1971 benthic report for the Grand River Valley

Biological determinations of water quality have been increasingly used as a measure of water quality rather than chemical determinations. Aquatic invertebrates are very sensitive to changes in their habitat, whether these changes are physical or chemical. The biological method is often capable of detecting minute gradual changes that would escape notice by chemical methods. Chemical analysis of the water quality gives an accurate picture of the chemical pollutants that are present in the water at the particular moment that the sample was taken. However, if this is an isolated chemical analysis of this particular stream, the results may not represent normal conditions of the stream. The invertebrate fauna of a stream not only represents present chemical conditions but also changes in water quality that have occurred in the past. Once a biologist is familiar with a stream, minor changes of water quality are revealed to him by replacement of species by other closely related species or by the gradual disappearance of some species. An overnight chemical discharge may go unnoticed by the chemist but is strikingly apparent to the biologist by the sudden absence of some organisms. By working upstream until these organisms are found, he can pinpoint the position of the chemical overload. This could be monitored chemically only by a great number of tests if the discharge had been noticed in the first place.The studies outlined in this report are G.R.C.A.'s first attempt at detailed biological surveys. The areas chosen for study were picked to determine the effects of reservoirs on the downstream fauna and water quality.