River Ecology and Restoration - River Dynamics and Integrated River Management - page 630

In arid and semi-arid areas, water is vital for the fauna since the only naturally occurring permanent
sources of water present are the streams. The high primary productivity and biomass of riparian areas is
largely a result of these moist environments, for the food sources and cover types of the surrounding
areas are very different from the riparian area. Stream corridors provide water, shade, evapotranspiration,
and cover, thus, ameliorating the temperature and moisture extremes of uplands. Nearly all amphibians,
many reptiles and mammals are found primarily in river corridors and riparian habitats.

10.1.2.2 Aquatic Ecosystem
Stream biota are often classified into seven groups—bacteria, algae, macrophytes (higher plants), protists
(amoebas, flagellates, ciliates), micro-invertebrates (invertebrates less than 0.5 mm in length, such as
rotifers, copepods, ostracods, and nematodes), macro-invertebrates (invertebrates greater than 0.5 mm in
length, such as mayflies, stoneflies, caddisflies, crayfish, worms, clams, and snails), and vertebrates (fish,
amphibians, reptiles, and mammals) as shown in Fig. 10.6. Undisturbed streams can contain a remarkable
number of species. For example, more than 1,300 species were found in a 2 km reach of a small German
stream, the Breitenbach, when a comprehensive inventory of stream biota was taken.
The most important elements of the aquatic ecosystem for river management are aquatic plants,
benthic invertebrates, and vertebrates (fish, reptiles, and amphibians). Aquatic plants usually consist of
mosses attached to permanent stream substrates and macrophytes including floating plants ˈ such as
Eichoimia crassips , submerged plants, such as Potamogeton , and emergent plants, such as Phragmites
communis trirn (reed). These plants provide primary productivity for the faunal community, and play an
important role in decontaminating the river water and providing multiple habitats for fish and
invertebrates. Bedrock or boulders and cobbles are often covered by mosses and algae. Figure 10.7
shows microhabitats with moss on cobbles, submerged macrophytes species Potamogeton , floating
plants species Lemna minor L. , and emergent plants species Phragmites communis trirn (reed). Rooted
aquatic vegetation may occur where substrates are suitable and high currents do not scour the stream
bottom. Luxuriant vascular plants may occur in some areas where water clarity, stable substrates, high
nutrients, and slow water velocities are present.

Fig. 10.6 Stream eco-system and bio-community (after FISRWG, 1997) (See color figure at the end of this topic)