In 1992, macroinvertebrate sampling was initiated in Pools 4, 8, 13, 26, and the Open
River reach of the Mississippi River, and La Grange Pool of the Illinois River as part of
the Long Term Resource Monitoring Program. This report summarizes the 1997
macroinvertebrate sampling. Long-term monitoring is needed to detect population
trends and local changes in aquatic ecosystems. Mayflies (Ephemeroptera), fingernail
clams (Sphaeriidae), and the exotic Corbicula species were selected for monitoring.
Midges (Chironomidae) were added to the sampling design in 1993 and zebra mussels
(Dreissena polymorpha) were added in 1995. Mayflies, fingernail clams, and midges,
members of the soft-substrate community, were chosen because they play an important
ecological role in the Upper Mississippi River System. Sampling was based on a
stratified random design and was conducted at approximately 125 sites per study area.
Mean densities of taxa were weighted by strata for extrapolation purposes. Pool 13 had
the highest mean number of mayflies and fingernail clams (146.6 and 231.4 m-2,
respectively). La Grange Pool reported the highest densities of midges (149.9 m-2).
Overall, the impounded areas, including Lake Pepin, and the contiguous backwaters
tended to support the highest densities of mayflies, fingernail clams, and midges.
Substrates with predominantly a silt clay constituent supported the highest mean
densities of mayflies, fingernail clams, and midges.
