Limnological Characterization of Gravataí River, Rio Grande do Sul State, Brazil.
SALOMONI1, S.E.; ROCHA2, O.& LEITE3, E. H., S.
1 Pos-graduate Program in Ecology and Natural Resources. Federal University of São Carlos. PO Box 676, Via Washington Luis km 235, CEP: 13.565-905, São Carlos, SP, Brazil.
2 Department of Ecology and Evolutionary Biology. Federal University of São Carlos. PO Box 676, Via Washington Luis km 235, CEP: 13.565-905, São Carlos, SP, Brazil.
3 State Foundation of Environmental Protection (FEPAM) of Rio Grande do Sul. Carlos Chagas 55. CEP: 90030-020, Porto Alegre, RS, Brazil.
ABSTRACT: A limnological study of Gravataí River, RS, Brazil (29° 45' - 30° 12'S and 50° 27'- 51° 12'W) was carried out in order to characterize the spatial and temporal changes of physical, chemical, climatic and microbiological variables along its course attempting to explain its functioning as a lotic system, in terms of current theories. A set of meteorological, hydrological, physical, chemical and microbiological variables were monitored each month at six selected locations along the Gravataí River, between September 2000 and August 2002. The variables analyzed were: water temperature, pH, transparency, conductivity, OD, BOD-5, COD, total nitrogen, organic nitrogen, orthophosphate, total phosphorus, chloride and faecal coliforms. Air temperature, rainfall, and river discharge data were also recorded. The results showed that there is a continuum from the headwater to the middle course of the river, characterized by a gradual decrease in dissolved oxygen concentration and rising turbidity, nutrients, conductivity, chlorides, and biochemical oxygen demand. A discontinuity in the gradient, caused by the input of large amounts of organic matter was found, where many variables increased or decreased abruptly with changes of one order of magnitude or more, characterizing two distinct portions of Gravataí River: a better-preserved upper and middle portion conforming with the river continuum model, and the polluted lower portion, a discontinuity imposed by the heavy input of organic wastes. A comparison of the present limnological conditions in Gravataí River with information available from earlier years reveals that significant changes have occurred over the last decade, indicating an accelerated process of eutrophication.
Key-words: Gravataí River, river ecology, river pollution, eutrophication.
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