Estimate of net primary productivity of aquatic vegetation of the Amazon floodplain using Radarsat and JERS-1

Synthetic aperture radar images, combined with field measurements, were used to estimate net primary productivity (NPP) of aquatic vegetation in the lower Amazon. Input data for a NPP model are (i) the total biomass of aquatic vegetation, determined by radar imagery and field measurements and (ii) the area occupied by aquatic vegetation, determined from radar imagery. After correction for monthly biomass losses, the NPP of one growth cycle of aquatic vegetation was calculated in the image domain. The total net primary productivity of Hymenachne amplexicaules, the dominant aquatic vegetation in the area, was on average 19 x 10(11) g C yr(-1) for the entire area. Spatially, lower values of produced organic carbon (< 900gCm(-2)yr(-1)) are confined to regions where the plants developed only in the beginning of the rising phase of the hydrological cycle. In general, values are higher (>5000 g Cm-2 yr(-1)) in areas closer to the Amazon River where the availability and influence of nutrient-rich water is greater.