The effect of water retention structures on the distribution and diversity of freshwater benthic macroinvertebrates in three northern Michigan streams.

Abstract

Disturbances, physical and biological, have been known to impact communities by killing or displacing organisms and/or changing their environment. The intermediate disturbance hypothesis proposes the idea that an intermediate amount of disturbance will enhance local diversity by providing more niches for different organisms and controlling the abundance of a competitively dominant species. Our study tested the validity of this hypothesis by examining three Northern Michigan streams, each containing a water retention structure. We tested our prediction that diversity would be greatest at an intermediately disturbed area by comparing three sites on each of three streams. Our upstream site, for the purposes of our study, was assumed to be relatively minimally disturbed, our site directly downstream of the structure was assumed to be relatively highly disturbed, and our site approximately 150 meters downstream from the structure was assumed to be relatively intermediately disturbed. We tested a variety of abiotic factors and collected macroinvertebrate samples from each site. After running the Shannon-Wiener Diversity Index on the orders of our organisms and running regression analyses on all of the abiotic data against the biotic data, we found that at two of our three rivers, diversity was highest at the intermediately disturbed site, and that there was no correlation (with the exception of flow rate) between the abiotic factors and macroinvertebrate diversity.