History of Transportation
For more than 175 years, humans have been changing the Mississippi River to make it easier for barges loaded with goods to travel safely and efficiently. The navigation industry is thriving, but the biological condition of the river isn't faring so well.
In order to function naturally, the Mississippi needs to be able to change course, rise and fall, and react to the conditions of the land around it. Sometimes, these changes are rapid, as in times of flood when banks and islands are eroded away in a matter of hours or days. Other changes are subtler and happen over years or decades. But no matter what the rate may be, change is the natural order for rivers.
Each change we've made over the years has taken away a little of the Mississippi's ability to change as nature intended. When wing dams and closing dams were built, beginning in the 1800s, the river's flow was forced into the center of the main channel and could no longer efficiently seek its own course and replenish the backwaters and side channels that are so vital to many of the floodplain's plant and animal species.
The most profound change in the Mississippi's character was the construction of the locks and dams. They transformed the river from a free-flowing watercourse to a series of long, relatively shallow pools. Immediately above the dams, these pools function like lakes, while further upstream, they are still pretty much river-like in character.
One of the fundamental characteristics of moving water is its ability to carry solid materials, called sediments, as it flows downstream. Generally speaking, the faster water is moving, the larger the material it can carry. River channels take their shape as water carries sediments when energy it energy is high, drops them when energy is low, and picks up new materials when energy increases again. The constant shuffling of sediments from the water to the riverbed and banks, and then back to the water again, creates the wide variety of habitats found on rivers.
When the Mississippi was dammed, it could no longer carry sediments as effectively as before. At the same time, the amount of sediment entering the river from its tributaries began to increase as more as agriculture became more intensive and lands were developed for urban uses. Even flood flows, which were now slowed by dams, could not flush out sediments from backwater and side channels any more.
The Mississippi River of today is in beginning to show signs of decline. Backwaters and side channels are disappearing, filled in by sediments that otherwise would have been carried downstream.
Many people, even those who live near the river and see it frequently, are not aware of the decline. That's because the river is being filled in from the bottom up. For the most part, the river is just as wide as it was fifty years ago. But in many areas along the river, backwaters and side channels that were once 15 feet or more in depth are now only a couple of feet deep.
This loss of backwater and side channel habitat is the cause of great concern. Many of the important fish species on the river depend on the areas away from the main channel for critical parts of their life history. For example, Northern pike spawn in shallow areas with thick aquatic weeds, and these areas are becoming fewer as time passes. Many fish species spend the winter months in backwater areas where the current is slow, and these areas are becoming too shallow for the fish to survive.
There is not complete agreement, however, as to how bad off the Mississippi River may be and what the causes of the decline really are. But the weight of the evidence suggests ecological health of the river is declining and that the lock and dam system is a major cause. Most experienced scientists who work on the Upper Mississippi agree that, if current trends continue, the river that we know today cannot be sustained into the future, let alone restored.
sAs Congress and the American public debate the future of the Mississippi River in the coming months and years, the decisions that are made will come down to a small number of crucial questions. First, we will need to decide if we can balance the desires of the barge industry with the ability of the Mississippi to sustain itself as a natural resource. If the answer to that question is yes, then we must decide how to pay for protecting the river as barge traffic continues to rise. If the answer is no, then we will need to decide which is more important. Unfortunately, none of these questions has yet been decided.
to be continued...
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