I need to do an experiment in a bog and find a relationship between to variables. Some ideas of dependent variables (variables that I measure) that I have are the pH levels and mineral levels in the water and soil. However, I'm stuck on finding an independent variable (the variable that I change). For example, I could do how the pH changes as depth changes, but I was hoping for something better. Can anyone give me any ideas? I've never been to a bog, btw, so you may need to be a little more specific. Thanks.