Processes Contributing to the Decrease of Coliform Bacteria in a Tidal Estuary

It has long been known that coliform bacteria introduced into tidal waters disappear rapidly so that the numbers decrease from many thousands per ml. in the region where the water is practically fresh to very few, or none at all, where the water approaches a salinity characteristic of sea water. Many factors have been postulated to account for such pronounced decreases, but their relative importance has never been quantitatively assessed. Dilution of the river water with sea water is important, but it is not sufficient to explain the enormous decreases that are observed. ZoBell (1936, 1946), Ketchum et al. (1949), and Vaccaro et al. (1950) have pointed out the importance of the bactericidal action of sea water. The zooplankton in the water remove organisms and particulate matter from the water which they filter, and Fuller (1937) and Harvey (1937) have evaluated the