Since 2004, hundreds of dike modifications have been constructed on the Missouri River in order to increase shallow water habitat to benefit the endangered pallid sturgeon (Scaphirhynchus albus) and other aquatic biota. Benthic macroinvertebrates, a sturgeon food source, are also presumed to be impacted by the modifications. In an effort to compare macroinvertebrate communities of dike structures, benthic macroinvertebrates were sampled at two sites bi-monthly from June to November 2005 on the Missouri River near Blair, Nebraska (41°31' N x 96°07' W). Sites included unmodified and lowered or notched structures and were divided into sampling cells upstream and downstream from each structure.

A total of 23 taxa and 5,143 individual benthic macroinvertebrates were collected. The most abundant taxa were Tubificidae, Hydropsychidae, Ephemeridae, Chironomidae, Ceratopogonidae, Baetiscidae, Sphaeriidae, Planorbidae, Hydrobiidae and Tricorythidae.

The greatest differences in the communities occurred between mean abundance upstream or downstream from structures. Mean abundance was significantly greater downstream of structures at both DeSoto Cutoff (p=0.001) and Tyson's Bend (p=0.066). This trend was also observed with nearly all taxa at both sites, with the exception of taxa that are heavily dependent on substrate stability (clams and snails).

At Tyson's Bend mean abundance was greater (p=0.0676) at unmodified versus notched structures. In fact, collection was greater at unmodified structures at both sites and for each of the most common taxa throughout the study. Finally, the magnitude of the increase downstream of structures was frequently greater at unmodified structures. The presence of dike structures in general seems to impact the macroinvertebrate community more so than whether or not they have been modified by either lowering or notching. However, it is possible that lowering or notching helps resolve disturbance effects of dikes in general. This study provides useful information for consideration in the recovery efforts for pallid sturgeon.