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Abstract:
Nitrogen is one of the most important macronutrients for all organisms. It reaches the floodplain in the dissolved and particulate load of the Amazon River during floods and from the atmosphere as dry and wet deposition and via nitrogen fixation. Anthropogenic sources are negligible in most parts of the várzea. From a few studies on nitrogen fluxes in Amazonian environments there is some evidence that nitrogen can be a limiting factor for primary production in the várzea, at least in the aquatic phase (Forsberg 1984; Setaro and Melack 1984; Furch and Junk 1993). For more insight into the pathways of nitrogen input and output, nitrogen fluxes were measured in various ecotopes at Lago Camaleão. This lake belongs to the class of várzea lakes that are not hydrochemically affected by the terra firme, in contrast to Lago Calado, which is a dendritic várzea lake influenced by the runoff from the terra firme. Both lakes have been examined intensively during the last two decades for the nitrogen exchange between river and lake, the input by precipitation and nitrogen fixation, and the output by denitrification (Furch 1982, 1984b; Melack and Fisher 1988; Junk and Piedade 1993c; Lesack 1993; Lesack and Melack 1995; Kern et al. 1996). The study at Lago Camaleão was focused on the gaseous nitrogen exchange between atmosphere, hydrosphere, and pedosphere, and provided new results for nitrogen fixation and denitrification in the Amazon floodplain.