Evaluation of aquatic macrophyte community response to island construction in the Upper Mississippi River

Abstract

Impounding large rivers has often led to reductions in aquatic habitat diversity over time. One approach used to restore habitat on the Upper Mississippi River is island construction. A specific purpose of island construction is to increase the growth and diversity of aquatic macrophytes. We addressed whether this purpose was met for islands constructed in a reach of the Upper Mississippi River. Aquatic macrophyte levels and richness around 2 constructed island complexes were compared with those in open water reference areas in 1998 and 2000. These data suggest that macrophyte levels increased in the construction area relative to the reference area for the second but not the first island complex. Findings were similar for both percent frequency of occurrence and richness index models. These differences in response are attributed to the differing maturities of the 2 island complexes. The first complex was completed 6 years prior to the initiation of aquatic macrophyte sampling, whereas sampling began midway through the construction phase of the second complex. The response of aquatic macrophytes in the first island complex may have stabilized prior to sampling, whereas aquatic macrophyte responses to construction of the second island complex were partially captured during the sampling period. These findings suggest that island construction positively influences aquatic macrophyte levels in impounded reaches of large rivers.