Change in Bacterial Populations Downstream in a Wyoming Mountain Drainage Basin

Ten bacteriological tests were utilized to monitor different bacterial populations found in water samples taken from streams draining high mountain rangeland. Livestock grazing and recreation constituted the major uses of the study area. Vegetation types were typical of those found in other sub-alpine and alpine zones in the central Rocky Mountains. Results show differences in counts of bacteria between sampling sites along individual streams sampled with the exception of those organisms capable of reducing nitrate were not significant. A seasonal variation in the numbers of bacteria were found between streams. This variation is not fully explained by drainage basin areas or related to runoff. In contrast, within each stream counts varied with season and could be related to runoff. Bacterial populations which indicate fecal pollution were low and probably derived from animals not man. Wet meadows and bog areas under snow may be possible sources for sulfate reducing bacteria and those organisms capable of reducing nitrate. Ten bacteriological tests were utilized to monitor bacterial populations found in water samples taken from streams draining high mountain rangeland. Skinner et al. (1974a, 1974b) sampled each population weekly over 2 years. The purpose of this study was to Authors are associate professor, Division of Range Management; associate professor, Microbiology and Veterinary Medicine; professor, Division of Range Management; professor, Agriculture Substation, University of Wyoming, Laramie 8207 I . This work was supported by the Office of Water Research and Technology under the Water Resources Research Act of 1964-PL 88-379 through the Wyoming Water Resources .Research Institute, University of Wyoming, Laramie. This article is published as Journal Article 1255 of the Wyoming Agricultural Experiment Station, Laramie. verify if water taken from sampling sites by Skinner et al. (1974, 1974b) and bacterial numbers were representative of each stream from headwater to each downstream tributary during different summer months. Bacterial tests were selected which are associated with fecal pollution, mineralizing cycles, and environmental conditions. Enteric bacteria, those indigenous to the intestinal tract of warm-blooded animals, consistently serve as indicators of fecal pollution to receiving waters (Morrison and Fair 1966, Fair and Morrison 1967, Carswell et al. 1969, Stuart et al. 1971, Skinner et al. 1974a, Stuart et al. 1976, Milne 1976, Buckhouse and Gifford 1976, Stephenson and Street 1978, Varness et al. 1978 and Doran and Linn 1979). Specific bacterial groups analyzed by these authors include fecal coliforms (FC), fecal streptococci (FS), or both. Ratios between FC/FS were often calculated to delineate original source of fecal bacteria between mammal or human users of rangeland. Bacterial populations indigenous to natural waters and those capable of growing only within discrete temperature ranges have been monitored in streams draining rangeland (Skinner et al. 1974b, Stuart et al. 1976). Organisms sampled from water and enumerated by the standard plate count procedure at 35" C, represent those capable of originating from warm-blooded animal sources. Plate counts incubated at 20°C are utilized to enumerate bacteria associated with the water's surrounding environment (Amer. Pub. Health Ass. 1976). JOURNAL OF RANGE MANAGEMENT 37(3), May 1984 269 Bacteria capable of fluorescing under long wave radiation (fluorescent bacteria) have been found in significant numbers in surface waters (Collins 1963, Silvey and Roach 1964). Johnstone (1970), Skinner et al. (1974b), and Skinner et al, (in press) have all monitored streams for these bacteria to detect differences in eutrophication of receiving waters. Skinner et al. (1974b) monitored bacteria capable of reducing nitrate to nitrogen gas and sulfate to hydrogen sulfide within well aerated mountain streams. The presence and metabolic activity of these organisms in an aerated environment was questionable because sulfate reducing bacteria are strict anaerobes. These reducing bacteria and their relationship to the presence of oxygen in soil and water has since been studied (Betlach and Tiedge 1981, Ingvorsen et al. 1981, Rake and Eagon 1980, Ryden et al. 1979, Keeney et al. 1979, Howorth and Teal 1979, Jorgensen 1979). Even though oxygen may be present, anaerobic microniches exist in wet soils thereby allowing survival of organisms associated with the anoxic portion of the nitrogen and sulfate cycles (Howarth and Teal 1979, Sorensen et al. 1979, Jorgensen 1977). Because anaerobic conditions may be created in soil pore space by water replacing air, water logged soils may increase reducing bacterial populations and activity. For example, Ryden et al. (1979) have shown fluctuations in the amount of nitrate reducing activity in pastures with variation in soil moisture. Higher activity occurred with increased soil moisture. Percolation or runoff of water from wet upland areas may in part explain their presence in well-aerated receiving streams. Interchange of stream water and bank storage may exist, carrying with it bacteria and chemicals (Morrison and Fair 1966 and Wesche 1982).