Community of lentic waters

COMMUNITY OF LENTIC WATERS

Organisms that live in a lake are interconnected due to the energy flow and circulation of substances through food chains, which enables their growth, development and reproduction. There are two layers in the lake: surface layer – an illuminated layer which includes the producers, photosynthetic organisms that transfer the solar energy into the chemical energy; and the deeper layer – a weaker illuminated layer where we find the consumers and decomposers, which feed on the producers. Dead organisms fall to the bottom where they become decomposed by bacteria – decomposers. Decomposition results in development of mineral substances, water and carbon dioxide, which are all then used again by the producers and therefore involved into a new food chain.

At the beginning of its existence, each lake is poorly productive because it contains few mineral salts necessary for the growth and development of plants, cyanobacteria and algae, which are responsible for the availability of nutrients for other organisms. With time, the accumulation of mineral salts occurs in a lake – this causes intensive growth of phytoplankton and plants, and the increase in animal numbers. Dead organisms fall to the bottom where they get decomposed by bacteria.

The undecomposed plant and animal detritus, together with the fine organic matter, settle to the bottom and increase the sediment layer, hence the lake becomes shallower and more productive. The edges of the lake are slowly covered up, and become inhabited by the communities of swamp and aquatic plants (reed, cattail, true fox-sedge), and bushy and woody plants like alder, willow and poplar. The water surface gradually decreases, the lake slowly transfers into a pond, and then into a swamp.

Lake Trakošćan is of anthropogenic origin. It is also exposed to the aging process that is greatly enhanced by organic and inorganic material brought via streams that flow into the lake, and by the development of phytoplankton and aquatic plants – their dying speeds up the covering up of the lake. This process ideally should be eliminated by occasional sediment removal and maintenance of biological balance in the lake.