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<br />,
<br />
<br />..
<br />
<br />Ecosystem perspective
<br />
<br />The management of river ecosystems is made difficult by a lack of basic
<br />knowledge. Our understanding of natural streams is confounded by the fact
<br />that few, if any, rivers remain pristine in the sense of being unaffected by
<br />man. Although it is clear that ecological processes on the Colorado delta
<br />historically were controlled by precipitation in distant mountains, the bio-
<br />physical interactions in evolution and maintenance of the river's unique fauna
<br />are much less clear. The main problem is defining an ecological time scale.
<br />Twenty-five thousand years ago the Colorado River was a system of lakes
<br />regulated by river segments in which the native fauna diversified. Today, the
<br />river exists as segments regulated by reservoirs in which an exotic fauna pre-
<br />dominates, This has happened in less than 100 years. Modern man is an
<br />inexorable element in the Colorado River ecosystem, but recall that his first view
<br />of the system revealed the vestiges of a still earlier community of stream
<br />regulators. Lessons in all manner of science are implicit in the regulation of the
<br />Colorado River.
<br />We have argued that stream regulation by some of the high dams may serve
<br />to test hypotheses about ecosystem processes (Ward & Stanford 1983, 1984).
<br />Reservoir tailwaters are tightly controlled by dam operations, and may be
<br />treated as an experimental microcosm by manipulating the timing and depth of
<br />reservoir releases. Paulson (1983) has extended this idea to control of the
<br />biophysical processes in downstream reservoirs by manipulation of upstream
<br />impoundments. Such approaches should permit significant contributions to
<br />limnology, and clarify the site-specific impacts of regulation. Whether such
<br />information will help maintain endangered fauna is unclear (many fish popu-
<br />lations probably are beyond salvation), but it may test the ecological validity of
<br />manipulations under the guise of resource management (e.g. salinity control
<br />projects and the enhancement of reservoir productivity).
<br />Rhetoric about the consequences of regulation in the Colorado River involves
<br />two major issues: (a) whether there is enough water to maintain desirable
<br />ecosystem attributes and (b) whether native and exotic fish can coexist. It
<br />appears that the answer on both counts is no. Consumptive use presently is
<br />allocated more water than the basin produces, compared to the estimated virgin
<br />flow, By the year 2000, deficits will occur whether or not additional developments
<br />occur (Spofford 1980). Severe water shortages, as always in the history of man,
<br />will preclude allocation of stream flows for fish or other ecological concerns.
<br />Some endemic fish may be cultured in hatcheries (e.g, squawfish: Hammon &
<br />Inslee 1982), but attempts to re-introduce native species to their former ranges
<br />(Miller et al. 1982) probably will fail. That some species (man included) fail
<br />while others proliferate in ecosystems undergoing change is tempered only by
<br />the time-frame within which one chooses to pose the problem,
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<br />370
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<br />
<br />Acknowledgements
<br />
<br />We thank Drs L. Paulson and R. Behnke for reviewing the manuscript.
<br />
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