Estimates suggest that 43% and 63% of the 300,000km² of Amazon floodplain area and of the 1.17 x 10(14) g C yr-1 of primary productivity, respectively, are attributed to the aquatic vegetation. These numbers change according to the flood pulse. For instance, in the dry season terrestrial herbaceous plants generally occupy areas that have lost their aquatic vegetation. The areal extent and productivity of these ecosystems are essential to construe even an initial understanding of the biogeochemistry of the Amazon. Field measurements were combined with synthetic aperture radar images to evaluate the use of RADARSAT and JERS-1 for estimating biomass changes and mapping of aquatic vegetation, and subsequently estimating the net primary productivity of aquatic vegetation in the lower Amazon. The combination of C and L bands provides the best correlation (r =0.82) and an intermediate saturation point (620 gm-2) for estimating above water biomass of aquatic vegetation. A combination of RADARSAT and JERS-1 images from each water period was classified using a region growing algorithm, and yielded accuracy higher than 95% for the seasonal vegetated areas of the floodplain. The combination of the seasonal mapped area of aquatic vegetation with the statistical SAR-algorithm for estimating above water biomass and the percentage of below water biomass yielded a total annual NPP of 1.9x10(12) g C yr-1 (±28%) for aquatic vegetation.
Radar satellite imagery; primary production; aquatic vegetation; várzea
