Ecosystem Responses to Restoration of Upper Mississippi River Islands and Backwaters

Lock and Dam 8 was put into operation in 1937 for the purpose of providing a 9-foot deep commercial navigation channel.  These pools of water led to several ecological changes to the Mississippi River floodplain. 

Impoundment of water created a series of islands in lower Pool 8.  These islands were the high points of land within the floodplain (natural levees).  Within 60 years, > 90% of the islands in lower Pool 8 had disappeared, resulting in wave fetch and associated sediment resuspension becoming a driver affecting habitat quality through contributing to losses of aquatic vegetation and structure.  Loss of the islands also resulted in the majority of the floodplain becoming subjected to measurable water velocities year round.  The loss of protected off-channel lacustrine areas reduced available habitat for backwater fish species.   

Habitat restoration in lower Pool 8 of the Upper Mississippi River (UMR), near La Crosse, Wisconsin, began with an idea proposed by UMR biologists and managers in the mid 1980’s.  Pool 8 Islands, Phase I, was selected as one of the first Habitat Rehabilitation and Enhancement Projects (HREPs) to be implemented under the UMR Environmental Management Program (EMP), which was authorized by congress in 1986 with passage of Section 1103 of the Water Resources Development Act.

Planning for Phase I began in early 1987, followed by Phase II (1995) and Phase III (2000).  Construction spanned 23 years (1989—2012), although construction activity was not continuous due to sequencing with other HREPs throughout the UMR and availability of funding.   Cumulatively, these three projects directly restored 99 ha of islands restoring 1,861 ha of habitat for fish and wildlife.

Vegetation response to Phase I was slower than expected, but provided a lesson learned that was applied to the other projects.  Phase I’s design did not address wind fetch from the prevailing summer winds.  Phase II was designed with these winds factored in, and vegetation response within a year was significantly different than response in control areas.  Vegetation response in Phase III indicates an increase in frequency of occurrence of rooted floating leaved and perennial emergent vegetation while submersed vegetation has not declined.   

Pool 8, Phase II, backwater fisheries response to restoration of centrarchid overwintering habitat changed from a pre-project CPUE of age 1 plus bluegills and bass from 0 and 6, respectively, to an average of 474 and 104, respectively, post-project. Assessment of fisheries response to Phase III is ongoing.