Macroinvertebrates

Between 1967 and 1978, Congress passes the Clean Water Act, the USEPA is created, and the State of Illinois creates the IEPA, institutes new regulations governing discharges, and establishes water quality parameters. The question is, has water quality improved? Anecdotal evidence can be found by talking to captains of towboats on the river. They “complain that the ice on the river is harder now than it was, a characteristic of clean water” (Tucker). More scientific information is needed to verify this change.

According to a report by William Tucker entitled, “An Intensive Survey of Illinois River and Its Tributaries: A Comparison Study of 1967 and 1978 Stream Conditions,” stream conditions in the Illinois River substantially improve between 1967 and 1978, particularly between Chillicothe and Havana. In this study, Tucker collects aquatic organisms, primarily aquatic macroinvertebrates at 30 stations. Each specimen is identified, and all organisms are assigned a pollution tolerance status (see Appendix A for list of species and their tolerance status).

The four tolerance status categories for the aquatic macroinvertebrates found in this study are:

• Intolerant - organisms whose life cycle is dependent on a narrow range of environmental conditions. These are rarely found in polluted or degraded waters and are typically replaced by more tolerant species when conditions decline in quality;
• Moderate - organisms that lack the extreme sensitivity to stress as shown by intolerant species but cannot adapt to severe environmental degradation;
• Facultative - organisms that are able to survive over a wide range of environmental conditions and possess a greater degree of tolerance to adverse conditions than the first two groups. This category also includes all species that depend on surface air for respiration; and
• Tolerant - organisms that not only have the ability to survive over a wide range of environmental extremes, but can thrive in waters of poor water quality, sometimes even under anaerobic conditions. These organisms are often found in large numbers in areas of organic pollution.

The IEPA uses a stream classification system based upon the abundance of intolerant organisms. The system being used at the time of this survey is:

• Balanced Environment: Intolerant organisms are abundant in number and species.

  Intolerant present > 50%
  Moderate, Facultative and Tolerant usually present < 50%

• Unbalanced Environment: Intolerant organisms are less in number than other, but combined with moderate organisms, outnumber those tolerant.

  Intolerant present < 50%
  Moderate, Facultative, and Tolerant usually present > 50%

• Semi-polluted Environment: Intolerant organisms are few or none; moderate and/or facultative individuals are present.

  Intolerant present < 10%
  Moderate, Facultative and Tolerant usually present > 90%

• Polluted Environment: Intolerant species do not exist; only intolerant organisms or no organisms present.

  Tolerant present = 100%

In the years following this survey, the USEPA changes the classification system to Good, Fair, and Poor. The IEPA now uses the same classification.