Regional Emission Estimates

The methane emission estimates are derived from the average fluxes and information about the flooded area. In spite of many questions about the relative contribution of the different transport mechanisms and the influence of the environmental variables about the Pantanal methane emission, this estimate may be a good indicator of the importance of the region to the global methane budget.

Hamilton et al. (2002) made estimates of flooding in the Pantanal region considering different flooding patterns. They estimated that the maximum flooding area is about 130,920 km2, so that the Pantanal may represent the biggest flooding area in South America. From this area, about 3,120 km2 represent open waters, like rivers and lakes, which have a small variation in their area during the year. They also estimated 172 days as the floodplain hydroperiod, which is defined as the time with the floodplain inundated above 50% of its maximum inundation area. Thus, the Pantanal has also the longest flooding period in South America.

One first crude regional estimate was determined from the average of all fluxes (116.8 mg CH4 m-2 d-1) and the average flooded area computed for both years (2004 and 2005), using the relation presented by Hamilton et al. (2002). This was worked out to be an emission of 1.37 Tg CH4 y-1 for the whole Pantanal. Considering separately the diffusive and the ebullitive fluxes, the contributions are respectively 0.15 Tg CH4 y-1 and 1.26 Tg CH4 y-1, with an annual emission of 1.41 Tg CH4 y-1. As the fluxes showed differences when they were stratified between the lakes and the floodplains, and as the vegetation increases the diffusive fluxes in the floodplains, a new evaluation may be obtained by considering the areas for the two habitats separately. Using the Hamilton et al. (2002) formulation, the floodplains area was estimated as 28,441 km2, which leads to an emission of 1.95 Tg CH4 y-1 from this environment. The lakes, with an annual flooded area of 3,120 km2, caused an estimated methane emission of 0.25 Tg CH4 y-1. The total annual emission resulting from the sum of each component computed separately is 2.20 Tg CH4 y-1. A summary of these results is presented in Table 7.2.

For Amazonia, with measurements performed in different areas and flooding conditions, the estimates of the annual emission present a range from 2 to 21 TgCH4 y-1, which is a large range mainly due to the uncertain flooded area estimates (Bartlett et al. 1990). Based on many measurements performed in Amazonia and using remote sensing techniques, Melack et al. (2004) estimated the flooding area as 42,700 km2, so that the revised annual methane emission from the Amazon basin was 1.73 Tg CH4 y-1. These authors also made an estimate for the Pantanal using measurements performed in Amazonian environments with savanna-like vegetation, which resulted in a mean methane flux of 95.2 mg CH4 m2 d-1. This result is near the value obtained in this work (116.8 mg CH4 m2 d-1) and higher than that one obtained by Smith et al. (2002) for the floodplains of the Orinoco River region (41.6 mg CH4 m2 d-1). Melack et al. (2004) computed the flooded area using the long-term mean flooded area (34,800 km2) estimated from Paraguay River stage records measured at Porto Ladario (from 1900 to 1999) by Hamilton et al. (2002); so, the annual emission was estimated as 3.32 Tg CH4 y-1. The results obtained above show that although there are several questions to clarify about the methane emissions from the Pantanal, this region is as important as Amazonia for the atmospheric methane balance.

Table 7.2 Annual emission of methane for each Pantanal habitat, with diffusive and ebullitive components and total flux (Tg CH4 y-1)

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