Eutrophication

Eutrophication is the gradual increase of the concentration of phosphorus, nitrogen and other plant nutrients in ageing aquatic ecosystems such as a river or a lake. Eutrophication is part of a cycle of for instance phosphorus. Plants use the nutrients as food to grow and the plants are food and shelter for other animals that live in the waterbodies. Algae is a fast-growing organism and lies on the surface of the water. The algae prevent sunlight to come through making it harder for plants that live on the bottom to survive resulting in fewer plants and thus less oxygen in the water. Eutrophic waters are often murky and may support fewer large animals due to lower oxygen levels in the water than non-eutrophic waters.

Cultural Eutrophication

Cultural eutrophication happens when human water pollution speeds up the ageing process by introducing sewage water, detergent, Fertilizers and other nutrient sources into aquatic ecosystems. Cultural Eutrophication has dramatic consequences on waterbodies and is one of the leading causes of aquatic ecosystem degradation.

Commonly cultural eutrophication results in extremely low oxygen concentrations. This condition is called hypoxia. Waters with hypoxia are also sometimes called dead waters. Hypoxic water result in massive fish kills with a rippling effect throughout the food chain and local economics. Some algae release toxins and lots of toxic algae blooms caused by eutrophication are also related to lots of fish and mollusc mortality.

Process of Eutrophication

Eutrophication sets off a chain reaction in ecosystems and depending on what the cause of the eutrophication is (natural or man-made), it does more or less damage to the entire aquatic ecosystem. Natural Eutrophication is in balance and only result in lower oxygen levels but not in hypoxic water and cultural eutrophication is a speed-up process without balance and results in hypoxic waters.

Cultural Eutrophication by steps:

1. Fertlizers that are rich in nutrients like nitrate and phosphate are washed into a river or lake systems
2. There is an increase in nutrients concentration in the water
3. Nutrients are food for algae. The algae will grow and reproduce very quickly and the algae form a thick green bloom in the water
4. The algal bloom will use and absorb the sunlight for Photosynthesis. The sunlight does not reach the water under the algal layer and the plants that live on the bottom will die because do not get any sunlight for photosynthesis.
5. When algae have eaten all the nutrients from the fertilizers they will also start to die
6. Bacteria will break down the dead plants and algae by using oxygen (aerobic process) and releases more nutrients back into the water which algae use to grow and resulting in more algae blooms
7. When bacteria consume the dead plants and algae, the water can run out of oxygen because the plant on the bottom cannot produce any oxygen caused to a lack of sunlight due to algae blooms. When the water ran out of oxygen completely, the water turns hypoxic
8. All life in the water will die

Ecoologic tragedy in Oder river due to eutrophication

In 2022 there has been a massive fish kill in the Oder river that flows through Germany as well as Poland. At first, the cause of this massive fish and mollusc kill was unclear, however, after lots of research the cause of this ecologic tragedy has become clear. There were many factors involved that resulted in this die-off. For instance: Salt discharges, abundant nutrients, high water temperatures and long residence time in barrages and in developed rivers. These factors altogether caused an extremely low oxygen level in the river. Because of the nutrients that leaked into the river a toxic algae bloom grew massively and the toxins, as well as the aerobic digestion of the dead algae and plant, made the river unliveable for the fish and molluscs resulting in thousands of dead fish. This has major consequences for the whole ecosystem and food chain because birds also get affected by this tragedy. Research of the water of the river showed that at the moment that the ecologic tragedy occurred the oxygen level was 0.6 milligrams per litre and normally it should be 4.0 milligrams per litre. The decomposition of the large quantities of dead animals would result in even less oxygen in the water resulting in extremely hypoxic water and a second wave of die-offs.