River Ecology and Restoration - River Dynamics and Integrated River Management - page 637

also can have terrible aesthetic consequences the worst of which is the death of fish. Eutrophication in
lakes and reservoirs is indirectly measured as standing crops of phytoplankton biomass, usually represented
by planktonic chlorophyll-a concentration. However, phytoplankton biomass is not generally the main
component of plant biomass in smaller streams because the growth of periphyton and macrophytes,
which live on the stream bed, is promoted by high substrate to volume ratios and periods of energetic
flow. When there are decreased flows and high temperatures, excessive algal mats develop and oxygen is
depleted due to eutrophication.
10.1.4 Ecological Functions of Rivers
The main ecological functions of rivers are habitat, conduit, filter, barrier, source, and sink. Ecological
restoration is done in order to enable river corridor functions to be effectively restored. However, the
goals of restoration are not only to reestablish the structure or to restore a particular physical or biological
process. Section 10.1 emphasizes matrix, patch, corridor, and mosaic as the most basic building blocks of
physical structure at local to regional scales. Ecological functions, too, can be summarized as a set of
basic, common themes that reappear in an ongoing range of situations.
Two characteristics are particularly important to the operation of stream corridor functions:
(1) Connectivity—This is a measure of the dimensions of a stream corridor and how far it continues
(Forman and Godron, 1986). This attribute is affected by breaks in the corridor and between the stream
and adjacent land uses. Transport of materials and energy and movement of flora and fauna are valuable
functions promoted by a high degree of connectivity in a stream between its natural communities.
(2) Width—In stream corridors, this refers to the distance across the stream and its zone of adjacent
vegetation cover. Width is affected by edges, community composition, environmental gradients and
disturbances/disruptions in adjacent ecosystems, including those with human activity. Average dimension
and variance, number of narrows, and varying habitat requirements are some example measures of width
(Dramstad et al., 1996).
10.1.4.1 Habitat Function
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. The important factors needed for
survival such as space, food, water, and shelter are provided by the habitat. As long as the conditions are
suitable, many species use river corridors to live, find food and water, reproduce, and establish viable
populations. Population size, number of species, and genetic variation are a few measures of a stable
biological community, which vary within known boundaries over time. Streams may positively affect
these measures at different levels. Since corridors are linked to small habitat patches, they have a great
value as habitats because they create large, more complex habitats with greater wildlife populations and
higher biodiversity. In general, stream corridors are habitats for plants, fish, invertebrates, and amphibians.
For instance, the Fazi River is an urban stream in Taichong City, as shown in Fig. 10.12. The river has
gravel bed with alternative lentic and lotic waters. Although the river is seriously polluted in the upstream
reaches several tens of species of macro-invertebrates, fish and birds are found in the river.
Habitat functions differ at various scales, and an appreciation of the scales at which different habitat
functions occur will help a restoration initiative succeed. The evaluation of a habitat at larger scales, for
example, may make note of a biotic community's size, composition, connectivity, and shape. To help
describe habitat over large areas at the landscape scale, the concepts of matrix, patches, mosaics, and
corridors can be used. Migrating species can be provided with their favorite resting and feeding habitats
during migration stopovers by stream corridors with naturally occurring vegetation. Some patches are too
small for large mammals like the black bear which need great, unbroken areas to live in. However, these
patches may be linked by wide stream corridors to create a large enough territory for bears.