Nutrient pollution in the South Asia Seas (SAS)

03 Dec 2019

Anthropogenic activities like (i) agriculture fertilisers, (ii) coastal pisciculture, (i) sewage discharge, (iv) industrial activity, (v) burning fossil fuels and (vi) effluents from ports increase nutrients in surface water and seas. Nitrate pollution is largely caused by agriculture run-off, discharge from industry and manure or sewage. Phosphate pollution is tied to improper treatment of detergents in wastewater and from agro-fertilisers. These land-based pollutants make their way to coastal waters through networks of rivers and streams and cause nutrient pollution in the marine environment. Fine anthropogenic nutrients or sediments causes increased water turbidity for larger periods and reduced levels of oxygen and light creating 'dead zones' with incidents like mass fish die-offs. Additionally, undesirable plant and algae growth happens due to excessive nutrients leading to loss of important coastal fish habitats, such as seagrass and kelp beds. In particular, turbidity from nutrient pollution threatens coral reefs and mangroves leading to bleaching and diseases in corals, and instability in mangrove habitats.

Nutrient Pollution
Source: TERI illustration

A study by Fourney 2017 suggests that increased fine sediment in oceans coupled with increased temperature of seas derived via climate models led to reduced coral recruit survival. Increasing population, urbanisation and intensive agriculture are challenging the balance of coastal ecosystems apart from a rise in sea temperatures. Worldwide, there were over 415 eutrophic coastal ecosystems (WRI, 2008). As a result of human population growth and increased pollution, this number continues to rise.

The Bay of Bengal region is significant in terms of ecological hotspots like mangroves and inter-tidal areas of the Sundarbans. The South Asia Seas (SAS) region is significant as it is not only extremely rich in biodiversity, corals and mangroves but also in regulating the dynamics of climate around the region via the ocean-land-air interactions.

Nutrient pollution in SAS countries

The overall coastlines of SAS countries amount to a total of 8,772 km where the Indian coastline is 7500 km including the islands, Bangladesh 734 km, Sri Lanka 1,625 km, Pakistan 990 km, and the Maldives consisting of 26 coral atolls. These countries have several rivers that support agrarian economies through their basins. Rivers Ganges, Godavari and Irrawaddy of India alone accounted for 75–80% of the total river export of Nitrates(N) and Phosphates(P) in India (Pedde, Kroeze, Mayorga, Seitzinger, 2017). These five countries are developing, have high population densities, are agrarian societies, and depend on natural resources and coast for economic activities. The GDP growth trends of the five countries are given in Table 1.

Table 1: GDP growth trends of South Asian countries

  2018 2019 2020 2021
Bangladesh 7.9 8.1 7.2 7.3
India 6.8 6 6.9 7.2
Maldives 6.7 5.2 5.5 5.6
Pakistan 5.5 3.3 2.4 3
Sri Lanka 3.2 2.7 3.3 3.7

Source: World Bank, Oct 2019

The share of agriculture in GDP of India was 17%, Bangladesh was 13.4%, the Maldives was 1%, Pakistan was 24% and Sri Lanka was 7.7% in 2016-17 as per each country’s economic surveys. All these developing nations experience the pollution of Nitrogen & Phosphorus (N&P) from cultivated land by use of agro-fertilisers that contain N&P. Annual consumption of fertilizers in India was recorded to be 28 million MT in 2010-11; annual imports of fertilisers in Bangladesh was 2.23 million tons in 2005-06; fertilizer consumption was 3.93 million tons during the year 2010-11 in Pakistan; 780 Mt of fertilizers was imported in 2009 in the Maldives. Nutrient consumption per Ha of arable land in 2011 was “178.8kg in India, 184.4kg in Bangladesh, 3.7kg in the Maldives, 217.1kg in Pakistan, 280.7 in Sri Lanka” (SACEP, n.d.) Agro-fertiliser application on cultivated land leads to diffuse water pollution due to run-off from land that eventually reaches oceans. However, it is to be noted that total pollution from N&P depends on the total consumption of fertilisers and the methods of application along with factors like slope that impact run-off. Fertiliser application varies in the five countries and management measures are not clear. Additionally, sewage treatment is inconsistent in these countries and untreated direct discharge to oceans is not uncommon, which adds to signs of degradation of aquatic, estuarine, coastal and marine ecosystems due to excessive loading of fine nutrient. Evidence of these can be seen at various locations in South Asia, with several reports on eutrophic zones due to excessive growth of algae and fish kills due to hypoxia (SACEP, n.d.). Although algae can act as carbon sinks but, in excess, they change the balance of ecosystems and create a loss of existing carbon sinks like seagrass beds, loss of habitat and biodiversity, which in turn leads to loss of food habitats and economics of fisherfolk.

Several policies that apply to N&P exist in all five countries including National Environment and Water Acts. However, policy, monitoring plans and regulation specific to nutrients are not in place. This, when compared with developed nations like the United States is different, where the Environment Protection Agency (EPA) has a set of indicators for nutrient measurement from different sources, impacted ecosystems, and their monitoring, linking them to actions like limits, permits and regulations. A gap in pollution abatement in South Asian countries centres on limited integrated management and measurement systems for nutrient pollution from land to water resources including coastal waters.

Way forward

The five South Asian countries discussed here have similar challenges and therefore common solutions can be presented. The following actions can be taken with initial scoping using detailed technical studies and regional planning exercises:

  • Creation of frameworks and indicators for nutrient load analysis and impact assessment on a cyclical basis.
  • Spatial modelling assessment of nutrient load to develop an understanding. Additionally, while collating data on nutrients is difficult as the pollution is diffuse in nature, modelling approaches that link the five countries can provide solutions.
  • Assessment of impacted ecosystems through spatial modelling.
  • Policy and regulation framing.
  • Implementing pollution abatement at source through best practices like management of the application of fertilisers, run-off, livestock manure, dredges from pisciculture, avoidance of chemical fertilisers and using biological nitrogen fixers (integrated plant nutrient management) among others.
  • Multi-country cooperation, sharing of data and actions through regional frameworks of dialogue and actions.


1. Fourney, F., Figueiredo, J. Additive negative effects of anthropogenic sedimentation and warming on the survival of coral recruits. Sci Rep 7, 12380 (2017) doi:10.1038/s41598-017-12607-w
2. Selman, M., Greenhalgh, S., Diaz, R. and Sugg, Z. (2008). Eutrophication and Hypoxia in Coastal Areas. [online] World Resources Institute. Available at: [Accessed 20 Oct. 2019].
3. Pedde, S., Kroeze, C., Mayorga, E. et al. Reg Environ Change (2017) 17: 2495.
4. World Bank. (2019). Overview. [online] Available at: [Accessed 11 Oct. 2019].
5. Anon, (2019). [online] Available at: [Accessed 19 Oct. 2019].

Reviewed by Dr. Suneel Pandey and Mr. Saurabh Bhardwaj