Benthic invertebrates in streams include such animals as snails, mussels or clams, worms, leeches, and the larvae of many insects. Some invertebrates spend their entire lives in the stream while others like the insect larvae only begin their lives there. Some are tolerant of a wide variety of environmental conditions and others have a very narrow range of conditions they can tolerate. Benthic invertebrates don't move around much so they are good indicators of conditions at a particular site. Data on species, their abundances, their pollution tolerance and other environmental preferences, allow computation of metrics for water quality assessment in a manner similar to that used for algae and fish. Metrics computed for benthic invertebrates may include the number of species and genera; Hilsenhoff Biotic Index; Shannon Diversity; and percent abundance of individuals and taxa in the orders Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies), also known as percent EPT. EPT taxa are generally sensitive to degradations in water quality.
As part of the USGS NAWQA program, the Western Lake Michigan Drainages Study Unit was one of 6 study units chosen to be part of the National Study on Effects of Urbanization on Stream Ecosystems. The WMIC Study was done in 2003-4 in the Milwaukee and Green Bay Area. Methods used were nationally consistent within the USGS to allow comparison with other areas of the US . Methods are described in Moulton and others (2002) for samples collected in Cycle II (2002-2004). Ecological data collected included distribution and abundance of algae, invertebrates, and fish, as well as stream habitat at stream sites.
As part of this Study of the effects of urbanization, we collected benthic invertebrate samples from 30 sites during late August to early September 2004. Two types of benthic invertebrate samples were collected: a Qualitative Multihabitat (QMH) sample and a quantitative Richest-Targeted Habitat (RTH) sample. Qualitative samples were collected to provide a list of species found at a site. Quantitative samples were collected to provide actual abundances of species found in selected habitats at a site and allow computation of measures or metrics. A QMH sample is intended to represent species from as many different types of habitats as possible. An RTH sample is intended to represent the habitat with the greatest diversity of species, usually a riffle.
Data analyses for this Study are currently in progress. Results will be published in 2006 and 2007 in USGS reports and journal articles.
Moulton II, S.R., J.G. Kennen, R.M. Goldstein, and J.A. Hambrook, 2002. Revised Protocols for Sampling Algal, Invertebrate, and Fish Communities as Part of the National Water-Quality Assessment Program. U.S. Geological Survey Open-File Report 02-150, 72 pp.