Dam reservoir eutrophication:: A simplified technique for a fast diagnosis of environmental degradation

The typologies of three lakes located in northeast Brazil were studied during dry (summer) and wet (winter) seasons to choose a reduced number of parameters for quick and low cost monitoring of sanitary quality and trophic level of lentic waters in semiarid tropic regions. A total of 14 parameters, commonly used for quality characterization (pH, temperature. turbidity dissolved oxygen, alkalinity, chloride, BOD5, ammonia, nitrate, total phosphorus, orthophosphate, fecal coliforms, fecal streptococci and chlorophyll "a") were measured in samples collected monthly during two years at 30 cm depth from litoral and limnetic zones. Principal components analysis showed that water typology was defined by 9 variables grouped in two principal factors, related with algae biomass and with sanitary state/eutrophication level. Redundant parameters were discarded from those sets highly correlated with each factor and other original variable, preserving those with easier and economic techniques. Reducing variable numbers from 14 to 7 (fecal colifonns, turbidity, orthophosphate, nitrate, dissolved oxygen, BOD5, pH) and remaking the principal components analysis neither altered the definition of both principal factors nor reduced information about internal ecosystem dynamics. (C) 1998 Elsevier Science Ltd. All rights reserved.