Annual Status Report: 1992 Macroinvertebrate Sampling. Long Term ResourceMonitoring Program

摘要

In 1992, as part of the Long Term Resource Monitoring Program, macroinvertebratesampling 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. 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. 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 approximately 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 (124 to the minus 2 power) and fingernail clams (90 to the minus 2 power). The lowest mean number of mayflies and fingernail clams (10 and 3 to the minus 2 power, respectively) was encountered in La Grange Pool. Silt/clay substrates supported the highest mean densities of mayflies in all reaches except for Pool 26 and La Grange. Silt/clay substrates also supported the highest densities of fingernail clams except for Pool 13 and La Grange.