Effects of Main Stem Impoundments and Channelization upon the Limnology of the Missouri River, Nebraska

Rigid control has been imposed upon the Missouri River by impounding over one-half of the upper 1,500 miles and by channeling most of the remaining river within permanent, narrow banks. These controls have caused environmental changes in the lower Missouri River, as shown by this study, of adjacent unchannelized and channelized sections of river below the main stem impoundments. Impoundments have regulated flow by evening maximum and minimum discharges and improved downstream water quality by decreasing turbidity and indirectly raising the dissolved oxygen. In addition the impoundments have contributed a limnetic cladoceran, Leptodora kindti, to the drift and have affected the distribution of benthos through the modification of turbidity. Channelization of the river has reduced both the size and variety of aquatic habitat by destroying key productive areas. Average standing crops of benthos were similar in unchannelized and channelized river (0.63 and 0.67 pounds per acre, respectively) but the benthic area had been reduced 67% by channelization. In the channelized river the average standing crop of drift was 8 g per acre-foot while in the unaltered river the average standing crop was 68 g per acre-foot. There was little similarity between the organisms of the drift and benthos; however there was similarity between the organisms in the drift and the aufwuchs