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.
