Wetland and Aquatic Habitat Management
Natural historic flood and drought cycles of the Upper Mississippi River have been significantly altered by the lock and dam system and flood control levees. Spiky, unpredictable water levels and the loss of summer low-water periods have reduced wetland habitat quality. In addition, sediment flowing into the system from upland agricultural areas is filling in important wetland and aquatic areas.
Great River NWR uses a variety of management techniques to enhance wetland and aquatic habitats in the Upper Mississippi River floodplain for fish and wildlife. Not all techniques are suitable in all areas and the river is often beyond management control. However, over time the refuge strives to create a natural diversity of wetland and aquatic habitats to benefit native wildlife and fish species.
Protected
Some refuge divisions are separated from the river by berms or levees. This protection reduces sediment input and the negative effects of artificial river level fluctuations. Historic wet/dry cycles can then be re-created using a combination of gravity flow, pumps, ditches, and water control structures.
Water is drawn off the wetlands in late spring, helping to solidify the bottom sediments and promote the growth of wetland plants that provide food resources for fish and wildlife. Mechanical manipulations such as mowing, discing, farming, and burning are sometimes used to set back encroachment of woody vegetation and to influence which species of wetland plants will germinate.
Slow re-flooding of the wetlands in the fall, makes the food available to waterfowl and shorebirds.
Unprotected
Some refuge divisions are unprotected by berms or levees. These aquatic areas are available year round to migratory birds and feeding, spawning, and overwintering fish, but are also subject to sedimentation, erosion, loss of natural wet/dry cycles, and loss of aquatic vegetation.
Shoreline rock or vegetation can be used to reduce erosion.
Sedimented backwaters and side channels can be dredged to restore deep water habitat for fish.
Spillways
Spillways with elevations slightly lower than the rest of the berm have been constructed on many protected divisions. These units provide some of the benefits of both protected and unprotected wetlands. The spillways allow controlled flooding during times of high water on the river. During floods, fish have access to the habitat for spawning and feeding, sediment input is reduced, and damage to refuge habitat and infrastructure is less likely. |
 |
|
During normal river levels, these units can still be independently managed for sediment consolidation and wetland plant growth.
Mark Twain NWR Complex | Site Map | Links | Home
