Definition in general:
The least needed amount of nutrients in a lake or other body/ source of water, which is exposed to the water regularly due to run-off from the land that results in a massed plant life growth.
Definition in terms of biology:
The progress of which a body of water is enhanced due to diffused nutrients such as phosphate, that encourages the aquatic plant life growth usually results in deficiency of dissolved oxygen.
How eutrophication occurs:
Overabundance of nutrients enters the source of water and the nutrients encourage plant growth , especially algae. When algae bloom occurs, it succumbs and is decomposed by bacteria. The decomposition of algae increases organic oxygen demand and causes oxygen levels to drop resulting death among aquatic life forms and even macro-invertebrates.
The significant influencing elements on water eutrophication encompasses , environmental factors such as carbon dioxide, salinity, temperature, element balance, hydrodynamics, nutrient enrichment, etc., and biodiversity and microbial.
Hydrodynamics influences the water mainly by the drift of winds and waves, which moves the sediment in the water body away from a certain area.
When the velocity is swift , it is unfavorable for eutrophication to occur although the nutrients are high enough to prompt it. Some algae would be washed away downstream by the flow before their growth reaches the highest point.
Then the necessity nutrients or elements for growth are destroyed and this will not result in eutrophication.
However, in slow-flowing water bodies like, reservoirs, lakes, bays, estuaries, inland seas and etc., the velocity is slow and the water body changes slowly. This condition slows down the process of the nutrients being washed away and provokes the accumulation of the nutrients especially nitrogen and phosphorus, which are the main nutrients for the intense reproduction of algae.
All actions in the drainage area of a lake or a reservoir are related either directly or indirectly to the water quality of these waters. However, a lake or a reservoir would be spontaneously atrophied when situated in an area with common nutrient enriched soils.
Furthermore, drainage water form the agricultural land also contains nitrogen and phosphorus which is high in content and is usually bound to soil components.
Excessive use of fertilizers results in significant percentages of nutrients particularly nitrogen, in agricultural runoff. If eroded soil reaches the lake, both phosphorus and the nitrogen in the soil contribute to eutrophication. Erosion is often caused by deforestation that also is caused from unwise planning and management of the resource.
Temperature and salinity are the two major contributors that urge alga bloom. Alga bloom always occurs at salinity between 23% and 28% and temperature between 23 °C and 28 °C.Since the variation of temperature and salinity affects the algal bloom, the ideal condition is said to be rise in temperature and decrease of salinity level in a short period. Also , carbon dioxide level is one of the general factor which controls water eutrophication. Cynophytes on the other hand, is capable of adapting to low levels of carbon dioxide and becomes more buoyant at low levels of CO2 and high in pH.Microbial activity is the inducement factor to alga bloom which can increase the levels of alga bloom breeding higher. Changes of the microbial community structure and purpose accompanies eutrophication.
The amount of microbial biomass is directly related to the content of organic matter and the volume of plankton in eutrophicated water. The decomposition of organic matter by bacteria actions may create nutrients and organic substances, which would encourage the algal bloom, break out.
The most obvious effect of eutrophication development is the foul-smelling phytoplankton which diminishes the clarity of water , disintegrated water quality and the production of dense blooms of toxic.Algal bloom reduces light penetration which lessens growth and cause plants to die-off in certain zones along impeding the survival of predators that uses light to obtain they prey.
Furthermore, high quota of photosynthesis associated with eutrophication can deplete dissolved inorganic carbon and increase pH to intense levels during the day.
Elevated pH can in turn ‘blind’ organisms that rely on perception of dissolved chemical cues for their survival by impairing their chemosensory abilities. When these dense algal blooms eventually decease, microbial decomposition rapidly depletes dissolved oxygen, creating a hypoxic or anoxic ‘dead zone’ lacking sufficient oxygen to support the organisms found in the waters. Dead zones are found in many freshwater lakes including the Laurentian Great Lakes (e.g., central basin of Lake Erie; Arend et al. 2011). Lastly, such hypoxic events are particularly common in marine coastal environments surrounding large, nutrient-rich rivers.
Water resource managers routinely employ a variety of strategies to minimize the effects of cultural eutrophication, including:-
(1) Diversion of excess nutrients
(2) Altering nutrient ratios
(3) Physical mixing
(4) Shading water bodies with opaque liners or water-based stains
(5) Application of potent algaecides and herbicides
Unfortunately, the mention strategies were unable to improve the situation and even said to be impractical, especially when associated to large also complex ecosystems.
Water quality may be improved by decreasing nitrogen and phosphorus inputs into aquatic channels, and there are several well-known examples such as the bottom-up control of nutrients which aided greatly by improving water clarity.
However, nutrient reduction can be difficult and expensive to control, especially in agricultural areas where the algal nutrients come from nonpoint sources. The use of algaecides, such as copper sulfate, is also effective at reducing HABs temporally. It may pose risks to humans, livestock, and wildlife, in addition to harming a variety of non-targeted aquatic organisms. Another alternative to improve water quality in nutrient-rich lakes is bio manipulation – the alteration of a food web to restore ecosystem health. The basic premise is that secondary consumers (planktivorous fishes) are removed either through the addition of tertiary consumers (piscivorous fishes) or harvesting, which allows the dominance of large-bodied, generalist grazers (e.g., Daphnia) to control phytoplankton.
In the 1960s and 1970s, Lake Erie was the most publicized example of eutrophication. Called a “dead lake,” the smallest and shallowest of the five Great Lakes was swamped for decades with nutrients from heavily developed agricultural and urban lands. As a result, plant and algae growth choked out most other species living in the lake, and left the beaches unusable due to the smell of decaying algae that washed up on the shores. New pollution controls for sewage treatment plants and agricultural methods by the United States and Canada led to drastic reductions in the amount of nutrients entering the lake. Forty years later, while still not totally free of pollutants and nutrients, Lake Erie is again a biologically thriving lake.