Science Buddies: "Ask an Expert"

Dear Science Buddies,

My name is Justin and my project question is: Which particular sediment from sediment run-off has the most toxicity and effect on daphnia magna? Instead of testing just sediment from a parking lot, I am testing sediment from a parking lot, construction site, sidewalk, and a playground. I have some questions regarding my project question and I was hoping you could help. Here are the questions and a bit of insight in my experiment:

1. In my experiment, I will have 8 containers for the four sediments. Two containers for each sediment. How many controls should I have? A control being just being a container with the daphnia and spring water. Would one be enough?
2. In terms of data, should temperature and pH levels be measured as well besides the daphnia viability (dead and alive daphnia magna)? How can I measure the pH level?
3. Where can I buy the daphnia and would I conduct my experiment with baby or adult daphnia magna?

Thanks and I look forward to your response.

Sincerely,

Justin

Hi Justin,

This sounds like an excellent science fair project. I'll go through your questions one by one:

1) I would do two containers for controls just as you are doing for the sediment. That way you can average the results from the controls. This helps control for random differences in daphnia survival between controls and also gives you a back up in case one of your control daphnia cultures dies off unexpectedly for no good reason.

2) It's never a bad idea to measure things like temperature and pH so you can be sure that they are as consistent as possible between your samples. While it's certainly possible your sediment run-off could chance the pH of your samples, in which case it's good to record that information so you can discuss it as a possible reason why the daphnia died, it is unlikely your temperature will be changing, so maintaining a log of temperatures will allow you to confirm that all of your samples and controls were at the same temperature, and thus temperature differences cannot explain any viability differences you see. To test pH levels you could either buy some pH strips (one use per strip so make sure you get enough) or use a pH meter if one is available to you. Some other ideas for testing pH are mentioned here: https://www.sciencebuddies.org/science- ... php?t=3945

3) Daphnia magna are available at Carolina Biologicals (www.carolina.com, http://www.carolina.com/daphnia/daphnia ... /142330.pr) and you can get a kit there for culturing them. Here are some instructions from our website project: https://www.sciencebuddies.org/science- ... #procedure and more instructions are available on Carolina Biologicals website. To conduct your experiment you'll be using an established culture of daphnia magna, so don't try to isolate out babies or anything like that. Adult daphnia should be fine.

Hope this helps and good luck!
JMP