Author(s): Rosangela Sampaio Reis; William Severi; Evaldo Luiz Gaeta Espindola; Newton Oliveira Carvalho
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Keywords: Sediments; Sao Francisco River-Brasil; Limnological characteristics
Abstract: Some limnological characteristics of a reservoir built for power generation in the semiarid region of Northeastern Brazil were analyzed quarterly, from September 1999 to December2000. Sampling stations were distributed about the reservoir, within the inflow canal, the area near the dam, and the recesses on the west side. Water samples were collected at three depths in each station (surface, midpoint, and bottom), and the following variables determined: total suspended solid concentration, temperature, p H, electrical conductivity, dissolved oxygen in water, Secchi transparency, total alkalinity, total hardness, chloride, ammonia, nitrogen, phosphorus, orthophosphate, and chlorophyll-a. Sediment traps were placed at 70% of the depth in the station near the dam and left there for at least 24 hours in December 1999, June 2000, and December 2000. Considering all the surveys, the range of variation in mean values along the vertical column was: 0.13 to 7.49 mg/l–total suspended solid; 24.2 to 29.1 0C–water temperature; 5.84 to 9.63 mg/l–dissolved oxygen; 5.5 to 8.59–pH; 52 to 106.9 S/cm–electrical conductivity; 0.8 to 8.0 m–Secchi transparency; 24.8 to 41.6 mg/L and 9.57 to 33.3 mg/l–total alkalinity and hardness, respectively; 0to 25.7 g/l–orthophosphate; 0.22 to 5.99 g/l–ammonia; 0.12 to 0.85. mg/l–nitrogen; 11.6 to 22.8mg/l–chloride, 13.6 to 68.0 g/l–total phosphorus, and 2.3 to 47.4 g/l–chlorophyll-a. Being the sixth in a cascade of 7 reservoirs built along the largest wholly Brazilian river, the surveyed reservoir had low values for suspended load, mainly because of sediment retention in the reservoirs upstream. A significant increase in the sedimentation rates of tripton was seen in the rainy season. The other parameters analyzed showed no annoxia at the bottom, thermal homogeneity along the water column and high levels of transparency. The variation observed is due to the proximity to the city of Paulo Afonso, with the contribution of organic waste (illegal household sewage).
Year: 2002