Simplify the following text for a Grade 9 native English-speaking person.
Original: Nitrogen is present in the environment in a wide variety of chemical forms including organic nitrogen , ammonium ( NH4 + ) , nitrite ( NO2 - ) , nitrate ( NO3 - ) , and nitrogen gas ( N2 ) .
Simplified: Where there is no oxygen , some bacteria will make nitrate into nitrogen gas ( N2 ) .