Cambio puntual de la calidad de agua en la laguna Chascomús durante la inundación 2001-2002: “efecto Moisés”

Abstract

Chascomús pond was affected between June-2001 and September-2002 by two periods of flood events (more than 8 m IGM reference) that had two maximum peaks of nearly 9 m. Such events were studied weekly in surface samples taken in three stations: centre and the zones with influence of the tributaries Vitel (affluent) and Arroyo Girado (effluent). The supply of water promoted a dilution that made the salinity to decrease to one third of the mean value of 1,570 mg/l obtained during 1999-2000. In March-2002 it was registered the maximum value of precipitation (538 mm) that caused the beginning of the second flood period. On March 18 differences were detected between the centre with the other two stations of parameters like salinity (222.5 with respect to 324.9 and 304.1 mg/l), specific conductivity (0.38; 0.55 and 0.56 mS/cm), pH (7.71; 7.94 and 8.00) and agar plate count (31,200; 7,260 and 6,600 UCF/ml). These differences were not detected in the next sampling. The phenomena is tried to explain on the basis of the runoff (physical hypothesis) and by the influence of the groundwater (chemical hypothesis). Because of the occasional separation into different quality of waters such phenomena was called “Moises effect”.