Since Industrial Revolution, humans have been burning fossil fuels, and increasing CO2 in atmosphere. Bacteria are essential to nitrogen cycle Nitrogen abundant in atmosphere, but very stable, so bacteria are needed to break apart N2. Nitrogen fixation is conversion of gaseous nitrogen to ammonia, usually by nitrogen fixing bacteria Enzyme nitrogenase is in some cyanobacteria, soil bacteria, Rhizobium in legume nodules. Enzyme only works in absence of oxygen. Nitrification is conversion of ammonia to nitrate Nitrifying bacteria convert nitrogen compounds to produce metabolic energy.
Ammonification is conversion of organic nitrogen compounds into ammonia.
Nitrogen-containing wastes are decomposed by ammonifying bacteria, which produce ammonia. Denitrification is conversion of nitrate to gaseous nitrogen, a net loss of available nitrogen in the system. Algae blooms, taking up a lot of nutrients. Area of Gulf of Mexico is dead zone, where no nutrients are left, so nothing is growing. In water algae take up phosphate, fish eat algae, excretion and decomposition returns phosphate to water.