Eutrophication: Causes, Consequences and Controls

Dr. Ranjitsinh S. Pawar, Dept. of Civil Engineering, SVERIs College of Engineering, Pandharpur, Email: rspawar@coe.sveri.ac.in

Introduction Eutrophication is a natural process, derived from the Greek word ‘eutrophos’ meaning well nourished or enriched. This enrichment leads to other slow processes referred to as natural ageing of lakes (Fig.1). Weber C. H. described eutrophication as nutrient rich conditions used to determine the flora of German peat bogs as eutrophe, mesotrophe and oligotrophe

Fig.1: Eutrophic water body

Eutrophication is characterized by increased aquatic plant and algal growth due to the excessive availability of nutrients and fertilizers. It is a chief cause of destruction of many freshwater as well as salt water ecosystems in the earth. It occurs naturally over centuries as lakes age and are filled in with sediments. However, human activities have accelerated the rate and extent of eutrophication through both point-source discharges and non-point loadings of limiting nutrients. Lakes are often classified according to their trophy or degree of enrichment with nutrients and organic matter. They are classified by their trophic state with the main classes of oligotrophic, mesotrophic, eutrophic, and dystrophic. A lake starts its lifecycle as oligotrophic i.e., a clear body of water. With the introduction of nutrients through land runoff and growth and decay of aquatic life, the lake collects a good amount of organic substances. Eventually, there is algal bloom when the lake becomes marsh or perishes. It will then turn into dry land.

Eutrophication is the persistent environmental hazards in the aquatic ecosystems causes’ distinct decline of the surface water quality and represents severe hazard to the biotic components of the aquatic body. Eutrophication and siltation have severely stressed many fringing and offshore reefs that prefer to grow in nutrient-poor waters, and cause physiological changes in growth and skeletal strength, decrease of reproductive effort, and a reduced ability to withstand disease.

Types of Eutrophication 

1. Natural Eutrophication (Fig.2a) – The process of lake ageing characterized by nutrients enrichment is called natural eutrophication.
2. Cultural Eutrophication (Fig.2b) – this process is generally enhanced by human activities.

Fig. 2(a): Natural Eutrophication

Fig. 2(a): Natural Eutrophication

Causes of Eutrophication

In recent years there has been an increased use of nutrients and fertilizers. Agricultural fertilizers generally contain one or more of the plant nutrients. Pollution problems can arise from excessive application rates. Plant nutrients, nitrogen and phosphorus stimulate the growth of algae and other aquatic plants. Excessive growth of these plants interferes with water uses as subsequent decay produces evil odours with a resultant increase in biochemical oxygen demand. 

More plant available nutrients in the water imply increased algal growth. In the photosynthesis process, green plants need chlorophyll, sunlight, carbon dioxide, and nutrients in order to produce oxygen and biomass. The most important nutrients are nitrogen, phosphorus, and silicate, but micro-nutrients like potassium, sulfur, iron, and molybdenum are also needed. The deeper down the sunlight can penetrate the water, the deeper algae can grow. Green plants need chlorophyll to bind energy from the sunlight. By measuring the concentration of chlorophyll in water the quantity of microscopic algae can be determined in the water in winter, before the spring bloom (Finnish Institute of Marine Research, 2002).

The main causes of eutrophication is the large input of nutrients to a water body, and the main effect is the imbalance in the food web that results in high levels of phytoplankton microalgae, with a silicon skeleton (diatom) biomass in stratified water bodies which can lead to algal blooms. In addition to carbon, oxygen, and hydrogen that plants can find directly in the water and carbon dioxide in the atmosphere, two major nutrients are necessary for the development of aquatic life, namely nitrogen (N) and phosphorus (P). A third one, namely silicate is necessary for the development of diatoms. During eutrophication, the concentrations of nutrients in the water change. In some cases one out of the three nutrients may be totally bound to the aquatic life and will not be available for further growth of algae.Besides nutrient inputs, some physical conditions supporteutrophication development. Thermal stratificationof water bodies (such as lakes and reservoirs),temperature, and light influence the development ofaquatic algae. Increased light and temperature conditionduring springs and summer explain why eutrophicationis a phenomenon that occurs mainly duringthese seasons. Eutrophication itselfaffects the penetration of light through the water bodybecause of the shadow effect coming from algae andother living organisms and this reduces photosynthesisin deep water layers (WHO 2002).

Consequences of Eutrophication

The effects of eutrophication on the environmentmay have deleterious consequences on the health ofexposed animal and human population through variouspathways (WHO 2002). The following are the impacts of eutrophication.

• Increase in production and biomass of phytoplankton, attached algae and macrophytes.
• Shift in habitat characteristic due to changes inassemblage of aquatic plants
• Replacement of desirable fish by less desirable species
• Production of toxins by certain algae: Some algal
• Deoxygenating of water, especially after collapse ofalgal blooms, usually resulting in fish kills
• Infilling and clogging of irrigation canals withaquatic weeds
• Loss of recreational use of water
• Violations of water quality standards
• Water clarity or water transparency
• Impediments to navigation due to dense weedgrowth.
• Economic loss due to change in fish species, fishkills, and shellfish.
• The most conspicuous effect of cultural eutrophication is the creation of dense blooms of noxious, foul-smelling phytoplankton that reduce water clarity and harm water quality.
• Degradation of water quality 
• Destruction of economically important fisheries
• Public health risks

Controls of Eutrophication

Given the far reaching degree of water quality debasement related with supplement enhancement, eutrophication has and keeps on representing a genuine risk to consumable drinking water sources, fisheries and recreational water bodies.

Water asset directors routinely utilize an assortment of techniques to limit the impacts of cultural eutrophication, such as Diversion of abundance or excess nutrients, Altering nutrients proportions or ratios, Physical blending or mixing, Shading water bodies with hazy or opaque liners or water-based stains and Application of potent or strong algaecides and herbicides.

Another option for improving water quality in supplement rich lakes has been bio manipulation – the adjustment of a nourishment web to reestablish biological system wellbeing.

When all is said in done, these techniques have demonstrated to be ineffectual, expensive, or potentially illogical, particularly for huge, complex biological systems. Water quality can frequently be improved by diminishing nitrogen or potentially phosphorus contributions to sea-going frameworks, and there are a few notable models where base up control of supplements has extraordinarily improved water clearness. Nonetheless, supplement decrease can be troublesome (and costly) to control, particularly in farming zones where the algal supplements originate from nonpoint sources.

References

1. Chislock, M. F., Doster, E., Zitomer, R. A. & Wilson, A. E. (2013) Eutrophication:  Causes, Consequences, and Controls in Aquatic Ecosystems. Nature Education Knowledge 4(4):10
2. WHO (2002) Guidelines for drinking – water quality, Geneva(WHO/SDE/WSH/03.04/39)
3. www.google.com