Annual status report, 1994: Macroinvertebrate sampling
Dates
Publication Date
1997-02
Summary
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 trends 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 [...]
Summary
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 trends 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 m-2 , respectively) and midges
(185 and 75 m-2, respectively). Fingernail clam estimated mean densities were highest in Pool 13 (594 m-2 ). The
lowest estimated mean number of mayflies, fingernail clams, and midges (19, 1, and 14 m-2, 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.
