Acid Rain And North America Essay, Research Paper
In the past century, one of the greatest threats to North America’s aquatic
ecosystem has been the widespread acidification of hundreds of thousands of
waterways. Acid rain has effected plant and animal life within aquatic
ecosystems, as well as microbiologic activity by affecting the rates of
decomposition and the accumulation of organic matter. What causes this poisonous
rain, and what can be done to improve North America’s water quality and prevent
future catastrophes? To answer these questions, we must first examine the cause
and formation of acid rain, as well as understand ways to decrease or prevent
its formation. Formation of acid rain. Acid deposition, more commonly known as
acid rain, occurs when emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx)
react in the atmosphere with water, oxygen, and oxidants to form acidic
compounds. This mixture forms a mild solution of sulfuric and nitric acid which
then falls to the earth in either wet (rain, snow, sleet or fog) or dry (gas and
particles) form. Approximately one-half of the atmosphere’s acidity falls back
to earth through dry deposition in the form of particles and gases, and are then
spread hundreds of miles by winds where they settle on surfaces of buildings,
cars, homes, and trees. When acid rain falls, the dry deposited gases and
particles are sometimes washed from buildings, trees and other surfaces making
the runoff water combine with the acid rain more acidic than the falling acid
rain alone. This new combination is referred to as acid deposition. The runoff
water is then transported by strong prevailing winds and public sewer systems
into lakes and streams. Although some natural sources such as volcanic
eruptions, fire and lightening contribute to the emissions of sulfur dioxide and
nitrogen oxides in the atmosphere, more than 90% is the result of human activies
such as coal burning, smelting of metals such as zinc, nickel and copper, and
the burning of oil, coal and gas in power plants and automobiles. When does rain
become acidic? Scientists determine whether rain or lake water is acidic by
measuring its pH (the measure of acidity or alkalinity of a solution on a scale
of 0 to 14). A value of 7 is considered neutral, whereas values less than 7 are
acidic and values over 7 are alkaline or basic. A change of one unit on the pH
scale represents a factor of ten in acidity; for example, a solution with a pH
of five is ten times as acid as one with a pH of six (Somerville, 1996, p.174).
Normal or clean rainfall–without pollutants–is slighty acidic due to carbon
dioxide, a natural gas in the air that dissolves in water to form weak carbonic
acid. But rain, snow, or other moisture is not called "acid rain"
until it has a pH value below 5.6 (Gay, 1992, p.44). Rainfall in eastern North
America is often acidic with a pH of 4 to 5. Why is North America greatly at
risk? Acid rain is more common in the Eastern U.S. and Canada than in the
Western U.S. because emissions rise high into the atmosphere and are carried by
prevailing winds from the west, falling out with precipitation in the east. Some
areas in the U.S. where acid rain is most common include the New York
Adirondacks, mid-Appalachian highlands, and the upper Midwest. Canada shows an
even greater threat with half of its acid deposition caused by a large amount of
metal smelting industries in Ontario and the other half attributed to pollution
from combustion in U.S. factories in Ohio, Indiana, Pennsylvania, Illinois,
Missouri, West Virginia, and Tennessee. Most lakes have a pH between 6 and 8;
however, some are naturally acidic even without the effects of acid rain. Lakes
and streams become acidic (pH value goes down) when the water itself and its
surrounding soil cannot buffer, or shield, the acid rain enough to balance its
pH level. In areas such as the northeastern United States and parts of Canada
where soil buffering is poor, many lakes now have a pH value of less than 5. One
of the most acidic lakes reported is Little Echo Pond in Franklin, New York,
which has a pH of only 4.2. In New York’s Adirondack region, acid deposition has
affected hundreds of lakes and thousands of miles of headwater streams, while
300,000 lakes in eastern Canada are now vulnerable to acid deposition. How does
Acid Rain effect Aquatic Ecosystems? As lakes and streams become more acidic,
the amount of fish, aquatic plants and animals that live in these waters
decrease. Although some plants and animals can survive acidic waters, others are
acid-sensitive and will die as the pH declines. Plants and animals living within
an ecosystem are highly interdependent. If acid rain causes the loss of
acid-sensitive plants and animals, organisms at all trophic levels within the
food chain may be affected which then causes a disruption to the entire
ecosystem. In New York’s Adirondack region, the diversity of life in these
acidic waters has been greatly reduced. Fish population have disappeared and
loons and otters have moved to other lakes where they can find food (Simonin,
1998, p4). In Canada, over 14,000 lakes have been acidified to the point where
they have lost significant amounts of fish. The chart below shows that not all
fish, shellfish or their foot insects can tolerate the same amount of acid. The
shaded bars represent the highest degree of pH balance that animal can tolerate
within an acidic lake before it becomes extinct from that lake. For example,
frogs seem to be the toughest survivor by being able to tolerate a pH up to 4.0,
whereas clams and snails are the weakest only being able to tolerate a pH of 6.0
before it will become extinct. (*Source: United States Environmental Protection
Agency; www.epa.gov): Animals pH 6.5 pH 6.0 pH 5.5 pH 5.0 PH 4.5 pH 4.0 Trout
Bass Perch Frogs Salamanders Clams Crayfish Snails Mayfly There are tw
that contribute to the disappearance of fish from acidic bodies of water. The
first pattern is known as "acid shock", which is a sudden drop in pH.
These pH shocks usually occur in early spring when melting snow releases acidic
elements accumulated during the winter into a lake or stream causing a rapid
decrease in pH level, which in turn causes fish to die. A second pattern is the
gradual decrease in pH level over a prolonged period of time interfering with
fish reproduction; therefore, causing decrease in fish population, and a change
in size and age of the population. Other animals are affected by acidic water as
well. For example, low pH will often stunt the growth of frogs, toads and
salamanders. Changes in pH level have caused alterations in the structure of the
aquatic plant life involved in primary production. Reducing the diversity of the
plant communities in lakes and streams and disrupting primary production will
most likely reduce the supply of food; therefore, the energy flow within the
ecosystem will decrease. Changes in these communities also reduce the supply of
nutrients. These factors limit the number of organisms that can exist within the
ecosystem (Brittenbender, B., et. al., p. 4) In addition to affecting the plant
and animal life, microbiological activity is also reduced affecting the rate of
decomposition and accumulation of organic matter. Organic matter plays a central
role in the energy flow of a lake’s ecosystem. "The biochemical
transformations of detrital organic matter by microbial metabolism are
fundamental to nutrient cycling and energy flux within the system, and the
trophic relationships within lake ecosystems are almost entirely dependent on
detrital structure" (Brittenbender, B., et. al., p. 5). There are two
responsible causes for the slowing rate at which organic matter decomposes
underwater. First, the disappearance of certain invertebrates such as snails
that shred organic debris as they feed; and second, a decrease in the metabolic
rate of decomposition bacteria at a low pH level. Fighting acid rain. There are
several ways to treat the acid rain problem. The answers depend heavily upon
local politics and global economics. One solution is to use low-sulfur coal as
opposed to high-sulfur coal. Unfortunately, high-sulfur coal is far more
expensive than low-sulfur coal due to the economics of mining and transporting
it. Another solution is to chemically treat high-sulfur coal before burning it.
Devices known as scrubbers can be installed on smokestacks to reduce the amount
of sulfur dioxide being released into the atmosphere. The pH levels in lakes can
be increased by a technique called liming. This process involves adding large
quantities of hydrated lime to the waters in order to increase the alkalinity
and pH. Areas that have used this method have had some success; however; liming
does not always work because the lake may be too large and therefore
economically unfeasible. In other cases, the lake may have a high flush rate, or
poor buffering, so they quickly become acidified again after liming. Liming the
acidic soils surrounding the lake so that the lime slowly dissolves over time to
wash alkalinity into the lake is a more simple answer as well as less expensive.
Although these solutions decrease sulfur dioxide in the atmosphere, nitrogen
oxides are still increasing. Reducing nitrogen oxides is more difficult to treat
because this type of acidic pollution is mainly caused by automobile exhaust.
Although a reduction in number of automobiles used is unlikely, regulating the
use of specially designed catalytic converters could control emissions.
Improvements are being made. Thanks to environmental regulations and agreements
to control pollution, lakes and streams in North America are beginning to
recover from acid rain and life is being restored. In 1995, phase I of the Clean
Air Act Amendment was launched. Through this Act, over 400 power plants in the
U.S. were instructed to reduce their sulfur dioxide emissions by 3 million tons.
Power plants are now instructed to reduce their use of fossil fuels, burn
low-sulfur coal or use scrubbers. In 1991, the United States and Canada
established the Air Quality Accord that controls the air pollution that flows
across international boundaries. In this agreement, acid deposition causing
emissions of sulfur are permanently capped in both countries (13.3 million tons
for the U.S. and 3.2 million tons for Canada) and plans were implemented for the
reduction of nitrogen oxides. Phase II of the Clean Air Act will kick off this
year, mandating even steeper cuts in sulfur emissions. The National Atmospheric
Deposition Program/National Trends Network (NADP/NTN) has 191 sites across the
country which measure the emissions of sulfur dioxide. Establishing more
organizations such as this will help us understand how and where to combat the
acid rain problem.
Bittenbender, B., Latendresse, K, Martysz, I., Mood, P. Acid Deposition and
its Ecological Effects. Retrieved April 24, 2000 from the World Wide Web:
http://bigmac.civil.mtu.edu/public_html/classes/ce459/projects/t17/r17.html Gay,
K. (1992, March). Acid Relief? (4p). Cricket, 19 (7). Retrieved April 24, 2000
from EBSCOhost database (masterfile) on the World Wide Web: http://www.ebsco.com
Simonin, Howard (1998, April). The Continuing Saga of Acid Rain (2p). New York
State Convervationist, 52 (5). Retrieved April 24, 2000 from EBSCOhost database
(masterfile) on the World Wide Web: http://www.ebsco.com Somerville, Richard C.J.
(1996). The forgiving Air: Understanding Enviornmental Change. Berkely and Los
Angeles, California: University of California Press United States Environmental
Protection Agency. Affects of Acid Rain on Water. Retrieved April 24, 2000 from
the World Wide Web: http://www.epa.gov/acidrain/student/water.html