colorado river delta el nino
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Brief Intoduction

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A Brief History

   The native people and environments of the Colorado River delta were much different before the damming of the Colorado River, which drains 244,000 square miles (1/12 the size of the lower 48 states) and divides the region as no other, being the most legislated, litigated, and debated river in the world (Pitt, 2001; Luecke, 2000). For more than 70 years the delta has been drying up, which causes wildlife and human lifestyles to change abruptly (Luecke et al, 1999). The sustainable lifestyle of the Cocopah Indians ("'river people' without a river") comprised of hunting mule deer and planting corn, squash, and tepary beans with the summer floods; they were able to produce a robust crop before the mud flats dried up again (Bowden, 1977; Williams, 1983).

   These people, who still live along the river, and the ancient Mohave and Yuma peoples, previously harvested wild Palmer's saltgrass (Distichlis palmeri), utilized arrowweed (Pluchea sericea) to build houses, and consumed fish each day, but these resources decreased when the water supply did (Felger and Moser, 1985). Both the quantity and quality of water have decreased dramatically: when the water is flowing, it runs murky brown, salty, and contains pesticides (EPA, 1998), although the agricultural contaminants were higher on the U.S. side (Garcia-Hernandez, 2001). Many species of fish and plants have disappeared (EDF, 1999). Two marine animals have been listed as endangered species, including the world's most endangered marine mammal, the vaquita porpoise (Phocoena sinus) and the totoaba fish (Totoaba macdonaldi) (Pitt, 2001). These fish used to grow as long as seven feet (2 m) and weighed 300-pounds (136 kg) (Postel et al., 1998); they bred at the mouth of the river in thick schools and the tides sent their eggs back into the deep, natural nursery of the delta (True et al., 1997; Cisneros-Mata et al., 1995). Another fish in the delta on the endangered species list is the desert pupfish (Cyprinodon macularius) (Zengel and Glenn, 1996; Varela-Romero et al., 1998; Nagler et al., 2000).

   Some native species still remain today (Glenn et al., 1996, 1999a, 1999b, 2001; Pitt, 2001). These include cottonwood trees (Populus fremontii) and willow trees (Salix gooddingii), the seepwillow (Baccharis salicifolia), and arrowweed (Pluchea sericea) (Glenn et al., 1996). The native people who irrigated the land by building ditches and dams used mesquite poles for building the dams (Felger and Moser, 1985). There are mesquite trees (Prosopis glandulosa) in the lowland areas, as well as in higher areas (Prosopis pubescens) in the delta (Glenn et al., 1996, 2001). The low-lying regions are filled with salt-tolerant species, such as saltbush (Atroplex spp.), the common reed (Phragmites australis) and saltgrass (Distichlis spicata) (Glenn et al., 1996, 2001).

   The riparian corridor of the lower Colorado River was historically a mixture of gallery forest habitat (cottonwood and willow trees) interspersed with backwater wetlands (dominated by cattail and other emergent plant species). These habitats were maintained by the natural flow regime, which consisted of spring floods that brought water out of the main channel to wash salts from the banks, germinate tree seeds, and create seasonal wetlands.

   Studies of the waterbirds of the delta have been conducted (Huerta et al., 1999; Garcia-Hernandez et al., 2000; Hinojosa-Huerta et al., 2001; Pitt et al., 2000). The vegetation in the riparian corridor and wetland habitats provides breeding and nesting ground for the southwest willow flycatcher (Empidonax traillii extimus) (Garcia-Hernandez et al., 2001a, 2001b) and the yuma clapper rail (Rallus longirostris yumanesis) (Hinojosa-Huerta et al., 2001), respectively, both of which still exist, in relatively small numbers; these two species are listed as endangered by ESA. Mexico lists two other endangered birds that are still found in the delta: the brown pelican (Pelecanus occidentalis) and the peregrin falcon (Falco peregrinus anatum); the yellow-footed gull (Larus livens), Heermann's gull (Larus heermanni), elegant tern (Sterna elegans), and reddish egret (Egretta rufescens) are listed as threatened (Pitt, 2001; Nagler et al., 2000). An additional three species are listed for special protection: the brant (Branta bernicla), house finch (Carpodacus mexicanus), and mockingbird (Mimus polyglottos); and one rare species: the great blue heron (Ardea herodius) (Pitt, 2001; Diario Officiel, 1994).

   Unknown species may have disappeared. For example, Kawaleski et al. (2000) reported on two trillion shells at the mouth of the Colorado River. And, where historically abundant fresh river water mixed with the salty Gulf of California, the delta clam, a bivalve mollusk (Mulinia coloradoensis), has only one small remaining population (Flessa and Tellez-Duarte, 2001).

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