Duckweed project

[KenXZu]

Hi,
I have recently started researching for my science fair project, and am thinking of studying the effect of excess nitrates in water on duckweeds ability to compete with algae. I was thinking of perhaps growing duckweed in water with different concentrations of nitrogen outdoors, so that algal competition was present. From what I've heard, higher concentrations of nitrate lead to explosive algae growth, hereby outcompeting duckweed for vital nutrients. Is this a feasible idea that could work? Please feel free to add an comments, questions, or suggestions. Thanks.

[MelissaB]

Ken,

This sounds like a great idea! However, it may take some trial and error as well as a lot of time to get to work, so I would suggest starting as early as possible.

I would suggest building or buying a number of fish tanks so you can better control the environment your plants and algae will be growing in. You will also need to consider what other factors can affect the growth of algae and duckweed so that you can control for these.

For the actual experiment, you will need to be careful that you do not use chlorinated water (or water with other substances in it) since that may kill the algae and/or duckweed. I would suggest going to the nearest pond or lake and bringing back several bucketfuls of pond/lake water--unless you are planning to seed each tank with a certain amount of algae.

You might consider trying just a preliminary experiment with a bunch of tank-fulls of algae at different nitrogen concentrations so you can better pinpoint which ones you will want to use in your experiment. Otherwise, you run the risk of getting way too much or way too little and getting the same result for all of your concentrations.

Once again, this sounds like a great project. I really like the fact that you have come up with the idea on your own, and you sound enthusiastic about it--in my experience, that makes for a successful project!

Good luck, and let us know if you have any more questions.

[KenXZu]

Hello,

Thanks for your reply. I've been researching for about a week now, but I have found it surprisingly difficult to find good information on growing algae or duckweed (like the type of water and stuff) and the factors that affect growth. Are there any good resources that might contain this information?

Also, I am planning on using a number to small plastic tubs/buckets to grow the specimens, they have the same general dimensions as a fish tank, so these should work too, right?

Thanks a bunch.

[donnahardy2]

Hi Ken,

Here’s an abstract that gives some useful information. It’s a study on a different plant, but the authors used from 0 to 97 mM (millimoles/liter) nitrate in a study on one algae. You can assume that duckweed would respond in the same range.

http://www.springerlink.com/content/w48 ... 8uk3n7/rdy

Here’s a project from the science buddies website that should give you some ideas for your project.
https://www.sciencebuddies.org/science- ... ODUsc2lkOj
AscDoyLGlhOlBsYW50Qmlv&from=TSW


And, here’s the science buddies guide for doing a science fair project. And check out the link for measuring plant growth.

https://www.sciencebuddies.org/science- ... ndex.shtml

Here’s a website that provides a protocol for measuring nitrate in water:

http://extension.usu.edu/waterquality/f ... e_test.pdf


Science projects should be designed to answer a question or solve a problem. What is your question, or what problem are you trying to solve with your project? Duckweed is an aquatic weed, so are you trying to discover how to control it?

http://www.clean-flo.com/weed-algae-ide ... ronment-2/

Or, perhaps you are interested in farming duckweed for a source of food:

http://www.p2pays.org/ref/09/08875.htm

Defining the purpose of your project will help you design a better experiment.

Let us know if you need more information.

Donna Hardy

[MelissaB]

Just to add to Donna's advice: if the buckets are transparent, it should be fine. But, if they are opaque, depending on how you place them relative to the sun, your algae and duckweed may not get enough sunlight to actually use up the nitrate you add. So, that's another variable you should consider.

I would suggest generally doing some searches on 'nitrogen limitation' and 'eutrophication'.

[KenXZu]

Hi again, thanks for the replies, they really helped me focus my research.

Speaking of research, after more of it I've found that the project idea I've chosen is waayyy too complicated, difficult, and time consuming to do. Growing duckweed and algae together, measuring them both, and adding and monitoring nitrate levels is far too technically challenging for me. I've done two science fair projects in the past and they both failed miserably due to the difficulty level.
I'm thinking of switching to a more managable and simplier idea. Such as using duckweed to absorb heavy metals, most notably copper, from drinking water. This idea has a purpose, as Donna suggested, and it will (hopefully) be much easier to successfully test on than the previous idea.
I know how to grow duckweed, and measure copper content in water, I just don't understand how to manipulate/add a specific amount of copper in water so that a specific concentration is reached. The EPA limit is 1.3 ppm, so, I'm thinking of adding copper sulfate so that the concentration in water is from 5-50 ppm or so. Can someone advise me on how this can be done? From what I've found, I would have to add 5 milligrams to one liter of water to get a concentration of 5ppm. How am I supposed to add such miniscule amounts of copper?
Thanks for the help

[donnahardy2]

Hi Ken,

I think you are smart to consider the difficulty of a project before your start, and I like your new idea. You will be doing a carefully controlled experiment with just one independent variable. What is your dependent variable going to be? I think you should set up a range of 0 to 50 ppm Cu. What is the dynamic range of the copper assay you have available? Can you go lower than 5 ppm?

Have you had basic chemistry yet? ppm is parts per million, or milligrams per liter. Do you have copper sulfate? This chemical usually comes as CuSO4 or CuSO4 pentahydrate. You need to look at the chemical label and calculate how much to weigh out to match the copper concentration to your standard curve, omitting the weight of the sulfate, and the water molecules. Please let me know what the formula of your copper sulfate is, and I’ll confirm your calculations. What is the accuracy of the balance you have available to use for this project?

Be sure to get the MSDS for the copper you plan to use so you can review safety information before you start.

Donna Hardy

[KenXZu]

Hi,

Thanks for your reply. I believe my dependent variable would be the copper concentrations in water, since its dependent on the duckweed. I'm planning to use a water test kit from chemetrics, its visual, so I'm not so sure about its accuracy but it ranges from 1-10 ppm, and can even get down to 0.05 ppm.
No, I have never taken an actual specific chemistry course, but I'm guessing that its the mass ratio of copper to the entire compound right? So for CuSO4 the ratio would be 63.55 to 159.61, or 1 to 2.51156, so to have one ppm for copper I would need to put about 2.5 milligrams of copper sulfate in one liter of solution. Please help me with this calculation, I really have no clue.

Such I put heavy curtains around the room to try and shut out as much diffuse light as possible? Since I am providing indoor lighting, it might interfere with the duckweeds growth rate.
Also, are aeration units necessary for floating aquatic plants? Snce most science journals with experiments like these don't even mention them.
Lastly, can I obtain nutrient solutions like Hoagland, Hutners, and Bonner-Devirans from garden stores, or are there other, better places that sell them.

Thanks a lot, I know this is a lot of questions.
Ken