Geoscience Reference
In-Depth Information
l ows”—are a hotly debated topic between farmers, i shermen, environmen-
talists, and scientists.
Healthy watersheds—and the ecosystems they support—go largely unap-
preciated because they lack a market value. Nevertheless, rivers provide food,
materials, and recreation, and freshwater ecosystems regulate environmental
conditions that benei t humans. For instance, wetlands improve water qual-
ity by i ltering out pollutants and impurities, and they provide an important
buf er during periods of l ooding.
environmental costs of the hydraulic era
Declining diversity in freshwater habitats in the western United States is
largely a result of the combined ef ects of natural hydrologic patterns, pol-
lution, and nonnative species invasions. In California, i sh provide the best
indicators of aquatic deterioration. Of the 129 native i sh species in the state,
40 percent are in decline, 37 percent are eligible for listing as threatened or
endangered, and 5 percent are extinct. Most of these species (60 percent) are
found exclusively in California, so their decline is thought to be due to fac-
tors within the state, directly related to water and land development.
h
e Salmon Story
h e plight of the once prolii c salmon on the Pacii c coast illustrates the
impact of water development on aquatic life. Salmon have important link-
ages with many ecosystems from the ocean to streams and are therefore
considered a keystone species. h e chinook salmon have evolved along with
western watersheds over thousands to millions of years and have been a main-
stay of coastal Native American diets for at least i ve millennia. Although
natural population sizes of salmon have l uctuated over this time period, at
no point in the past have their numbers dropped as low as they have over the
past century.
h e natural range of chinook salmon encompasses the northern Pacii c
Ocean from California to the Gulf of Alaska and includes entire watersheds
of the western states: from the rain forests of the Cascades in the Northwest
to the Sierra Nevada range and deserts of California and as far inland as
Rocky Mountain streams. Salmon by the millions once migrated up rivers
along the Pacii c coast, transforming streams into sparkling “silver pavement.”
