Impacts of Anthropogenic Perturbations on Reactive Nitrogen Dynamics in Mangrove Ecosystem: Climate Change Perspective

This review paper deals with the most pressing problems of increasing anthropogenically induced reactive nitrogen (Nr) and investigates how they severely altered the global nitrogen cycle and its enhanced effect on climate change. Global scale assessment reveals that Nr loading increases dramatically from pre-industrial (111 Tg/year) to the contemporary era (223 Tg/year) and shows shifting of Nr loading from primary fixation based (89%) in the pre-industrial state to heterogenous mix in modern times. Globally, natural ecosystems like wetlands, estuaries and mangrove are acting as net sink of reactive nitrogen and can mitigate the negative consequences of excess Nr loading on climate change. Pristine mangrove act as a sink of Nr while impacted/eutrophied mangrove may act as a source of it. Nr removal efficiency varies with latitude, wetland class, and Nr loading. Fresh water and natural wetlands have more efficiency in removing Nr than tidal and constructed wetlands as salinity negatively affects anammox reaction. Comparing the warming effects of Nr (N₂O emission, tropospheric ozone formation and phytotoxic effects) with the cooling effects (carbon sequestration, altered methane lifetime and aerosol formation) reveals the net cooling of –16 (–47 to +15) mWm-2 and –240 (–500 to +200) mWm-2 for European and global Nr release respectively. Radiative forcing on global scale reveals that positive and negative forcing to some extent balance each other with net cooling effect but growing anthropogenic Nr is rapidly decreasing the part that is cooling, and increasing the part that is warming.