Acid Rain And North America Essay Research

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; 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 two patterns

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: Gay,

K. (1992, March). Acid Relief? (4p). Cricket, 19 (7). Retrieved April 24, 2000

from EBSCOhost database (masterfile) on the World Wide Web:

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: 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:


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