Marine environment : The marine environment is characterised by high concentration of salt and mineral ions. The salt concentration in the open sea is about 3.5 per cent. Salinity of the surface water and the water at various depths and latitudes varies. Salinity is least near the poles and river mouths. The sea is not a single environment. More important determinants of marine eco-systems are depth of water, distance from the shore and drainage of glaciers and rivers.
Fresh water environment : Lakes and ponds are stagnant fresh water bodies and occur particularly in every biome. They vary in size from less than a hectare to hundreds of hectares. The relatively shallow lakes called eutrophic lakes, have a rich accumulation of organic products. The fresh water ponds are called autotrophs and have microscopic phytoplanktons.
Streams and rivers differ in volume, temperature etc. The nature and composition of flora and fauna depend on the source of river and the land environment.