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<br />Grazing by domestic I ivesto:K and mining operations have been major <br />influences on the watershed. Arroyo cutting has occurred along Rio Sonoyta <br />and its ephemeral tributaries, re~.ulting in ~OIAI.,.r~d I.-'Hter tables and <br />degraded floodplains. Agricul tural developments in Mexico commenced in the <br />19705, spurred by pumpage from the Rio Sonoyta aquifer, and presumably have <br />resulted in further lowering of water tables in the area. This, plus <br />pesticide blowover and leaching from fields and domestic wastewater inputs <br />have influenced fish populations in the Rio Sonoyta mainstream, and native <br />Icngfin dace and desert pupfish are becoming rare. Pesticides also have <br />been noted at Qui tobaqui to Spring (Kynard 1979). <br /> <br />Quitobaquito Spring has been for years modified by man, and its <br />original state will liKely nel)H be Knmvn. Amerinds presumably used it for <br />water supply and irrigation, as did later settlers. Spring outflows were <br />di tched and canal ized and its downflow area was impounded to create a small <br />pond. The original fauna also included longfin dace and a distinctive form <br />of desert pupfishj the former has disappeared and the latter remains <br />abundant. Introduction and establishment of golden shiner necessitated <br />renovation of the system in the early 1970s, pupfish were removed, the ~ond <br />drained, rotenoned, and deepened, and the pupfish successfully reintroduced <br /><Hinckley 19(3). However, the longfin dace population was destroyed at <br />that time. The Quitobaquito form of desert pupfish also was maintained in <br />artificial habitats on the Monument for a number of years, but those have <br />now been removed to ASU <USNPS personnel, pel's. comm.). The USNPS has an <br />active program of management for the spring and its fauna (Section II, p. <br />29) . <br /> <br />Lo~er Colorado River System <br /> <br />Mainstream Colorado River <br /> <br />The Colorado River is one of the greatest desert rivers in the world, <br />with a 632,000 km2 watershed and a total length of 2,334 Km. This master <br />stream originates at the Continental Divide in RocKy ~1ountain National <br />ParK, Colorado. It enters the Region at the Arizona-Utah border to flow <br />west and south to exit the United States near San Luis, Arizona, and enter <br />the Gulf of California in Nexico. <br /> <br />This is one of the most highly modified and controlled systems in <br />North America and is now quite different from its original state (MincKley <br />1979a; FradKin 1981). Prior to impoundments, spring snowmelt in the RocKy <br />Mountains resulted in peaK flows during May and June, followed by gradual <br />decl ines through remainder of the year. Flash flooding frequently cau~ed <br />second peaKs in late summer. Recorded discharges ranged from les~. than 1.0 <br />m3/~.econd (Di 11 1944) to mer? than 11,000 m3.ls.econd (USFI...JS 1980). High and <br />I ow f 1 O~'J 0:;.' C 1 e s res u 1 t e din c >' c 1 i c a I e I' 0 s ion an c de p 0 sit ion 0 f san d and <br />silt, L~it~:ediment load:: 'Jarytng fr.em near 30,000 metr.:c ton: ~e!" day t;! <br />flood to essential 1; none :n periods of low flow. The stream thus ranged <br />fr.':m the con:.i.:.ti?nc/ 0+ ht'Ot'..'/:r.e~.m il flood to c:-./:.t:<.l C~2H. at lc~v <br />C :-~ ': ~ a r ,; e s: r 0 r tie r .:t n d B 1 a r: e. 1? 2 S; D ill 1 944; Dc 1 an e tal. 1 'I (' 4 ) . <br />Seasona' water temceratures ranged from minima near 00 to maxima of more <br />tr-,an3Jc1 C (~.1inc:~1t?>' 1979.:<.). iC'da/, 10 :n:<.j,:,r d2,m.: 2,nd ')J.ater. manipulation <br />