Diurnal behaviour of Rio Grande Reservoir (Billings Complex) 23º 52’ S í 46º 31’ W: Riacho Grande, SP, Brazil

Abstract

The diurnal behavior of the reservoir was analyzed during the warm and rainy period (October-March) and cold and dry (April-September). During diurnal cycles (24 hours) the temperature, color, oxygen saturation, electrical conductivity, pH, alkalinity, calcium, silica, ammonia variation were analyzed. Instability as well as a circulation and internal watercourse were produced by changes on the speed and route wind, mistiness presence and rain fall, in spite of the seasonal cycle phases. These events reaffirm the daily cycle's importance over the dynarnics and metabolism of the tropical aquatic ecosystems. The variability of the daily behavior was also established by the seasonal variations and by the water trophy grade modification, as the time goes by. Corroborating previous researches, the thermal stratification does not occur, under the diurnal heating leveI. The cold dry seasons (June/1981, July/1985 and April/1986) showed low gradient and instable environment poorly favorable to develop, even temporarily, thermal and chemical stratifications. Besides circulation, the warm is subject to temporary events as superficial, bottom or middle water column night currents. In July, the solar heating reached the bottom, 10.5 m. The warm rainy season (February/1982