Separate and combined effects of solar radiation, temperature, salinity, and pH on the survival of faecal coliforms in seawater

The presence of sunlight was the major factor controlling the survival of faecal coliforms (FC) in seawater. The responses of FC survival to intensity of solar radiation, temperature and salinity were inversely proportional. The optimum pH for FC survival was between pH 6 and pH 7 with rapid decline both above and below these values. The combined effect of solar radiation and temperature on the survival of FC was expressed by multiple linear regression. The coefficients of partial correlation and beta coefficients (β), which are used in determining the relative importance of solar radiation and temperature, suggest that variations in solar radiation have more effect than variations in temperature in bringing about changes of T90 (time required for a 90% reduction in bacterial number) for FC. The increase of temperature and salinity was more detrimental to FC survival in the presence of sunlight suggesting that the sunlight may have acted synergistically with temperature or salinity.