Page 428 - Environment: The Science Behind the Stories

Non-point sources of water pollution Pollutant Point sources of water pollution

Farms, Fertilizers,
lawns, and herbicides, and
golf courses pesticides

Animal feedlots
(also non-point source)

Nutrients, waste,
and bacteria

Salt on winter roads;
Residential neighborhoods oil, grease, and
and urban streets chemicals Sewage treatment plants
from urban runoff

Industrial waste Factories and
and toxic chemicals disposal sites

Construction
sites, and
deforested and Eroded soil
overgrazed
land

Oil spills

Abandoned mines Acid Oil tankers
(also point source) drainage

Figure 15.22 Point-source pollution (on right) comes from discrete facilities or locations, usually
from single outflow pipes. Non-point-source pollution (such as runoff from streets, residential neighborhoods,
lawns, and farms; on left) originates from numerous sources spread over large areas.

each year from drinking water contaminated with pathogens. growth. Algae then spread and cover the water’s surface, depriv-
Worldwide, the United Nations estimates that 3800 children ing underwater plants of sunlight. As algae die off, bacteria con-
die every day from diseases associated with unsafe drinking sume them. Because this decomposition requires oxygen, the
water, such as cholera, dysentery, and typhoid fever. While increased bacterial activity drives down levels of dissolved oxy-
nearly 800 million people still lack reliable access to safe gen. These levels can drop too low to support fish and shellfish,
drinking water and 37% do not have sanitation/sewer facili- leading to dramatic changes in aquatic ecosystems.
ties, we are making slow but steady progress worldwide in A “dead zone”—an area of very low dissolved oxygen lev-
supplying people with these services (p. 383). els—appears annually in the northern Gulf of Mexico, fueled CHAPTER 15 • Fr E shwat E r s yst E m s and rE sour CE s
We reduce the risks posed by waterborne pathogens by by nutrients from Midwest farms carried by the Mississippi
using chemical or other means to disinfect drinking water and Atchafalaya rivers (see The Science behind The STory, pp.
(p. 432) and by treating wastewater (pp. 432–433). Other 428–429). The low oxygen conditions have adversely affected
measures to lessen health risks include public education to marine life and reduced catches of shrimp and fish to half of
encourage personal hygiene and government enforcement of what they were in the 1980s, impacting people whose liveli-
regulations to ensure the cleanliness of food production, pro- hoods depended on seafood harvests.
cessing, and distribution. Eutrophication (Figure 15.23, see p.430) is a natural pro-
cess, but nutrient input from runoff from farms, golf courses,
Nutrient pollution The Chesapeake Bay’s dead zone shows lawns, and sewage can dramatically increase the rate at which
how nutrient pollution from fertilizers and other sources can it occurs. We can reduce nutrient pollution by treating waste-
lead to eutrophication and hypoxia in surface waters (Chapter 5, water, reducing fertilizer application, using phosphate-free
pp. 123, 126). When excess nitrogen and/or phosphorus enters a detergents, and planting vegetation and protecting natural
water body, it fertilizes algae and aquatic plants, boosting their areas to increase nutrient uptake. 427

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