Untitled Flashcards Set

Point sources of pollution have single locations while nonpoint sources have diffuse locations

47-1 What is the difference between point and nonpoint sources of pollution?

Regardless of the specific contaminant, aquatic and terrestrial pollution can come from either point sources or nonpoint sources. In this section we will look briefly at each. A point source is a distinct location from which pollution is directly produced. Examples of point sources include a particular factory that buries its waste underground or a sewage treatment plant that discharges its wastewater from a pipe into the ocean, as shown in FIGURE 47.1a. For atmospheric pollution, which we discussed in Module 42, a point source would be a smokestack that releases harmful chemicals into the air.

Point source

A distinct location from which pollution is directly produced.

FIGURE 47.1 Two types of pollution sources. Pollution can enter water bodies in two ways. (a) Point sources, such as a sewage pipe, are distinct locations where water pollution is produced. (b) Nonpoint sources are more diffuse areas that produce pollution. For example, rainwater that runs off hundreds of square kilometers of agricultural fields and into streams can carry pollutants with it.

In contrast, a nonpoint source is a more diffuse area that produces pollution, such as an entire farming region, a suburban community with many lawns and septic systems, or storm runoff from a large number of parking lots. In each of these cases, there is a large number of relatively small contributions to pollution that are spread over a large area. For example, we can consider the thousands of cattle that live on hundreds of farms near a stream or river, as shown in Figure 47.1b. While each cow makes a small contribution of manure that can release excess nutrients that are carried to the stream, collectively the thousands of cattle spread across a large area represent a nonpoint source of pollution.

Nonpoint source

A diffuse area that produced pollution.

The distinction between the two sources can help us control pollutants on land and in water. If a city can determine one or two point sources for most of its pollution, it can target those specific sources to reduce pollution outputs. An interesting example of a point source of pollutants is the cruise ship industry. In recent years, it has been reported that many cruise ships have been dumping their sewage and other waste overboard into the oceans. In fact, the larger cruise ships can produce 1 metric ton of garbage per day. Public outcry over this behavior has led many cruise ship companies to improve their programs for recycling, incinerating, and treating their waste rather than dumping all of it into the oceans. Controlling pollution from nonpoint sources is much more challenging because the sources can span a large area. For example, in Module 5 we saw that the enormous Mississippi River watershed is subject to pollution from tens of thousands of farms because of fertilizer and pesticide runoff.