Annual Status Report, 1994: Macroinvertebrate Sampling.
1997
Sauer, Jennifer S.
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. Long-term monitoring is needed to detect population tends and local changes in aquatic ecosystems. Mayflies (Ephemeridae), fingernail clams (Sphaeriidae), and the exotic Corbicula species were selected for monitoring. Midges (Chironomidae) were added to the sampling design in 1993. 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 about 125 sites per study area. Mean densities of organisms were weighted by strata for pool or reachwide estimates. Pools 4 and 13 had the highest mean number of mayflies (203 and 194/sq m, respectively) and midges (185 and 75/sq m, respectively). Fingernail clam estimated mean densities were highest in Pool 13 (594 sq m). The lowest estimated mean number of mayflies, fingernail clams, and midges (19,1, and 14/sq m, respectively) was encountered in the Open River study area. 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.
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