Page images
PDF
EPUB
[blocks in formation]

Increased sediment yield as a result of the proposal would not have a significant impact on the whole of the JKS YUS, but could have significant adverse impacts on water quality in localized areas, particularly small stream reaches. Those activities which would impact small streams include yarding, road construction, slash disposal, and mechanical scarification. Other phases of the management plan would not significantly increase sediment yield. Harvest by clearcutting and shelterwood methods, and slash burning would enrich streams with nitrogen and other nutrients. Impacts of herbicide treatment upon water quality would not be significant if all design features were successful.

3.4.2.1 Sediment Yield

Sediment yield of forest lands is estimated at 150 tons per square mile per year based on the average sediment yield of other sites in western Oregon (Fredriksen 1970). Areas disturbed by yarding practices would produce 1.6 times the average sediment yield for the JKSYUS (Megahan 1972) or 240 tons per square mile per year. The 21,160 acres disturbed by tractor and cable yarding under the proposed action would yield an additional 8,925 tons of sediment over the 5 years needed to return to undisturbed levels.

Sediment yield from the 1,770 acres disturbed by road construction would triple over present yields in the first year after road construction (Brown et al. 1971 In U.S. EPA 1973). This would be an average for the first year, as sediment yield may increase 250 times following the first storm event after construction (Fredriksen 1965). This means initial sediment yield would increase by 830 tons. Within 5 years, the new roads would stabilize and produce only one-third more sediment than undisturbed forest lands. Total sediment yield for the first 5 years following road construction would be 2,900 tons.

Reconstruction of 100 miles of road would increase sediment yield to levels approximately two-thirds that of newly constructed roads, or 300 tons per square mile. Over the 5 years needed to reach "stable" yields (200 tons/ square mile) approximately 825 tons of sediment would enter streams as a result of reconstruction.

Surfacing 50 miles of road would eventually reduce sediment yield. Initially, however, sediment yield would probably increase by the same amounts as in reconstruction. Within 5 years, yields would decline to that of undisturbed forest lands as a result of surfacing. Therefore, approximately 310 tons of additional sediment would be produced over 5 years after surfacing.

Gross yarding would increase sediment yield by an average 24 tons per square mile on about 30 percent of the lands compacted and disturbed by the activity. Sediment yield from these disturbed lands would increase 1,115 tons over the 5 years needed to return to undisturbed levels.

Extremely hot slash fires destroy vegetation and litter which protect the soil surface. This, rather than changes in the actual mineral soil, is the most important impact of fire (U.S. EPA 1976a). Severely burned areas (all litter and vegetation destroyed) account for a very small portion of the total burn (from less than 3 to 8 percent) (Dyrness et al. 1957; Tarrant 1956), but contribute most of the sediment produced after a burn. At present it is not known how much sediment is produced by broadcast burning, but it would be only a small amount when compared to roads and yarding and loading (Fredriksen 1972).

Mechanical scarification would increase sediment yield on treated areas 10 percent over the average rate of the planning area or 15 tons per square mile. This means the sediment yield from 22,300 acres would increase 1,575 tons in the 5 years before the areas once again stabilized. This could have slight adverse impacts on water quality of streams immediately adjacent to the areas being scarified.

In

Analysis of the 3-year timber sale plan showed seven sales where increased sediment yield from logging activities could impact streams that already have a severe sediment problem and/or severe stream bank erosion problems. These sales include 80-13, 80-20, 80-22, 81-17, 81-19, 81-21, and 82-17. addition, failure of slopes of those sales discussed in Section 3.3.1 (Yarding subsection) and/or of roads in those sales listed in Table 3-2 could increase sediment yield of adjacent streams somewhat. Because of the lack of research in southwestern Oregon forests, however, quantification of increased sediment yield on a site-specific basis is not possible.

[blocks in formation]

The quality of runoff water from lands subject to timber harvest would be affected by the release of nutrients from the soil (see Chapter 2, Soils). Nitrogen is the element of most concern since it is very mobile and may cause eutrophication of water bodies (Tarrant et al. 1969 Cited in Anderson et al.

1976).

An estimated 0.16 pounds of nitrogen per acre would enter streams as a result of clearcutting and 0.05 pounds per acre after shelterwood harvest (Calculated from U.S. EPA 1976a; DeByle et al. 1972 Cited in Sopper 1975).

A total of 9,015 pounds of nitrogen would be lost to runoff in the 5 years needed to reestablish nutrient cycles. Assuming a natural discharge rate from studies of 16 pounds per acre over 4 years (Cole et al. 1967 Cited in Moore et al. 1974 In Cramer 1974), this would be an increase of about 1.3 percent over the natural discharge. Nitrogen losses would of minor short-term significance for both terrestrial and aquatic systems (Brown 1972; U.S. EPA 1976a).

The other elements of concern (phosphorous, potassium, calcium and magnesium) would not increase in the total runoff from the JKS YUS to any significant extent following harvest. Losses would occur when the mineralized elements were leached out of the soil.

IMPACTS ON WATER RESOURCES

Slash burning accelerates the release of chemicals, some of which reach streams and influence water quality (Rothacher et al. 1974 In Cramer 1974). It is assumed for this analysis that the increased loss of nitrogen would be equal to that from clearcutting. Therefore, 3,800 pounds of nitrogen would be lost the first year after burning, and a total of 11,400 pounds over the 5 years before losses were minimized by regrowth.

The adverse impacts of nutrient enrichment of streams would be site specific immediately downslope from the activity and would vary in intensity, depending upon degree of disturbance upslope and to stream channels. Because only acreage and not actual burn sites were identified for each sale in the 3-year timber sale plan, site-specific analysis is not possible. Approximately one-fourth of the planned burns are scheduled in the first 3 years.

and Rothacher (1969) showed that broadcast slash burning increased summer water temperatures in some western Oregon streams by as much as 14°F above that caused by harvesting. This was a result of removing shading vegetation from the watershed. Impacts from slash burning on stream temperatures could be significant on small stream reaches and have adverse impacts upon the fisheries in the JKSYUS only if streamside vegetation is accidentally burned.

There are approximately 765 miles of Class I streams within the JKSYUs, approximately 195 miles of which are on public lands. Water quality could be impacted by herbicides by rapid overland flow of water from roads or other compacted areas, treatment of adjacent riparian zone vegetation, or by accidental application directly on the water surface.

The herbicides are proposed to be used in a manner that minimizes the possibilities for water contamination. These project design features are described briefly in Chapter 1. All the herbicides listed in the proposed action could have some short-term impacts on water quality. Available information indicates that although some 2,4-D may enter those streams flowing through or adjacent to areas being sprayed, the levels in the streams would be very low. In 6 years of monitoring spray operations in western Oregon, scientists have never found 2,4-D residues exceeding 0.1 parts per million in streams. The length of persistence (usually a few hours, but up to a few days) was a function of the hydrologic nature of the area treated.

Generally, groundwater supplies would not be impacted unless spraying was done on or near wetlands (areas with high water table). Long-term, lowlevel pollution would be found if 2,4-D were accidentally applied directly on marshy areas (USDA, FS 1975), but these areas would be quite small and isolated. Large marshy areas would be identified and project design features (Section 1.3.4.2) would be applied to them.

Potential impacts of herbicides on water quality are identified and described in the environmental statement prepared by BLM on the spraying program for western Oregon (USDI, BLM 1978d). Some herbicide traces (a few parts per billion) could appear for a short period in nearly all streams which flow

immediately adjacent or through treatment areas only if there were no buffer zone. Potential also exists for contamination of water due to the erosion of soil particles containing herbicides and from leaching in shallow, stony, rapidly drained soils. However, studies have shown that since nearly all the herbicides found in streams were introduced by direct application of spray materials to the surface of the water, careful application should mean that impacts of herbicide application water quality would be insignificant.

Table 3-5 contains a summary of the characteristics of herbicides proposed for use in the planning area. Extensive monitoring of present-day operational applications of herbicide in forests show most applications do not result in measurable concentrations of herbicide in nearby streams.

The

Monitoring results from the mainstems of the Rogue and South Umpqua Rivers are shown in Table 3-6. They show virtually no detectable level of herbicides. Fertilization would likely increase nitrogen concentration in streams. typical reaction of a watershed to fertilization would be a urea concentration peak in the runoff water within a few hours of fertilizer application. Following this peak (over a period of a few days), there would be a smaller ammonia peak, and a few days later, a smaller nitrate peak. The nitrogen from the fertilizer application would fall to background levels after a few weeks. Most of the fertilizer loss would occur from November through January in runoff. Levels of nitrogen in streams draining one watershed in southwest Oregon that had been fertilized with nitrogen have not exceeded Federal public health standards as a result of fertilizer application alone. Impacts to the water quality of streams of the planning area would be expected to exhibit similar responses as observed in studies in western Oregon and Washington (Fredriksen et al. 1973). Quantification, however, is not possible since dilution factors, time of application, and time of application, and the total annual yield for the water year involved in such calculations all vary. Impacts of fertilizers on water quality would not be expected to be significant.

[blocks in formation]

Increase in water yield from 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 peak flows.

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, total water yield of the major watersheds would not be significantly impacted.

[blocks in formation]
« PreviousContinue »