SURVIVAL OF FECAL-COLIFORMS AND FECAL STREPTOCOCCI IN STORM-DRAIN SEDIMENT

This study defined major factors influencing the survival of the bacterial indicators, fecal coliforms (FC) and fecal streptococci (FS), in separate storm drain sediments during dry weather periods. FC and FS abilities to survive were determined by field sampling and experimental treatments of laboratory stream models. The effects of interspecific competition, antagonism, and predation on FC and FS survivals were determined using recirculating models that contained either untreated drain water and sediment, cycloheximide-treated drain sediment, or autoclaved drain water and sediment seeded with drain isolates of FC and FS. Storm drain sediment FC and FS counts were stable at 10(5)/100 ml during dry weather (4-6 days), with little or no bacterial supplementation from the water (10(1)-10(2)/100 ml). Untreated (control) model FC and FS populations stabilized at 10(3)/100 ml for 7-9 days. In cycloheximide-treated models, FS and FC survived at 10(4) and 10(5)/100 ml, respectively. In autoclaved-seeded models, FS and FC initial counts of 10(4)/100 ml increased to and stabilized at 10(7)-10(9)/100 ml. Separate storm drain sediments serve as reservoirs of high concentrations of FC and FS during warm, dry weather periods. FC exhibited some ability to multiply in drain sediment. Native microfloral competition/antagonism (including bacterial predation) and protozoan predation are major biotic factors influencing FC and FS survivals. During warm, dry weather periods, abiotic factors were generally stable and had minimal affects on FC and FS survivals.