1/ LD 50 Season of application may vary depending upon local conditions. = a standard measure of toxicity; the lethal dosage rate of a substance that will kill 50 percent of a group of experimental organisms. Table 3-6 IMPACTS ON WATER RESOURCES Results of Herbicide Monitoring in South Umpqua and Rogue Rivers Station No. 14312260 South Umpqua River near Roseburg, Oregon 1/ The source (USGS) reported these values in micro grams per liter (ug/L) rather than parts per billion (ppb). The two values are essentially the same at these small concentrations. 2/ None signifies specifically looked for but not detected. Source: Computer printout from the U.S. Geological Survey "WATSTORE" system for western Oregon. Increase in in water yield from the 30,500 acres the 30,500 acres treated under the proposed action would be 4,500 acre-feet per year. This increase would occur on individual watersheds and could have significant adverse effects, especially on smaller stream reaches. The velocity of streamflow would increase causing some additional erosion (personal communication, Harr 1978). Road construction would also cause an increase in average peak flows following the first major storm of the season. Major peak flows would not change significantly since they normally occur in winter months when the soil is saturated (Rothacher 1973). Absolute increases in minimum streamflow would be small, but the relative change would be significant (Harr 1976b). The annual water yield from BLM-administered lands would be less than the past 5 years as a result of the proposed action, and total yield would decrease somewhat as previously disturbed lands returned to equilibrium. Because the acreage treated under the proposed action is a fairly small percentage of the acreage of the JKSYUs, peak flows and total water yield of the major watersheds would not be significantly impacted. Sediment yield from disturbed lands would increase 15,650 tons under the proposed action. This increase is about 1.5 percent of the present sediment yield of the JKSYUs. While impacts to overall water quality would not be significant, localized areas could be significantly affected, particularly after the first major storms of the season. Should these areas feed recreational water bodies, impacts to water quality for recreation may occur (Section 3.7.1). Harvesting by both clearcutting and shelterwood methods, and slash burning, nutrient enrichment (nitrogen and other nutrients) of streams. Impacts would be localized immediately downstream of activities and may result in algal blooms or changes in the aquatic habitat. Use of herbicides and fertilizers in the JKSYUs would not significantly impact water quality. A summary of the effects of the proposed action on water quality of the JKSYUS is found in Table 3-7. This is a summary only, and does not replace the information contained in the text. The removal of trees creates openings in the forest canopy, which allows more light to penetrate to lower forest strata. Timber harvesting initiates secondary plant succession similar to that caused by natural disturbances. Different cutting practices open the forest canopy to different degrees, thereby influencing the plant composition and duration of the plant communities differently. |