Summary
Difficulties arise during limnological investigations on the floodplains of the Middle Amazon, the so-called várzea, when the concepts, terminology and methodology of classical standing water and flowing water systems are applied. The pronounced periodical water level fluctuations, in combination with large-scale alternations between aquatic and terrestrial phases, produce ecological conditions which correspond neither to lakes and rivers nor to swamps or temporary water bodies. A survey of the limnological and ecological literature shows a notable lack of studies on the land-water relationships, including those related to the terrestrial and aquatic phases characteristic of flood-plains. There are several reasons for this, including the great complexity of the floodplain system, and a certain overlap between limnology and terrestrial ecology which has led to a neglect by both. The ecological conditions of floodplains are described, using the várzea as an example, and the impact of the alternations between the land and water phases on fauna, flora and nutrient balance is discussed. Emphasis is given to the fact that floodplains are special ecsystems different from standing and flowing water bodies.