Pune: A growing number of India’s national parks are likely to face harmful levels of nitrogen pollution by 2030, the first high-resolution assessment of nitrogen deposition across the country’s protected areas has revealed.Too much nitrogen can damage ecosystems in several ways. It can make soil and water more acidic, reduce essential nutrients, change plant communities and encourage invasive species to spread. It can also harm native plants and animals. Researchers attributed the increase primarily to growing nitrogen oxide emissions from vehicles and industries.The study, published in Scientific Reports, was carried out by scientists from Indian Institute of Tropical Meteorology (IITM), Pune, and UK Centre for Ecology & Hydrology. Using computer modelling, researchers estimated nitrogen deposition across 104 national parks and compared 2015 levels with projections for 2030.As India lacks its own ecological safety benchmarks, the team assessed the results against “critical load” thresholds developed in US, Europe and China. These thresholds indicate the level of nitrogen deposition beyond which ecosystems begin to suffer damage.The findings showed 18 parks had exceeded US critical-load thresholds in 2015, while 12 crossed European limits and six breached Chinese standards. By 2030, the number of parks surpassing US limits is projected to rise to 25, while those exceeding Chinese thresholds could double to 12. Exceedance of European limits is expected to remain unchanged at 12 parks, the assessment showed.Nationally, annual reactive nitrogen deposition is projected to increase by about 50%, rising from roughly 3.2 teragrams in 2015 to 4.7-4.8 teragrams by 2030. “Twelve states and Union Territories — Maharashtra, Goa, Daman and Diu, Chhattisgarh, Odisha, Madhya Pradesh, Karnataka, Andhra Pradesh, Telangana, Haryana, Uttar Pradesh and Rajasthan — are projected to see deposition rise more than 50% compared to baseline levels, affecting 40 ecologically sensitive zones within them,” the study said.The researchers warned that excess nitrogen deposition could trigger a cascade of ecological impacts. “In mangrove ecosystems, such as Bhitarkanika, higher nitrogen levels can weaken carbon-storage capacity and fuel harmful algal blooms, while forest ecosystems may experience a decline in the diversity of soil organisms critical for ecosystem health,” the study said.The threat extends beyond protected forests. Nitrogen deposited on surrounding land can be washed into wetlands, lakes and other aquatic systems, increasing nutrient loads and raising the risk of algal blooms even where direct atmospheric deposition is relatively low.Alpine ecosystems emerged as particularly vulnerable. Kishtawar National Park in Jammu & Kashmir recorded nitrogen deposition of 19.4kg per hectare annually in 2015, placing it among 12 of the 15 Himalayan alpine parks already exceeding US safety thresholds. Bhitarkanika National Park, India’s only mangrove national park, also exceeded US limits in 2015 and is projected to see deposition rise sharply from 17.4kg per hectare to nearly 28kg per hectare by 2030.The study said Desert National Park in Rajasthan and Sultanpur National Park in Haryana already exceeded US critical-load thresholds, with Desert National Park expected to cross even China’s higher threshold by 2030. Among deciduous forests, Rajaji National Park in Uttarakhand and Similipal National Park in Odisha have already breached US limits, and four more parks are expected to join them by the end of the decade.While evergreen forests currently remain below both US and Chinese thresholds, the study found that nitrogen deposition in these ecosystems could increase by as much as 124%, signalling a need for close monitoring.The researchers, however, cautioned that the findings should be interpreted carefully. Because India has not yet developed its own ecosystem-specific critical-load values, the study relied on thresholds established in countries with different climates, vegetation and soil conditions. The authors described the exceedances as indicative rather than definitive and called for long-term field studies to establish India-specific ecological thresholds.The study also highlighted risks to major wetland ecosystems, including Chilika Lake in Odisha, Keoladeo National Park in Rajasthan and Loktak Lake in Manipur, where nitrogen runoff from surrounding landscapes could further intensify ecological stress.
