Possible consequences of eutrophication
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Contents
- 1 Introduction
- 2 Ecological impacts
- 2.1 Increased biomass of phytoplankton resulting in algal blooms
- 2.2 Toxic or inedible phytoplankton species (harmful algal blooms)
- 2.3 Increased in blooms of gelatinous zooplankton
- 2.4 Increased biomass of macroalgae
- 2.5 Decreases in water transparency (increased turbidity)
- 2.6 Dissolved oxygen depletion or hypoxia resulting in increased incidences of fish kills and / or dead benthic animals
- 2.7 Species biodiversity decreases and the dominant biota changes
- 3 Human health impacts
- 4 Socio-economic impacts
- 5 References
Introduction
Enhanced plant production and improved fish yields are sometimes described as positive impacts of eutrophication, especially in countries where fish and other aquatic organisms are a significant source of food. However detrimental ecological impacts can in turn have other negative consequences and impacts which are described below. Essentially the entire aquatic ecosystem changes with eutrophication.
Ecological impacts
Increased biomass of phytoplankton resulting in algal blooms
Phytoplankton or microalgae are photosynthesizing microscopic organisms. They contain chlorophyll and require sunlight in order to live and grow. Most phytoplankton are buoyant and float in the upper part of the ocean where sunlight penetrates the water. In a balanced ecosystem they provide food for a wide range of organisms such as whales, shrimp, snails and jellyfish. Among the more important groups are the diatoms, cyanobacteria, dinoflagellates and coccolithophores. Phytoplankton species also require inorganic nutrients such as nitrates, phosphates, and sulfur which they convert into proteins, fats and carbohydrates. When too many of these nutrients (by natural or anthropogenic cause) are available in the water phytoplankton may grow and multiply very fast forming algal blooms. Algal blooms may occur in freshwater as well as marine environments. Only one or a small number of phytoplankton species are involved and some blooms discolor (green, yellow-brown or red) the water due to their high density of pigmented cells.
Toxic or inedible phytoplankton species (harmful algal blooms)
Increased in blooms of gelatinous zooplankton
Increased biomass of macroalgae
Decreases in water transparency (increased turbidity)
Dissolved oxygen depletion or hypoxia resulting in increased incidences of fish kills and / or dead benthic animals
Species biodiversity decreases and the dominant biota changes
Human health impacts
Harmful algal bloom species have the capacity to produce toxins dangerous to humans. Algal toxins are observed in marine ecosystems where they can accumulate in shellfish and more generally in seafood reaching dangerous levels for human as well as animal health. Examples include paralytic, neurotoxic and diarrhoeic shellfish poisoning. Several algal species able of producing toxins harmful to human or marine life have been identified in European coastal waters. The table gives an overview of some species that are regularly observed and represent a risk for seafood consumers.
| Disease | Symptoms | Species | Carriers |
| Amnesic shellfish poisoning (ASP) | Mental confusion and memory loss, disorientation and sometimes coma | Diatoms of the genus Nitzschia | Shellfish (mussels) |
| Neurotoxic shellfish poisoning (NSP) | Muscular paralysis, state of shock and sometimes death | Genus Gymnodinium | Oysters, clams and crustaceans |
| Venerupin shellfish poisoning (VSP) | Gastrointestinal, nervous and hemorrhagic, hepatic symptoms and in extreme causes delirium and hepatic coma | Genus Prorocentrum | Oysters and clams |
| Diarrhoeic shellfish poisoning (DSP) | Gastrointestinal symptoms (diarrhoea, vomiting and abdominal pain) | Genus Dinophysis and Prorocentrum | Filtering shellfish (oysters, mussels and clams) |
| Paralytic shellfish poisoning (PSP) | Muscular paralysis, difficulty in breathing, shock and in extreme causes death by respiratory arrest | Genus Alexandrium and Gymnodinium | Oysters, mussels, crustacean and fish |
Other marine mammals can be vectors for toxins, as in the case of ciguatera, where it is typically predator fish whose flesh is contaminated with the toxins originally produced by dinoflagellates and then poison humans. Symptoms include gastrointestinal and neurological effects.
Socio-economic impacts
Nearly all of the above described impacts have a direct or indirect socio-economic impact.
Aesthetic impacts
Algal blooms are unsightly and can have unpleasant odors. For example the appearance of a white yellowish foam on the beach in spring on the shores along the North Sea. The foam is formed by the wind that sweeps up the decaying remains of Phaeocystis algal colonies.
Impact on recreation and tourism
The enrichment of nutrients to an ecosystem can result in a massive growth of algae. The existence of such areas of increased vegetation can inhibit or prevent access to waterways. This decreases the fitness for use of the water for water sports (swimming, boating and fishing).
Economical impacts
In some specific cases local authorities must rely on eutrophic waters for production of drinking water. Infected waters increases the costs of water treatment in order to avoid taste, odor and toxin problems in the treated water. Due to the toxins produced by harmful algal blooms commercial fish and shellfish may become unsuitable for consumption (the water becomes unsuitable for drinking even after treatment) resulting in potential economical and financial problems for the fishing industries. In extreme cases beaches are closed due to the presence of toxic algal blooms.
References
- Eutrophication and health. European Commission (2002). Office for Official Publications of the European Communities: Luxembourg. ISBN 92-894-4413-4.28 pp.
- The National Eutrophication monitoring Programme Implementation Manual (Murray et al., 2002).
