Acidity is measured on the per-hydrogen or pH scale. This is a measure of the
concentration of positively charged ions in a given sample. It ranges from 14 (alkaline or negatively charged ions) to 0 (acidic or positive ions). Pure water has a pH of
7 (neutral). Most rainwater is slightly acidic (pH about 6). A change in the pH scale
of one unit reflects a tenfold (10X) change in the concentration of acidity. Generally,
rain with a pH value of less than about 5.3 is considered acid rain. Most of the
rainwater, which falls in the Eastern United States, has a pH between 4.0 and 5.0.
This is generally lower (more acidic) than the national average. The use of tall
smokestacks installed to reduce local pollution has contributed to the spread of acid
rain by releasing gases into regional atmospheric circulation, with deposition occurring at a considerable distance downwind of the emissions [53].
8.1 Effects of Acid Rain
The impacts of acid rain and deposition are varied and often interrelated, creating
complex and far-reaching consequences to aquatic and terrestrial ecosystems, visibility, and public health:
1. Acid precipitation can increase the acidity of lakes and streams by either passing
through soils or falling directly on water bodies. Changes in the acidity of lakes
and streams can impact the survival of fish and amphibian populations by
impairing the ability of certain fish and water plants to reproduce, grow, and
ultimately survive.
2. Terrestrial ecosystems can also be altered by increasing acidity of precipitation
and heavy metal deposition. Acids strip forest soils of essential nutrients needed
to sustain plant life. This process threatens the reproduction and survival of trees
and other forest vegetation.
3. Acid deposition of acidic particles is known to contribute to the corrosion of
metals and to the deterioration of stonework on buildings, statues, and other
structures of cultural significance, resulting in depreciation of the objects’ value
to society. Acid deposition can also damage paint on buildings and cars.
4. Additionally, the same gases that cause acid deposition are responsible for the
formations of small particles in the air that greatly reduce visibility and can
adversely affect human health. Sulfate aerosol particles and, to a lesser extent,
nitrate particles in the atmosphere produced from SO 2 and NO x emissions
account for more than 50% of the visibility reduction in the Eastern United States
and heavily influence concentrations of small particles or PM. These particles are
small enough in size to be inhaled deeply into lung tissue, aggravating the
reparatory and cardiopulmonary systems, especially in sensitive populations
(people with asthma, emphysema, or other respiratory illnesses).
The most obvious environmental effect of acid rain has been the loss of fish in
acid-sensitive lakes and streams. Many species of fish are not able to survive in
acidic water. Acid rain affects lakes and streams in two ways: chronic and episodic
7 Lake Restoration
281
concentration of positively charged ions in a given sample. It ranges from 14 (alkaline or negatively charged ions) to 0 (acidic or positive ions). Pure water has a pH of
7 (neutral). Most rainwater is slightly acidic (pH about 6). A change in the pH scale
of one unit reflects a tenfold (10X) change in the concentration of acidity. Generally,
rain with a pH value of less than about 5.3 is considered acid rain. Most of the
rainwater, which falls in the Eastern United States, has a pH between 4.0 and 5.0.
This is generally lower (more acidic) than the national average. The use of tall
smokestacks installed to reduce local pollution has contributed to the spread of acid
rain by releasing gases into regional atmospheric circulation, with deposition occurring at a considerable distance downwind of the emissions [53].
8.1 Effects of Acid Rain
The impacts of acid rain and deposition are varied and often interrelated, creating
complex and far-reaching consequences to aquatic and terrestrial ecosystems, visibility, and public health:
1. Acid precipitation can increase the acidity of lakes and streams by either passing
through soils or falling directly on water bodies. Changes in the acidity of lakes
and streams can impact the survival of fish and amphibian populations by
impairing the ability of certain fish and water plants to reproduce, grow, and
ultimately survive.
2. Terrestrial ecosystems can also be altered by increasing acidity of precipitation
and heavy metal deposition. Acids strip forest soils of essential nutrients needed
to sustain plant life. This process threatens the reproduction and survival of trees
and other forest vegetation.
3. Acid deposition of acidic particles is known to contribute to the corrosion of
metals and to the deterioration of stonework on buildings, statues, and other
structures of cultural significance, resulting in depreciation of the objects’ value
to society. Acid deposition can also damage paint on buildings and cars.
4. Additionally, the same gases that cause acid deposition are responsible for the
formations of small particles in the air that greatly reduce visibility and can
adversely affect human health. Sulfate aerosol particles and, to a lesser extent,
nitrate particles in the atmosphere produced from SO 2 and NO x emissions
account for more than 50% of the visibility reduction in the Eastern United States
and heavily influence concentrations of small particles or PM. These particles are
small enough in size to be inhaled deeply into lung tissue, aggravating the
reparatory and cardiopulmonary systems, especially in sensitive populations
(people with asthma, emphysema, or other respiratory illnesses).
The most obvious environmental effect of acid rain has been the loss of fish in
acid-sensitive lakes and streams. Many species of fish are not able to survive in
acidic water. Acid rain affects lakes and streams in two ways: chronic and episodic
7 Lake Restoration
281