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

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

fauna in stream

ecosystem An ecosystem (or ecological system) is a system formed by Organism, organisms in interaction with their Biophysical environment, environment. The Biotic material, biotic and abiotic components are linked together through nutrient cycles and en ...

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 freshwate ...

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

oxygen depletion Hypoxia (''hypo'': 'below', ''oxia'': 'oxygenated') refers to low oxygen conditions. Hypoxia is problematic for air-breathing organisms, yet it is essential for many anaerobic organisms. Hypoxia applies to many situations, but usually refers to ...

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 A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

(or

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

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

detritus In biology, detritus ( or ) is organic matter made up of the decomposition, decomposing remains of organisms and plants, and also of feces. Detritus usually hosts communities of microorganisms that colonize and decomposition, decompose (Reminera ...

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 causal inference, a confounder is a variable that influences both the dependent variable and independent variable, causing a spurious association. Confounding is a causal concept, and as such, cannot be described in terms of correlation ...

, 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 Eponymous indices Water pollution Environmental science Water quality indicators {{Arthropod-stub