Estuarine nitrite maxima and nitrifying bacteria (Ems-Dollard estuary)

Abstract

Nitrifying bacteria were isolated from the Ems-Dollard estuary and cultured in batch as well as in continuous cultures. It was shown that the ammonia oxidizing bacteria of the genus Nitrosomonas are able to adapt to the whole estuarine salinity range, though they react to salinity changes initially with an increased lag phase. At the culture conditions (25°C, salinity 15) the ammonia as well as the nitrite oxidizer ( Nitrobacter) had specific maxium growth rates (μ m) and half saturation values ( K s) that are similar to those reported for non-marine conditions. For Nitrosomonas from the Dollard μ m and K s at 25°C are 0.036 h −1 and 55.4 μmol · 1 −1 ammonia for Nitrobacter 0.064 h −1 and 267.2 μmol · 1 −1 nitrite respectively. From a mixed continuous culture of both organisms it is concluded that below 95 μmol · 1 −1 O 2 oxidation of nitrite and below 32.5 μmol · 1 −1 O 2 also the oxidation of ammonia is inhibited. It is argued that oxygen limitation in the top sediments of the Dollard is responsible for development of a nitrite maximum in sediment pore water and for a relative high ratio of ammonia oxidizers to nitrite oxidizers. By resuspension of bacteria associated with suspended particles their anomalous ratio is contributing to nitrite development in the water phase also.