What is eutrophication?
Eutrophication is a form of pollution caused by an increase in the rate of supple organic matter in an ecosystem. When a body of water, such as a river, lake, or pond, aquires a high amount of nutrients, it causes excessive growth of algae. The term "eutrophic" literally means well-nourished and thats exactly what eutrophication is, a well-nourished body of water with an excessive concentration of phosphates and nitrates. Eutrophication occurs naturally on its own but it is a slow-aging process. Human activity is what speeds it up. Although eutrophication is evident mostly in slow-moving rivers and shallow lakes it can occur in ditches, coastal waters, and groundwater.
What are the causes?
Increase in nitrate fertilizers from 1960-2000
When the tropic status of a body of water increases greatly it is likely that people are involved. The tropic status of a body of water describes the relationship between the nutrient status of a body of water and the growth of organic matter in those waters. If a lake, river, etc. is said to have an oligotrophic status then that means the nutrients in the water are very poor. Most waters that are oligotrophic are young lakes or man made reservoirs. If it is said to be hypertrophic then it is nutrient rich. Old lakes are usually very nutrient rich, however extremely nutrient rich lakes are usually caused by human activity and can become a serious problem. Hypertrophic waters are usually caused by run-off from farms and other nutrient rich land areas. Fertilizers have become an essential part of agriculture all around the world, and as economy and agriculture continue to grow, so do the amount of fertilizers used. A graph is displayed on the left showing the increase in the use of nitrate fertilizers from the years 1960-2000. In short, agriculture is to blame. European agriculture alone contributes to 60% of the total riverine flux of nitrogen in the North Sea and 25% of the total phosphorus loading. Manure produced by cattle, pigs, and poultry are used as organic fertilizer in europe and all over the world. Since fertilizers are full of nutrients to help nourish dead soil, run-off of these fertilizers can have serious tropic effects. Below is a list of the main materials that cause eutrophication.
- natural run-off of nutrients from soil and weathering of rocks
- run-off of inorganic fertilizer from farms (containing phosphate and nitrate)
- run-off of manure from farms (containing nitrates, phosphates, and ammonia)
- run-off from erosion (following mining, construction, or poor land use)
- discharge of detergents (containing phosphates)
- discharge of partially treated or untreated sewage (containing nitrates and phosphates)
In most lakes, ponds, etc., the limiting nutrient is phosphorus. When inorganic and organic fertilizers containing phosphorus in the form of phosphate ions (PO4/3-) enter a body of water with limited phosphorus, it results in an increase of biological activity. Particularly in the production and biomass of phytoplankton, attached algae, and microphytes.
How does eutrphication effect the environment?
The effects of eutrophication somewhat happen in a chain of events. The first would be the increase of nitrates and phosphates which causes an increase in the growth of algae. This rapid growth of algae in a body of water is known as an "algal bloom". As the rate of algae gets bigger, more and more algae die and decompose high levels of organic matter. The decompostition of these organisms depletes the amount of available oxygen in the water which causes the death of fish and other organisms. This process is known as deoxygenation. When fish start to die because of algal growth, a decrease in species diversity can follow. Less diversity in an ecosystem causes a change in the dominant biota (plant/animal life) and distrupts the biological equilibrium.
Eutrophication also cause competition for resources between organisms. At first the increased nutrients cause a massive increase in plant and animal biomass. This creates a great deal of competition for limited resources and predator pressure. The struggle for resources and the high chemical and physical stress put on organisms make survival more difficult. This eventually causes a decrease in biodiversity as well.
Increase in algae also effect the turbidity and rate of sedimentation. Turbidity is "the measure of the degree to which the water loses its transparency due to suspended particles". The more particles, or in this case algae, there are in the water the murkier it seems to appear and the higher the turbidity. This makes water less drinkable which becomes a problem for people and animals. In order for water to be potable the WHO (Worldwide Health Organization) establishes that it should not be more than 5 NTU: Nephelometric Turbidity units, and ideally below 1 NTU. Murky waters are also hotter as the particles absorb heat from the sun and further reduce the concentration of oxygen in the water. This becomes a problem for organisms that cannot live in warmer waters. Particles in the water also scatter the light which lowers the photosynthetic activity of plants and algae on the bottom of the lake and decreases oxygen levels even more! Reproduction and respiration of organisms become difficult when particles settle on the bottom of shallow lakes, smothering and killing fish eggs and insect larvae, or clogging the gills of fish.
Eutrophication also cause competition for resources between organisms. At first the increased nutrients cause a massive increase in plant and animal biomass. This creates a great deal of competition for limited resources and predator pressure. The struggle for resources and the high chemical and physical stress put on organisms make survival more difficult. This eventually causes a decrease in biodiversity as well.
Increase in algae also effect the turbidity and rate of sedimentation. Turbidity is "the measure of the degree to which the water loses its transparency due to suspended particles". The more particles, or in this case algae, there are in the water the murkier it seems to appear and the higher the turbidity. This makes water less drinkable which becomes a problem for people and animals. In order for water to be potable the WHO (Worldwide Health Organization) establishes that it should not be more than 5 NTU: Nephelometric Turbidity units, and ideally below 1 NTU. Murky waters are also hotter as the particles absorb heat from the sun and further reduce the concentration of oxygen in the water. This becomes a problem for organisms that cannot live in warmer waters. Particles in the water also scatter the light which lowers the photosynthetic activity of plants and algae on the bottom of the lake and decreases oxygen levels even more! Reproduction and respiration of organisms become difficult when particles settle on the bottom of shallow lakes, smothering and killing fish eggs and insect larvae, or clogging the gills of fish.
Human Activities
Eutrophication can also effect human activities. As mentioned before, it makes water less potable and makes the cost of cleaning water from drinking purposes much more difficult and costly. In certain countries, groundwater is an essential, if not only, source of drinking water. Groundwater can also be polluted by eutrophication and if this happens the water is no longer fit to drink. The amenity of water declines and water can also become dangerous to health. In areas where lakes or ponds are recreational, if an excessive amount of eutrophication occurs, the water may no longer be safe to swim in. Commercially important species of fish may dissappear which causes an impact in economy. Under certain conditions of darkness and warm temperatures, algal blooms may die and decompose which causes an awful, sewage-like odor and if the water is cleaned for drinking use, it can leave a strange taste.