Basic Concepts and Management Issues of Rivers - River Dynamics and Integrated River Management - page 25

the U.S., second only to pinyon-juniper among eight other forested cover types in the region. Fifty-two
of the 68 mammal species found in west-central Arizona, the U.S., in Bureau of Land Management
inventories use riparian habitats. Stamp and Ohmart (1979) found that riparian areas had a greater diversity
and biomass of small mammals than adjacent upland areas.
Aquatic ecosystems and aquatic habitat —The biological diversity and species abundance in streams
depend on the diversity of available habitats. Naturally functioning, stable stream systems promote the
diversity and availability of habitats. A stream's cross-sectional shape and dimensions, its slope and
confinement, the grain-size distribution of bed sediments, and even its planform affect aquatic habitat.
Under less disturbed situations, a narrow, steep-walled cross section provides less physical area for habitat
than does a wider cross section with less steep sides, but may provide more biologically rich habitat in
deep pools compared to a wider, shallower stream corridor. A steep, confined stream is a high-energy
environment that may limit habitat occurrence, diversity, and stability.
Habitat —Habitat is a term used to describe an area where plants or animals (including people) normally
live, grow, feed, reproduce, and otherwise exist for any portion of their life cycle. Habitats provide
organisms or communities of organisms with the necessary elements of life, such as space, food, water,
and shelter. Under suitable conditions often provided by stream corridors, many species can use the corridor
to live, find food and water, reproduce, and establish viable populations. Habitat increases with stream
sinuosity. Uniform sediment size in a streambed provides less potential habitat diversity than a bed in
which many grain sizes are represented. Habitat subsystems occur at different scales within a stream
system (Frissell et al. 1986). The grossest scale, the stream system itself, is measured in thousands of meters,
while segments are measured in hundreds of meters and reaches are measured in tens of meters. A reach
system includes combinations of debris dams, boulder cascades, rapids, step/pool systems, pool/riffle
sequences, and or other types of streambed forms or “structures,” each of which could be 3 m or less in
scale. Frissell's smallest scale habitat subsystem includes features that are 0.3 m or less in size. Examples
of these microhabitats include leaf or stick detritus, sand or silt over cobbles or other coarse material,
moss on boulders, or fine gravel patches.
Wetlands —Wetlands is a general term used to describe areas, which are neither fully terrestrial nor fully
aquatic. Wetlands are lands where saturation with water is the dominant factor determining the nature of
soil and vegetation development. The International Union for the Conservation of Nature and Natural
Resources organized an international conference for wetland protection in Ramsar in 1971 and the
member states signed the Convention on Wetlands of International Importance Especially as Waterfowl
Habitat, which is known as Ramsar Wetland Convention. China has become a member state since 31 July
1992. As shown in Fig. 1.20 wetlands are defined by the wetland convention as areas of marsh, everglade,
fen, peatland and swamp, where natural or artificial, permanent or temporary, with water that is static of
flowing, fresh, brackish or salt, including areas of marine water, the depth of which at low tide does not
exceed six meters (www.ramsar.org).
The minimum essential characteristics of a wetland are recurrent, sustained inundation or saturation at
or near the surface and the presence of physical, chemical, and biological features that reflect recurrent
sustained inundation or saturation. Common diagnostic features of wetlands are hydric soils and hydrophytic
vegetation. These features will be present except where physicochemical, biotic, or anthropogenic factors
have removed them or prevented their development (National Academy of Sciences, 1995). Wetlands
may occur in streams, riparian areas, and floodplains of the stream corridor. Wetlands are transitional
between terrestrial and aquatic systems where the water table is usually at or near the surface or the land
is covered by shallow water (Cowardin et al., 1979). For vegetated wetlands, water creates conditions
that favor the growth of hydrophytes-plants growing in water or on a substrate that is at least periodically
deficient in oxygen as a result of excessive water content (Cowardin et al., 1979) and promotes the