Fertilizer Overflow in Natural Waters

The Ecological Cycle in Natural Waters

In absolutely clean water, only small numbers of animals and plants live together. Fish and small aquatic animals feed on the plants and use up oxygen. Plants generate oxygen and supply food. When bacteria decompose dead organisms and re-build nutrients from them, they need oxygen. In clean waters there are few bacteria since only a few organisms die. An ecological balance exists.

Nitrate and phosphate are food for the plants. Therefore, they are used as fertilizers in agriculture. Some detergents contain phosphate, too. Indeed, fertilizers based on nitrate and phosphate lead to an increased growth of plants, but their salts are washed into brooks, rivers and lakes by the rain and the ground water. Phosphate also gets into the environment through domestic sewage.

In that way, humans introduce additional nutrients into the environment, which may cause an imbalance in the ecosystem of the natural waters.

When there are more nutrients present, the organisms multiply more and there are more dead organisms as a result. The bacteria that decompose these organisms get more food and multiply, too. By doing so, they use up more oxygen than is at their disposal, though, and algae are able to multiply. The algae prevent light from reaching the ground of the natural waters. The plants living there can no longer carry out photosynthesis, and so they die and rot. The oxygen content decreases more and more, and fish, snails and crab die due to a lack of oxygen - the water is dead.