Environmental Engineering Reference
In-Depth Information
ally is, in fact, manufactured in the United States. Unfortunately, there is a chance that when we
import
goods
from these countries that use DDT, the products we import may contain trace amounts of the chemical.
The results of historic DDT use in the United States include the decline and near extinction of birds of prey
such as hawks, ospreys, brown pelicans, peregrine falcons, and bald eagles. The existence of DDT in water
sources led to its proliferation throughout food webs where it began to bioaccumulate in organisms and bio-
magnify throughout food webs. In birds of prey, the pesticide weakens egg shells; ultimately, eggs break before
hatching. This led to the decline in the birds' populations, and in the case of many, helped to endanger the spe-
cies.
Although DDT was banned in 1973, it has persisted in the environment and is still found in some groundwater
and aquifers in the United States.
Kudzu Invasion
Kudzu is an invasive plant that was intentionally introduced in the United States from Asia in 1876 for decorat-
ive purposes and also was used as soil cover to help control erosion in much of the Southeastern United States.
Although it has helped reduce erosion problems, kudzu is a fast-growing, hard-to-kill vine and can quickly
smother other plants and trees by depriving them of carbon dioxide, water, and sunlight. Kudzu photosynthes-
izes quickly, has the ability to fix atmospheric nitrogen, absorbs large amounts of water through its roots, and
can take root in almost any soil, allowing it to frequently out-compete native species. Biodiversity can decrease
and entire ecosystems can be altered due to the kudzu invasion.
Grazing has been successful in reducing and controlling kudzu populations when done regularly during grow-
ing seasons. This weakens their tissues over time, and ultimately reduces their growth. Other methods of re-
moval include the use of herbicides and removal of the plant and its roots. Of course, all of this requires time
and money. The control and removal of kudzu costs companies, the U.S. government, and individuals millions
of dollars every year. The repair of damage from kudzu also contributes to the cost of the invasive species. Be-
cause of its ability to grow almost anywhere quickly, it can grow on buildings, railroad tracks, and other veget-
ation. The weight and the roots can damage and deteriorate these structures. Many efforts are in place to elim-
inate kudzu, but it is a continual and never-ending battle. In the United States, kudzu is now listed as a federal
noxious weed.
Reintroduction of Gray Wolves to Yellowstone National
Park
The gray wolf is native to North America and once roamed the United States in large numbers. The coloniza-
tion of the country, though, brought a dramatic decline in the population of gray wolves throughout the United
States. To protect livestock and large game animals, humans killed over 1 million wolves, leaving a meager
population throughout the northern United States (excluding Alaska). In 1974, the gray wolf was designated an
endangered species.
We now have a better understanding of the species and its importance. The gray wolf acts as a keystone spe-
cies, helping to keep the ecosystem in balance by controlling the populations of prey species and by providing
food for other animals such as scavengers. With the dramatic decrease in their population, herbivores such as
elk and deer became more prevalent and consumed more vegetation, drastically decreasing vegetation in areas
including Yellowstone National Park. Vegetation loss led to soil erosion, loss of ecosystem niches, and less
food for herbivores.
