QUALIDADE FÍSICO-QUÍMICA E HIDROBIOLÓGICA DA ÁGUA NO RESERVATÓRIO DO RIBEIRÃO JOÃO LEITE EM GOIÂNIA/GO

Abstract

João Leite Stream consists on an approximate area of 765 km ², in which its main watercourse has a length of 135 km. The chosen study area was the reservoir implanted in João Leite Stream, situated in the upstream of Goiania, along with Balm hill. The sampling points were: P1 (situated in the upstream of Terezópolis reservoir), P2 (reservoir), P3 (situated in the downstream of bus reservoir) and P4 (catchment - SANEAGO). This study aimed at data attainment to evaluate the changes in the reservoir, as well as at correlating the results of hydrobiological and abiotic components through statistical analysis. The variables studied were: climatic (air temperature and precipitation), physicochemical (water temperature, transparency, pH, energy conductivity, turbidity, dissolved oxygen, organic matter, total phosphorus and nitrate) and hydrobiological (chlorophyll a, pheophytin a and phytoplankton density). During the study, the amount of rainfall recorded was 1529 mm. In the reservoir, the temperature varied from 26.3°C to 28.2ºC in the dry season, and from 22.6°C to 26.8°C during the rains, exceeding the amounts recorded for the other locations in the same period. The reservoir lentic waters environment favored the retention of cleaner waters, with low turbidity amounts compared to other sampling locations. The lowest concentrations of DO saturation were observed in P2. The highest concentrations of oxygen were detected in March/2010 at points P1, P2 and P3. The organic matter at all sampling locations was the highest from January/10 to April/10 and the lowest amounts recorded were in January/11 at all locations (0.4 mg / L to 0.5 mg / L). The t test applied to the data, demonstrated the existence of significant differences between the sampling locations, except for the variables in phosphate, organic matter and cyanobacteria that suggested amounts closer to the records of the sampled locations. Mostly, the parameters analyzed were classified among the minimum required by CONAMA 357/2005. Predominantly, it was at the reservoir that occurred the largest temporal and seasonal variations, demonstrating the particular characteristics of the lentic environments in relation to lotic environments. The richness of the total Chlorophyceae exceeded 34%, followed by the Cyanophyceae, with over 18% at all locations, whereas all other classes contributed less than 5% of the total rate of richness. In P2 the richness of the rate recorded was higher when compared with the other locations. During March 2010, it was recorded the first occurrence of flowering, being the dominant species Cylindrospermopsis raciborskii, a cyanobacterium with toxicity showed in other studies. The distance of 10.42 kilometers traveled by the water to the point of catchment may explain the low density of Cylindrospermopsis raciborskii in catchment (P4), in the same period in which flowering was occurring in P2. The rating of P2 regarding the degree of hypertrophy ranged from oligotrophic to mesotrophic using chlorophyll a parameter during the sampling period.