Distribution of Nitrifying Activity in the Seine River (France) from Paris to the Estuary

T he distribution o f nitrification has been m easured with the 111 '( ( ) ; incorporation m ethod in the Seine River and its estuary during sum m er conditions. T he Seine River below Paris receives large am ounts o f am m onium through w astewater discharge. In the river itself, this am m onium is only slowly nitrified, while in the estuary nitrification is rap id and com plete. We show that this contrasting behavior is re la ted to the d ifferen t hydrosedim entary conditions o f the two systems, as nitrifying bacteria are associated with suspended particles. In the river, particles and their attached bacteria e ither rapidly settle o r have a sestonic behavior. Because o f the sh o rt residence tim es o f the w ater masses, the slow growing nitrifying population has no tim e to develop sufficiently to nitrify the available am m onium . T he estuary is characterized by strong tidal dynamics. Particles settle and are resuspended continuously with the strong curren t inver­ sions o f ebb and flood. As a result o f these dynamics, particles and their attached nitrifying bacteria experience longer residence tim es in a tem porary suspended state than the w ater m asses them selves, providing to slow growing nitrifying bacteria the opportunity to develop a large population capable o f nitrifying all the available am m onium .