Hello,
Biofixation, fixation, and bioremediation all have very similar meanings, but all three ARE different from one another...
Bioremediation is just anything that uses live organisms (usually bacteria, fungi, etc.) or enzymes to restore the natural environment that has been affected by some kind of contaminant(s)...For example, this includes the cleanup of oil spills by using bacteria/enzymes, strengthening soil by adding nitrates, etc.
(Here's an article that you can browse through for more info:
http://en.wikipedia.org/wiki/Bioremediation)
Biofixation is the same thing except it refers to the use of organisms(usually plants or other photosynthetic organisms) for the sole purpose of removing carbon dioxide from the atmosphere...photosynthetic organsims do this by using carbon dioxide for photosynthesis which is their source of energy and thereby reduces CO2 levels and helps lessen the effects of global warming...
Fixation is the same thing as biofixation except it doesn't refer to the exclusive use of organisms but any other method used to remove carbon dioxide also falls under fixation (example = chemical, mechanical etc.)...So in other words, biofixation is a subcategory,or specific type, of fixation...
Hope that helped!!
Feel free to post if you have additional questions/clarifications...
