General effects of eutrophication

Algae differ from microscopic animal life in our water bodies in their mode of respiration: they release more oxygen during the day than they use, and absorb more carbon dioxide than they release, while animal and other non-photosynthetic organisms release carbon dioxide and absorb oxygen from their environment. Algae usually react in an opposite manner during the night, when they act as dead organic matter adding BOD load. It is important to carefully consider any action of removal of algae from a body of water: oxygen supplied by algae during photosynthesis in beneficial to most forms of life in streams, thus the removal would often be a detriment rather than a benefit.


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]:

Clean water algae

Pollution algae – Algae common in organically enriched areas

Blue-green Algae

Agmenellum quadriduplicatum glauca type

Agmenellum quadriduplicatum tenuissima type

Calothrix parietina

Anabaena constricta

Coccochoris stagnina

Anacystis montana

Entophysalis lemaniae

Artospira jenneri

Microcoleus subtorolosus

Lyngbya digueti

Phormidium inundatum

Oscillatoria chalybea

Oscillatoria chlorina

Oscillatoria formosa

Oscillatoria lauterbornii

Oscillatoria limosa

Oscillatoria priceps

Oscillatoria putrida

Oscillatoria tenuis

Phormidium autumnale

Phormidium uncinatum

Green Algae

Ankistrodesmus falcatus, var. acicularis

Chlorella pyrenoidosa

Bulbochaete mirabilis

Chorella vulgaris

Chaetopheltis megalocystis

Chlorococcum numicola

Cladophora glomerata

Scenedesmus quadricola

Draparnaldia plumosa

Spirogyra communis

Euastrum oblogum

Stichococcus bacillaris

Gloecoccus schroeteri

Stigeoclonuim tenue

Micrasteria truncata

Tetraedron muticum

Rhizocolonium hieroglyphicum

Stuarastrum punctualum

Ulothrix aequalis

Vaucheria geminata

Diatoms

Amphora ovalis

Gomphonema parvulum

Cocconeis placentula

hantzschia amphioxys

Cyclotella badanica

Melosire varians

Cymbella cesati

Navicula cryptocephala

Meridion circulare

Nitzschia acicularis

navicula esigua var. capitata

Nitzschia palea

Navicula gracilis

Surirella ovata

Nitzschia linearis

Pinnularia nobilis

Pinnularia subcapitata

Surirella spendida

Synedra acus var. angustissima

Red algae

batrachospermun vagum

Hildenbrandia rivularis

Lemanea annulata

Flagellates

Chromulina rosanoffi

Carteria multifilis

Chroomonas nordstetii

Chlamydomonas reinhardi

Chroomonas setoniensis

Chloroginium euchlorum

Chrysococcus major

Cryptoglena pigra

Chrysococcus ovalis

Euglena agilis

Chrysococcus rufescens

Euglena deses

Dinobryon stipitatum

Euglena gracilis

Euglena ehrenbergii

Euglena oxyuris

Euglena spirogyra

Euglena polymorpha

Mallomonas caudata

Euglena viridis

Phacotus lenticularis

Lepocinclis texta

Phacus longicauda

pandorina morum

Rhodomonas lacustris

Phacus pyrum

Pyrobotrys gracilis

Pyrobotrys stellata

Spondylomorum quaternaruim

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

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