Reactive Nitrogen in Coastal and Marine Waters of India and Its Relationship With Marine Aquaculture

India’s Riverine Nitrogen Runoff Strongly Impacted by Monsoon Variability

“…Prior literature has also alluded to the fact that a large fraction of the nitrogen input in India is lost to the atmosphere as ammonia and nitrous oxide emissions, converted back to nitrogen gas via denitrification, or retained in groundwater as nitrate. , Our results support these findings, suggesting that agricultural intensification in India is likely impacting groundwater quality and atmospheric emissions more so than riverine fluxes. This hypothesis is also supported by observations of high nitrate concentrations in groundwater in various states across India , and by increasing ammonia and nitrous oxide emissions that have been attributed to agricultural intensification. − Quantifying nitrogen losses to groundwater and the atmosphere as well as nitrogen export via agricultural products at a basin scale would make it possible to attribute the increase in fertilizer application to each of these four end points but is beyond the scope of the current study.…”

Anthropogenic nitrogen pollution threats and challenges to the health of South Asian coral reefs

“…These regions are located far from the major riverine inputs occurring in the northern Bay of Bengal, where strong salinity fluctuations and high sediment loadings largely prevent coral colonization. The mean annual nitrate concentrations for the surface waters of India's Exclusive Economic Zone (EEZ) are typically 0-2.5 mmol L -1 (Arabian Sea), 0-3 mmol L -1 (Bay of Bengal) and 0-3.5 mmol L -1 (Andaman Sea) (Nair, 2010;Prema et al, 2017). Monsoon-driven seasonality is recognized as the dominant mode of environmental variability across the region with impacts that include the reversal of coastal currents (Shetye, 1998), seasonal coastal upwelling (Retnamma et al, 2020), substantial freshwater and nutrient discharge to Indian coastal waters (Singh and Ramesh, 2011;Krishna et al, 2016;Rao et al, 2017), and increased terrestrial runoff in the Andaman and Nicobar Islands (Raghuraman et al, 2013).…”

“…(Kaly, 2004;BOBLME, 2010;BOBLME, 2014;BOBLME, 2015)), and particularly within India via national nitrogen assessments (Abrol et al, 2017), much remains unknown about the fate and impact of anthropogenic nitrogen on coastal environments. For example, the Indian Nitrogen Assessment (Abrol et al, 2017), highlighted both an 11-fold increase in fertilizer N consumption within India between 1970 and 2011 and a 4-fold increase in the loss of fixed nitrogen to the environment (Abrol and Adhya, 2017) but concluded that the evidence to document an impact on the marine environment was currently patchy and incomplete (Prema et al, 2017;Ramesh et al, 2017). Consumption of fertilizer nitrogen in India now exceeds 18.8 Mt N per year (as of 2019-2020; (The Fertilizer Association of India, 2022)), with over 80% of this fertilizer nitrogen represented by ureabased products (Tewatia and Chandra, 2017).…”

“…Yet, despite improved efforts to quantify and track fertilizer nitrogen application and loss across agricultural lands and through the landocean continuum, the lack of comprehensive monitoring of coastal waters severely limits efforts to quantify the export of applied nitrogen to the ocean (Kaly, 2004;BOBLME, 2010;BOBLME, 2014;BOBLME, 2015;Abrol and Adhya, 2017). Prema et al (2017) estimated that India's rivers export 1.6-1.8 Tg N yr -1 , an amount equivalent to around 9% of applied fertilizer nitrogen. On this basis, they argued that the remaining 91% of nitrogen fertilizer was converted to crops, lost to the atmosphere, or recycled and retained within rivers and estuaries.…”

“…On this basis, they argued that the remaining 91% of nitrogen fertilizer was converted to crops, lost to the atmosphere, or recycled and retained within rivers and estuaries. This exported nitrogen remains significant, however, and was estimated to support ~13% of coastal new production (Prema et al, 2017). Fertilizer application and coastal discharge are not, however, uniform with 73% of fertilizer N applied to catchments that drain to the east coast (Bay of Bengal), and the remaining 27% draining to the west coast (Arabian Sea) (Swaney et al, 2015;Ramesh et al, 2017).…”