The Hilsenhoff Biotic Index (HBI) is a quantitative method of evaluating the abundance of

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

fauna in stream

ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...

s as a measurement of estimating

water quality 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 tr ...

based on the predetermined pollution tolerances of the observed taxa. This

biotic index A biotic index is a scale for showing the quality of an environment by indicating the types and abundances of organisms present in a representative sample of the environment. It is often used to assess the quality of water in marine and freshwater ...

was created by William Hilsenhoff in 1977 to measure the effects of

oxygen depletion Hypoxia refers to low oxygen conditions. Normally, 20.9% of the gas in the atmosphere is oxygen. The partial pressure of oxygen in the atmosphere is 20.9% of the total barometric pressure. In water, oxygen levels are much lower, approximately 7 p ...

in Wisconsin streams resulting from organic or nutrient pollution.

Calculating the HBI

The collection sample should contain 100+ arthropods. A tolerance value of 0 to 10 is assigned to each arthropod

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

(or

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...

) based on its known prevalence in stream habitats with varying states of

detritus In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...

contamination. A highly tolerant species would receive a value of 10, while a species collected only in unaltered streams with high water quality would receive a value of 0. The sum products of the number of individuals in each species (or genera) multiplied by the tolerance of the species is divided by the total number of specimens in the sample to determine the HBI value.

HBI = \frac

; where ''n'' = number of specimens in taxa; ''a'' = tolerance value of taxa; ''N'' = total number of specimens in the sample. Precautions should be taken to account for

confounding variables In statistics, a confounder (also confounding variable, confounding factor, extraneous determinant or lurking variable) is a variable that influences both the dependent variable and independent variable, causing a spurious association. Con ...

, such as the effects of dominant species over-abundance, seasonal temperature stress, and water currents. Limiting the collection of individuals from each species to a maximum of 10 (10-Max BI) has been shown to minimize the effects of these phenomena on the True BI. The biotic index is then ranked for water quality and degree of organic pollution, as follows:

References

Arthropod ecology Environmental indices Water pollution Environmental science Water quality indicators {{Arthropod-stub