Methane emissions from lakes and floodplains in Pantanal, Brazil

To evaluate the tropical wetlands contribution to the methane (CH4) burden better, field campaigns were performed during 2004 and 2005 near the Miranda River, in five sites inside the Brazilian Pantanal region. The CH4 fluxes were determined using the static chamber technique. Environmental variables that may affect CH4 emissions, as the water depth, the water and air temperatures were also measured. The overall average of the 320 individual CH4 flux measurements made between March/2004 and March/2005 was 142±314 mg CH4 m−2 d−1, which is a value near the ones observed in other tropical flooded regions. About 47% of the fluxes measurements presented nonlinear increases in the chamber concentrations, which were assumed to be linked to CH4 losses through bubbles. The bubble flux represented about 90% of the total CH4 losses in the measurements and ranged from 1 to 2187 mg CH4 m−2 d−1 with an average of 292±410 mg CH4 m−2 d−1 (median: 153 mg CH4 m−2 d−1). The diffusive flux ranged from 1 to 124 mg CH4 m−2 d−1, with an average of 10±17 mg CH4 m−2 d−1 (median: 5 mg CH4 m−2 d−1). The fluxes from lakes were smaller than those observed in the floodplains, where the flooding was more dependent on the seasonal cycle. The diffusive flux showed a slight, but not statistically significant seasonal variation, following the seasonal variation of the flooding of the Pantanal region. A rough estimative of the total annual CH4 emission shows that the contribution of the Pantanal is about 3.3 Tg CH4 yr−1, which represents about 3.3% of the total CH4 emissions estimated to be originated in wetlands ecosystems. It may be a conservative estimate, which may present a large interannual variation, since it was obtained during one of the lowest flood of the Pantanal in recent years.