7923

• UCREFRP Catalog Number: 7923
• Author: Carter, J. G. and V. A. Lamarra.
• Title: An Ecosystem Approach To Environmental Management, Chapter 17.
• USFW Year: n.d.
• USFW - Doc Type: 261-287
• Copyright Material: YES

nutrients may ameliorate this effect to some extent.
Species composition of primary producers also is
influenced by suspended and deposited sediment. Changes
in species and biomass are related to changes in suspended
solids concentrations, rate of deposition, bed-load
movement, and substrate type (Whitton, 1975).

Sediment influences macroinvertebrates by modifying
habitats and inducing movement out of areas with high
rates of deposition (Cummins, 1975). These high rates of
deposition often reduce the number of benthic organisms by
burial of sessile organisms and alteration of the
substrate. Increased suspended sediment levels often
result in an increased rate of insect drift out of the
affected area. Filter-feeding invertebrates, especially
certain molluscs and crustaceans, are adversely affected
by high levels of suspended solids over extended periods
of time. There is little evidence for sediment-induced
mortality for groups other than the molluscs. Recovery by
mobile invertebrates is rapid, following the resumption of
normal conditions. Recovery depends upon how the habitat
was modified, the substrate preference and life history of
the organism, the types of refugia available, and the mode
of migration. Recolonization may involve downstream
drift, upstream migration from within the substrate, and
reproduction (Hynes, 1970).

Suspended sediments affect fish by increasing
mortality, altering rates of reproduction, and modifying
growth rates. Suspended sediment does not appear to be
lethal for juvenile and adult fish, but may reduce their
resistance to disease and also damage gill tissues. Fish
may avoid localized areas of increased sediment
concentrations. The deposition of clay to sand-size
particles adversely affects reproduction in some groups,
particularly the salmonids. This results from reducing
the flow of water and, hence, the renewal of oxygen to
deposited eggs. Habitat modification, particularly the
loss of cover for juvenile fish, and removal of suitable
spawning sites may reduce certain fish populations. The
endemic fishes found in the White River have special,
unique adaptations to overcome the natural turbidity of
this ecosystem.

The amount of solar energy entering the White River
ecosystem is important when attempting to predict the
effect of changes in other physical characteristics. The
light climate of each major habitat type may explain the
benthic community responses to changes in flow, silt load,
temperature, and chemical alterations. It is evident that
net production and respiration closely follow available

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