In riverine systems, sediment flux and organic matter
inputs are important components of habitat structure
and dynamics. Natural sediment regimes are those that
accompany natural flow variation. Natural organicmatter
regimes include seasonal inputs from terrestrial
environments. Terrestrial organic matter inputs, especially
in smaller rivers and streams, are particularly
important sources of energy and nutrition, while large,
coarse, woody material provides substrate and habitat
for organisms (Cummins 1974, Gregory et al. 1991).
In lakes and wetlands, all but the finest inflowing sediment
is permanently stored, so that over time these
systems fill. The invertebrates, algae, bryophytes, vascular
plants, and bacteria that populate the bottoms of
freshwater systems are responsible for much of the water
purification, decomposition, and nutrient cycling
that occurs (Palmer et al. 2000). They are highly adapted
to the specific sediment and organic matter conditions
of their environment, as are many fish species,
and do not persist if changes in the type, size, or frequency
of sediment inputs occur (Swanson et al. 1988,
Allan 1995).