Abstract A feedback control system was applied to establish defined redox conditions in sediment-water systems: the H 2S release was counterbalanced by adding of air oxygen on arbitrarily chosen pH 2S setpoints. pH 2S was measured by a pH 2S electrode cell as the controlled variable. E. coli and Enterococci were inoculated into the system to study their survival. Applying a new kinetic approach different growth patterns were revealed, indicating that E. coli, in contrast to Enterococci, shows significant dependence on the predominating redox conditions. Enterococci may thus be a more reliable indicator of fecal contamination in cases were sulfide is present.