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CHAPrii ER 1. I NTROOUC r I oN <br />The Colorado River has played a <br />major role in shaping the physical, <br />biotic, and cultural history of a <br />large portion of western North <br />America. In the arid Southwest it is <br />a permanent source of water in an <br />otherwise arid environment. Its <br />waters collect from melting snows and <br />become heavily laden with sediments <br />from the continent's interior. Ul- <br />timately, these sediments were depos- <br />ited to form the delta at the Gulf of <br />California when the river flowed under <br />natural conditions. <br />An ecological description of the <br />lower Colorado River system today <br />cannot be made without discussing the <br />drastic and rapid modification that <br />the system has undergone during the <br />last 150 years of human use. The <br />Colorado River once inspired only <br />explorers, geologists, and biologists. <br />The modern river is now controlled and <br />manipulated by politicians, lawyers, <br />engineers, farmers, and recreationists <br />who strive to harness its power, to <br />irrigate desert lands, and otherwise <br />make use of Its water. The politics <br />of water is a fundamental aspect of <br />life in the Southwest today simply <br />because water is vital to human exis- <br />tence in desert environments. This <br />reality in itself has been detrimental <br />to natural resources along the Colo- <br />rado River within a relatively few <br />years. <br />The lower Colorado River is one of <br />the most manipulated ecological sys- <br />tems in North America. The taming of <br />the lower Colorado River and changes <br />in its faunal and floral diversity <br />make it an important ecosystem to <br />study. Therefore, this community <br />profile of the lower Colorado River <br />addresses both past and present eco- <br />logical dynamics of the system. We <br />attempt to outline present and future <br />management problems on the lower Colo- <br />rado River, based on community dynam- <br />ics and prospective solutions to these <br />problems. <br />This community profile is intended <br />for use by a number of parties. Pri- <br />marily, this document should encompass <br />much of the general information on the <br />past and present conditions of the <br />river and its associated flora and <br />fauna. We hope that the information <br />included here is basic enough to be <br />understood by the general public, and <br />detailed enough for use by profes- <br />sional managers and researchers. <br />Greater detail on issues and informa- <br />tion presented here may be gained <br />through the Literature Cited section <br />of this document. <br />This first chapter defines the <br />study area, its climate, and a brief <br />discussion of the floodplain riparian <br />vegetation, which constitutes a major <br />focus of this profile. Chapter 2 <br />summarizes a history of human occur- <br />rence in the lower Colorado River <br />Valley, with general descriptions of <br />documented floral and faunal changes. <br />Chapter 3 describes the physical, <br />chemical, and Iimnological nature of <br />the aquatic environment, and also in- <br />cludes a brief discussion of the <br />physicochemical nature of the ter- <br />restrial environment. Chapter 4 sum- <br />marizes the extent of agriculture in