By Matt Young
Throughout history, North America’s rivers have been flyways for waterfowl and other migratory birds. Look at a national map plotted with the locations of where banded ducks have been harvested, and you will clearly see the outlines of the Mississippi, Missouri, Ohio, Illinois, Susquehanna, Platte, Columbia, and other familiar waterways formed by dense clusters of band recovery reports. Rivers not only serve as landmarks that help guide waterfowl during their epic transcontinental migrations but also are directly linked to a variety of valuable wetlands in their adjacent floodplains and watersheds.
From oxbow lakes and bottomland hardwood forests to riverine marshes and wet prairies, floodplain wetlands provide vital habitat for waterfowl, fish, and an abundance of other wildlife. These unique habitats owe their productivity to seasonal fluctuations in water levels influenced by extended periods of wet and dry weather. During the summer, when most rivers and streams recede to low levels, many floodplain wetlands go dry, allowing wet soils and organic matter to consolidate and vegetation to flourish. When floodwaters return—typically during late fall through spring—a profusion of seeds and mast produced by trees and annual vegetation during the growing season becomes available to feeding ducks, geese, and other water birds. The fertile, nutrient-rich waters also teem with aquatic invertebrates, which provide other sustenance for fish and wildlife.
In addition to their habitat value, wetlands help control flooding and purify water supplies. Like giant sponges, wetlands trap and hold sediment-laden runoff in their basins, decreasing the speed and volume of flood water flowing into and through adjacent waterways. At the same time, sediments and other suspended pollutants settle to the bottom, where aquatic plants and microorganisms absorb excess nutrients and remove other contaminants.
During the past two centuries, most of North America’s major rivers have been altered for flood control, navigation, irrigation, hydropower, and a variety of other uses. Extensive ditching and dredging and construction of levees, locks, and dams have transformed entire ecosystems by changing stream flows and severing rivers from their former floodplains. Along North America’s two largest rivers—the Mississippi and Missouri—the impacts of wetland drainage have been staggering. According to a recent report, roughly 80 percent of the Mississippi’s 2,320-mile length has been fixed for navigation, and 90 percent of the river’s original floodplain has been cut off from its source.
Farther north along the lower Missouri River, channelization, diking, and bank stabilization projects have shortened the original river channel by more than 50 miles and reduced its surface area by more than 61,000 acres. In fact, the bank-to-bank width of the “wide Missouri” described by Lewis and Clark has been reduced to a relatively straight, 300-foot-wide channel in many places, dramatically reducing the region’s natural flood storage capacity. The midstream sandbars, islands, and oxbows that once supported innumerable ducks, geese, and other waterbirds during migration are also largely gone, as well as most of the prairie, forest, and wetlands that once existed in the Missouri’s broad floodplain.
Despite these losses, many productive wetlands remain in the Missouri and Mississippi river basins. Some of the best remaining waterfowl habitat is found where these two great rivers meet just north of St. Louis. Located in St. Charles, Lincoln, Pike, and St. Louis counties, this area is known to waterfowl hunters and conservationists as the “Confluence Floodplain.” The majority of the Mississippi Flyway’s waterfowl—including at least 14 million ducks—pass through the Confluence each year, making this region acre-for-acre one of the most important waterfowl migration areas on the continent. In addition to waterfowl, the region supports hundreds of other species of other birds, fish, mussels, and mammals native to the Mississippi and Missouri river basins.
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