Bad effects: Planting rice in Nangarhar province, Afghanistan. Wide application of fertiliser in agriculture has left huge amounts of nitrogen in the environment, and consequently, various adverse impacts. - AFP
Excessive use of nitrogen is causing problems ranging from coastal dead zones to fish kills and global warming.
Nitrogen continues to be used inefficiently as a plant nutrient in agriculture, according to the United Nations Environment Programme (UNEP) Year Book 2014.
The amount of usable nitrogen produced by humans is now about 190 million tonnes per year, greater than the 112 million tonnes created through natural processes. As nitrogen moves through the environment, the same nitrogen atom can contribute to multiple negative effects in the air, on land, in freshwater and marine systems, and on human health. This sequence continues over a long period and is referred to as the “nitrogen cascade”.
Excess nitrogen in the environment contributes to many problems, including:
> Coastal dead zones and fish kills due to severe eutrophication (a high concentration of nutrients, which leads to excessive plant growth and oxygen deprivation). There are currently over 500 known coastal dead zones in well-studied areas of the world, whereas in 2003 only around 150 such oxygen-depleted areas were reported. Once other regions start reporting, it is estimated that 1,000 coastal and marine areas will be identified as experiencing the effects of eutrophication.
> Nitrogen emissions to the air, notably those of nitrous oxide (N2O), contribute to climate change. Sometimes referred to as the “forgotten greenhouse gas”, N2O is over 300 times more effective at trapping heat in the atmosphere than carbon dioxide over a 100-year period. Human activities such as agriculture, deforestation and fossil fuel combustion are increasing the amount in the atmosphere.
Better management practices are essential to reduce nitrogen losses to the environment from agricultural sources.
According to the commissioned UNEP report, Our Nutrient World, a 20% improvement in global nutrient use efficiency by 2020 will reduce annual use of nitrogen by an estimated 20 million tonnes.
The report also highlights the hazards of fish farming. Aquaculture production has increased since the 1950s from 650 thousand tonnes to almost 67 million tonnes, and today provides half of all fish for human consumption. Marine aquaculture production by volume grew by 35% during the last decade, while production in fresh and brackish water grew by 70% and 83%, respectively.
While progress has been made towards making marine aquaculture more sustainable, environmental concerns remain. Fish farms can release nutrients, undigested feed and veterinary drugs to the environment. They can also increase risks of diseases, parasites and harmful algal blooms. In some countries, certain forms of shrimp farming have destroyed large areas of coastal habitats, such as mangrove forests.
Healthy marine ecosystems are fundamental to securing food and providing jobs. Environmentally sound development of the marine aquaculture sector is needed to avoid the loss of important ecosystem services. Technical innovations, the growing skills of aquaculture producers, and improved knowledge of environmental impacts provide hope for a sustainable marine aquaculture sector.
The report also says that air quality is deteriorating in most cities. The World Health Organisation (WHO) estimates that in 2012, air pollution led to around seven million premature deaths (one out of eight total global deaths), more than double previous estimates. It is the leading cause of environmentally related deaths. The WHO guideline for average annual fine particulate matter is 25 microgrammes per cubic metre. Cities in low- and middle-income countries far exceed this level. For example, in Kathmandu, Nepal, particulate matter (PM2.5) levels of over 500 microgrammes per cubic metre have been measured.
The cost of air pollution to the world’s most advanced economies, plus India and China, is estimated at US$3.5tril (RM11.3tril) per year in lives lost and ill health. In Organisation for Economic Co-operation and Development countries, the monetary impact of death and illness due to outdoor air pollution is estimated to have been US$1.7tril in 2010. Research suggests that motorised on-road transport accounts for about 50% of that amount.
In light of the high costs related to the health and environmental effects of air pollution, all countries should invest in clean air policies, the report says. — UNEP
Poisoning our food supplies