Limnology of reservoirs in the Southeastern part of São Paulo State, Brazil. II Water circulation and stratification.

Abstract

On the tropical region from Atlantic Planalt, located between 22°40' - 24°20'S and 43°31' - 48°57'W and 83 - 2000 m of altitude, 17 reservoirs were studied. The seasonal cycle has a warm and rainy season (October-March) and another, cold and dry (April-September). The temperature and oxygen profiles measured at quarterly intervals (1979) at one station in each reservoir showed that the only one located up 860 m (Itapeva 2000 m) presented a temperature variation related to the altimetric differences. Most of the reservoirs showed polymictic behavior with different winter circulation. The shallower reservoirs (Itapeva, Batista, Riacho Grande, Itupararanga, Pedreira, São José and Rio das Pedras, maximum 25 m deep) presented circulation in May-September and the deeper ones (maximum 52 m) in June-July (Ponte Nova, Funil, Alecrim, Fumaça and França) or only in July (Juqueri and Serraria). As a consequence of the instable climatic conditions, many times the water circulation took the place of the summer stratification and was observed more frequently in the beginning of the hot and rainy season (November-December) and many times was a diurnal process (surface). It reached all the column in Ponte Nova, Itapeva and mainly in Parque Ecológico (maximum 5 m deep) reservoirs. The holomictic behaviour (all year circulation) was presented by Guarapiranga and Águas Claras.