Pollution in a lowland river system.: A case study:: The Reconquista River (Buenos Aires, Argentina)

The Reconquista river is a lowland watercourse; about three million people and several thousands of industries are settled in its flood plain. It can be considered as one of the most polluted rivers of Argentina. The present work is an attempt to describe the quality of the surface water through 16 physicochemical variables measured monthly in five sites (S-1 to S-5) during 1994. Univariate and multivariate analyses of data showed a clear difference of S-1 and S-2 respect to S-4 and S-5 for ammonium, ortophosphate, pH, hardness, chloride, phenols, BOD, COD, and DO values. S-3 appears to be a transition site. DO content showed a significant negative regression respect to the distance from the mouth. In the multivariate analyses between seasons the concentration of phenols appeared as an important feature. However it can be considered that seasonal variations were difficult to explain because of the river is the receptor of both regular and intermitent pollution pulses. It was concluded that the deterioration of this water body was progressive downriver, the contribution of the Moron creek in S-4 determined a sharp adverse change in the physicochemical conditions. In the two downstream sampling stations (S-4 and S-5) the values were far from natural conditions.