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'. =.~- lhe conlluence with the San Miguel River, ponions of eight 13LM grazillg allolments (Allotment Numbers 7004, 70 II, 7025, 7034, 7036, 7039 [Pasture No.3 J, 8004, and 8068) are located along the river banks. Historically, trailing occurred through the arca now occupied by McPhce Reservoir. ~Iitigation for this loss included a Irail down Ihe south canyon wall, immediately downstream from the dam. Livestock holding corrals werc also constructed near Metaska Recreation Sitc and near Bradfield Bridge. Losses of wetland or riparian vegetation associaced wich che trailing activities are considered to be insignificant. [{istorical grazing practices and adjacent irrigated agriculcural activities (haying) resulced in che presence of noxious plants on these lands at the time they were acquired by the United States. Lack of sufficient resources to eiadicate these plants in the years subsequent to acquisition has resulted in areas of heavy infestation. The most common noxious plant species include the following: Musk thistle (Carduus nutans) Canada thistle (Cirsium arvense) Russian knapweed (Acrootilon repens) Attempts to control these infestations have focused on herbicide applications, In addition, during the past five years, the USFS has conducted prescribed burns in the Lone Dome area in the fall, followed in the spring with selective herbicide treatment. The "ELM has conducted similar eradication efforts in the Bradfield Bridge area. Recently, insect predators have also been introduced to combat musk thistle. An inrrodud:d flower- head weevil (Rhinocvllus conicus) has migrated to this area from other locations in souihwest Colorado, and has become established on the floodplain below McPhee Dam. In 1993, a crown boring weevil (Trichosirocalus horridus) was introduced in this area. It is anticipated that the combined impacts of these two insect species will grearly decrease Ihe vigor and ability of musk thistle to reproduce to the extent that it displaces native plants. 2. ENVIRONMENTAL CONSEQUENCES ALTERNATIVES 1,2 AND 3 - At a release level of 78 cfs from McPhee Dam, tYPical summer flow loss from that point to Bedrock, Colorado is approximalely 18 cfs (Dolores River [nstream Flow Assessment, p. 25). Tne supply of a perennial water source under any of the managed pool allernatives during dry years may benefit riparian communities on the lower Dolores River, which mighl otherwise lose most or all of its flow during the summer. ALL ALTERNATIVES - Little or no additional impact to wetland or riparian communities is predicted with any of the alternatives under consideralion. The invasion of salt cedar in the river downstream of the confluence with Disappointment Creek may be influenced by the constant supply of water due to releases from McPhee Dam. This situation would not be changed by implementation of any of the alternatives. Pool management and acquisitjon of addilional water would nOI aller the hydrology supporting wetland and riparian communities downstream of McPhee Dam. Acquisition of additional water under any of the alternatives would not aller the hydrology supporting wetland/riparian communities adjacent to the river. In addition, seasonally fluctuating downstream releases would be designed to accommodate downstream fish and wildlife resources. It is likely lhat higher flows would be induced during summer, and lower flows during the winter. No impacts to the dominant, groundwater-supponed cottonwood forests or the associated riparian shrub lands and emergent werlands is predicted. No impaclS to livestock grazing or trailing are expected as a result of any of the alternatives under consideration. No impacts to the esrablished infestations of noxious plants would occur from any of the alternatives under consideration. F, WATER QUALITY I. AfFECJ'ED ENVIRONMENT. for pU'1loscs of this analysis, Water quality is CQmprised of two 30