Three decades of biomonitoring (1979 -2007) in the Mississippi National River and recreation area, Minneapolis-Saint Paul, Minnesota

The Metropolitan Council Environmental Services started biomonitoring the three large rivers in the Minneapolis-Saint Paul Metropolitan Area in 1979, as a key component of a long-term water quality monitoring program. Macroinvertebrates have been sampled annually at 9 long-term biomonitoring stations on the Upper Mississippi River, 2 stations on the Minnesota River, and 2 stations on the St. Croix River, using Hester-Dendy artificial substrate samplers and Ponar sediment samplers. Macroinvertebrate community assemblages at Upper Mississippi River stations within the Mississippi National River and Recreation Area (MNRRA) were analyzed using multiple metrics, including Taxa Richness, Shannon Diversity Index, Hilsenhoff Biotic Index, percent EPT, percent Ephemeroptera, and percent Chironomidae. Long-term trends in macroinvertebrate community metrics within MNRAA indicate improved conditions both upstream and downstream of Minneapolis-Saint Paul in years with average and high river flows, but short-term declines downstream in years with reduced flows. We hypothesize that improving trends in macroinvertebrate metrics are related to improving water quality trends within MNRRA, and may be attributed to improved wastewater treatment plant performance and a marked reduction in combined sewer overflow (CSO) discharges.