Problems associated with tropical freshwater, Biology tutorial


Eutrophication is a enrichment of surface waters with plant nutrients. It is the procedure of change from one trophic state to the higher trophic state by the addition of nutrient. Eutrophication is the procedure of nutrient enrichment of waters that results in stimulation of the array of symptomatic changes, among which increased production of algae and aquatic macrophytes, deterioration of water quality and other symptomatic changes are found to be unwanted and interfere with water uses. Eutrophication is the procedure of too much nutrient enrichment of waters which usually results in problems related with macrophyte, algal or cyanobacterial growth.

While eutrophication takes place naturally, it is usually related with anthropogenic sources of nutrients. Trophic status of lakes is central concept in lake management. It describes the relationship between nutrient status of a lake and the growth of organic matter in the lake. Eutrophic systems contain a high concentration of phosphorus (~30+μg/L), nitrogen (~1500+μg/L), or both. Phosphorus enters lentic waters from wastewater treatment effluents, discharge from raw sewage, or from runoff of farmland.

Bacteria require large amounts of oxygen to decompose the material, decreasing oxygen concentration of the water. This is particularly pronounced in stratified lakes when thermocline prevents oxygen rich water from surface to mix with lower levels. Low or anoxic conditions preclude existence of several taxa which are not physiologically tolerant of these situations. Though both nitrogen and phosphorus contribute to eutrophication, classification of trophic status generally focuses on the nutrient that is limiting. In the majority of cases, phosphorus is the limiting nutrient. While the effects of eutrophication like algal blooms are voluntarily visible, the procedure of eutrophication is complex and its measurement hard.

The major causes of eutrophication are:

  • Natural run-off of nutrients from soil and weathering of rocks
  • run-off of inorganic fertilizer (having nitrates and phosphates)
  • run-off of manure from farms (having ammonia, nitrates, and phosphates)
  • discharge of detergents (having phosphates)
  • discharge of partly treated or untreated sewage (having phosphates and nitrates)

Sources of eutrophication:

These are point sources and nonpoint sources. The point sources of eutrophication comprise:

  • Wastewater effluent (municipal and industrial)
  • Runoff and infiltration from animal feedlots
  • Runoff from mines, oil fields, unsewered industrial sites
  • Overflows of combined storm and sanitary sewers
  • Runoff from construction sites less than 20,000 m² (220,000 ft²)

The Nonpoint sources of eutrophication include:

  • Runoff from agriculture/irrigation and pasture and range
  • Urban runoff from unsewered areas
  • Runoff from construction sites >20,000 m²
  • Atmospheric deposition over a water surface
  • Other land activities generating contaminants

Role of agriculture in eutrophication:

Fertilization of surface waters (eutrophication) results in, for instance, explosive development of algae that causes disruptive changes to biological equilibrium. This is true both for inland waters (ditches, river, and lakes) and coastal waters. Groundwater is being polluted mostly by nitrates. In all countries groundwater is the significant source of drinking water. In numerous areas the groundwater is polluted to the extent that it is no longer fit to be utilized as drinking water according to present standards

Symptoms of Eutrophication:

The symptoms and impacts of eutrophication are:

  • Increase in production and biomass of phytoplankton, attached algae, and macrophytes.
  • Shift in habitat characteristics because of change in assemblage of aquatic plants.
  • Replacement of desirable fish (like salmonids in western countries) by less desirable species.
  • Production of toxins by certain algae.
  • Increasing operating expenses of public water supplies, comprising taste and odour problems, particularly during periods of algal blooms.
  • Deoxygenation of water, particularly after collapse of algal blooms, generally resulting in fish kills.
  • Infilling and clogging of irrigation canals with aquatic weeds (water hyacinth is the problem of introduction, not essentially of eutrophication).

Problems of eutrophication on human societies:

1) Water supply may have unacceptable taste and odour

2) Impediment of water flow and navigation due increased vegetation in water

3) Disappearance of commercially significant species (eg salmonids and coregonids)

4) Water may be injurious to health

5) Difficulty in treatment of water

Control of Eutrophication: Best Management Practices

Managing nutrient loading in streams will decrease not only magnitude of maximum algal biomass, but also frequency and duration of benthic algal problems in streams. To better protect and restore streams, control of both point and nonpoint sources of nutrient loadings in streams is necessary. Control of point sources, like treated wastewater, can be enhanced with new technology. Still the persistent problem for implementation of criteria will be control of nonpoint sources. It will need pioneering technologies and better understanding of stream ecosystems to reduce nutrient loadings from nonpoint sources in streams. Best management practices must be implemented comprising riparian buffer and wetland protection, and smart use of fertilizers in agricultural and silviculture.


Water pollution is an introduction of materials or energy to water bodies to the level that the water quality gets depleted. Materials not only unconstructively influence quality of the water but also influence aquatic organisms and water dependent or water associated organisms. The procedure of water pollution may take place as a result of direct discharge of materials in water bodies or through runoff from close by contaminated/polluted terrestrial environment. Increased microbial load, and change in physicochemical nature of water result because of water pollution.

Causes of Water Pollution:

Industry, agriculture and domestic actions are main anthropogenic activities accountable for polluting soft water. Pollution can be caused by organic (waste being thrown out without being treated) and microbiological matter. This kind of pollution causes aquatic wildlife to asphyxiate. Organic matter, particularly human excrement is major cause of river pollution. On the one hand, it saturates water and prevents ecosystems working normally and on the other hand, it puts pathogenic microorganisms in water. These can pass on diseases to Man if water is not purified before consumption.

There are basically two kinds of water pollution, in terms of the sources, and each is accountable for roughly half of the water pollution. Point source pollution, which, as name signifies, is pollution which comes from the discrete source, like where the pipe carrying factory wastes dumps in a river. Nonpoint source pollution, again as name implies, is pollution which comes from more diffuse sources, like runoff from parking lots and roads, or from agricultural fields.

Effects of Water Pollution on ecosystems:

Numerous negative effects arise due to water pollution. These are given below:

a) Reduced water depth due to siltation and sedimentation. This leads to reduced navigation and recreational use of water. This can also happen because of deposition of non-degradable metallic carcasses.

b) Reduced light penetration and productivity because of increased turbidity due to colored effluents and suspended dust particles.

c) Inhibition of gaseous exchange between water system and the atmosphere. This generally happens because of deposition of hydrophobic materials such as oil, grease and petroleum hydrocarbons.

e) Depletion of dissolved oxygen content of water bodies and increase in biological oxygen demand because of high level biodegradable materials in water bodies.

f) Death of aquatic organisms and water dependent organisms because of oxygen depletion and presence of harmful materials in water bodies. Increased temperature (thermal pollution) can also lead to death of aquatic organism

g) Change in abundance and composition of aquatic biotic community. Some species may have increased richness while the abundance gets reduced.

Water-related diseases:

Water related diseases are diseases which affect man and/ animals as a result of contact with water, drinking of water or by being attacked by aquatic organisms. Such diseases are caused by bacteria, viruses, parasites and protozoa which live entirely in water or spend part of their lives in water. Some of these organisms are either deposited directly into the water bodies or are carried by runoff to the water bodies. Consumption of the untreated or nonproperly treated water can lead to these diseases.

One Example of Water-related disease: Diarrhea

Diarrhea takes place world-wide and causes 4% of all deaths and 5% of health loss to disability. It is most usually caused by gastrointestinal infections that kill approx 2.2 million people globally every year, generally children in developing countries. Use of water in hygiene is the significant preventive measure but contaminated water is also the significant cause of diarrhea.

The disease and how it affects people:

Diarrhea is a passage of loose or liquid stools more often than is normal for individual. It is mainly the symptom of gastrointestinal infection. Depending on kind of infection, the diarrhea may be watery (for instance in cholera) or passed with blood (in dysentery for instance).

Diarrhea because of infection may last a few days, or a number of weeks, as in persistent Diarrhea. Severe Diarrhea may be life threatening due to fluid loss in watery Diarrhea, mainly in infants and young children, the malnourished and people with impaired immunity. Impact of repeated or persistent Diarrhea on nutrition and effect of malnutrition on vulnerability to infectious Diarrhea can be associated in vicious cycle amongst children, particularly in developing countries. Diarrhea is also related with other infections like malaria and measles. Chemical irritation of gut or non-infectious bowel disease can also result in Diarrhea.

Causes of Diarrhea:

Diarrhea is the symptom of infection caused by the host of bacterial, viral and parasitic organisms most of which can be spread by contaminated water. It is more frequent when there is the shortage of clean water for drinking, cooking and cleaning and essential hygiene is significant in prevention.

Water contaminated with human feces for instance from municipal sewage, septic tanks and latrines is of special concern. Animal feces also have microorganisms which can cause Diarrhea. Diarrhea can also spread from person to person, provoked by poor personal hygiene. Food is another main reason of Diarrhea when it is prepared or stored in unhygienic conditions. Water can pollute food during irrigation, and fish and seafood from polluted water may also contribute to disease.


Infectious agents which cause Diarrhea are present or are sporadically introduced throughout world. Diarrhea is the odd happening for most people who live in developed countries where sanitation is extensively available, access to safe water is high and personal and domestic hygiene is comparatively good. Worldwide approx 1.1 billion people lack access to enhanced water sources and 2.4 billion have no basic sanitation. Diarrhea because of infection is widespread throughout developing world.

Key measures to decrease number of cases of Diarrhea comprise:

  • Access to safe drinking water.
  • Enhanced sanitation.
  • Good personal and food hygiene.
  • Health education about how infections spread.

Main measures to treat Diarrhea comprise:

  • Giving more fluids than usual, comprising oral rehydration salts solution, to prevent dehydration.
  • Continue feeding.
  • Consulting the health worker if there are signs of dehydration or other problems.

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