Re: How does water pollution effect plante growth?

Stephanie:

Water pollution affects plant growth in so many different ways that it is 
impossible to answer the question in detail. However, I can give you some 
information that should help. 

Basically, plants need to do three things: maintain their metabolic 
processes, grow in size and maturity, and reproduce. Pollutants in water 
can disrupt any or all of these three vital functions of plant life. 

It is a good idea to classify water pollutants so that we can talk about 
them and distinguish their different effects. There are several different 
ways to do this. For instance, one could classify pollutants according to 
how they are transported. 
     Some compounds are dissolved. This means that they break apart into 
pieces of submolecular size that typically carry an electrical charge. 
Ordinary salt is sodium chloride (NaCl). Salt dissolves in water, becoming 
the positively charged sodium ion and the negatively charged chloride ion. 
Salt is an essential nutrient for animals, but too much of it poisons both 
plants and animals. Plants that get too much salt will die. 
     Some compounds are suspended. This means that small pieces are 
carried in the water, but they retain their essential character; they do 
not break apart chemically as do dissolved compounds. Suspended material 
includes bits of wood and leaves, clay, and other materials that tend to 
make water cloudy or are visible as floating specks. This kind of 
pollution can smother plants and kill them. Mud from a construction site 
travels in water as suspended particles that can cover and kill plants.

Another way to classify pollutants is according to how they got to the 
water. Some sources of pollutants considered this way are farms, lawns, 
streets, factories, landfills, and chemical spills. Lawns, for instance, 
provide leaves, pesticide, and fertilizer. All of these things can harm 
plants. One of the kinds of lawn-derived pollution that is most harmful to 
plants is herbicide. Herbicide chemicals are used to kill weeds. If they 
get into water they can kill other plants. 

A third way to classify pollutants is according to their chemical nature. 
Salt (NaCl) is an inorganic compound. There are many kinds of these:  
other salts and metals are two classes of inorganic compounds that are 
commonly found in polluted water. Both kinds of compounds can be harmless 
or harmful, and the ways they injure plants are varied too. Another major 
kind of pollutant consists of organic compounds. Most organic compounds 
are made by organisms. For example, sugar is an organic chemical made by 
plants; the toxin that walnut trees use to kill other plants around them 
is also an organic compound. Most organic chemicals are made of hydrogen, 
carbon, oxygen, and nitrogen, with in some cases small amounts of other 
elements. Natural organic compounds can be very harmful to plants; they 
can also be beneficial. For instance, some natural organic compounds kill 
microorganisms that would otherwise harm plants. However, most herbicides 
are organic compounds, and they are bad for plants. Also, some organic 
compounds are made by people in laboratories. Just like natural organic 
compounds, these manufactured ones can be harmful, beneficial, or have no 
effect on plants. The most common organic materials in polluted water are 
phosphates, nitrates, and bacteria. The bacteria make the water dangerous 
for people, but not usually for plants. The phosphates and nitrates help 
algae grow very fast, which is good for the algae, but bad for other 
organisms living in the water. 

pH is a property affected by many compounds, but in the context of 
pollution it is usually mentioned with regard to acid rain. Various human 
activities (such as power generation using coal) can make rain water more 
acidic than usual, and this makes river and lake water acidic as well. 
Some plants benefit, but many other plants (and animals) are harmed by 
acid rain.

I do not know if you want to study the chemical processes by which 
pollutants harm plants. This can get pretty complicated, but it can be 
very interesting. Understanding exactly how the harm is done can lead to 
new ideas about how to prevent or cure the damage. I do not have the room 
in the message to go into this subject; I suggest that you talk to a 
botanist or environmental scientist at the nearest university. This person 
should be able to suggest some books that will help you. 

I hope I have showed you that your question is a very big one. I recommend 
that you try to study only one part of this problem for your project. For 
instance, you could look at the effects of acid rain in a certain part of 
the world. Or, if you will be doing some experiments, you could experiment 
with different amounts of salt or other chemicals in water that you give 
your plants. 

Your local library, and even your school library, should contain many 
books about pollution, the environment, and plants, that will help you 
learn about this subject.

Good luck!

David Kopaska-Merkel
Geological Survey of Alabama
P.O. Box 869999
Tuscaloosa AL 35486-6999
USA
(205) 349-2852
FAX (205) 349-2861
www.gsa.state.al.us