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<br />250
<br />
<br />Flooding and Aquatic Ecosystems
<br />
<br />Table 9.6. Potential effects of contaminants on various life stages of animals
<br />(modified from Sheehan et aJ., 1984)
<br />
<br />Life stage
<br />
<br />Egg
<br />
<br />Larva
<br />
<br />Juvenile
<br />
<br />
<br />Adult
<br />
<br />. I
<br />
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<br />I'
<br />,
<br />. \
<br />
<br />Vital life process
<br />
<br />Meotic division of cells,
<br />fertilization, cleavage
<br />mitoses of fertilized
<br />egg, hatching, respiration
<br />
<br />Metamorphosis.
<br />morphological development,
<br />feeding, growth, avoidance of
<br />predators, susceptibility to
<br />parasites and disease
<br />
<br />Feeding, growth, development
<br />of immune system and
<br />endocrine glands, avoidance
<br />of predators susceptibility
<br />to parasites and diseases
<br />
<br />Feeding, growth, sexual
<br />maturation
<br />
<br />Critical effect of contaminants
<br />
<br />Gene damage, chromosome
<br />abnormalities, damage to egg's
<br />membrane, direct toxicity to embryo
<br />from contaminant, impaired respiration.
<br />reduced hatch
<br />
<br />Toxicity from bioaccumulated
<br />poisions in yolk sac during
<br />early feeding, biochemical
<br />changes, physiological damage,
<br />deformities, behavioral alterations
<br />
<br />Direct toxicity, reduced feeding
<br />and growth, altered predator-prey
<br />relations, impaired
<br />chemoreception, reduced
<br />resistance to parasites and diseases
<br />
<br />Direct toxicity, adverse alteration of
<br />environmental conditions (e.g.,
<br />dissolved oxygen), physiological
<br />and biochemical changes,
<br />behavioral alterations
<br />
<br />through an arid to semiarid landscape that is supplied by only 2.9 ha-m of
<br />precipitation per km2; this is less than any other major river in the United
<br />States.
<br />During the past century, water development in the upper Colorado River
<br />basin (Figure 9.1) to serve agricultural, domestic, industrial, and min-
<br />ing activities altered the natural river ecosystem (Carlson and Muth, 1989;
<br />Maddux et aI., 1993; Miller et aI., 1982; Wydoski, 1980; U.S. Fish and
<br />Wildlife Service, 1990a, 1990b, 1991). Dam construction and water storage
<br />to serve human needs changed the natural hydrograph through dam opera-
<br />tions that released water for seasonal irrigation or for generating power dur-
<br />ing daily peak-use periods. Historic spring peaks in the hydrograph were
<br />dampened (Figure 9.2) and streamflows were increased when the rivers
<br />would naturally become low after the spring runoff. Changes in the hydro-
<br />graph have, in turn, altered aquatic habitats, particularly backwater and
<br />floodplain habitats that are considered vital to survival in early life stages of
<br />native fishes. Cold-water releases from dams reduced water temperatures
<br />of the natural and historic warm-water aquatic ecosystem. Nonnative fish
<br />species were introduced into the rivers and manmade reservoirs, both in-
<br />tentionally and accidentally, and this changed the species composition of
<br />the fish community. Habitat alteration and nonnative fish introductions
<br />were considered to be the two most important factors in the extinction of
<br />40 native North American fishes (27 species and 13 subspecies) during the
<br />past century (Miller et aI., 1989). These two factors also appear to be extre-
<br />mely important in the decline of the four endangered Colorado River fishes.
<br />Altered rivers in the upper Colorado River basin (Upper Basin) had a ma-
<br />jor negative effect on some native fishes - to the point where the razorback
<br />sucker (Xyrauchen texanus), bonytail (Gila eJegans), Colorado squawfish
<br />
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