Page 427 - Environment: The Science Behind the Stories

have long been a source of conflict between farms and grow- (such as temperature and turbidity—the density of suspended
ing cities in the arid West. The states of Georgia, Alabama, particles in a water sample), and biological properties (such as
and Florida are also currently embroiled in disputes over water the presence of harmful microorganisms or the species diver-
withdrawals from shared rivers. Conflicts also visited the Mis- sity in aquatic ecosystems).
sissippi River during the extreme drought in the Midwest in Some water pollution is emitted from point sources—
2012. Deprived of precipitation, river levels dropped signifi- discrete locations, such as a factory or sewer pipe. In contrast,
cantly, and this pitted upriver states who wanted to hold river pollution from non-point sources is cumulative, arising from
water behind their dams against downriver states who wanted multiple inputs over larger areas, such as farms, city streets,
greater releases from those dams to facilitate barge travel and and residential neighborhoods (Figure 15.22). The U.S. Clean
increase water supplies. Water Act (p. 194) addressed point-source pollution with
Yet on the positive side, so far many nations have cooper- some success by targeting industrial discharges. As a result,
ated to resolve water disputes. India has struck agreements to water quality in the United States today suffers most from
co-manage transboundary rivers with Pakistan, Bangladesh, non-point-source pollution, resulting from countless common
Bhutan, and Nepal. In Europe, nations along the Rhine and activities such as applying fertilizers and pesticides to lawns,
Danube rivers have signed water-sharing treaties. Such pro- applying salt to roads in winter, and changing automobile oil.
gress gives reason to hope that “water wars” will be few and To minimize non-point-source pollution of drinking water,
far between in coming decades. governments limit development on watershed land surround-
ing reservoirs.
Freshwater Pollution

and Its Control Water pollution takes many forms
Water pollution comes in many forms that can impair water-
We have seen that people affect aquatic systems by with- ways and threaten people and organisms that drink or live in
drawing too much water and by altering the systems’ natural affected waters. Let’s survey the major classes of water pollut-
processes by engineering waterways with dams, diversions, ants affecting waters in the world today.
and levees. However, people also affect aquatic ecosystems
and threaten human health when we introduce toxic sub- Toxic chemicals Our waterways have become polluted
stances and disease-causing organisms into surface waters and with toxic organic substances of our own making, includ-
groundwater. ing pesticides, petroleum products, and other synthetic
Developed nations have made admirable advances chemicals (pp. 385–386). Many of these can poison animals
in cleaning up water pollution over the past few decades. and plants, alter aquatic ecosystems, and cause an array of
Still, the World Commission on Water recently concluded human health problems, including cancer. In addition, toxic
that over half the world’s major rivers remain “seriously metals such as arsenic, lead, and mercury damage human
depleted and polluted, degrading and poisoning the sur- health and the environment, as do acids from acid precipita-
rounding ecosystems, threatening the health and livelihood tion (pp. 491–492) and from acid drainage from mining sites
of people who depend on them.” Levels of impairment are (p. 657). With its massive watershed encompassing rural,
similar in U.S. waterways. In 2013 EPA reported that 55% urban, and suburban areas, the Mississippi River is one
of the 2000 U.S. streams and rivers sampled in 2008–2009 waterway that receives toxic pollutants from several sources,
were in poor condition to support aquatic life. The largely including agriculture, industry, homes, and businesses.
invisible pollution of groundwater, meanwhile, has been Issuing and enforcing more stringent regulations on
termed a “covert crisis.” Preventing pollution is easier and industry can help reduce releases of many toxic chemicals.
more effective than mitigating it later. Many of our current We can also modify our industrial processes and our purchas-
solutions to pollution problems embrace preventative strate- ing decisions to rely less on these substances.
gies rather than “end-of-pipe” treatment and cleanup, which
is often expensive and impractical.
Pathogens and waterborne diseases Disease-
causing organisms (pathogenic viruses, protists, and bacteria)
Water pollution comes from point can enter drinking water supplies when these are contaminated
and non-point sources with human waste from inadequately treated sewage or with
animal waste from feedlots (p. 269). Specialists monitoring
Pollution is the release into the environment of matter or water quality can tell when water has been contaminated by
energy that causes undesirable impacts on the health or well- such waste when they detect fecal coliform bacteria, which
being of humans or other organisms. Pollution can be physi- live in the intestinal tracts of people and other vertebrates.
cal, chemical, or biological and can affect water, air, or soil. These bacteria are usually not pathogenic themselves, but they
Water pollution comes in many forms and can cause diverse serve as indicators of fecal contamination, alerting us that the
impacts on aquatic ecosystems and human health. water may hold other pathogens that can cause ailments such
Most forms of water pollution are not conspicuous to as giardiasis, typhoid, or hepatitis A.
the human eye, so scientists and technicians measure water’s Biological pollution by pathogens causes more human
chemical properties (such as pH, nutrient concentrations, and health problems than any other type of water pollution. In
426 dissolved oxygen concentration), physical characteristics the United States, an estimated 20 million people fall ill

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