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NitrificationModelRutgersABedit

by Annette Brickley (Submitted: 02/02/2015)

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WHAT IS IT?

This model demonstrates how the nitrogen cycle works in an aquarium. This is part of in important biogeochemical cycle.

HOW IT WORKS

As a fish is placed in a tank, they produce ammonia through excretions. Bacteria are recruited from the air. These bacteria use nitrogen compounds, ammonia or nitrite, for energy. Bacteria need to appear randomly in patches once ammonia and nitrate reach a certain level. Nitrosomonas (the cyan patches) appears before Nitrobacter. Nitrosomonas reproduces more rapidly than Nitrobacter/Nitrospira (violet patches). Each bacteria needs some level of nitrogen compound to reproduce. Nitrosomonas use enzymes to convert ammonia to nitrite (NH4+ to NO2-) with some probability. Nitrobacter convert nitrite to nitrate (NO2- to NO3-) with a smaller probability than above. To prevent overpopulation, bacteria have limited life spans. Molecules of N-species are converted on contact with bacteria (probablistically noted above) and move randomly around the tank. Plants take up nitrate, so if there are many plants, the nitrate levels will be lower. Nitrates also removed through regular water changes.

HOW TO USE IT

Set the number of fish at 1 and number of plants as desired.

THINGS TO NOTICE

The red circles are ammonia, the white circles are nitrite, the yellow circles are nitrates. The cyan patches are nitrosomonas, the violet patches are nitrobacter/nitrospira. Notice the sequence of the tank cycling by watching the plot and appearance of bacteria species.
Fish have been added to original and if water is not changed when requested, number of fish will decrease by one. At toxic levels, all fish will die.

THINGS TO TRY

See what happens if you add more fish, more or less plants.
Look at the effects of regular water changes.

EXTENDING THE MODEL

Decomposition of solid waste, uneaten food and plants creates ammonia and consumes dissolved oxygen-- this would be an interesting extension of the model to include dissolved oxygen as an additional variable.
Denitrifying bacteria convert nitrate to nitrite and nitrogen gas. How would the aquarium benefit from this additional variable?

RELATED MODELS

Fishspawn2 (part of reptools at Rutgers)

CREDITS AND REFERENCES

Created by Cindy Hmelo-Silver July 2005
http://reptools.rutgers.edu/RevisedNitrificationmodel.nlogo

Modified by Annette Brickley, Feb 2015 for Teacher Professional Development purposes.

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