EUTROPHICATION Definition in general: The needless amount of nutrients in a lake or other body /sourceof water, that is exposed to the water regularly due to run-off from the landcauses a massed growth of plant life.
Definition in terms of biology: The progress by which a body of water becomes enhanced indiffused nutrients such as phosphates, that encourages the growth of aquaticplant life usually resulting in the deficiency of dissolved oxygen. How eutrophication occurs: • Overabundance of nutrients enters the source of water.• Nutrients encourage plant growth, especially algae.
• Algal bloom occurs.• Algae succumb and are decomposed by bacteria.• Decomposition of algae increases organic oxygen demand.• Oxygen levels begin to drop.
• Macro-invertebrates, fishes and other aquatic life forms die. Major Contributors:The major influencing factors on water eutrophication includehydrodynamics, nutrient enrichment, environmental factors such as carbondioxide, salinity, temperature, element balance, etc., and biodiversity andmicrobial.
Hydrodynamics affect the water mainly by the drift of winds andwaves, which move the sediment in the water body away from a certain area. Whenthe flow velocity is swift, it is difficult for eutrophication to occur even ifthe concentration of nutrients are high enough to trigger it, because somealgae could be washed away downstream by the flow before their growth hasreached its highest point. Then the necessity for growth is destroyed and willnot result in eutrophication. However, in slow-flowing water bodies like,reservoirs, lakes, bays, estuaries, inland seas, the flow of velocity is slowand the water body changes slowly. This condition slows down the spread of thenutrients and provokes the accumulation of the nutrients especially nitrogenand phosphorus, which offers the main nutrients for the rapid reproduction ofalgae. All actions in the whole drainage area of a lake or reservoirare related either indirectly or directly in the water quality of these waters.
A lake or reservoir may, however, be spontaneously atrophied when situated in afruitful area with common nutrient enriched soils. Drainage water fromagricultural land also contains nitrogen and phosphorus. It usually has muchmore nitrogen because phosphorus is usually bound to soil components. Excessiveuse of fertilizers results in significant percentages of nutrients particularlynitrogen, in agricultural runoff. If eroded soil reaches the lake, bothphosphorus and the nitrogen in the soil contribute to eutrophication. Erosionis often caused by deforestation that also is caused from unwise planning andmanagement of the resource. Temperatureand salinity are the two major contributors that urge alga bloom.
Alga bloomalways occurs at salinity between 23% and 28% and temperature between 23 °C and28 °C. The variation of temperature and salinity also affects algal bloom, andthe ideal conditions for algal bloom is the rise in temperature and rapiddecrease of salinity than ever in a short period. Carbon dioxide level is oneof general factor controlling water eutrophication. Cyanophytes are morecapable of adapting to low levels of carbon dioxide and become more buoyant at lowlevels of carbon dioxide and high pH. Microbialactivity is the inducement factor to alga bloom. It can increase high levels ofalga bloom breeding. Nutrient-enhanced microbial production of organic elements,or eutrophication, is easily accompanied by changed microbial communitystructure and purpose.
The amount of microbial biomass is directly related to the content of organicmatter and the volume of plankton in eutrophicated water. The decomposition oforganic matter by bacteria actions may create nutrients and organic substances,which may encourage the algal bloom, break out. Effects/Consequences: The most noticeable effect of development of eutrophication isthe production of dense blooms of toxic, foul-smelling phytoplankton that decreasethe clarity of water and ruin the water quality. Algal blooms reduces lightpenetration, lessen growth and causing die-offs of plants in certain zoneswhile lowering the success of predators that use light to pursue and get theirprey.
Furthermore, high quota of photosynthesis associated with eutrophicationcan deplete dissolved inorganic carbon and increase pH to intense levels duringthe day. Elevated pH can in turn ‘blind’ organisms that rely on perception ofdissolved chemical cues for their survival by impairing their chemosensoryabilities. When these dense algal blooms eventually decease, microbialdecomposition rapidly depletes dissolved oxygen, creating a hypoxic or anoxic’dead zone’ lacking sufficient oxygen to support the organisms found in thewaters. Dead zones are found in many freshwater lakes including the LaurentianGreat Lakes (e.g.
, central basin of Lake Erie; Arend et al. 2011). Lastly, suchhypoxic events are particularly common in marine coastal environments surroundinglarge, nutrient-rich rivers. Measurestaken:Waterresource managers routinely employ a variety of strategies to minimize theeffects 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 Sadly,these strategies have not been able to improve the situation and are consideredto be impractical, especially for large, complex ecosystems. Water quality maybe improved by decreasing nitrogen and phosphorus inputs into aquatic channels,and there are several well-known examples where bottom-up control of nutrientshas greatly improved water clarity. However, nutrient reduction can bedifficult and expensive to control, especially in agricultural areas where thealgal nutrients come from nonpoint sources.
The use of algaecides, such ascopper sulfate, is also effective at reducing HABs temporally. It may poserisks to humans, livestock, and wildlife, in addition to harming a variety ofnon-target aquatic organisms. Another alternative to improve water quality innutrient-rich lakes is bio manipulation- the alteration of a food web to restore ecosystem health. The basic premiseis that secondary consumers (planktivorous fishes) are removed either throughthe addition of tertiary consumers (piscivorous fishes) or harvesting, whichallows the dominance of large-bodied, generalist grazers (e.
g., Daphnia) tocontrol phytoplankton.