Present and Future Atmospheric Nitrogen Deposition and Ecological Critical Load Exceedances in National Parks of India

Human activities have tremendously altered the global nitrogen cycle, leading to enhanced atmospheric nitrogen deposition to terrestrial environments. This endangers the functioning of ecosystems and their biodiversity and can have an adverse impact on plants. India is a global hotspot for nitrogen pollution. However, the impact of ensuing nitrogen deposition on Indian ecosystems has not yet been addressed. Here, using a chemical transport model with modern and future emission scenarios, we investigate the critical loads of nitrogen deposition on the national park ecosystems in India, spanning alpine and subalpine forests, desert, mangroves, tropical and subtropical deciduous forests, and evergreen forests. We find that nearly 80% of all of the national parks experience nitrogen deposition exceeding the critical load. Future climate change projections simulated using Representative Concentration Pathway (RCP) scenarios indicate nitrogen deposition will increase further, with a median change of +17% to +30% across all ecosystems. This indicates an irreversible risk to native floral biodiversity, as ecosystems elsewhere have been unable to recover to native vegetation. Thus, urgent attention is needed to integrate atmospheric nitrogen deposition and ecosystem impacts into nitrogen management policies.