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Vennesla 2001

 
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Ponds and marshes are both a part of the eco-system called wet area. Quite often you can observe that ponds becomes overgrown with plants, and turns into so-called wet areas.

Bogies you find where the fertile soil is too humid for trees to grow, and they mainly consist of a thick layer of partly decayed plants evolved through hundreds of years. This thick layer is peat, that can become several meters thick, and have been used as fire wood. The reason why this putrefaction process is not finished before the growth of new plants is started, is that our cold climate and the high humidity slows the process.

In many marshes you find ponds. This certifies that there once upon a time have not been marshes here. Why has this happened? Eutrophication of the local surroundings is the most serious defilement problem in wet areas here in Norway, in relation to the biological diversity. Eutrophication mainly has a local affect, but form a serious threat to the biological diversity.

• Eutrophication

Eutrophication is often the main reason why small lakes or ponds turn into marshes. Increased input flow of nutritive substances from plants, uncleaned sewage drain and industry can cause eutrophication in wet areas. The consequences can be that fish and other living beings dies because of a lack of oxygen or a vast prosperity of toxic algae. The algae is dependent on both nitrates and phosphates. A high content of both gives the algae a propitious living conditions, but a lack of one will stabilise the stock.

• Embittered areas:

Embittering of wet areas often cause changes in the stocks of many species, among these insects, fish and plants. If the contamination is severe, the whole eco-system in an area may be changed. Liming can improve the water for a short period, but the long-term affect is these days unknown.

Embittered lakes, often named as swamp lakes or dystrophic lakes, most often have a high content of litter. Different kinds of peat and macro vegetation are common among the vegetation. Organic material grown in this way is transformed and broken down very slowly. It is the low pH-level that has a restraining effect on the bacterial decomposition and the litter’s antiseptic effect that cause the slowness in the process and the creation of peat.

Plants are dependent on, among other things, CO_2, but do not need oxygen. Therefor they will not berestrained of any oxygen-lack. The accumulation of nutritive substances by the water line makes the plants able to grow further and further out in the pond. The pond becomes smaller, but the marsh that surround it becomes larger.

The causes of eutrophication is noticeable on the stock of fish. If it is not already exterminated there will sooner or later be too bad living conditions for the fish to stay here. Therefor they will have to move (if possible). If not, the stock will die of the reasons mentioned under "Eutrophication". Further information concerning the consequences, you can find here.

When embittering occurs, the causes will be a reduced amount of species, both plants, insects and animals. It will only be the ones able to adjust themselves to the new living conditions, that will survive. The biological diversity will be reduced while new species will come.