Environmental Engineering Reference
In-Depth Information
The most obvious roles of plants are those that affect fish and wildlife. At the landscape level, the
fragmentation of native cover types has had a negative impact on the wildlife needing large areas of
ongoing vegetation. In some systems, small fractures in the continuity of corridors can greatly affect
animal movement and can negatively impact the conditions in a stream which permit it to host certain
aquatic species. Narrow stream corridors that are essentially edge habitat may encourage generalist species,
nest parasites and predators, and where corridors have been established across historic barriers to animal
movement, they can disrupt the integrity of regional animal assemblages (Knopf et al., 1988).
The conditions of nearby habitats must be taken into account when planning to restore riparian areas.
Carothers (1979) found that non-riparian birds frequently use the edges of riparian areas as habitats.
However, smaller riparian birds carry out activities within the riparian area during the breeding season
and larger species often forage in nearby areas (Carothers et al., 1974). In fact although the larger species
may forage many miles away from the riparian area, they would still depend on them critically (Lee et al.,
1989).
If the conditions upstream of an ecosystem have been significantly altered by, for example, a dam or
any other water diversion project, it will be impossible to restore that ecosystem to its natural, perfect
condition. This stands even if complete restoration is a possibility. For example, the creation of areas of
woody vegetation in the channel below several dams in the Platte River Valley in Nebraska has
significantly decreased areas of wet meadow—an important habitat. The area has been declared a critical
habitat for the Whooping Crane, the Piping Plover, and the Interior Least Tern (Aronson and Ellis, 1979).
10.1.3 EcologicalConditions
Flow— Streams are distinguished from other ecosystems by a flow of water from upstream to downstream.
The micro-and macro-distribution patterns of many stream species are affected by the spatial and
temporal characteristics of stream flow, such as fast versus slow, deep versus shallow, turbulent versus
laminar, and flooding versus low flows (Bayley and Li, 1992: Reynolds, 1992; Ward, 1992). Flow
velocity affects the deliverance of food and nutrients to organisms, however, it can also dislodge them
and prevent them from remaining at a certain site. When a stream has a very slow flow, the fauna on the
banks and the bed are similar in composition and configuration to those present in stagnant waters
(Ruttner, 1963). High flows are cues for timing migration and spawning of some fish. When fish detect
high flows, some will migrate and some will spawn.
Temperature— Water temperature can vary markedly in a stream system and between different stream
systems. It is a very important factor for cold blooded aquatic organisms for it affects many of their
physiological and biochemical processes. Stream insects, for example, often grow and develop more
rapidly in warmer portions of a stream or during warmer seasons. Some species may complete two or
more generations per year at warmer sites yet only one or fewer at cooler sites (Sweeney, 1984; Ward,
1992). This can also be applied to algae and fish for their growth rates increase with increased water
temperature (Hynes, 1970; Reynolds, 1992). Some species are only found in certain areas due to the
correlation between temperature and growth, development, and behavior.
Riparian vegetation— Decreased light and temperature in steams can be a result of riparian vegetation
(Cole, 1994). When the flow of water is slow, direct sunlight can significantly warm up the water,
especially in the summer. In Pennsylvania, the average daily stream temperatures increased by 12 ć
when flowing through an open area in direct sunlight but then decreased significantly during flow
through 500 m of forest (Lynch et al., 1980). However, during the winter, a lack of cover has the opposite
effect and causes a decrease in temperature. Sweeney (1992) found that temperature changes of 2 to 6 ć
usually altered key life-history characteristics of some species. It has been observed that riparian forest
buffers help to prevent changes in natural temperature patterns and also to mitigate the increases in
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