Salinity change induces distinct climate feedbacks of nitrogen removal in saline lakes.

Abstract

Current estimations of nitrogen biogeochemical cycling and N₂O emissions in global lakes as well as predictions of their future changes are overrepresented by freshwater datasets, while less consideration is given to widespread saline lakes with different salinity (representing salinization or desalinization). Here, we show that N₂O production by denitrification is the main process of reactive nitrogen (Nr, the general abbreviations of NH₄⁺-N, NO₂^--N and NO₃^--N) removal in hypersaline lake sediments (e.g. Lake Chaka). The integration of our field measurements and literature data shows that in response to natural salinity decrease, potential Nr removal increases while N₂O production decreases. Furthermore, denitrification-induced N₂ production exhibits higher salinity sensitivity than denitrification-induced N₂O production, suggesting that the contribution of N₂O to Nr removal decreases with decreasing salinity. This field-investigation-based salinity response model of Nr removal indicates that under global climate change, saline lakes in the process of salinization or desalination may have distinct Nr removal and climate feedback effects: salinized lakes tend to generate a positive climate feedback, while desalinated lakes show a negative feedback. Therefore, salinity change should be considered as an important factor in assessing future trend of N₂O emissions from lakes under climate change.