The way we humans make use of our rivers cannot be separated from discussions about ecology. We are, after all, part of the river ecosystem. In fact, our influence on the river ecosystem is much greater than that of any of what we call keystone species.
|Keystone predators have so much influence on a system that their removal, or their addition, to an ecosystem can completely change the make-up of that system. An example of a keystone species is the seastar, Pisaster ochraceous. R. T. Paine, then a professor at the University of Washington in Seattle, Washington, studied a rocky seashore community in the early 1960's and developed the concept of keystone species from what he observed. When he removed P. ochraceous from its seashore habitat, the mussel Mytilus californianus was able to dominate the intertidal community, and exclude most of the other usual intertidal species of animal from that site. In other words, the mussel would completely take over, by denying any other species a place to attach themselves to the rocks. The presence of the seastar ensured a vital, diverse seashore community because the seastar preyed on the mussel and kept its numbers down.|
As powerful an influence as a keystone species has, or a volcano or an earthquake or a tidal wave has, human influence on rivers can be far more dramatic. As a case in point, the Columbia River in Washington State is dammed from one end to the other: it was changed from a wild, tumbling river of many changes to a constant, steady series of lakes. The habitat was so altered that salmon have little chance of reproducing successfully, surviving in its waters, or making it back to the ocean. As a consequence, most salmon species utilizing the Columbia are now endangered. Contrast this to the late 1800's, when white people first started fishing the river: anyone could pull out so many salmon that it would be a major effort to get them home. Steelhead almost suffered the same fate, but humans found that they could (believe it or not) put them in trucks and drive them around the dams! Sadly, this technique never worked for the salmon.
Dams, of course, have been built on nearly all of America's rivers; their ill-effects are not limited to Washington State. And there are many other ways that humans have made powerful ecological changes to rivers. Here we will look at the many uses people find for rivers: how rivers help them make money, get food, live more comfortably, raise crops, have fun, learn, and just plain relax. Along the way, we will see how some of these activities can harm rivers' ecosystems.
Some commercial fishing still takes place on rivers, but for the most part commercial fishing has already so decreased the numbers of formerly abundant species that it is no longer profitable. Some major river fisheries of the past were the Columbia River salmon, the Russian sturgeon that provides caviar, and Mississippi River mussels.
Today, by far the largest part of stream fishing is done by recreational fishers: the average citizen with a fishing pole and tackle box. He is joined by the recreational hunter who enjoys working with dogs and gun to bring down waterfowl like ducks. These casual resource users work very effectively with environmental groups to help protect streams and other bodies of water, because they know better than anyone that without healthy streams their sports will vanish.
Many people find fishing a relaxing and enjoyable way to escape the pressures of modern living. They may fish from boats or from the banks, and there are many who fly-fish. Many fishermen now practice catch-and-release. When they catch a fish, they leave it in the water, gently remove the hook from its mouth, and support it until it can swim away.
Catfish are often caught, but the hands-down favorite of most of the fishing public is trout. Because of this, streams are stocked annually with the trout that the public wants to catch. These hatchery fish disrupt ecological systems because they are usually larger and more aggressive than native fishes, including native trout. Hatchery fish may also breed with native species, diluting their chromosomes and making their survival more precarious.
In America, paddleboats and steamboats became a popular mode of transportation in the late 1800's, especially along the Mississippi River. Even the wild and woolly Columbia River--before it was tamed--hosted a few brave ferry captains. A few of the old paddleboats and ferries can still be found and are used today to generate tourist dollars. In a few places where bridges can't be built, people must still use ferries to cross rivers.
Large rivers are often major shipping routes for modern industry. Tugboats can be seen pulling long barges up and down rivers. Ocean-going ships enter the mouths of some rivers to reach major cities. Some examples of these rivers are the Columbia, the Hudson, and the St. Lawrence River in Quebec.
Early in America's history, rivers were used to transport logs downstream. This was a fast and easy way for loggers to move logs to where they could be loaded onto trains or ships. Unfortunately, it was also devastating to the environment, scouring the rivers of the debris that had provided animals with habitat. Today efforts are underway to replace this debris with large jams of logs bolted together.
Although hydroelectric dams don't need water to cool them down, they need water to generate electricity. In the half-century of their operation, dams arguably have caused the most fish to be placed on endangered species lists, and they have driven a number of species to extinction.
Coal and uranium mining don't take place in or next to rivers. But river water is drawn out and used to wash ores. This takes water away from rivers--and whatever water returns to the river by runoff is contaminated with heavy metals and radioactive material.
When water is withdrawn from wells instead, aquifers are quickly depleted. As aquifers are drawn down, rivers--which are connected to aquifers--sink below their beds and disappear.
When water is returned to the rivers after use, it is contaminated with heavy metals, pesticides, herbicides, medicines, hormones, and other toxic chemicals, most of which are not removed by water treatment plants.
Farmers and ranchers--like hunters and fishermen--often make strange bedfellows with stream biologists and hydrologists; increasingly, they are working together to ensure that negative human impact on our water resources is minimized. By protecting the waters that run through their lands they hope to ensure abundant and healthful supplies for their crops and herds. In turn, scientists and environmental groups are well aware that even agricultural lands that are not well cared for hold far less threat to stream health than development, with its urban runoff, armoring of the watershed, pollution from lawns and refuse, and overuse of water.
But most stream pollution lies much closer to home. The used water (sewage) of urban areas is run through water treatment plants before being dumped as effluent into the closest river or stream. Only the most offensive pollutants are removed. Many others--such as heavy metals, pesticides, herbicides, drugs, and hormones--enter the river unchanged. When the capacity of the treatment plant is overwhelmed by too much rain, the plant dumps its raw, untreated sewage directly into the stream.
Streams are also used to dispose of urban runoff. This is water which instead of soaking into the ground runs off over roofs, parking lots, and roads. Water that goes into drains is piped directly into the nearest stream. This runoff carries many human-made chemicals, but the primary ones are hydrocarbons from cars, buses, and trucks. These hydrocarbons are nearly all carcinogens.
To learn more about streams and how we use them, check out the reading list, where you will find some excellent references listed. (You will be able to order them from here, too).
Thousands of tons of Mississippi River mussels per year were once harvested for use in jewelry. At first, European-Americans searched only for the mussels that had formed pearls inside their shells. Later, they used the iridescent inner surface of the shells to make mother-of-pearl buttons. Today, mussels are harvested and their shells ground into beads, to be inserted into oyster shells. The irritation of the beads causes oysters to form pearls.