In 1998, MCHD completed its first annual collection of benthic macroinvertebrates from streams throughout the county. There are many advantages of using benthic macroinvertebrates to assess the quality of a stream. Monitoring of the biological communities is relatively inexpensive in comparison to the cost of assessing chemical or bacterial parameters. It also has minimal detrimental effect on the resident biota. The benthic macroinvertebrates are good indicators of localized conditions, as many of the animals have limited migration patterns or a sessile mode of life.
Most species have a complex life cycle of one year or more.
Metrics or indices are the number values used to interpret the site data. The data analysis used by the MCHD integrates several community, population and functional parameters into the interpretation. Each parameter, or metric, measures a different component of community structure and has a different range of sensitivity to pollution stress. This approach provides a more valid assessment due to the variety of parameters evaluated. The modified Hilsenhoff Biotic Index in which individual taxa are classified on the basis of their tolerance or intolerance to various levels of domestic wastes.