The Recovery of Stream Benthic Insect Communities Following Coal Strip Mining in the Cumberland Mountains of Tennessee

The aquatic insect faunas of twenty-three streams in the Cumberland Mountains of Tennessee were investigated. The purpose of the study was to analyze the recovery through time of the aquatic insect faunas of streams polluted by runoff from contour strip mines. Quantitative determinations of the benthic insect fauna were made using two methods. The first involved removing substrate particles and picking off the insects with forceps. The second was a Surber Sampler type method of placing a screen in the streams and disturbing the substrate upstraem of the screen. Rather than sample one stream over a period of years, simultaneous samples were taken in streams of similar flow and substrate characteristics, both in watersheds which had been disturbed by strip mining activities at various times in the past and in control streams. It was possible in this manner to analyze changes in community structure occurring over a twenty-two-year period following the cessation of strip mining activities. General recovery trends were analyzed quantitatively by plotting the number of individuals, number of taxa, and a species diversity index against time. It was found that all three parameters decreased after the cessation of mining, reaching a minimum after four to six years. After this time the values began to increase, returning essentially to predisturbance levels after twenty-two years. Qualitative analysis of the insects actually present, however, shows that the structure of the community was altered and even after twenty-two years it had not returned to normal. The change in faunal composition does not appear to be due to acid mine drainage but most probably to the effects of siltation. The role of increased concentrations of dissolved constituents was not evaluated and it is possible some of the effects on the insect faunas are attributable to this factor