8/10/2019 Environment - Terms

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Oligotrophic

An oligotrophic lake is a lake with low primary productivity , the result of low nutrient content. These lakes have low algal production,

and consequently, often have very clear waters, with high drinking-water quality. The bottom waters of such lakes typically have

ample oxygen ; thus, such lakes often support many fish species, like lake trout , which require cold, well -oxygenated waters. The

oxygen content is likely to be higher in deep lakes, owing to their larger hypolimnetic volume.

Ecologists use the term oligotrophic to distinguish unproductive lakes, characterised by nutrient deficiency, from productive,

eutrophic lakes, with an ample or excessive nutrient supply. Oligotrophic lakes are most common in cold regions underlain by

resistant igneous rocks (especially granitic bedrock).

MesotrophicMesotrophic lakes are lakes with an intermediate level of productivity. These lakes are commonly clear water lakes and ponds with

beds of submerged aquatic plants and medium levels of nutrients.

The term mesotrophic is also applied to terrestrial habitats. Mesotrophic soils have moderate nutrient levels.

Eutrophic

A eutrophic body of water, commonly a lake or pond, has high biological productivity. Due to excessive nutrients, especially nitrogen

and phosphorus, these water bodies are able to support an abundance of aquatic plants. Usually the water body will be dominated

either by aquatic plants or algae. When aquatic plants dominate the water tends to be clear. When algae dominates the water t ends

to be darker. The algae engages in photosynthesis which supplies oxygen to the fish and biota which inhabit these waters.

Occasionally an excessive algae bloom will occur and can ultimately result in fish kills due to respiration by algae and bottom living

bacteria. The process of eutrophication can occur naturally and by human impact on the environment.

Eutrophic comes from the Greek eutrophos meaning well-nourished , from eu meaning good and trephein meaning to nouris h [5]

HypereutrophicHypereutrophic lakes are very nutrient-rich lakes characterized by frequent and severe nuisance algal blooms and low transparency.

Hypereutrophic lakes have a visibility depth of less than 3 feet, they have greater than 40 micrograms/litre total chlorophyll and

greater than 100 micrograms/liter phosphorus .

The excessive algal blooms can also significantly reduce oxygen levels and prevent life from functioning at lower depths creating

dead zones beneath the surface.

Likewise, large algal blooms can cause biodilution to occur, which is a decrease in the concentration of a pollutant with an increase

in trophic level . This is opposed to biomagnification and is due to a decreased concentration from increased algal uptake.

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