8142

• UCREFRP Catalog Number: 8142
• Author: Horn, M. J.
• Title: Nutritional Limitation of Recruitment in the Razorback Sucker ‎(
• USFW Year: 1996.
• Copyright Material: NO

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national issue, and federal subsidies were used to construct a series of major dams (Table

2), the foremost of which was Hoover Dam, completed in 1935 to impound Lake Mead.

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High dams on the lower Colorado River controlled flooding, so channelization,

levee construction, and other amenities to manipulate and deliver water proceeded apace

with increasing demands. The dams also produced electricity for pumps and other

devices to expand agriculture and develop industry. Domestic water supplies were

abundant, and along with expanded economy and a salubrious "Sunbelt" climate,

stimulated retirement and recreation industries, such that human populations burgeoned

and their demands on resources increased.

Reservoirs retain sediment, effectively ending bedload transport of inorganic

material from upstream and curtailed transport in the form of suspended turbidity.

Chemical nutrients are retained due to biologic uptake and sedimentation under lentic

conditions, although release of hypolimnetic water may mitigate that effect (Stanford

1994). Organic materials from the watershed are similarly affected. Particulate sediment

and dissolved organics are altered and often reduced under reservoir conditions.

Downstream impacts include significant changes in thermal regimes and increased

degradation of bottom and banks by clear water with high erosional competence, the latter

compensated for by further channel modification (Williams and Wolman 1984). The

process of degradation selectively removes fine sediments, leaving large-particle or

"armored" bottoms. Additionally, discharge patterns downstream from regulatory

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