[1] A comparative view of inundation patterns in the large floodplains of South America was derived by analysis of the 37-GHz polarization difference observed by the Scanning Multichannel Microwave Radiometer (SMMR; Nimbus-7 satellite, 1979Nimbus-7 satellite, -1987 Interannual variability in the maximum extent of inundation is greatest in the Pantanal, followed by Roraima and Bananal. Based on these extended records, the longterm mean inundation areas (in km 2 and including rivers and lakes) were as follows: mainstem Amazon 46,920, Moxos 29,460, Bananal 13,110, Orinoco 34,700, Roraima 3,480, and Pantanal 34,880. This information is fundamental for hydrological, biogeochemical, and ecological studies of these floodplain-river systems and will improve estimates of methane and other trace gas emissions to the atmosphere from these vast wetlands.
Stable carbon and nitrogen isotope ratios in autotrophs, aquatic invertebrates and fishes from the Orinoco River floodplain of Venezuela reveal that microalgae, including both phytoplankton and epiphytic (attached) forms, are predominant energy sources for many aquatic animals, even though aquatic vascular plants are much more abundant. Floating mats of the grass Paspalum repens and the water hyacinth Eichhornia spp. harbor particularly high densities of aquatic animals, but isotopic evidence indicates that few species are dependent on organic carbon originating from these plants. The stable isotopic evidence for the trophic importance of algae contradicts traditional interpretations of food webs in freshwater wetlands, which are generally thought to be based largely on detritus originating from vascular plants.
Abstract. This study examines dissolved 02, CO2 and CH4 in waters of the Pantanal, a vast savanna floodplain in Brazil. Measurementsare presented for 540 samples from throughout the region, ranging from areas of sheet flooding to sluggish marsh streams to the major rivers of the region. Dissolved 02 is often strongly depleted, particularly in waters filled with emergent vascular plants, which are the most extensive aquatic environment of the region. Median Or concentrations were 35 PM for vegetated waters, 116 PM for the Paraguay River, 95 PM for tributary rivers, and 165 ,uM for open lakes (atmospheric equilibrium, 230-290 PM). Airwater diffusive fluxes were calculated from dissolved gas concentrations for representative vegetated floodplain waters, based on data collected over the course of an annual cycle. These fluxes reveal about twice as much CO2 evasion as can be accounted for by invasion of 02 (overall means in nmol cm-= s-': 02 0.18, CO2 0.34, and CH4 0.017). Methanogenesis is estimated to account for ca. 20% of the total heterotrophic metabolism in the water column and sediments, with the remainder likely due mostly to aerobic respiration. Anaerobic respiration is limited by the low concentrations of alternate electron acceptors. We hypothesize that 02 transported through the stems of emergent plants is consumed in aerobic respiration by plant tissues or microorganisms, producing CO2 that preferentially dissolves into the water, and thus explaining most of the excess CO2 evasion. This hypothesis is supported by measurements of gases in submersed stems of emergent plants.
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