How is fertilizer harmful to a lake?

Question

How is fertilizer harmful to a lake?

Answer 1

Mainly it is harmful because it promotes excessive growth of vegetation & algae which upsets the balance, not just of food/space etc but oxygen in the water as well.

Some fertilizers are also poisonous to organisms & therefore upset the balance by killing off flora or fauna & upsetting the food chain.

Answer 2

Eutrophication is an increase in chemical nutrients -- typically compounds containing nitrogen or phosphorus -- in an ecosystem. It may occur on land or in water. The term is however often used to mean the resultant increase in the ecosystem's primary productivity (excessive plant growth and decay), and further effects including lack of oxygen and severe reductions in water quality, fish, and other animal populations.

Eutrophication is frequently a result of nutrient pollution such as the release of sewage effluent and run-off from lawn fertilizers into natural waters although it may also occur naturally in situations where nutrients accumulate (e.g. depositional environments) or where they flow into systems on an ephemeral basis. Eutrophication generally promotes excessive plant growth and decay, favors certain weedy species over others, and is likely to cause severe reductions in water quality. In aquatic environments, enhanced growth of choking aquatic vegetation or phytoplankton (that is, an algal bloom) disrupts normal functioning of the ecosystem, causing a variety of problems such as a lack of oxygen in the water, needed for fish and shellfish to survive. The water then becomes cloudy, colored a shade of green, yellow, brown, or red. Human society is impacted as well: eutrophication decreases the resource value of rivers, lakes, and estuaries such that recreation, fishing, hunting, and aesthetic enjoyment are hindered. Health-related problems can occur where eutrophic conditions interfere with drinking water treatment.

Eutrophication was recognized as a pollution problem in European and North American lakes and reservoirs in the mid-20th century Since then, it has become more widespread. Surveys showed that 54% of lakes in Asia are eutrophic; in Europe, 53%; in North America, 48%; in South America, 41%; and in Africa, 28%.

Although eutrophication is commonly caused by human activities, eutrophication can also be a natural process in lakes; thus, eutrophy is a natural condition for many lakes (e.g., in temperate grasslands). Paleolimnologists now recognise that climate change, geology and other external influences are critical in regulating the natural productivity of lakes. Some lakes also demonstrate the reverse process (meiotrophication), becoming less nutrient rich with time.

Eutrophication can also be a natural process in seasonally inundated tropical floodplains such as the Barotse Floodplain of the Zambezi River. The first floodwaters to move down the floodplain after the onset of the rainy season, called "red waters", are usually hypoxic and kill many fish as a result of eutrophication brought on by material picked up by the flood from the plain such as cattle manure, and by the decay of vegetation which grew during the dry season.The process may be made worse by the use of fertilisers in crops such as maize, rice and sugarcane grown on the floodplain.

Human activities can accelerate the rate at which nutrients enter ecosystems. Runoff from agriculture and development, pollution from septic systems and sewers, and other human-related activities increase the flux of both inorganic nutrients and organic substances into terrestrial, and aquatic ecosystems. Elevated atmospheric compounds of nitrogen can increase nitrogen availability.

Phosphorus is often regarded as the main culprit in cases of eutrophication in lakes subjected to point source pollution from sewage. The concentration of algae and the trophic state of lakes correspond well to phosphorus levels in water. Studies conducted in the Experimental Lakes Area in Ontario have shown a relationship between the addition of phosphorus and the rate of eutrophication. Humankind has increased the rate of phosphorus cycling on Earth by four times, mainly due to agricultural fertilizer production and application. Between 1950 and 1995, 600,000,000 tonnes of phosphorus were applied to Earth's surface, primarily on croplands. Control of point sources of phosphorus have resulted in rapid control of eutrophication, mainly due to policy changes

Answer 3

Fertilizers increase the rate of plant growth.  While that may initially be a "good" thing - more shade, food, shelter, and oxygen production, eventually all but the plants and algae at the very top would be deprived of enough sunlight for photosynthesis and they would die.  Bacterial decomposition of the dead plants uses dissolved oxygen, and would decrease the oxygen available to fish and other aquatic organisms.  It also increases the rate of eutrophication (the buildup of material at the bottom of the lake).