Evolution of Enterobbacterial Populations along the Aljezur Costal Stream as Correlated to the Occuring Physical-Chemical Characteristics of the Water

Abstract

Fecal coliforms and fecal enterococci are used as indicators of enteric pathogenic organisms in aquatic environments, including bathing waters. There, sewage effluents, agricultural runoff and wildlife are important sources of such enterobacteria. After being discharged into the water their numbers decrease with time due to sedimentation, dilution and death. While solar UV-irradiation is believed to be the major cause of bacterial death in stream and marine waters, indicator die-off rates also depend on salinity, temperature, nutrient availability and predation. Owing to their potential to release hepato-, neuro- and dermato-toxic cyanotoxins, occurrence of cyanobacterial blooms are added hazards to bathers. We studied the evolution of fecal coliforms and fecal enterococci contamination plumes, and assessed the occurrence of algal blooms along ca. 8 km of the Aljezur stream and beaches system. In addition to microbiological analysis, 13 physical-chemical parameters were determined in water samples colleted from 10 monitoring stations located upstream and downstream of the Aljezur wastewater treatment plant, fish farming plant and wetlands. Results from a series of 4 surveys, which covered different seasons and samples collected over entire tidal cycles, showed that both indicators decayed to insignificant numbers along the first half of the stream. The importance of solar irradiation and salinity as causes of bacterial die-off was precluded by the observed UVA and UVB water-extinction-coefficients, and by results obtained from microcosmos experiments, respectively. However, the fecal coliforms and fecal enterococci numbers clearly correlated with the values observed for a number of physical-chemical parameters, including, PO4 3-, total N and SiO4-. In addition, high concentrations of chlorophyll a were detected in samples from one monitoring station, thus suggesting the possibility of cyanobacterial blooming in the stream.