Nitrifiants autotrophes et heterotrophes en zone littorale et estuarienne

This study concerns bacterial nitrification in a small estuary of NW France and its outlet. Both autotrophic and heterotrophic nitrifiers were studied. Sediment and water samples were examined for the presence of nitrifiers using an MPN microtechnique. Several isolates were examined in pure culture for specific nitrifying activity. The numbers of both autotrophs and heterotrophs, whether benthic or pelagic, decreased the nearer one got the sea-outlet and were much more abundant in the sediment than in the water; heterotrophic nitrifiers were much more abundant than autotrophic types. The ratio of heterotrophs to autotrophs was 100:1 in the estuary but only 10:1 in the sub-littoral zone. Although less numerous, laboratory experiment showed that the nitrifying activity of the autotrophs was some x 10 super(4) greater than that of the heterotrophs: the significance of population sizes and specific activities are discussed.