© Sam Wirzba/AgStock Images/CorbisPeter Arnold, Inc./Alamya. Point source
pollution. Landfill
leachate flows out
of a pipe in Vashon,
Washington.b. Nonpoint source pollution. Livestock wastes from a feedlot
such as this one in Alberta, Canada, can be carried by runoff to
local bodies of water.pollution, also called polluted runoff. Nonpoint source pol-
lution occurs when precipitation moves over and through
the soil, picking up and carrying away pollutants that are
eventually deposited in lakes, rivers, wetlands, groundwa-
ter, estuaries, and the ocean ( Figure 10.17b). Nonpoint
source pollution includes agricultural runoff (such as fertil-
izers, pesticides, livestock wastes, and salt from i rrigation),
mining wastes (such as acid mine drainage), municipal
wastes (such as inorganic plant and algal n utrients), con-
struction sediments, and soil erosion (from fields, logging
operations, and eroding stream banks). Although non-
point sources cover more than one site and can be hard to
i dentify, their combined effect can be huge.the presence of vast numbers of algae and cyanobacteria
(see parts b and d). When these organisms die, microor-
ganisms that decompose them use up much of the lake’s
oxygen. The lake floor has a high BOD, and the only fish
that survive there are warm-water species that tolerate
low levels of oxygen.
Over vast periods, oligotro phic lakes, estuaries,
and slow-moving streams become eutrophic naturally.
The bodies of water are slowly enriched and grow shal-
lower from the immense number of dead organisms
that have settled in the sedi-
ments. Gradually, plants take
root, slowly forming marshes.
Some human activities, however,
greatly accelerate eutrophica-
tion. This fast, human-induced
process is usually called artificial
e utrophication to distinguish
it from natural eutrophication.
Artificial eutrophication results
from enrichment of aquatic eco-
systems by nutrients found pre-
dominantly in fertilizer runoff and sewage.
Sources of Water Pollution
Water pollutants come from both natural sources and
human activities. Natural sources of pollution such as
mercury and arsenic tend to be local concerns, but
human-generated pollution is generally more widespread.
The sources of water pollution are classified into
two types: point source pollution and nonpoint source
pollution. Point source pollution is discharged into the
environment through pipes, sewers, or ditches from spe-
cific sites such as factories or sewage treatment plants
( Figure 10.17a). Point source pollution is relatively easy
to control legislatively, but acci-
dents still occur.
The enormous damage sus-
tained by a nuclear reactor in Fu-
kushima, Japan, following a March
2011 earthquake and tsunami,
produced point source pollution
in the form of tainted reactor wa-
ter. A year after the disaster, tech-
nicians struggled to prevent the
release of radioactive water from
the leaking reactor compound.
Pollutants that enter bodies of water over large areas
rather than at a single point cause nonpoint source
artificial
eutrophication
Overnourishment of
an aquatic ecosystem
by nutrients such
as nitrates and
phosphates due to
human activities
such as agriculture
and discharge from
sewage treatment
plants.point source
pollution Water
pollution that can be
traced to a specific
point of entry.
nonpoint source
pollution Pollution
that enters bodies of
water over large areas
rather than being
concentrated at a
single point of entry.-ÕÀViÊvÊÜ>ÌiÀÊ«ÕÌÊUÊ}ÕÀiʣ䰣ÇÊ