Blue‐green algae‐lichen crusts (Atriplex confertifolia, Eurotia lanata, and Artemisia tridentata sites) from the Great Basin Desert have a laboratory potential of fixing atmospheric nitrogen at rates up to 84 g of N ha‐1 hour‐1. Nitrogen fixation is optimal when the crust is moistened to ‐⅓ bar pressure, temperature is 19 to 23C, and the light intensity is 200 microeinsteins m‐2 sec‐1 with incandescent light. The acetylene reduction technique provided a useful assay to measure in situ nitrogen fixation which was correlated with potential values obtained in the laboratory under optimum conditions. Nitrogen fixation was found to be reduced under desert shrub canopies possibly due to allelopathic effects of the shrubs. Aqueous leaf extracts of desert shrubs significantly inhibited nitrogen fixation. Annual nitrogen fixed was estimated at 10 to 100 kg of N ha‐1 year‐1, depending upon microenvironmental conditions.

Escherichio COP concentrations of bottom sediment and overlying water were determined from a variety of streams in southwestern Idaho by a one-step most probable number technique. Results show E. coli concentrations of bottom sediments to be from 2 to 760 times greater than from the overlying water. E. coticoncentrations of bottom sediment were found to be resuspended following disturbance simulation and a rainstorm event, contributing to pollution of the overlying waters. It is, therefore, suggested that microbial analysis of bottom sediments be considered a part of water-quality evaluations for rangeland streams. During the past decade, Federal legislative action has brought attention to sources of nonpoint pollution related to livestock grazing on public lands. Collectively, the National Environmental Policy Act of 1969, the Federal Water Pollution Control Act Amendments of 1972, and the Federal Land Policy and Management Act of 1976 have specified the need to establish criteria for identifying pollution sources and to improve environmental quality of streams through improved management. To achieve the goals set forth in these acts, many research programs have been initiated to identify and document pollution sources. One of the findings has been the implication that livestock grazing on western rangeland watersheds is a source of bacterial pollution of streams

In the examination of stream waters for fecal coliforms, pale yellow colonies regularly appeared on m-FC broth base medium plates. The yellow colonies may comprise 70% or more of the colonies on an m-FC plate. More than 80% of these colonies were identified as Escherichia coli by the API 20E identification system and by serotyping. The atypical yellow E. coli strains were not environmentally stressed E. coli since the atypical colonies continued to be yellow on m-FC medium after growth in a nonselective medium. However, 50% of the atypical E. coli strains were o-nitrophenyl-,8-D-galactopyranoside positive, and 20% produced gas in EC medium at 44.5°C. Failure to consider these atypical E. coli strains in water quality analyses could lead to a significant error in the estimation of water quality in some instances.

Lactose-negative Escherichia coil from cattle feces appeared as yellow, atypical colonies on m-FC medium plates with water samples from rangeland streams. The lactose-negative E. coil may impact stream water quality analyses if infrequent samples are collected;are less antibiotic resistant than the lactose-positive E. coil isolated from rangeland streams; and are colicinogenic toward all the laboratory strains of E. coil examined and toward 61 percent of the lactosepositive E. coil rangeland-stream isolates that were tested. This latter result could explain the potentially low degree of antibiotic resistance transfer from lactose-positive to lactose-negative E. coil. In addition, the colicinogenicity of the lactose-negative E. coil may interfere with microbiological water quality analyses that depend upon lactose fernientations with mixed populations of coliforms.(KEY TERMS: Escherichia coil; cattle feces; antibiotic resistance; colicinogenicity; water quality.)