"Natural Science 4" is an interactive encyclopedia that includes scientific information in the understanding of fourth grade students, wonderfully illustrated and animated.
.
www.edituraedu.ro
.
* Chapter 2 Lesson 8 *
* The River *
The river is flowing water. It increases in flow by joining several streams. It flows downstream due to gravity and empties either into another river or river, or into a lake, sea, or ocean.
Did you know that most of the water in rivers comes directly from rainfall runoff?
Over time, the waters of the rivers shaped the land, carried huge amounts of rock and silt into the oceans, dug caves and carved the mountains and hills.
Mountain rivers have fast, cold, clear and oxygen-rich water. They flow over stones and boulders. This is where the brown trout lives. You'll recognize it by its mottled green back. And the pike, a fish related to the trout but much larger, is a fast swimmer. It appears as an elegant fish, wrapped in a web of tiny scales, with many black dots on its back and sides. The frog shares its territory with the green frog and the newt.
Rivers in the lowland area flow slowly, in wide beds, and have turbid, oxygen-poor water. The bottom of these rivers consists of sand and silt. In their waters live the carp, the pike, the redfish, the tench, the frog, the snail, the crayfish and various species of snakes.
Trees (firs, beeches, oaks, willows, alders) and other water-loving plants (reeds, reeds) grow on the banks of rivers. Many birds nest here (ducks and wild geese, swans, pelicans, mallards). On the sheen of the water you can see the silk of the frog, algae, moss, as well as the beautiful water lilies. Numerous insects fly over the beds (dragonflies, midges, mosquitoes). You will also encounter mammals such as otter, water rat and beaver.
In order to live in the aquatic environment, animals show specific adaptations. Thus, some invertebrates can attach themselves to stones. Birds, such as ducks, and some mammals, such as beavers, have their toes joined by a membrane called a web. This is very useful in moving through water. Other birds, like storks, have long, thin, featherless feet, with the toes joined at the base to prevent them from sinking into the mud at the water's edge. Waterfowl produce a grease with which they coat their feathers to keep water out.
What other adaptations to this environment do you know?