The influence of sediment composition on isotopic variation of CH4 in the eastern Amazonian streams
Jos� Mauro
Sousa
Moura, CENA/USP, jmauro@esalq.usp.br
(Presenting)
Christopher
Sargent
Martens, University of North Carolina, cmartens@email.unc.edu
Marcelo
Zacharias
Moreira, CENA/USP, mmoreira@cena.usp.br
Howard
P
Mendlovitz, University of North Carolina, mendlovitz@unc.edu
Risonaldo
Leal
Lima, Projeto LBAECO, risonaldo@lbaeco.com.br
Irene Cibelle
Gon�alves
Sampaio, Projeto LBAECO, cibelle@lbaeco.com.br
The isotopic composition of methane varies seasonally and spatially between wetland environments as a result of changes in microbial production and oxidation mechanisms. We have been measuring the isotopic composition of CH4 in Maica and Jamaraqua, two different streams in the eastern Amazonia, since Aug/2000. The mean isotopic values found on the methane were in a range of -77.97� to -46.14�, with a significant difference on the delta13C between the seasons, mainly during the end of dry season (Oct � Jan), when the difference reaches maximum values of -25�. In Maica, the delta13C-CH4 varied from -40.72� to -69.68�, at Jamaraqua the values varied from -89.05� to -54.03�.
In order to explain the differences we will look for heavier delta13C values in Maica sediments as results from deposition of grasses which are enriched in 13C and we also intend to analyze the composition of organic matter present in the vegetation that grows in these streams and describe the process by which it is decomposed.
We took cores sediment(~35cm) in the open water at each site. The cores were sub-sampled every 5 cm and all samples were dried and processed to be analyzed in a Finnigan Delta Plus mass spectrometer. Samples of litter and vegetation were else collected. Simultaneously, we measured the water temperature and its dissolved oxygen (DO) level. We found little difference in the water temperature, 31.2 �C and 27.3 �C at Maica and Jamaraqua, respectively. There was an inverse correlation between the DO against deep in water column at Maica. This trend wasn�t observed at Jamaraqua. The water content in the sediment samples of Maica was 27.43%, which is 2x smaller than of Jamaraqua.