River Ecology and Restoration - River Dynamics and Integrated River Management - page 625

10 River Ecology and Restoration
Abstract
The biological community of a river ecosystem is determined by the characteristics of both terrestrial and
aquatic ecosystems. The terrestrial ecosystem depends mainly on the plant community and the aquatic
ecosystem comprises aquatic plants, benthic invertebrates, and vertebrates. The main ecological functions
of rivers are habitat, conduit, filter, barrier, source, and sink. Ecological stresses are defined as the
disturbances that bring changes to river ecosystems. The ecological stresses are natural events or
human-induced activities that occur separately or simultaneously. The structure of a system and its
capability of carrying out important ecological functions may be changed by stresses, regardless of
whether they act individually or in combination. Damming, gravel and sand mining, channelization, water
diversion, habitat fragmentation, exotic species, landslides and debris flows, and intensive fluvial
processes are the most common stresses on stream ecology.
For quantitative assessment of river ecology indicator species are selected, which are defined as a
set of organisms whose characteristics are used as an index of attributes or environmental conditions
of interest, which are too difficult, inconvenient, or expensive to measure for other species. Benthic
invertebrates and fish are used as indicator species for most stream ecology assessment. The ecosystem
can be assessed by monitoring the species richness (number of species) and the number density (or
abundance) for each species. Many parameters representing biodiversity of river ecosystems have been
proposed. Management and restoration of river ecosystems are based on an understanding of the relations
between physical, chemical, and biological processes at varying time scales. Often, human activities have
accelerated the temporal progression of these processes, resulting in unstable flow patterns and altered
biological structure and function of stream corridors. Various strategies for ecological restoration are
discussed in this chapter.
Key words
Stream corridor, Ecological stresses, Indicator species, Benthic invertebrates, Ecological restoration,
Biodiversity
10.1 River Ecosystems
10.1.1 Spatial Elements of River Ecosystems
Ecosystems of rivers vary greatly in size. Taking a deeper look into these ecosystems can help to explain
the functions of landscapes, watersheds, floodplains and streams, as shown in Fig. 10.1. In ecosystems
movement between internal and external environments is common. This may involve movement of
materials (e.g. sediment and storm water runoff), organisms (e.g. mammals, fish and insects) and also
energy (e.g. heating and cooling of stream waters).
Many sub-ecosystems form a river ecosystem which, in turn, can also be part of a larger scale landscape
ecosystem. The structure and functions of the landscape ecosystem are in part determined by the structure
and functions of the river ecosystem. The river ecosystem may have input or output relations with the
landscape ecosystem, thus, the two are related. In order to plan and design a river ecosystem restoration,
it is vital to first investigate the relations between the ecosystems. Landscape ecologists use four basic
terms to define spatial structure at a particular scale:
1. Matrix—the land cover that is dominant and interconnected over the majority of the land surface.
Theoretically the matrix can be any land cover type but often it is forest or agriculture.