In a study of cumulative effects of riparian disturbance by grazing on the trophic structure of high desert trout streams, watersheds with greater riparian canopy had higher standing crops of rainbow trout Oncorhynchus mykiss, lower daily maximum temperatures (range, 16-23°C compared with 26-31°C), and perennial flow. Watershed aspect influenced the response of trophic structure to grazing influences. Standing crops of rainbow trout were negatively correlated with solar radiation and maximum temperature in watersheds flowing northward. A different relationship was observed for a set of watersheds with a southern aspect, perhaps due to the presence of spring seeps and stream desiccation in the heavily grazed stream. Trout biomass was negatively correlated with solar radiation, whereas positive relationships were found for discharge and depth. Algal biomass was positively correlated with solar insolation (r = 0.91), total invertebrate biomass (r = 0.77), and herbivorous invertebrate biomass (r = 0.79) in all watersheds. Invertebrate biomass was not significantly correlated with rainbow trout standing crop. High irradiance apparently resulted in increased algal biomass and invertebrate abundance. However, temperature elevations to levels close to lethal may impose high metabolic costs on rainbow trout, which may offset higher food availability and affect the availability of prey.

The impact of grazing cattle (Bostauras) on water quality has been the subject of considerable interest as water quality standards become more restrictive. Benthic sediments have been found to harbor significantly higher concentrations of enteric bacteria than the overlying water. In this study, the survival of fecal coliform and fecal streptococci organisms was demonstrated to be significantly longer in sediment laden waters than in those without sediment and further the survival was longer in the sediment-laden waters than in a supernatant from that same sediment suspended in water. Fecal coliform and fecal streptococci bacteria revealed half-lives from II to 30 d and 9 to 17 d, respectively when incubated with sediment. This is longer than when they are similarly incubated without sediment.

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Highlight:During 19 73 and 1974 wildland water quality analyses were performed on a semiarid, chained and seeded, pinyon-juniper site in southeastern Utah. The area was treated in 1967 and protected from grazing until 1974. In 1974 livestock grazing was introduced and investigations continued to determine if any deleterious land use effects were present from fecal contamination by cattle. No significant changes were noted in fecal and total coliform production (fecal pollution bacterial indicators) from grazing use. There is an element of risk involved whenever data generated from a small area are projected to larger land areas. However, it appears that this level of livestock grazing (2 hafA UM) did not constitute a public health hazard in terms of fecal pollution indicators onthe semiarid watershed. JOURNAL OF RANGE MANAGEMENT 29(2), March 1976

Table 1. Streambank erosion observation periods and treatment identification. Streambank erosional patterns have been studied for 3 years (1 year of calibration and 2 years of active grazing treatment) on the Starkey Experimental Forest and Range in the Blue Mountains of northeastern Oregon. Livestock grazing use at the rate of 3.2 ha/AUM (8 acres/AUM) has not accelerated streambank degradation on Meadow Creek. Most erosion occurred during wintering periods and this erosion has been independent of grazing season treatments. It appears that high runoff and occasional ice flows are the most significant factors in bank cutting on this stream. Literature Cited Hayes, F.A. 1978. Streambank stability and meadow condition in relation to livestock grazing in mountain meadows of central Idaho. M.S. Thesis. Univ. of Idaho. Moscow, Id_91 p.