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<br />64
<br />
<br />F. ZAMORA-ARROYO ET AL
<br />
<br />Nilsson, C., Jansson, R. & Zinko, U. (1997). Long-tenn responses of river-margin vegetation to
<br />water-level regulation. Science, 276: 798-800,
<br />Ohmart R. Anderson, B. & Hunter, W. (1988). Ecology of the Lower Colorado River from Davis
<br />Dam ~o the Mexico-United States Boundary: A Community Profile, Alexandria, Virginia, USA:
<br />National Technicallnfonnation Service.
<br />Poff, N., Allan, J., Bain, M., Karr, J., Prestegaard, K., Richter, B., Sparks, R. & Stromberg, J.
<br />(1997). The natural flow regime. Bioscience, 47: 769-784. .
<br />Stromberg J, (1998a). Dynamics of Fremont cottonwo,od (pof?Ulus fremontll) an~ saltc~dar
<br />(Tamarix chinensis) populations along the San Pedro River, Anzona. Journal of And EnVIron-
<br />ments,40: 133-155.
<br />Stromberg, J. (1998b). Functional equivalency of saltcedar (Tamarix chinensis) and Fremont
<br />cottonwood (Populus fremonlii) along a free-flowing river. Wetlands, 18: 675-686,
<br />Seaforth, P., Stromberg, J. & Patten, D, (2000). Woody riparian veg~tation response to dif-
<br />ferent alluvial water table regimes, \:!7estern North American Naturalist, 60: 66-76,
<br />Springer, A., Wright, J., Seaforth, p" Stromberg, J. & Patten, D. (1999). Coupling groundwater
<br />and riparian vegetation models to assess effects of reservoir releases. Water Resources
<br />Research, 35: 3621~3630.
<br />U.S. Bureau of Reclamation (1996). Description and Assessmenl of Operations, Mainlenance, and
<br />Sensitive Species of the Lower Colorado River. U.S. Bureau of Reclamation, Boulder City,
<br />Nevada.
<br />Valdes-Casillas (1998). Infannalion Dalabase and Local Outreach Program for Ihe Restota.tion of the
<br />Hardy River Wetlands, Lower ColOl'ado River Delta, Baja California and Sonora, MexiCO. North
<br />American Wetland Conservation Council, Arlington, Virginia, USA.
<br />
<br />
<br />Journal oj Arid EnvironmenlS (2001) 49: 65-89 @
<br />doi:IO,1006/jare.2001.0836, available online at hnp:/iwww.idealibrary.com on IDE~1
<br />
<br />~
<br />
<br />Selenium, selected inorganic elemellts, and
<br />organochlorine pesticides in bottom material
<br />and biota from the Colorado River delta
<br />
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<br />C,.l.)
<br />
<br />Jaqueline Garcia-Hernandez*, Kirke A. Kingt, Anthony L. Velascot,
<br />Evgueni Shumilint, Miguel A. Mora~ & Edward P. Glenn*
<br />
<br />*Environmental Research lAboratory, University of Arizona,
<br />2601 E. Airport Drive Tucson Arizona, 85706-6985, U.S.A.
<br />to.s. Fish and Wildlife Service, Arizona Ecological Services Field Office,
<br />2321 W. Royal Palm Road, Suite 103 Phoenix, Arizona 85021, U.S.A.
<br />/Centro lnterdisciplinario de Ciencias Marinas, Av. lPN, sin, Col.
<br />Playa Palo de Sta. Rita, A.P. 592, La Paz, B.C.S. 23096, Mexico
<br />go.S. Geological Survey, Department of Wildlife and Fisheries Sciences,
<br />Texas A&M University, 2258 T AMU~ College Station,
<br />Texas 77843-2258, U.S.A.
<br />
<br />Concentrations of selenium (Se) in bottom material ranged from 0.6 to 5.0 J.lg
<br />g - I, and from 0' 5 to 18'3 I!g g - I in biota; 23% of samples exceeded the toxic
<br />threshold. Concentrations ofDDE in biota exceeded the toxic threshold in 30%
<br />of the samples. Greater concentrations of selenium in biota were found at sites
<br />with strongly reducing conditions, no output, alternating periods of drying and
<br />flooding or dredging activities, and at sites that received water directly from the
<br />. Colorado River. The smallest Se concentrations in biota were found at sites
<br />where an outflow and exposure or physical disturbance of the bottom material
<br />were uncommon.
<br />
<br />@ 200 1 Academic Press
<br />
<br />Keywords: Colorado River delta; DDE; DDT; dynamics of selenium; metals;
<br />redox potential; selenium; wetland management
<br />
<br />Introduction
<br />
<br />The Colorado River delta has an arid climate with hot summers and mild winters, its
<br />annual rainfall is often less than 10 cm and evaporation exceeds 2 m year - I (Palacios-
<br />Fest, 1990). Agriculture is the mainstay of the region and is supported mostly by
<br />irrigation from the Colorado River. The agricultural zone of the Mexicali and San Luis
<br />Valleys, located in the northern portion of the Colorado River delta, covers an area of
<br />250,000 ha and uses 52% of the 1.8 x 109 m3 year-I of water allotted to Mexico from the
<br />Colorado River (Valdes-Casillas et ai., 1998).
<br />Most of the former Colorado River channels are currently irrigation canals or
<br />agricultural drains. There are 17 agricultural drains in the Mexicali Valley which flow
<br />into the Hardy River with an annual volume of 63.3 x 106 m3 and have created the
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<br />0140-1963/01/090065 + 25 535.00/0
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<br /><C 2001 Academic Press
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