What is primarily released through the process of denitrification?

Denitrification is a critical microbial process in the nitrogen cycle, where nitrates (NO3-) are reduced to nitrogen gas (N2) or, in some cases, nitrous oxide (N2O), which is then released into the atmosphere. This process is primarily carried out by anaerobic bacteria in environments with low oxygen levels, such as waterlogged soils and sediments.

The significance of denitrification lies in its ability to convert excess nitrates in the soil—which can contribute to pollution and eutrophication—back into nitrogen gas, thus helping maintain the balance of nitrogen in ecosystems. Nitrogen gas, being a major component of the Earth's atmosphere, is not reactive and allows for the return of nitrogen to atmospheric reserves.

The other options—ammonia, carbon dioxide, and nitrates—do not represent the primary outcome of denitrification. Ammonia is usually a product of ammonification or nitrification processes, carbon dioxide is primarily released during respiration and decomposition, and nitrates are the substrates that undergo reduction during denitrification rather than being the product.