According to the FAO, agriculture is the biggest water pollutant due to the excess of nutrients, and you can easily imagine that with a growing population and growing food demand, this situation is only expected to get worse. Which will make the challenge of feeding 10Bn people by 2050 (UN DESA) even greater.

The excess of nutrients means that too many nutrients, mainly nitrogen and phosphorus, are introduced to bodies of water and spark an excessive growth of algae. The process is known as eutrophication.


The nutrients come mainly from  two  sources: 

  • Fertilizer runoff  

  • Animal manure



Fertilizer runoff

Each year 200 mn tons of fertilizer are consumed worldwide. Unfortunately, about half of that fertilizer is being wasted.

Fertilizer is applied more heavily than crops can absorb and it is washed away by rain or irrigation before it can be incorporated.

Animal manure

 Animal waste is stored in open ponds (called lagoons) or pits and is applied untreated as fertilizer to farm fields. Most lagoons are lined only with clay and can leak, allowing the waste to seep into groundwater.

These excess nutrients end up in aquatic systems like rivers, lakes and eventually the ocean.  


A significant fraction of the applied nitrogen and phosphorus makes its way to the sea and can push marine and aquatic systems across ecological thresholds of their own.


According to the International Nitrogen Management System “ we must halve the amount of nitrogen we dump into the environment by mid-century or our ecosystems will face epidemics of toxic tides, lifeless rivers, and dead oceans.”

The problem of excess of nutrients impacts the environment, the people and the economy.

We all know that water is essential for life, but what are the consequences of having an excess of nutrients in water?

Our water reserves are at risk of suffering irreversible and abrupt environmental changes and aquatic ecosystems are facing severe biodiversity loss.

More difficult access to clean water, higher costs for drinkable water, higher food security and health risks and diminished recreational and economic benefits from activities that depend on the conservation of water bodies. Think about fish farming, tourism and diving for instance.

Freshwater pollution by phosphorus and nitrogen costs government agencies, drinking water facilities and individual Americans at least $4.3 Bn annually (Kansas State University), while the environmental and health damages are estimated to be $157 Bn annually (Environmental Research Letters). 

What is a dead zone and how will climate change impact?

Dead zones are low-oxygen or hypoxic areas in the world’s oceans and lakes, where life is no longer possible (NOAA). 


Scientists expect that with climate change algae and dead zones will worsen. Many regions have seen an increase in heavy rains and warmer temperatures, more rain means more nitrogen runoff into rivers, fueling algae growth.

Over 500 dead zones worldwide, up from just 9 dead zones in the 1960s.

World's largest dead zone
is in the Gulf of Mexico adjacent to the Mississippi River.

More than 235,000 tons of food is lost due to hypoxia in the Gulf of Mexico.

Baltic Sea dead zone extends across 70,000 km2,  an area almost twice the size of Denmark

Almost all the major rivers in America, Europe and Asia experience dead zones.

Source: NASA Earth Observatory

Learn more about this problem 



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