History of the Hilsenhoff Biotic Index
Originally developed in 1977 by Dr. William Hilsenhoff of the University of Wisconsin - Madison, to assess low dissolved oxygen caused by organic loading in streams. The idea of using a biotic index however is not all that new. The earliest research into biomonitoring in the United States originated from Forbes (1887) biological community concept. Basically under this concept plant and animal communities in a river corridor could be used to assess degree of organic pollution. This concept was further carried out later as Forbes and Richardson (1913, 1928) classified zones of pollution along the Illinois River. The first use of a biotic index however came about in Germany in the early 1900's when Kolkwitz and Marson (1908, 1909) developed the idea of saprobity (the degree of pollution) in rivers as a measure of the extent of contamination by sewage, which results in decreases in dissolved oxygen and the effect that this oxygen decrease has on life in rivers (Cairns and Pratt 1993).
The Wisconsin Department of Natural Resources (WIDNR) began using the HBI (Hilsenhoff 1977, 1982, 1987) in 1979 to assess water quality in streams and rivers as part of several non-point source pollution monitoring programs within the agency. These monitoring efforts have continued to expand through the years and now statewide efforts by several bureaus collect ca. 450 BI samples/year. The procedures for sampling and laboratory processing were standardized by the WIDNR in 1983 and statistical analysis procedures for applying the BI were developed by Narf et al. Hilsenhoff (1977, 1982, 1987) developed a range of BI values (0-10) for water quality classifications and degree of organic pollution that are used by the WIDNR in their water quality assessment and monitoring programs (Table 1 below).
Aquatic arthropods and a few other select
macroinvertebrates are used to evaluate water quality with a numerical index that
allows quantification and assessment of water quality. These organisms
appear to be ideally suited for this purpose because they are common in
essentially all streams, they are easily collected, are not very mobile, are
relatively easy to identify, and they have life cycles up to a year or greater (Hilsenhoff
1977). Because they are continually exposed during their life cycles to
extremes in the environment, they can serve as effective indicators of environmental
changes.
Although originally developed to assess low dissolved
oxygen caused by organic loading, a purpose for which it works best (Hilsenhoff
1977, 1982, 1987), the BI may also be sensitive to the effects of impoundment,
thermal pollution, and some types of chemical pollution (Hilsenhoff 1998, Hooper
1993). Only arthropods that require dissolved oxygen for respiration are
used in the calculation of the BI. Organisms that are most sensitive to
low concentrations of dissolved oxygen have low tolerance values, and organisms
which have a wide tolerance, have high tolerance values. Organism
tolerance values and the BI range from 0 to 10 and most Wisconsin aquatic
macroinvertebrate species used in the calculation have determined tolerance
values.
Table 1. Water
quality classifications for the Hilsenhoff Biotic Index (BI) (Hilsenhoff 1987)
Bi Value Water Quality Degree of Organic Pollution
0.00-3.50 Excellent No apparent organic pollution
3.51-4.50 Very Good Slight organic pollution
4.51-5.50 Good Some organic pollution
5.51-6.50 Fair Fairly significant organic pollution
6.51-7.50 Fairly Poor Significant organic pollution
7.51-8.50 Poor Very significant organic pollution
8.51-10.00 Very Poor Severe organic pollution