A considerable degree of denitrification must, therefore, take place in the ocean, for the concentration of combined nitrogen is always excessively small.
Many bacteria are known which are capable of denitrification, some of them being abundant in fresh dung and upon old straw.
Denitrification filters convert nitrate to nitrogen gas, the bacteria in such filters are anaerobic.
It is maintained by Brandt and others belonging to the Kiel school of marine biologists that the process of denitrification is, on the whole, more significant in the sea than that of nitrogen-fixation.