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species of fishes so the concentration of 3 mg/l (ppm) will be used to effectively kill black bullheads that are among the most resistant fish species (Marking and Bills 1976). Zooplankton communities are drastically reduced following rotenone treatments -- cladocerans and copepods are very sensitive while rotifers are most tolerant (Kiser et al. 1963). Generally, immediate reductions in numbers of benthic organisms ranged from 0 to 70% with a mean of 25% in freshwater treatments (Bradbury 1986). Zooplankton and benthic communities, however, recover quickly with no change in the original species compositibn -- zooplankton completely recover in 2 to 12 weeks and benthic communities generally recover within 2 months following treatment with rotenone (Bradbury 1986). Phytopl ankton, rooted aquatic plants, and terrestrial plants are unaffected by rotenone treatments at concentrations used to kill fish (Bonn and Holbert 1961). Rotenone is relatively nontoxic to birds (Bradbury 1986) and mammals (Marking 1988), primarily because of the mode of entry and oxidizing enzyme systems in these two groups of animals (Fukami et al. 1969, 1970). Generally, the natural detoxification of rotenone is rapid and adequate in lakes, ponds, and reservoirs where the chemical will detoxify naturally within 2 days to 2 weeks in late summer and early fall, depending upon water temperature, sunl ight penetration, and a 1 ka 1 i nity of the water (Bradbury 1986). Detoxification is inhibited by turbidity and deep water because of decreased light penetration. Where chemically induced detoxification is necessary in cases such as percolation into streams, potassium permanganate is usually added in an amount equal to the rotenone concentration plus the permanganate demand of the water (Davies and Shelton 1983). No Impacts Anticipated on Veqetation or Historic/Cultural Resources. No impacts to vegetation or historic and cultural resources would result from actions taken in this alternative. The following environmental impacts are expected under this alternative: land Use. Some disruption of present land use would be occur temporarily while actions are taken employ mechanical or chemical methods to control nonnative, warmwater fishes in the floodplain ponds. In general, no more than one day (actual treatment for a 0.5-acre pond would be several hours) would be required to chemically treat a pond. However, if ponds are drained, the temporary disruption will be increased according to the volume of water in the ponds and the pump capacity. An estimate of the time to dra in a pond woul d be 3 to 5 days. Ponds that are drained and then chemically treated would require varying lengths of time to refill. In some cases, ponds can refill qUickly if recharge occurs from irrigation return flows. Ground water recharge would depend upon the substrate composition, substrate saturation with water, and gravity flow. In most ponds, recharge is expected to occur within one or two weeks. About 25 ponds would be treated during 1997 over a 13-week period between July and September (Martinez and Nesler 1996). However, the scenario for treating 25 ponds is based on an idealized schedule for optimum success in accessing and chemically treating ponds during the summer months when the water temperatures are warm and a shorter exposure time to the chemical is 16