Describe major ecosystems of the earth.

Aquatic Eco-systems : Aquatic ecosystems include fresh water lakes, rivers, estuaries, neritic zones, etc. The concentration of dissolved oxygen and the sunlight penetration of water and the availability of nutrients are limiting factors for aquatic organisms.

Fresh Water Lakes : These are deep; there are two zones : (i) surface layer and (ii) bottom layer. Surface layer is warm and exposed to sunlight penetration while bottom layer is cold. Surface layer is rich in oxygen and bottom layer is rich in nutrients. Seasonal mixing of water between these two layers enables the survival and growth of organisms. These have variety of plants and water birds.

Rivers : Rivers have wide variety of organisms. In the upper layer aquatic plants and animals are anchored to rocky surfaces. In the lower reaches, layers of alluvial sediments provide habitats for burrowing animals and bottom feeders.

Estuaries : These are the most productive among the aquatic ecosystems. Because of sunlight penetration, tidal action which enable mixing of nutrients, there is a luxuriant plant growth. Thus a variety of organisms like crabs, Oyesters, shrimps, fishes and birds etc. are found.

Neritic Zones : These zones are the richest fishing grounds. Beyond the edge of the continental shelf productivity is low thus open oceans are biological deserts.

Terrestrial Ecosystems : These are of greater concern because we live on land and needs for our food and other materials are met from terrestrial ecosystems. The surface of the land has a cover of vegetation of different kinds depending on climatic conditions such as moisture, temperature, etc. Plants occur in distinct groups of communities in areas having similar climatic conditions and these are called biomes.