Annual status report, 1993:  Macroinvertebrate sampling


Sauer, J. S.  1997.  Annual status report, 1993:  Macroinvertebrate sampling.  U.S.
Geological Survey, Environmental Management Technical Center, Onalaska, Wisconsin,
February 1997.  LTRMP 97-P001.  17 pp.  (NTIS #PB97-153662)


ABSTRACT

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 detect 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.   These three 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 extrapolation purposes.  Pool 13
had the highest mean number of mayflies (155 m-2), fingernail clams (2,596 m-2), and
midges (509 m-2).  The lowest mean number of mayflies, fingernail clams, and midges (7,
1, and 10 m-2, respectively) was encountered in Pool 26.  Overall, the impounded areas,
including Lake Pepin, 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. 


KEYWORDS

benthic aquatic macroinvertebrates, Corbicula, fingernail clams (Sphaeriidae), mayflies
(Ephemeridae), midges (Chironomidae), Mississippi River