Amounts of uncombined nitrogen in seawater vary between 8.4 and 14.5 ml/€.
Nitrogen-fixing bacteria are known to occur in the sea, but the quantity of nitrates formed by their activity is probably very small. There is also some return of nitrogen from the oceans to the atmosphere by the nitrogen-freeing activity of denitrifying bacteria and blue-green algae. With increasing quantities of atmospheric nitrogen being fixed by industrial processes for fertilizers, the biological freeing of nitrogen from nitrate becomes of increasing importance in maintaining the equilibrium of the nitrogen cycle.
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