i. Ponds and Lakes

i. Ponds and Lake
  • These regions range in size from just a few square meters to thousands of square kilometers. Scattered throughout the earth, several are remnants from the Pleistocene glaciations. Many ponds are seasonal, lasting just a couple of months while lakes may exist for hundreds of years or more. Ponds and lakes may have limited species diversity since they are often isolated from one another and from other water sources like rivers and oceans. Lakes and ponds are divided into three different “zones” which are usually determined by depth and distance from the shoreline.
  • The topmost zone near the shore of a lake or pond is the littoral zone. This zone is the warmest since it is shallow and can absorb more of the Sun’s heat. It sustains a fairly diverse community, which can include several species of algae (like diatoms), rooted and floating aquatic plants, grazing snails, clams, insects, crustaceans, fishes, and amphibians. In the case of the insects, such as dragonflies and midges, only the egg and larvae stages are found in this zone. The vegetation and animals living in the littoral zone are food for other creatures such as turtles, snakes, and ducks.
The zone of lake

  • The near-surface open water surrounded by the littoral zone is the limnetic zone. The limnetic zone is well lighted (like the littoral zone) and is dominated by plankton, both phytoplankton and zooplankton. Planktons are small organisms that play a crucial role in the food chain. Without aquatic plankton, there would be few living organisms in the world, and certainly no humans. A variety of freshwater fish also occupy this zone.
  • Plankton have short life spans - when they die, they fall into the deep-water part of the pond, the profundal zone. This zone is much colder and denser than the other two. Little light penetrates all the way through the limnetic zone into the profundal zone. The fauna are heterotrophs, meaning that they eat dead organisms and use oxygen for cellular respiration.

Classification of lakes

On the basis of formation of lakes they are broadly grouped into two
    1. Natural
    2. Artificial
1.Natural lake 2.Artificial lake
On the basis of productivity, lakes are grouped into two
  • Oligotrophic : Very little plant and animals, poor in nutrients
  • Eutrophic : More plants and animals, rich in nutrients
1.Oligotrophic lake 2.Eutrophic Lake
Thermal stratification of lakes
  • Epilimnion : Upper stratum of water exposed to sunlight
  • Hypolimnion : Basal stratum when water remains always cool and does not circulate
  • Thermocline : Transitional zone between eplimnion and hypolimnion where temperature changes occur
Thermal stratification of lakes
On the basis of light penetration lakes have the following zones
  1. Euphotic zones : Sunlight present in this region extends up to 53 m.
  2. Disphotic zones : Sunlight is present but the quantity of sunlight in low. Extends up to 200 m.
  3. Aphotic zones : Light is absent in this region. Extend from 200 m to bottom of the lakes.

Last modified: Thursday, 29 March 2012, 9:12 PM