What is the result of anaerobic bacterial metabolism in the denitrification process?

The denitrification process involves anaerobic bacteria that convert nitrates (NO3-) and nitrites (NO2-) into nitrogen gas (N2) or, to a lesser extent, nitrous oxide (N2O) under low-oxygen conditions. This microbial activity effectively reduces the levels of nitrate in the environment, thus completing the nitrogen cycle by returning nitrogen to the atmosphere in a gaseous form. This process helps to prevent the accumulation of nitrates in water systems, which can contribute to problems such as eutrophication.

The other possible results, such as production of hydrogen gas or excretion of organic matter, are not the primary products of the denitrification process and do not characterize the metabolic pathway that anaerobic bacteria undergo when reducing nitrates. Additionally, increased oxygen levels would not be a result of denitrification, as this process occurs under anaerobic conditions where oxygen is limited or absent. Therefore, the correct response accurately reflects the essential aspect of denitrification in aquatic ecosystems and soil environments.