, k (cm hr -1 ) k = wind speed r 2 = Wind (fan) speed (m s -1 ) Wind speed <3 m/s >3 m/s k values used by Richey et al., 2002

Eddy Covariance Calculations F CO2 = c΄w΄ where: c = atmospheric CO 2 mixing ratio w = vertical wind speed ΄ = fluctuation about the mean

Tapajós-Amazônas Data F CO2 estimate: 1.7 umol m -2 s minutes - upwind transect across river system boundary

Conclusions Eddy covariance looks promising for measuring CO 2 fluxes over freshwater systems with large pCO 2 gradients Previous estimates of CO 2 outgassing from the Amazon Basin (0.5 Gt C y -1 ) may be conservative, based on the underestimation of gas transfer velocity, pCO 2 in Rio Negro, etc.

Acknowledgments Technical/design assistance: Patrick Crill, John Kumph, Randy Fabro Funding: NASA-LBA and NSF Logistics: LBA staff in Santarém, Palmas, and Manaus Field and lab assistance: Anthony Aufdenkampe, Erin Ellis, Cleber Salimon, Chris Doughty, Hillândia Brandão da Cunha, Tania Pimentel, Daniel Amaral, Dariusz Kurzatkowski, Rita da Mata Ribeiro, Erich Collicchio, Fernando Frickmann, Walter, Luis, Jean Ometto, Michael Goulden

S. Denning (RAMS): Tapajós River Evasion Signal ~ 5  mol m -2 s -1

Next Phase Improvements to the floating dome: –ADV (Acoustic Doppler Velocimeter) to measure micro-scale, water-side turbulence –Anemometers –Thermistors

CO 2 evasion rate vs. pH pH CO 2 evasion (umol m -2 s -1 ) evasion = pH r 2 = 0.621

Wind Speed and Temperature Effects on Gas Transfer Velocity Water temperature (°C) Gas transfer velocity (k,cm hr -1 ) Wind speed (m s -1 ) Wanninkhof (1992), Cole et al. (1998)

Evasion Rates vs. River pCO 2 pCO 2 (ppm) CO 2 evasion (umol m -2 s -1 ) Low wind

Evasion Rates vs. River pCO 2 pCO 2 (ppm) High wind CO 2 evasion (umol m -2 s -1 )