Nitrogen-Fixing Heterotrophic Bacteria in Coastal Waters: A Comparison of the Contribution Made by Sewage Effluent in a Temperate and a Tropical Environment

Abstract

Using identical techniques a comparison has been made between the distribution and survival of heterotrophic nitrogen-fixing bacteria from sewage in cold seawater of Morecambe Pay, UK, and warm seawater of Oahu, Hawaii, USA. In the colder seawater the predominant nitrogen-fixing bacteria are salinity-tolerant strains of Enterobacteriaceae (mainly klebsiellas) which come from sewage effluent discharged into the rivers and estuaries flowing into the bay. In the inshore warmer waters of Oahu, similar numbers of heterotrophic nitrogen-fixing bacteria are found but, although most are salinity-tolerant, they are not predominantly Enterobacteriaceae. Sewage effluent from Honolulu discharged into the sea is rapidly dispersed and the bacteria quickly killed by UV light which penetrates into the clear water. In Morecambe Bay, bacteria are found much further out to sea and they survive for much longer periods because sunshine levels are relatively low and light penetration is inhibited by high turbidity from suspended solids. Salinity-tolerance does not appear to have a high survival value for the nitrogen-fixing klebsiellas.