Detection of carbon dioxide efflux from the rivers in the atmosphere.
Joe
Berry, Carnegie Institution, Dept of Global Ecology, joeberry@stanford.edu
(Presenting)
Jean
Pierre
Ometto, CENA, jpometto@cena.usp.br
Jim
Ehleringer, Univ. of Utah, Dept of Biology, jim@biology.utah.edu
Jon
Wells, LiCor Inc., jwells@licor.com
Evasion of CO2 from supersaturated surface waters of rivers and flooded forests is thought to be a substantial source of CO2 that needs to be accounted for in constructing a carbon budget of the Amazon Basin. We hypothesized that CO2 evading from the rivers should carry a different isotopic label than CO2 from surrounding forests and that this should be detectable in the nocturnal boundary layer. In May, 2003 we chartered six flights with a light aircraft near Santarem. These flights occurred just before sunset – as the surface atmosphere becomes stable and just after dawn - before convection begins to dissipate the nocturnal boundary layer of the previous night. Continuous measurements of CO2 concentration, potential temperature, water vapor mixing ratio, atmospheric pressure and gps location were collected with a modified LiCor 6400 photosynthesis system. In addition, flask samples of dried air were taken for laboratory analysis of CO2 concentration and isotopes - employing a new automated technology. Good agreement was obtained between flask measured CO2 concentrations and those measured by the LiCor 6400. Both systems were referenced to a CMDL calibrated tank. The flights sampled air from transects at an elevation of approximately 150 m above surface over areas selected to have long fetches in the prevailing wind direction over river or upland forest. Each flight concluded with a sounding to 3000 m. CO2 accumulated in the nocturnal boundary layer both over the river and land. However, the concentrations were substantially higher over land. This observation could be attributed to spreading of air containing respired CO2 from the forests over the rivers during the night. However, the oxygen isotopes of CO2 collected over the rivers show that a substantial portion of the CO2 present in the nocturnal boundary layer in the morning above the river evaded from the river.
Submetido por Joseph A Berry em 17-MAR-2004
Tema Científico do LBA: CD (Armazenamento e Trocas de Carbono)