World environment day : Eutrophication: a major environmental problem

Deepak Raj Subedi


Nepal, being a landlocked country with no direct access to seas and oceans, has immense source of freshwater with applicable potential. However, we have been facing serious environmental problems associated with water. It is high time that we realised the impacts associated with water pollution and to strove towards its preservation. Eutrophication refers to enriching water, mostly with plant nutrients such as nitrogen and phosphorous and sometimes with silicon, potassium, calcium, manganese or iron, leading to increased plant growth, which results in visible algal growth. During decomposition, this plant material leads to depletion of oxygen reserves of water bodies causing an array of secondary problems, such as fish mortality, liberation of erosive gases like methane and hydrogen sulphide, toxins, organoleptic substances, etc.

The eutrophication has been changing eutrophic lakes and rivers into hypertrophic ones, where an excessive nutrient content results from the heavy influx of wastes, drainage from agriculture lands, river basin development, runoff from urban areas, burning of fossil fuels, etc. This accelerated enrichment results in chemical and environmental changes and causes major shifts in plant and animal life. External loading to water bodies is next source. Rivers are major routes of transfer of nitrogen and phosphorous to many lakes and reservoirs. Mining of phosphate, industrial fixation of nitrogen and agricultural, industrial and domestic use of nitrogen has increased. Clearing of forests, excessive urbanisation and extensive cultivation have enhanced the transport of nutrients from terrestrial to aquatic ecosystems. Similarly, internal supply of nutrients from sediments of lakes can sustain eutrophic conditions for long. For example, ammonia is produced by decomposition of organic matter in water bodies.

The most important cause is related to accelerated eutrophication. The process of accelerated eutrophication is essentially caused by three elements, which are interrelated and directly linked to world wide demographic changes: rapid increase in population, industrialisation and agricultural intensification. Since water bodies are the lifeblood of nature, their preservation from the process of eutrophication is a must. Wise management policies for economic development with an aim to moderate eutrophication should encompass a whole watershed of the water body. To bring eutrophication under control, ad hoc designed and technical aspects need to be sustained by supplementary, comprehensive medium and long term policies and strategies.

Two major elements to be included in its management are information on loading rate of nutrients and an assessment of their impacts. It is important to note that prevention is better than cure as control of eutrophication is, though technically feasible, not economically viable in countries like ours. The author is Research and Communication officer, School of Environmental Management and Sustainable Development.

Eutrophication problems

•Water quality impairment

•Recreational impairment

•Fisheries impairment

•Reduced water flow