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Vertex Glossary

Vertex Glossary of Aquatic Terms

ACCLIMATIZATION: The adaptation by an organism to new physical and/or environmental conditions. With respect to water, it is frequently used in reference to the ability of a species to tolerate changes in water temperature, degradation of water quality, or increased levels of salinity.

AERATION: The act of adding oxygen. In lake management it is adding oxygen to the water to stabilize the oxygen for beneficial bacteria, fish and other life forms.

AEROBIC: Occurring in the presence of oxygen or requiring oxygen to live. In aerobic respiration, which is the process used by the cells of most organisms, the production of energy from glucose metabolism requires the presence of oxygen.

ALKALINITY: Measure of the ability of a solution to neutralize acids, which can limit dangerous pH swings caused by the introduction of highly acidic or basic substances, the effects of which can be compounded by the consequent loss of plant, algal, and other aquatic life.

ANAEROBIC: Occurring in the absence of oxygen or not requiring oxygen to live. Anaerobic bacteria produce energy from food molecules without the presence of oxygen.

AQUATIC OXYGEN DEMAND: The need for oxygen to meet the needs of biological and chemical processes in water. Even though very little oxygen will dissolve in water, it is extremely important in biological and chemical processes. The lack of oxygen leads to fish kills, stratification, high algae and midge fly concentrations.


BATHYMETRIC MAP: A map showing the depth (bottom contours) of water in lakes, streams, or oceans. Can be used to calculate accurate lake volume to better design aeration systems and other treatment options

BENTHIC ZONE: The bottom zone of a lake.

BIOCHEMICAL OXYGEN DEMAND (BOD): A measure of the amount of oxygen removed from aquatic environments by aerobic micro-organisms for their metabolic requirements. Measurement of BOD is used to determine the level of organic pollution of a stream or lake. The greater the BOD, the greater the degree of water pollution. The amount of dissolved oxygen needed to break down organic materials to carbon dioxide, water, and minerals in a given volume of water at a certain temperature over a specified time period. Also, referred to as Biological Oxygen Demand (BOD).


CARBON DIOXIDE: CO2 gas is a product of respiration and a necessity for photosynthesis. High levels of dissolved CO2 in the water can stress or kill fish.

CARLSON’S TROPHIC STATE INDEX (TSI): A measure of Eutrophication of a body of water using a combination of measures of water transparency or turbidity (using Secchi Disk depth recordings), Chlorophyll-a concentrations, and total phosphorus levels. TSI measures range from a scale 20-80 and from Oligotrophic waters (maximum transparency, minimum chlorophyll-a, minimum phosphorus) through Mesotrophic, Eutrophic, to Hypereutrophic waters (minimum transparency, maximum chlorophyll-a, maximum phosphorus). Also referred to as the (Mean) Trophic State Index (TSI). Also see Total Inorganic Nitrogen (TIN) and Total Inorganic Phosphate (TIP).

COD or COD Test: Chemical Oxygen Demand – In environmental chemistry COD test is commonly used to indirectly measure the amount of organic compounds in water. Most applications of COD determine the amount of organic pollutants found in lakes and rivers, making it a useful measure of water quality. It is expressed in milligrams per liter (mg/L), which indicates the mass of oxygen consumed per liter of solution.


DESTRATIFICATION: Vertical mixing within a lake or reservoir to totally or partially eliminate separate layers of temperature, plant, or animal life.

DIFFUSION: The movement of a substance from an area of high concentration to an area of low concentration. Turbulent diffusion results from atmospheric motions diffusing water, vapor, heat, and other gaseous components by exchanging parcels called eddies between regions in space in apparent random fashion.

DISSOLVED OXYGEN (DO): The amount of oxygen dissolved in a body of water as an indication of the degree of health of the water and its ability to support a balanced aquatic ecosystem.

DYSTROPHIC LAKE: A lake characterized by a lack of nutrients, and often having a low pH (acidic) and a high humus content. Plant and animal life are typically sparse, and the water has a high oxygen demand. This stage follows the Eutrophic Phase in the life cycle of a lake.



EUTROPHICATION: The process of enrichment of lakes with nutrients, and the biological and physical changes associated with the process.


FRESHWATER: Water that contains less than 1,000 milligrams per liter (mg/L) of dissolved solids, including salt; generally, more than 500 mg/L of dissolved solids is undesirable for drinking.


LENTIC WATERS: Ponds or lakes (standing water).


MIDGE FLY: Any of numerous minute dipterous insects, especially of the family Chironomidae, somewhat resembling a mosquito.

MITIGATION: To lessen in force, moderate or make less severe. In aquatic management it is used to denote actions taken to restore or replace lake, pond or wetland areas that have been damaged or lost due to commercial or environmental factors.


NITROGEN: A product of the natural metabolism of plant and animal matter, and fertilizer runoff. Organic nitrogen can take many forms in water, including Nitrate, Nitrite, and Ammonia. When available, these nutrients promote plant and algae growth. Ammonia concentrations below 0.3 mg/L significantly limit plant and algae populations.


STRATIFICATION: The separation of lakes into three layers:

The thermal stratification of lakes refers to a change in the temperature at different depths in the lake, and is due to the change in water’s density with temperature. Cold water is denser than warm water. Where lake water warms up and cools, a cyclical pattern of overturn occurs that is repeated from year to year as the densest water at the top of the lake sinks.


WATER QUALITY: The chemical, physical, and biological characteristics of water, usually in respect to its suitability for a particular purpose.

WATERSHED: The land that sheds water from the surface or underground into the same place, often a pond or lake.