Experiments without controllable variables.

[cosmobikki]

In my experiment I am investigating if the amount of rainfall has a measurable effect on water clarity in local streams. I have measured water clarity each week at the same time over the past half year or so. I have gathered data on rainfall in the same area from an online database. I obviously cannot control my independent variable but still have evidence to support my hypothesis. Is this still a well formed Science project or will I need to find one that I can make changes to the independent variable? Is collecting data and comparing the two sets still a strong science fair project I will get good marks for?

Thanks

[SciB]

Hi,

I understand that you have no control over the rainfall, but that's OK. The problem I have is with your hypothesis. I assume that what you are thinking is that the rain washes soil and debris into the stream and makes it more turbid. Why is this important? Is it supposed to affect water plants, fish, snails, daphnia, etc?

What I think you should have done to make this a better project was to measure some biological aspect of the stream and correlate it with water turbidity. You have already done your readings so there's no way to go back and check the effects of rainfall on aquatic life. If you have some time before the project is due you could make a few more measurements of turbidity and a biological effect before and after a rain.

The question then is what biological effect you should measure. This site has some suggestions for determining affects of turbidity on aquatic life: http://www.pca.state.mn.us/index.php/vi ... l?gid=7854

Let us know what you want to do and we'll try to help you complete the project.

Good luck!

Sybee