A biotic index is a scale for showing the quality of an

environment Environment most often refers to: __NOTOC__ * Natural environment, all living and non-living things occurring naturally * Biophysical environment, the physical and biological factors along with their chemical interactions that affect an organism or ...

by indicating the types and abundances of

organism In biology, an organism () is any life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy (biology), taxonomy into groups such as Multicellular o ...

s present in a representative sample of the environment. It is often used to assess the

quality of water Water quality refers to the chemical, physical, and biological characteristics of water based on the standards of its usage. It is most frequently used by reference to a set of standards against which compliance, generally achieved through tre ...

in marine and freshwater ecosystems. Numerous biotic indices have been created to account for the

indicator species A bioindicator is any species (an indicator species) or group of species whose function, population, or status can reveal the qualitative status of the environment. The most common indicator species are animals. For example, copepods and other sma ...

found in each region of study. The concept of the biotic index was developed by Cherie Stephens in an effort to provide a simple measurement of stream

pollution Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the ...

and its effects on the biology of the stream.

Technique

To assign a biotic index value to a specific water site, the tester first collects macro invertebrates from portions of the sample area of the stream, river or lake, and separates them into groups of similar-looking organisms. More extensive testing can be done by looking for certain microscopic organisms. Then an identification key is used to help determine which category or group the organism belongs in and allows a numerical value be assigned to that organism. A worksheet is then used to calculate the final value or score of all the organisms found. Depending upon the worksheet's equations, the score determines the condition of the water quality.

Usefulness of macro invertebrates

Aquatic macro invertebrates have some general characteristics that make them very useful to assess stream health: # They are abundant and found in water bodies throughout the world # They are not extremely mobile # They carry out part or all of their life cycle within the stream or river. Macro invertebrates limited mobility and extended presence in the water means that they are exposed on a continuous basis to water quality in that stream or river. In particular, many of these organisms breath dissolved oxygen that is in the water. They are also easier to see at the time of sampling. Not all the macro invertebrates found in samples are listed on the biotic index scoring sheets. This is because some do not rely on oxygen within the water for survival. Many are able to collect air from the atmosphere and hold a bubble alongside their body to use like a scuba diver uses a tank of oxygen. For those macro invertebrates that do rely on dissolved oxygen, some can only live in water that has a lot of oxygen. Others can live in water that doesn't have much oxygen dissolved in it at all. Generally, it is assumed that the more pollution there is in the water, the less oxygen.

Classification

The biotic index works by assigning different levels of tolerance to pollution to the different types of organisms. The types of macro invertebrates and other organisms found during sampling are broken into 4 groups: # Pollution intolerant: These organisms are highly sensitive to pollution (Stonefly or Alderfly Larva) # Semi-Pollution intolerant: These organisms are sensitive to pollution (Dragonfly Larva or Craw fish) # Semi-Pollution tolerant: These organisms will be found in clean and slightly polluted waterways (Snails or Black Fly Larva) # Pollution tolerant: These organisms will be found in polluted, as well as clean aquatic ecosystems (Leeches, Blood worms) Some index worksheets combine groups 2 and 3 together, giving only 3 groups. Each group has a number assigned to it and is multiplied by the number of organisms found in that group. This is why identifying the type of organism is important.

Examples of Biotic Indices

* AZTI's Marine Biotic Index * Extended Biotic Index * Family Biotic Index * Hilsenhoff Biotic Index * Sludge Biotic Index * Trent Biotic Index

References

*William E. Sharpe, William G. Kimmel, and Anthony R. Buda (2002
"Biotic Index Guide."
Pennsylvania State University. *Water Action Volunteers

University of Wisconsin Extension office. {{Refend Aquatic ecology Environmental science Water pollution Environmental indices

Technique

Usefulness of macro invertebrates

Classification

Examples of Biotic Indices

See also

References