Influence of elevated CO2 on nitrification and denitrification in water bodies: A review.

Abstract

Elevated atmospheric CO2 has imperceptible impacts on carbon cycle in aquatic ecosystems. However, it remains a question how this process will impact nitrogen cycle that is naturally coupled with carbon cycle. The nitrification and denitrification are two critical processes in the nitrogen cycle. It is reasonable to expect that elevated atmospheric CO2 will influence both processes. We reviewed the previous literatures concerning the effects of elevated atmospheric CO2 on the physico-chemical properties, nitrification, denitrification and nitrogen transformation in water bodies. The published results revealed that the elevated CO2 would reduce the water pH, increase CO2 and HCO3- concentrations, but with different effects on the nitrification and denitrification between eutrophic and oligotrophic water. Elevated atmospheric CO2 could inhibit nitrification and denitrification in oligotrophic water, thereby reduce N2O flux from water. The nitrification process in the eutrophic water bodies was also inhibited, but its denitrification might be promoted by the elevated CO2. In the eutrophic water bodies, there could be an increase of N2O flux when pH was maintained in the range of 7-9. These might eventually result in the accumulation of NH4+ and reduction of NO3- in water, producing an impact on the microbial diversity. Based on these reviews, we proposed some research gaps related to the relevant research fields as well as some scientific questions that is worth to be further explored. This review would be helpful to better understanding on how the greenhouse effect caused by the elevated atmospheric CO2 would affect nitrogen cycle in aquatic ecosystem.