Dead Zones – China’s nutrient crisis

Like many places around the world, China is struggling with the impact from excessive use of fertilisers on agricultural land. Fertiliser contains nutrients that assist in helping agriculture crops grow, however a large proportion of the nutrient ends up being washed into waterways such as rivers and lakes. Generally, rivers discharge nutrients (phosphorus and nitrogen) into the sea which in turn produce massive algal blooms along the coast.

A recent article was published at https://chinadialogueocean.net/2959-algal-blooms-are-starving-chinas-seas-of-oxygen/?mc_cid=317808eeea&mc_eid=432e6e4ac6 and highlights the problems facing China. Apparently large quantities of nutrients are being washed off the coast of China and create dead zones where, reportedly, ocean life can no longer survive.

Dead zones are created when algae dies and decompose. They deplete the amount of oxygen in coastal waters and create putrid areas where aquatic organisms struggle to survive.

“Beside the algal blooms of the Yellow Sea, another recurring Chinese ocean dead zone is off the Changjiang (Yangtze) estuary in the East China Sea. In 2013, the oxygen loss was estimated at more than five million tonnes. Scientists have linked it to the loss of fish in the East China Sea, and the failure of bans on trawling to allow fish stocks to recover.”

Thousands of tonnes of algae, washed up on beaches, have been cleared by bulldozers. However a large proportion of algae remain in the coastal zones.

“The giant algal “blooms” are an annual phenomenon offshore, though they do not always reach beaches. The largest in the Yellow Sea so far have occurred in 2013 and 2017, when they covered almost 30,000 square kilometers of coastal waters (a quarter of the size of North Korea).”

Fertilisers are not the only source of nutrients entering the waters; however a large percentage is from agricultural runoff.

“In China’s national effort to feed more than 1.3 billion people, its farmers pour more fertiliser onto every hectare of land than farmers anywhere else – more than 200 kilograms. That is twice as much as their European compatriots, for instance, and more than 50 times the application rates in China in the early 1960s.”

The article comments that the problem in China is not isolated.

“Worldwide, some 120 million tonnes of synthetic nitrogen – fixed from the atmosphere is used on the world’s farms each year. That is twice the amount coming from natural sources such as animal manure, crop residues or nitrogen fixing plants.”

“More than half of the synthetic fertiliser ever applied to the world’s fields has been applied in the past 30 years. But of the 120 million tonnes applied to fields, only about 50 million tonnes reaches plants. The rest runs off into the wider environment and most eventually lands up in the ocean.”

Phoslock Environmental Technologies (PET)  is working with our Chinese partners to effectively address a number of issues caused by the excessive use of nutrients (nitrogen and phosphorus). A number of chemical and engineering interventions have been undertaken by PET in China with results showing effective nutrient and algal reduction.