Unit 6: The diversity of the ecosystems                                      1   2   3

3.2. Continental water ecosystems

Continental waters are usually freshwater, although sometimes they can also be brackish, as occurs in some lakes.

Continental waters make up less than 3% of the Earth’s surface waters and aren’t very deep compared to the waters in the oceans and seas.

Depending on how fast they move, continental waters are classified into still waters or running waters. Organisms that live in these different types of waters have special adaptations for the conditions there. For example, running waters are well-oxygenated, but some still waters can have low levels of oxygen, so organisms in these waters must be able to survive with less oxygen.

a) Still waters (lentic ecosystems)

Still waters include lakes, lagoons, ponds and wetlands (marshes and swamps) and the deeper ones can be divided into regions similar to the ocean zones.

There is an enormous biodiversity of living things in these ecosystems.

Their vegetation consists of plants adapted to very wet or aquatic environments. Algae and aquatic and floating plants are abundant in the water. And along their flooded shores bulrushes and reeds are commonly found.

There is a great variety of animals like invertebrates, fish, reptiles and amphibians. But the most characteristic fauna are birds. Some live here permanently, while others use them as stopover sites during their migrations.

b) Running waters  (Lotic ecosystems)

Flowing or running waters are rivers, streams and springs.

Running waters are usually colder than still waters, and generally contain abundant oxygen.

The most significant factor which affects life in these waters is the speed of the water current; for this reason, the plants and animals which live in them often have organs that they use to stay in place, or they are excellent swimmers.

3.3. What are the differences between lotic and lentic ecosystems?