The relationships between bacteriological and viral indicators of sewage pollution (TC, FC, E coli, FS, Salmonella, somatic coliphages and F-RNA phages) and environmental variables in coastal water and weather were studied at three beaches in San Sebastian, the Basque Country. The microbiological indicators in bathing water presented high counts associated with the following conditions: early morning, overcast skies, low and high tides, groundswell, intense turbidity and the presence of flotsam (P = <0.05). Coliphage density was significantly related (P = <0.05) to cloud cover, groundswell and flotsam. Correlations between microbiological indicators proved high (0.62 ≤ r ≤ 0.90, P = <0.001). The percentage of Salmonella presented significant (<0.05), albeit low (r < 0.4), correlations with all microbiological parameters. Somatic coliphages also revealed highly significant (0.32 ≤ r ≤ 0.66) correlations (P = <0.001). Those obtained for F-RNA phages, in contrast, were low (r ≤ 0.33). The equations obtained using a multiple regression analysis with a view to predicting microbiological, viral, and Salmonella indicator density demonstrated that environmental variables facilitate the construction of highly significant equations, but that these have low predictive capability (R2 = <0.50).
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