| MadSci Network: Environment/Ecology |
Andrea Porter asked:
How do I set up my experiment on the benefits of wetlands?
I have done the research on wetlands, but I am having trouble figuring out how to set up an experiment that will help me determine whether or not wetlands help to purify polluted water. Can you give me some suggestions?
I'm not surprised you're having trouble! Studies in this area are difficult even for professional scientists using the full range of modern biological methods and instruments. I'll make some suggestions, but what you'll actually be able to do will depend very much on the resources you've got available at home or at school.
Before presenting my suggestions, I'll discuss a few issues which I think are relevant. You might have already thought of these points, or read about them, but the other people who might read this might not have.
Your question just mentions "polluted water" but, of course, there are several different types of pollutants and they usually affect aquatic life in different ways.
Particulates are fine materials which get suspended in the water. This is usually sand, mud or silt. It often gets into waterways (lakes, rivers, streams and creeks) from erosion after terrestrial vegetation is cleared from the nearby area. Most waterways carry some particulate matter. It usually only becomes a problem when there is too much: then it can bury and smother organisms, and choke waterways.
Nutrients are chemicals—such as potassium, phosphorus and nitrogen—which plants need to grow. The most common sources of these are from fertlizers, which get washed into waterways, and from untreated, or improperly treated, sewage. Nutrients must be present for plants to grow, but excessive amounts can lead to excessive growth, or the growth of problem plants, clogging waterways. Plants take in carbon dioxide and give off oxygen but they also take in oxygen at night. When plants become very abundant they can use up all the oxygen, killing the animals. Another problem is that the bacteria which breakdown the dead plant material may use oxygen, making the problem even worse.
The most common of these are metals such as lead, copper and zinc. These may be released by industries or get washed into waterways by urban runoff. Urban runoff is water running over built up areas and washing into waterways. It carries with it pollutants from the surfaces it washes over, such as lead (from petrol), copper (from pipes and wires) and zinc (from galvanised iron). These chemicals simply poison organisms, usually by interfering with the chemical reactions in cells.
There are two types of studies which biologists commonly do:
Either type of study can be done in the field or laboratory. Many laboratory studies are, however, manipulative, because a common reason for bringing organisms into the laboratory is to be able to manipulate them. In contrast, many field studies are observational, because it can be difficult to set up the required conditions or equipment outside. This is likely to be the case for you.
I strongly recommend that you:
Now I'm finally getting to your question...
To see if wetlands do purify polluted water, you're going to need some way of measuring the amounts (levels) of pollutants in a sample of water.
There are couple of ways you can measure particulates in a sample of water.
You will need some type of water testing kit.
To do these it would be besit if you could visit two polluted waterways, one which runs through a wetland and one which doesn't. Look at the (rough) diagram below.
Stream 1 ============================================= water flow -->
| | | | |
A B C D E
| | | | |
[<- vegetation here ->]
Stream 2 ============================================= water flow -->
[<- vegetation here ->]
Take samples at the points marked A, B, C, D and E, measure the nutrients and turbidity and plot the results, as roughly illustrated below (1 is the reading on Stream 1, 2 the reading for Stream 2). I'll leave it to you to work out what this means.
Nutrient/Turbidity
|
| 1 1 1
| 2 2 1 1
| 2
|
| 2
|
| 2
----------------------------
A B C D E
Sample
If you don't have a situation similar to the one in my first diagram, see if there is some way in which you can collect observations which will allow you to make the same sorts of comparisons.
To do these you will have to set up and maintain some wetland plants in an aquarium. A salt marsh plant like Spartina might be a good choice (I'm in Australia, so I'm a long way away from where you are and just guessing). You should also set up one aquarium with just soil and water as a control (ideally, each treatment should be done at least twice—why?—but you would probably find this too much to do).
You could then add nutrients to the water of both aquaria and observe how the levels change over time. You could also add silt, or fine mud, and make the same kinds of observations: this experiment is, however, probably not as realistic (why?).
Starting with my suggestions, you may be able to come up with other ideas of observations you could make or experiments you could do. Just follow the same sort of approach.
In drawing your conclusions, you should also consider the possible effects of the pollutants on the wetlands themselves. A wetland may purify polluted water but is this a good thing if it damages the wetland?
Good luck!