Plâncton e produção primária em sistemas aquáticos da bacia da Amazônia Central ^*

Summary

Three aquatic environments of the Central Amazon Basin were sampled during the low water phase: Rio Solimões (Amazon), rio Negro, and lago Janauaca. In the nutrient-rich rio Solimões, primary productivity averaged 0.063 gC/m^2.d, hut net growth of phytoplankton is impossible because of the depth, poor light penetration, and cur rent-driven turbulence. In the chemically-poor Rio Negro, a daily cycle of CO₂ was caused by photosynthetic demand in surface waters, and primary productivity averaged 0.19 gC/m².d. In Lago Janauaca, a lake bordering the Solimões, nutrients were low in concentration and intensively recycled; large phytoplankton populations produced up to 3.5 gC/m².d (average = 2.2). The ten meter annual change in water level of the Amazon river provides and drains most of the water in lakes along the river. During storage of river water in the lakes the particulates settle and the dissolved inorganic nutrients are converted to organic forms by intense phytoplankton growth. These lakes may be a major source of organic matter for the river ecosystem.