Sandra Postel and Brian Richter, authors of Can We Save Earth's Rivers?
Ganges, Nile and Amazon — these river names conjure powerful images of exotic locales, rich with history. They are places where people and rivers seem inseparable. Yet, amid this pantheon of great rivers, one exists much closer to home — the Mississippi.
The Mississippi is the world's third-longest river, and its very name means "great river." It stretches a whopping 2,320 miles from its headwaters at Lake Itasca in Minnesota to the Gulf of Mexico. So great is this distance that a raindrop falling in Lake Itasca would arrive at the Gulf in about 90 days. Yet, we often fail to recognize the river's importance in our history, livelihoods and quality of life.
Part of what makes the Mississippi and these other rivers "great" is the dynamic interchange that historically existed between the river and the lands that surround it. Known as the river's floodplain, these lands were subject to natural spring floods and then low stable water levels during the summer growing season. Low and high water flows created a mosaic of backwater wetlands, sloughs and channels.
In addition to the habitat they provided, floodplains were a major energy source for the river ecosystem. Diverse and abundant plant beds growing in backwater areas captured sunlight and stored it as carbohydrates. These plants were eaten by insects and other animals, which, in turn, provided food for more animals including fish, mussels and other invertebrates, both in the backwaters and out in the river.
Through the interplay between the river and its floodplain, nutrients were exchanged, habitat was maintained and biological productivity was boosted. We enjoyed cleaner drinking water, saw more wetland birds, caught more fish and were buffered from flood damages when this system worked. In many places, though, it no longer does.
Changes to the Mississippi during the last 100 years are destroying this formerly rich mosaic of floodplain plant communities and the fish and wildlife species the floodplain-river ecosystem sustains. Below Dubuque, Iowa, most of the Mississippi now flows between massive levees that prevent the interchange of water, nutrients, sediment and aquatic organisms between the river and its former floodplain. Today, the main stem of the river no longer connects with 50 percent of its floodplain in the upper river and 90 percent in the middle and lower stretches of the river.
In addition to the direct loss of important natural habitats, reduced water storage capacity on the floodplain contributes to unnatural water level fluctuations. Combined with effects from navigation dams, these altered water levels severely limit the abundance and diversity of native plant communities in the river and its floodplain. Loss of floodplain storage also contributes to abnormally high floods and associated damages to private property and human life.
There are, however, reasons for hope. The Mississippi still retains much of its biological diversity, and it is resilient.
"When given a chance, river systems often heal. Reconnect a river with its floodplain, and fish and riparian plant communities will rebound," write Sandra Postel and Brian Richter in Can We Save Earth's Rivers?
Today, there is a growing understanding that we must do more to ensure the long-term health of our rivers. Armed with better science and research, a cadre of conservationists, civic leaders and industry insiders are leading the charge to restore health and vitality to this system.
The Nature Conservancy's Mississippi River program is committed to this work. It has a dedicated group of scientists and land conservation managers who are working with a variety of partners to restore and protect 1 million acres of the river's floodplain. Science is telling us that a functional floodplain is needed for the river system to be healthy and able to support the diversity of the region's native plants and animals. If the program achieves this goal, then it also will have helped ensure that the river continues to provide additional societal benefits, such as purifying waters and moderating floods.March 04, 2011