Hey Everyone,

I'm new around here. THe reason I joined is because I'm trying to conduct an experiment for my biology class and I need some experienced advice. What I'm trying to do is show the effects of Nitrogen run-off on aquatic environments.

My question is:

What kind of plants and fish should I put in a 20 g tank that would most closely emulate the organisms in a natural pond or lake.

and

What other factors should I consider.

Thanks :)

Welcome to the forum.

Sounds like a great expiriment. For the most accurate results, I would recommend taking a sampling of a local lake's water and vegitation (including the "scum" at the bottom). It is nearly impossible to replicate an entire eco-system one species at a time, because there are microbial life forms that can play major roles in the eco system. You will also want to add some minnows ( I would think a local bait store should have plenty of the right kind to use ) to replicate the eco-systems ability to turn oxygen into carbon-dioxide. This will become important when you start adding a lot of nitrogen.

You may want to consider putting the tank outside as well, to get natural sunlight, as light does play an important role in any eco-system.

I presume you will be adding nitrogen from a high-nitrogen lawn fertilizer to replicate the impact of nitrogen fertilizer runoff? I would imagine that given the preceeding setup, and adding nitrogen via fertilizers, within 2-3 weeks time the algae in the tank will be so thick (even though the minnows will be eating it), that it will look like one big green jellatinous blob. At this stage you will see bubbles in the algae, which is the algae creating oxygen from photosynthesis using the fish's CO2 emissions as well as any O2 exchange at the surface. This stage shouldn't last very long, as the algae will quickly consume all of the trace elements as well as starve of CO2... so it should turn brown and start decaying. At this point methanogens will take over and create methane gas out of the decaying debris, and killing a good number of minnows. At least this is what I would expect to happen in a freshwater eco system. Do let us know how it turns out.