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Introduction: What Causes Acid Rain? One of the main causes of acid rain is
sulfur dioxide. Natural sources, which emit this gas, are Volcanoes, sea spray,
rotting vegetation and plankton. However, the burning of fossil fuels, such as
Coal and oil, are largely to be blamed for approximately half of the emissions
of this gas in the world. When sulfur dioxide reaches the atmosphere, it
oxidizes to first form a sulfate ion. It then Becomes sulfuric acid as it joins
with hydrogen atoms in the air and falls back down to earth. Oxidation occurs
the most in clouds and especially in heavily polluted air where other compounds
such as ammonia and ozone help to catalyze the reaction, changing more sulfur
dioxide to sulfuric acid.
However, not all of the sulphur dioxide is changed to
sulfuric acid. In fact, a substantial amount can float up into the atmosphere,
move over to another area and return to earth unconverted. In the following
pages I will show the effects of acid rain on: · Effect on Trees and Soils ·
Effect on Lakes and Aquatic Systems · Effect on Materials · Effect on Atmosphere
· Effect on Architecture · Effect on Humans Effect on Trees and Soils One of the
most serious impacts of acid precipitation is on forests and soils. Great damage
is done when sulfuric acid falls onto the earth as rain. Nutrients present in
the soils are washed away. Aluminium also present in the soil is freed and the
roots of trees can absorb this toxic element. Thus, the trees are starved to
death as they are deprived of their vital nutrients such as calcium and
magnesium. Not all of the sulphur dioxide is converted to sulfuric acid. In
fact, a substantial amount can float into the atmosphere, move over to another
area and return to the soils unconverted.
As this gas returns back to earth, it
clogs up the stomata in the leaves, thus hindering photosynthesis. Research has
been made where red spruce seedlings were sprayed with different combinations of
sulfuric and nitric acid of pH ranging from 2.5 to 4.5. The needles of these
seedlings were observed to develop brown lesions. Eventually, the needles fall
off. It was also found that new needles grew more slowly at higher
concentrations of acid used. Because the rate at which the needles were falling
was greater than the rate at which they were replenished, photosynthesis was
greatly affected, The actual way in which these needles were killed is still not
yet known. However, studies have shown that calcium and magnesium nutrients are
washed away from their binding sites when sulfuric acid enters the system. They
are replaced by useless hydrogen atoms and this inhibits photosynthesis. Effect
on Lakes and Aquatic Systems One of the direct effects of acid rain is on lakes
and its aquatic ecosystems. There are several routes through which acidic
chemicals can enter the lakes.
Some chemical substances exist as dry particles
in the air while others enter the lakes as wet particles such as rain, snow,
sleet, hail, dew or fog. In addition, lakes can almost be thought of as the
sinks of the earth, where rain that falls on land is drained through the sewage
systems eventually make their way into the lakes. Acid rain that falls onto the
earth washes off the nutrients out of the soil and carries toxic metals that
have been released from the soil into the lakes. Another harmful way in which
acids can enter the lakes is spring acid shock. When snow melts in spring
rapidly due to a sudden temperature change, the acids and chemicals in the snow
are released into the soils. The melted snow then runs off to streams and
rivers, and gradually make their way into the lakes. The introduction of these
acids and chemicals into the lakes causes a sudden drastic change in the pH of
the lakes - hence the term spring acid shock.
The aquatic ecosystem has no time
to adjust to the sudden change. In addition, springtime is an especially
vulnerable time for many aquatic species since this is the time for reproduction
for amphibians, fish and insects. Many of these species lay their eggs in the
water to hatch. The sudden pH change is dangerous because the acids can cause
serious deformities in their young or even annihilate the whole species since
the young of many of such species spend a significant part of their life cycle
in the water. Subsequently, sulfuric acid in water can affect the fish in the
lakes in two ways: directly and indirectly. Sulfuric acid (H2SO4) directly
interferes with the fish's ability to take in oxygen, salt and nutrients needed
to stay alive. For freshwater fish, maintaining osmoregulation is key in their
survival.
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