The main effects caused by eutrophication can be summarized as follows [3]:

1. Species diversity decreases and the dominant biota changes

2. Plant and animal biomass increase

3. Turbidity increases

4. Rate of sedimentation increases, shortening the lifespan of the lake

5. Anoxic conditions may develop

Because of the high concentration of organisms in a eutrophic system, there is often a lot of competition for resources and predator pressure. This high degree of competition and the sometimes-high chemical or physical stress make high the struggle for survival in eutrophic systems. As a result the diversity of organisms is lower in eutrophic than in oligotrophic systems.
Palmer (1962) gives an enumeration of both clean water forms of algae and algae associated with organically enriched watercourses [4]:

The changes in nutrient levels and biology can directly affect human activities. The main occurring problems can be summarized as follows:

1. The water can be injurious to health

2. The amenity value of the water may decline

3. Increased vegetation may impede water flow and navigation

4. Commercially important species of fish may disappear

5. Treatment of drinking water may be difficult and supply can have an unacceptable taste or odour

Algal and cyanobacterial blooms

Cultural eutrophication causes excessive algal bloom in water bodies, with consequent algal overload. Under certain conditions of darkness and warm temperatures these blooms may die, decompose and produce offensive sewage-like odor. If the receiving water is used as a raw water supply for some public or private agency, algae may be difficult to remove and hence add certain objectionable tastes to the delivered water. Algae also have the tendency to absorb and concentrate mineral nutrients in their cells. When they die, at the end of the growing season, they settle to the stream or lake bottom, from which they release these mineral and organic nutrients at the beginning of the next growing season. In this way they serve as a form of secondary pollution.
One of the most common symptoms of lake eutrophycation is the development of blue-green algal (Cyanobacteria) blooms. They can be generated by human activity: for example, sediment runoff from construction sites may greatly diminish water clarity and therefore decrease the amount of light available for phytoplankton. Cyanobacteria are able to maintain themselves near the surface of the water by means of special gas-filled vacuoles that give the plants slight positive buoyancy. Once cyanobacteria or more generally algal blooms reach high concentrations, problems can occur: they have a negative impact on water quality, creating taste and odorous problems and interfering with certain water treatment processes. When certain bacteria populations reach very high proportions, they can also produce toxins that can render water unsafe for consumption.

Excessive aguatic macrophyte growth

Increased nutrient levels can stimulate other forms of primary production, in addition to algae and cyanobacteria. The littoral zones of many nutrient-enriched water bodies are often chocked with excessive growths of aguatic macrophytes, which can influence recreational and industrial activity and alter the structure of the food web. Excessive growth of phytoplankton and macroscopic plants in the water create aesthetic problem and reduce the value of the body water as a recreational resource. From a purely aesthetic point of view, crystal clear water characteristic of oligotrophic systems is most attractive for swimming and boating. High phytoplankton concentrations cause the water to appear turbid and aesthetically unappealing. Macroscopic plants can completely cover the entire surface of eutrophic lakes making the water almost totally unfit for swimming and boating.

Deepwater oxygen depletion

Oxygen is required for all life forms on this planet, with the exception of some bacteria. For this reason oxygen depletion is considered to be a serious lake management problem often associate with eutrophycation: this causes an increased organic matter production, so more material is sedimenting down into the profundal waters, consuming oxygen. Since it is impossible for some organisms to function efficiently unless the oxygen concentration in the water is near saturation, such organisms are often absent from eutrophic environments. This problem can preclude fish or other biota from inhabiting deepwater regions of anoxic lakes. It may be a seasonal or nocturnal phenomenon.

Related topics

• Algae description and types

• Eutrophication
  Sources
  Effects
  Solutions: Nutrients limitation
  Algae filtration
  Ultrasonic irradiation --> AL 50
  Al 50 D
  AL 20
  AL 10
  AL5
  Others

• Conclusions

• References

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