Ecology on the Interstate Highway System
Overview
Since the Interstate Highway System was built, it has made travel much more efficient in the country, among other tangible benefits. However, the effects on the environment of roads, and highways in particular, are sometimes devastating to the environment for a variety of reasons.
Unnatural Barriers
When a road is built, it effectively splits a habitat into two parts. Sometimes, populations of animals are split into two smaller populations when the road is built. Smaller populations, studies have shown, are more likely to have larger fluctuations in their population size, and may have trouble surviving in the long term. Also, there is less genetic diversity among the smaller population.
Highways also pose a problem because they often result in roadkill. It is estimated that one million vertebrates are killed on roadways each day in the United States, and many more insects than that are killed. However, this doesn't often become a serious problem except in a few instances of endangered species.
A larger problem is that animals tend to stay away from roads. They fear the light, the noise, or perhaps getting run over. Birds are particularly sensitive. When animals move farther away from their roads, they often are forced to change their food, movement, and breeding habits, and may have a harder time breeding.
Drainage
When rain or snow hit highways, the water has to go somewhere. Asphalt doesn't absorb very much water, so the water runs off the edges of the highway into ditches. In many cases, the water gains speed while it's running off of the road, but this depends on the road, the materials, and a host of other factors. However, when runoff water does gain run quickly enough, it can sometimes cause problems for two main reasons.
- The ground may not have enough time to absorb the water, so the water just moves over it and sometimes pick up and carries light sediment on the ground with it.
- Fast-moving water can carve streams out of the earth, which can cause drainage problems by forming unwanted pools. Also, new streams may divert water from natural streams and ponds, in which case the ponds may dry up.
Chemical Runoff
The more than forty million miles of highways in the United States make for a lot of surface area that salt, chemicals and other materials can coat. When it rains or snows, these chemicals are carried by the runoff water into the ground, fields, or streams, effectively spreading chemicals far and wide into the ecosystem.
Salt (NaCl), the most commonly used road deicer, is particularly dangerous in runoff. It's toxic to many freshwater fish, plants, and other wildlife, and studies have shown that it damages leaf growth in trees up to 16 feet away from the road. Also, more dangerous heavy metals (such as Sodium, Chlorine, Calcium, and Magnesium) travel more easily through soil that is contaminated with salt. Plus, salt is corrosive to cars as well as bridges.
Other chemicals are dangerous in runoff water, too. For instance, herbicides which may be used to kill plant life on roadsides may get caught in runoff water and destroy plants they weren't intended to.
Highways that are heavily traveled have additional problems. In particular, large amounts of heavy metals get deposited onto the road, which are then carried by runoff water into streams or are absorbed into roadside plants.
Solutions
There's no simple solution to the ecological problems posed by roads. Some problems are caused by the very nature of roads, and the fact that they exist. Other problems have simple solutions; for example, different de-icers could be used that are more friendly to the environment. Emissions on cars could also be tightened. To aid in the problem of runoff and barriers, though, new highways have to be designed to take natural habitats into account.
For More Information
For more information about how the road interacts with the environment, try the following:
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