Variação espaço temporal da comunidade fitoplanctônica e de fatores ecológicos em um sistema lêntico de recente formação.

Abstract

This work analyzed the phytoplankton spatial and temporal composition and the physico-chemical dinamics to find organic pollution indicators and the trophic index of Sao Salvador dam and its main inffluent, the Sao Salvador river. The effect of dry and wet seasons was also analyzed. This aquatic ecosystem is located at Sape municipality ( 7 06 S; 35 14 5W) in the lower catchment area of Paraiba river at the geographical microregion of Agreste da Paraiba. This ecosystem receives natural and artificial pollution, as drainage of agricultural areas and sewage discharges Samples were taken bi-monthly (3 in the river and 7 in the reservoirs) from feb - jul/96 (rainy season) and sept - dec/96 (dry season) and analized for temperature, pH, electrical conductivity, dissolved oxygen, BOD5, ammonia, nitrate, kjeldahl nitrogen, soluble orthophophate, total phosphorous, sulphate,sulphide, alkalinity, hardness, chlorophyll a and phytoplankton diversity. In all sampling stations, values of temperature, pH, elecnical conductivity, alkalinity and hardness were homogeneous during all experimental period. Concentrations of sulphate, sulphide, BOD5 were low. However fluctuations of macronutrients of P and N were observed and associated to climatic conditions particularly during rainy season due to superficial run-off. Sao Salvador river algae diversity showed, in both season, predominance of Navicula spp (Bacillariophyta) and Oscillatoria spp (Cyanophyta). The phytoplankton disttibuition of Sao Salvador dam divided this ecosystem in three sections: one near the river entrance, where human activities such as agriculture, pastures and bathing, raised the values of nitrogen and phosphorous; Navicula spp and Synedra spp (Bacillariophyta) were predominant. The second zone was near the supply water collection, less disturbed with the predominance of Anabaena spp, Oscillatoria spp (Cyanophyta) and Melosira spp, Synedra spp (Bacillariophyta). The third region comprised the dam central region with almost no disturbance where Anabaena spp, Oscillatoria spp (Cyanophyta), Trachelomonas spp (Euglenophyta) and Melosira spp (Bacillariophyta) were predominant. Algae diversity was a good indicator for the ecological changes observed during this research. The trophic index of Carlson (1977) showed variations accordingly to the parameter considered and to climatic season. Sao Salvador dam was hipereutrophic during the rainy season due to the high phosphorous concentrations and eutrophic at dry season with the reduction of this nutrient. When chlorophyll "a" was used this aquatic ecosystem was mesotrophic.