BACTERIAL POLLUTION OF WATERS IN PRISTINE AND AGRICULTURAL LANDS

Concentrations of thermotolerant coliform bacteria, presumptive E. coli, and presumptive fecal streptococci were determined from ditches, brooks, and natural ponds in six agricultural areas and 22 uninhabited pristine areas in southern Finland in the summer of 1987. For comparison, the same fecal indicators were enumerated from the effluents of three wastewater treatment plants. The objective was to compare the importance of these waters as sources of fecal indicators in receiving waters. The numbers of bacteria in waters in agricultural areas often exceeded the limit of acceptable swimming water (1000 bacteria per 100 mL), especially during wet periods, which shows that diffuse loading can be a significant source of fecal pollution. Fecal indicators were detected in about half of the samples of pristine areas, sometimes in concentrations exceeding the limit of good swimming water (100 bacteria per 100 mL). This contamination was probably caused by wild animals, especially by elk (Alces alces) and deer (Odocoileus virginianus) living in the areas. The concentrations of bacteria were higher in running waters than in ponds. The reliabilities of routine enumeration methods for the bacteria were evaluated by carrying out confirmation tests for isolated strains. Thermotolerant coliforms were reliable indicators in waters contaminated by diffuse loading. The reliability of enumeration of fecal streptococci in these waters should be studied further.