Denitrification in freshwater sediments primarily removes which form of nitrogen from the water column?

• A. Ammonia
• B. Nitrate
• C. Nitrite
• D. Organic nitrogen

Answer: (B)

Denitrification is a microbial process that uses nitrate as the terminal electron acceptor under low-oxygen conditions in sediments, converting nitrate (NO3-) to nitrogen gas that bubbles out of the water. Because of this, it directly removes the dissolved inorganic nitrogen form most relevant to nutrient availability in the water column—nitrate. Ammonia and nitrite are different nitrogen forms involved earlier in the nitrogen cycle (ammonia can be oxidized to nitrate, or assimilated by organisms; nitrite is an intermediate in those processes), and organic nitrogen must first be mineralized to inorganic forms before any denitrification can occur. So the primary form removed by denitrification in freshwater sediments is nitrate.