Acid Rain

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to Earth Processes / Structures / Extreme Weather...

adapted to HTML from lecture notes of Prof. Stephen A. Nelson Tulane University

...see also Acid Rain in our self-education section

What is acid rain?
Effects of acid rain
The problem of aluminium
The problem of chlorine
The effects of pH
The sulphate ion


Acid rain is a great problem in our world. It causes fish and plants to die in our waters. As well it causes harm to our own race as well, because we eat these fish, drink this water and eat these plants. It is a problem that we must all face together and try to get rid of. However acid rain on it's own is not the biggest problem. It cause many other problems such as aluminum poisoning. Acid Rain is deadly.


Main source of acid rain is sulfur dioxide and nitrogen oxides in the atmosphere. Power plants are a major source for sulfur dioxide and as well nitrogen oxide. Automobiles, trucks and buses are major contributors of nitrogen oxides in urban and suburban environments.  Acid rain is all the rain, snow, mist etc that falls from the sky onto our planet that contains an unnatural acidic. It is not to be confused with uncontaminated rain that falls, for that rain is naturally
slightly acidic. It is caused by today's industry. When products are manufactured many chemicals are used to create it. However because of the difficulty and cost of properly disposing of these products they are often emitted into the atmosphere with little or no treatment.

The term was first considered to be important about 30 years ago when scientists in Sweden and Norway first believed that acidic rain may be causing great ecological damage to the planet. The problem was that by the
time that the scientist found the problem it was already very large. Detecting an acid lake is often quite difficult. A lake does not become acid over night. It happens over a period of many years, some times decades. The changes are usually to gradual for them to be noticed early.


At the beginning of the 20th century most rivers/lakes like the river Tovdal in Norway had not yet begun to die. However by 1926 local inspectors were noticing that many of the lakes were beginning to show signs of death. Fish were found dead along the banks of many rivers. As the winters ice began to melt off more and more hundreds upon hundreds more dead fish (trout in particular) were being found. It was at this time that scientist began to search for the reason. As the scientists continued to work they found many piles of dead fish, up to 5000 in one pile, further up the river. Divers were sent in to examine the bottom of the rivers. What they found were many more dead fish. Many live and dead specimens were taken back to labs across Norway. When the live specimens were examined they were found to have very little sodium in their blood. This is typical a typical symptom of acid poisoning. The acid had entered the gills of the fish and poisoned them so that they were unable to extract salt from the water to maintain their bodies sodium levels.

  Many scientist said that this acid poising was due to the fact that it was just after the winter and that all the snow and ice was running down into the streams and lakes. They believed that the snow had been
exposed to many natural phenomena that gave the snow it's high acid content. Other scientists were not sure that this theory was correct because at the time that the snow was added to the lakes and streams the
Ph levels would change from around 5.2 to 4.6. They believed that such a high jump could not be attributed to natural causes. They believed that it was due to air pollution. They were right. Since the beginning of the
Industrial revolution in England pollution had been affecting all the trees,soil and rivers in Europe and North America.

However until recently the loses of fish was contained to the southern parts of Europe. Because of the constant onslaught of acid rain lakes and rivers began to lose their ability to counter act their affects. Much of the alkaline elements; such as calcium and limestone; in the soil had been washed away. It is these lakes that we must be worried about for they will soon become extinct.

A fact that may please fishermen is that in lakes/rivers they tend to catch older and larger fish. This may please them in the short run however they will soon have to change lakes for the fish supply will die quickly in these lakes. The problem is that acid causes difficulties the fish's reproductive system. Often fish born in acid lakes do not survive for they are born with birth defects such as twisted and deformed spinal columns. This is a sign that they are unable to extract enough calcium from the water to fully develop their bone. These young soon die. With no competition the older,stronger can grow easily. However there food is contaminated as well by the acid in the water. Soon they have not enough food for themselves and turn to cannibalism. With only an older population left there is no one left to regenerate themselves. Soon the lake dies.


  By the late 1970s many Norwegian scientists began to suspect that it was not only the acid in the water that was causing the deaths. They had proved that most fish could survive in a stream that had up to a 1 unit difference in PH. After many experiments and research they found that their missing link was aluminum.

Aluminum is one of the most common metals on earth. It is stored in a combined form with other elements in the earth. When it is combined it cannot dissolve into the water and harm the fish and plants. However the acid from acid rain can easily dissolve the bond between these elements. The Aluminum is then dissolved into a more soluble state by the acid. Other metals such as Copper (Cu), iron (Fe) etc can cause such effects
upon the fish as well however it is the aluminum that is the most common.

or example:

CuO + H2SO4 ----------> CuSO4 + H2O

In this form it is easily absorbed into the water. When it comes in contact with fish it causes irritation to the gills. In response the fish creates a film of mucus in the gills to stop this irritation until the irritant is gone. However the aluminum does not go always and the fish continues to build up more and more mucus to counteract it. Eventually there is so much mucus that it clogs the gills. When this happens the fish can no longer breath. It dies and then sinks to the bottom of the lake. Scientists now see acid, aluminum and shortages of calcium as the three determining factors in the extinction of fish.


As well there is the problem of chlorine. In many parts of the world it is commonly found in the soil. If it enters the fish's environment it can be deadly. It affects many of the fish's organisms and causes it to die. As well it interferes in the photosynthesis process in plants.

    NaOH + HCl ----> NaCl + H2O

The carbon in the water can become very dangerous for fish and plants in the water if the following reaction happens:

    CaCO3 + 2HCl ---> CaCl2 + H2CO3 then
     H2CO3 ---> H2O + CO2

The salt created by this reaction can kill. It interferes directly with the fish's nervous system.

Acid lakes are deceivingly beautiful. The are crystal clear and have a luscious carpet of green algae on the bottom. The reason that these lakes are so clear is because many of the decomposers are dead. They cannot break down that material such as leaves and dead animals. These materials eventually sink to the bottom instead of going through the natural process of decomposition. In acid lakes decomposition is very slow. "The whole metabolism of the lake is slowed down."


During this same period of time the Canadian department of fisheries spent eight years dumping sulfuric acid (H2SO4) into  Ontario lake to see the effects of the decrease in the PH over a number of years. At the PH of 5.9 the first organisms began to disappear. They were shrimps. They started out at a population of about seven million, but at the pH of 5.9 they were totally wiped out. Within a year the minnow died because it could no longer reproduce it's self.

At this time the pH was of 5.8. New trout were failing to be produced because many smaller organisms that served as food to it had been wiped out earlier. With not enough food the older fish did not have the energy to reproduce. Upon reaching the pH of 5.1 it was noted that the trout became cannibals. It is believed this is due to the fact that the minnow was nearly extinct.

At a pH of 5.6 the external skeletons of crayfish softened and they were soon infected with parasites, and there eggs were destroyed by fungi. When the pH went down to 5.1 they were almost gone. By the end of the experiment none of the major species had survived the trials of the acid. The next experiment conducted by the scientists was to try and bring the lake back to life. They cut in half the amount of acid that they dumped to simulate a large scale cleanup. Soon again the cuckers and minnows began to reproduce again. The lake eventually did come back; to a certain extent; back to life.

  A scientist in Norway had a problem believing that it was the acid rain on it's own that was affecting the lakes in such a deadly way. This scientist was Dr Rosenqvist.

"Why is it that during heavy rain, the swollen rivers can be up to
fifteen times more acid than the rain? It cannot be the rain alone that is
doing it, can it?" Many scientist shunned him for this however they could
not come up with a better answer. Soon the scientists were forced to
accept this theory.
    Sulfuric acid is composed of two parts, know as ions. The hydrogen
ion is what make a substance acid. The other ion is sulphate. When there
are more hydrogen ions then a substance is acid. It is this sulphate ion
that we are interested in. When the rain causes rivers to overboard onto
the banks the river water passes through the soil. Since the industrial
revolution in britain there has been an increasing amount of sulphur in
the soil. In the river there is not enough sulphur for the acid to react
in great quantities. However in the soil there is a great collection of
sulphur to aid the reaction. When it joins the water the pH becomes much
lower. This is the most deadly effect of acid rain on our water!!! The
water itself does not contain enough sulphur to kill off it's population
of fish and plants. But with the sulphur in the soil it does.


Penguin Publishing House, 1987 , Pearce Fred Acid Rain. What is it and
  what is it doing to us?
New York Publishers, 1989, William Stone Acid Rain. Fiend or Foe?
Lucent books, Inc. 1990, Steward Gail Acid Rain.