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 105/100 ml during dry weather (4-6 days), with little or no bacterial supplementation from the water (10~-102/100 ml). Untreated (control) model FC and FS populations stabilized at 103/100 ml for 7-9 days. In cyctoheximide-treated models, FS and FC survived at 104 and 10~/100ml, respectively. In autoclaved-seeded models, FS and FC initial counts of 104/100ml increased to and stabilized at 107-109/100ml. 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.

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Recent studies with the isolated perfused rat kidney have demonstrated the existence of an intrinsic renal adaptation to conserve K+ in response to ingestion of a low K+ diet for 3 days. To determine whether the colon alters its K+ transport properties in a similar fashion, we measured transmural 86Rb fluxes across sheets of distal colonic epithelium under short-circuit conditions. Preliminary studies using a double-isotope technique demonstrated that 86Rb and 42K fluxes were similar; therefore 86Rb flux was considered equivalent to K+ flux. The distal half of the colon from each rat was divided into two segments, referred to as early and late distal colon. Experiments were carried out using rats fed a K+ -free, control (0.15 mmol/g), and high K+ (1.13 mmol/g) powdered diet of otherwise identical electrolyte content. Net K+ secretion (Jnet) by the early distal colon was reduced from 0.45 in the controls to -0.02 mueq X cm-2 X h-1 by a low K+ diet as a result of a decrease in serosal-to-mucosal flux (Jsm), with no change in mucosal-to-serosal flux (Jms). Conductance (GT) and short-circuit current (Isc) were unchanged. Jnet by the late distal colon averaged 0.17 in the controls and 0.01 mueq X cm-2 X h-1 with a low K+ diet, but this difference was not significant statistically. In comparison with the controls, a high K+ diet had no effect on Jnet by the early distal colon (0.48 mueq X cm-2 X h-1) but increased Jnet by the late distal colon substantially (0.77 mueq X cm-2 X h-1).(ABSTRACT TRUNCATED AT 250 WORDS)

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