The Odessa complex represents a small fragment of the vast expanse of shallow wetlands that covered the Mississippi River floodplain when European settlers began arriving in the early 1800s. In those days, spring floods spread out over the entire floodplain and filled thousands of shallow basins and sloughs scattered from bluff to bluff. Many of those basins would dry during late spring and summer, and a variety of wetland plants would germinate and grow in them. Depending on depth and soils, some would be dominated by perennial plants like cattails, bulrush or buttonbush, and others would grow annual seed-producing plants like smartweeds and millets. Normal fall rains produced a slight rise in the river that filled many of those basins again, making all that seed available to migrating waterfowl. In the spring, those heavily vegetated basins produce an eruption of tiny aquatic organisms, including insect larvae, tiny crustaceans, and others that biologists refer to generally as invertebrates. They supply spring migrating waterfowl a crucial source of protein for their northward journey, especially to hens building energy reserves for egg laying. Ideal conditions wouldn't have been present everywhere on the river every year, but because of the vast resources stretching its length from bluff to bluff, vast areas would have been present for birds to refuel on their migration.
The river and floodplain are now a completely different system. The river has been reduced to a narrow ribbon cut off from most of the floodplain by adjacent levees, and drainage systems keep most of the floodplain dry year around for agriculture and other development. The river itself has been converted to a series of impoundments by the navigation dams, and while it still floods, the drying cycle has been eliminated and so too has most of the wetland vegetation that once sheltered and fed migrating waterfowl.
At the Odessa Complex, managers have a unique opportunity to mimic the water level fluctuations that once produced everything waterfowl needed during their migrations. An inlet above Lock and Dam 17 allows water to flow in from the pool, while an outlet below the dam allows water to be drained. The normal operation is to slowly drain water out of the Complex once the spring flooding is over to reach the lowest levels by mid-summer when nearly a thousand acres of wetland substrate is exposed; Those mudflats will sprout a profusion of seed-producing moist soil plants if water is kept off them for a month or so. When the water is slowly raised throughout the fall to incrementally flood each slight rise in elevation, the birds can take advantage of the different food that has been produced at each of those levels. A maximum fall level is usually reached by late November.
Moist Soil Management:
Port Louisa NWR used to manage much of the upper end of the complex through cooperative farming. Farmers cropped the area and in return left a certain percentage of the crops for wildlife. While this strategy worked well for mallards, geese, deer and turkeys, it provided very little food or habitat for the vast majority of migratory bird species or resident wildlife that depend on wetland habitat. In addition, local farmers were having a hard time making ends meet through this type of agreement because of the soils and severe conditions. A common complaint was the area was either too wet or too dry to farm successfully.
In 2001 the refuge decided to turn these farm units into Moist Soil Management areas. Commonly referred to as Moist Soil Units, these wetlands are intensively managed through water level manipulation and disturbance. Goals of management are to grow dense stands of wetland plants that produce a high volume of seeds and cover for a wide variety of wetland dependent species. This shift is important because now we can provide habitat for numerous wildlife species throughout the entire year instead of just a handful during the fall.
Some small dikes were constructed to contain water in individual units, and a few small water control structures were installed to precisely regulate water levels in those units. A series of ditches originally dug years ago to drain the area are now used to feed water to those units. In addition, pumps are used to flood some units that are too high to flood by gravity flow in normal years. Although these units are separated from the lake proper by small dikes, they are still connected hydraulically and heavily influenced by the water level of the lake. Part of moist soil management also includes soil disturbances like mowing and/or disking to influence what type of plant community develops, so fairly dry conditions are required at least in some years.
When managed properly these units can provide 5 times the available food than under the original cooperative farming agreements and also provide a wider variety of food, habitat and cover to support all migratory bird and animals that are dependent on wetland habitats. As the name implies, moist soil plants are far less susceptible to and sometimes thrive on short duration flooding during the growing season. That also makes them a much more dependable food resource than farming, which frequently resulted in complete failure of production due to flooding. This type of habitat once occurred on a wide scale along the Mississippi River Basin but has severely declined due to drainage, flooding and stable high water levels of the pools.
* Odessa Peak Waterfowl Counts (1983 - 2012)
Wetlands like these are valuable habitat for waterfowl
The following is a general chronological list of the seasons.
Warming shallow water produces a tremendous amount of invertebrates needed by shorebirds and waterfowl in order to elevate protein levels for the nesting season. The dense beds of moist soil plants produced the year before provide the substrate and food for this explosion of tiny aquatic life.
Draining the water produces mudflats and small pools providing excellent feeding conditions for shorebirds and wading birds. The exposure of mudflats also allows for germination of moist soil plants like millets, smartweeds, pigweeds, sedges and many others. These plants are prolific seed producers, and some produce shallow root nutlets as well. Mowing and/or disking may be used to eliminate or set back undesirable plants and provide conditions to promote desirable ones.
Actively growing plants are periodically flooded which supplies the water needed by these plants but also provides for excellent habitat for secretive marsh birds, amphibians and reptiles. Periodic flooding can also be used to eliminate some undesirable plants.
Slowly flooding the units makes the new habitat available first to early migrating rails and bitterns, then to the wide variety of waterfowl on their annual trek south. Throughout the fall, the water level in individual units is continuously raised so each wave of newly arriving waterfowl has a newly flooded food source available to them. This is done at a slow steady rate to avoid getting the water too high too fast and making foods unavailable to waterfowl. Dabbling ducks such as mallards, pintails, teal, and gadwall prefer to feed in water depths of less than 6 inches.
Some water is maintained in units to support local furbearers such as mink and muskrat along with providing adequate soil moisture for invertebrates and hibernating amphibians and reptiles.