Successional changes in habitat caused by sedimentation in navigation pools

Abstract

Upstream of St. Louis, Missouri, navigation on the Upper Mississippi River is made possible by a series of lock and dam structures. Many of the pools formed by these navigation dams have nearly reached a new equilibrium condition for scour and deposition of sediment. Several pools with extensive backwater or channel border areas are still accumulating sediment at rates similar to those for man-made lakes. The original open-water habitats in these pools are changing to aquatic macrophyte beds and then to marsh or terrestrial floodplain conditions because of sediment deposition.

Two pools are used as examples of this phenomenon. 1) Pool 19 on the Mississippi River was formed when the lock, dam, and power house at Keokuk, Iowa were completed in 1913; and 2) Peoria Lake which has been affected by the diversion of Lake Michigan water into the Illinois River in 1900 and the construction of a lock and dam in 1939. Both pools have had well over 50 percent of their original volume filled with sediment. Three areas in Pool 19 illustrate the successional changes that occur as sedimentation raises the river bottom into the photic zone. Sedimentation has made boating impossible on large areas of both pools. The continuing process is likely to change open waters to floodplains. Peoria Lake lacks aquatic plant beds because of excessive turbidity and frequent resuspension of bed material by wind- or boat-generated waves. It seems likely that these river reaches will become a narrow channel without any broad and highly productive channel borders.