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

Eutrophication of terrestrial forest ecosystems threatens ecosystem functioning and biodiversity. India is a hotspot of biodiversity and also nitrogen (N) pollution. Forest types in India range from Alpine/Sub-Alpine in the north and north-east, to sub-tropical/tropical in the north-east and south, desert in the west and deciduous/semi-deciduous in central parts. N pollution sources include fertilization, coal-based power generation, other industrial processes, agriculture, livestock management, and vehicular emissions. Still, studies on N deposition in India are rare. Here, we assess the threats to Indian national parks (NPs) from present and future N deposition using a critical loads exceedance approach. N depositions to 104 NPs were modeled using a chemical transport model, GEOS-Chem. Present (2010) emissions were from the MIX and GEIA emissions inventories and future emissions from the IPCCs representation concentration pathways (RCPs). N deposition was computed every ten years between 2010 and 2050. N deposition values for each vegetation type were compared with critical load (CL) values for the corresponding types determined in the US, Europe and China (CL studies conducted in India are almost non-existent), and with a uniform value of 10 kg-N/ha/a which has been used by other researchers to assess threats to protected areas based on empirical CL studies in Europe. It was observed that in 2010, 50 NPs in India exceeded CL values of US and 13 of 100 NPs (excluding mangroves for which no Chinese data was available) exceeded CL values of China and 13 of 16 NPs in alpine/subalpine regions exceeded CL values of Europe. Eighty-three out of 104 NPs had CL values > 10 kg-N/ha/a. Alpine/Sub-Alpine and deciduous forests were more vulnerable. Fifty-four percent [median; range: 3.381.6%] of total N deposition in the NPs was contributed by domestic emissions, 28% (1.760.6%) by emissions in rest of Asia, and 18% (095%) by natural emissions. Under future RCP scenarios, N deposition to 4058 of 104 NPs still exceeded the US CLs, 913 of 100 NPs exceeded Chinese CLs, and 12 of 16 exceed Europes CLs, and 4666 NPs still exceeded 10 kg-N/ha/a. Therefore, there is a substantial present and future ecological threat to Indias NPs from N deposition, and emissions reductions in India and, to some extent, the rest of Asia are required.