Invertebrates are an excellent indicator of habitat and water quality. The habitat requirements and tolerance to various pollutants is known for many species. Monitoring invertebrate diversity, density, species richness, and species composition can therefore be used to assess physical and/or chemical habitat changes.

Macroinvertebrates Associated with Chevron Dikes, Mississippi River Miles 289.5,

Chevron dikes were constructed in 1992 near Mississippi River Mile 289.5, Pool 24, to divert flow into the thalweg, reduce dredging and open water disposal, create islands, and create fish and macroinvertebrate habitat. Natural resource agencies agreed that these dikes should benefit fish and wildlife, however, monitoring was needed to confirm these benefits. ESI was contracted to analyze invertebrate populations on the dikes and in the surrounding river bed to determine if the chevron dikes were providing macroinvertebrate habitat. The macroinvertebrate assemblages were compared between the interior dike rock, exterior dike rock, interior soft substrate, and the surrounding soft substrate in 1994, 1995, and 1996. No unionids were found due to previous open water dredge disposal in the area. However, the dikes and protected areas behind dikes are providing habitat for invertebrates and fish. Diversity and taxonomic richness was higher on dikes than in the surrounding soft substrates in all three years.

Macroinvertebrates Associated with Lock and Dam 26 I-wall Demolition Rubble, Mississippi River Mile (MRM) 202.9,

Lock and Dam 26 (MRM 202.9) near Alton, Illinois (Madison County) on the upper Mississippi River was replaced by the Melvin Price Locks and Dam (MRM 200.78) in February 1991, and the old structure, except for the intermediate lock wall (I-wall), was demolished. During summer and fall 1995, the I-wall above 392.0 National Geodetic Vertical Datum (NGVD) was demolished and the rubble was left in place. ESI was contracted to monitor aquatic macroinvertebrate use of the remaining rubble. The hard surfaces and interstitial spaces of the I-wall rubble provide a unique habitat, and a source for food and refugia for fish and macroinvertebrate species, compared to the surrounding sand and silt substrate. Sampling with rock baskets during 1996 and 1997 indicated a diverse species assemblage (59 and 64 taxa, respectively, dominated by the hydropsychid caddis flies Hydropsyche orris and Potamyia flava) had colonized the I-wall rubble. Stomach contents of flathead catfish and freckled madtom indicated their diets consisted primarily of Hydropsychidae larvae (mostly H. orris). In 1997 and 1998, the macroinvertebrate assemblages of the I-wall rubble were compared to those of the soft channel substrate. Only 34 taxa were found in the soft channel substrate and dominant species included the caddis fly P. flava, the mussel Dreissena polymorpha, the chironomid midge Polypedilum scalaenum, and immature tubificids.

Macroinvertebrates Associated with Carl Baer Bendway Weirs, Mississippi River Mile 163.5,

Five bendway weir channel maintenance structures were constructed in April 1996 near Mississippi River mile 163.5, to increase the effective width of the river navigation channel by scouring the channel at the outer edge and reducing point bar development on the inner side of the bend. Natural resource agencies felt that the creation of complex habitats in the relatively homogeneous main channel would be beneficial to the ecosystem. ESI was contracted to investigate invertebrate species community colonization and composition associated with the weirs. Macroinvertebrates were sampled upstream, downstream, and directly on weirs, with rock baskets and buoy rock scrapes. Density, diversity and species composition did not differ among sampling methods. The samples were dominated mostly by hydropsychid caddis flies, Hydropsyche orris and Potamyia flava. Chironomids, such as Rheotanytarsus exiguus group and Polypedilum convictum, were also fairly abundant. Although bendway weirs are still relatively new at this time, the rock substrate of the weirs appears to provide valuable invertebrate habitat over surrounding homogenous sand. However, colonization of individual rocks was extremely variable.

Nine bendway weirs were constructed at Price’s Bend near Mississippi River mile 30 with the purpose of widening the effective width of the navigation channel by reducing point bar development on the inner side of the bend. The addition of rock substrate to an otherwise homogenous sand substrate should provide increased habitat for a more diverse invertebrate community. Macroinvertebrates were sampled on the nine Price’s Bendway Weirs and a bend without weirs to determine invertebrate community characteristics and distribution. Taxonomic richness and diversity were higher at Price’s Bend, the bendway with weirs, than at Thompson’s Bend, the bendway without weirs. Macroinvertebrate communities at bendway weirs were dominated (67%) by hydropsychid caddisflies (Hydropsyche orris) which are a filter feeding species that clings to hard rock substrates, but Potamyia flava (11%), Dreissena polymorpha (8%), and Dugesia tigrina (4%) were also fairly common. Macroinvertebrate communities at the bendway without weirs were dominated (89%) by oligochaete worms (Barbidrilus paucisetus), a burrowing species that utilizes large river sand habitats, and only one other taxa, Turbellaria (7%), was relatively common. Correspondence analysis of the macroinvertebrate communities confirmed the distinction in habitat between the bendway weirs and the bendway without weirs, and suggested variation in macroinvertebrate communities within both bendways.