Green algae bloom hits coastal waters off Shandong province

CGTN reported on 16-June-2021 that an algal bloom (Enteromorpha algae) has invaded the waters of Qingdao City, on coast of China’s Shandong Province.

The explosive growth of wild green algae in the foreshores can lead to green tides, which can destroy the ecological balance of water, affect the coastal landscape and destroy the aquaculture, among other negative impacts.

The city has issued a blue warning (Level 4) for marine algae disasters and launched a four-level emergency response on Wednesday. Authorities have organized staff to clean up the sea and land to protect the coastal environment.

Photo: Algae-covered water along the coast of Qianhai.

Algal blooms are a global problem – China sees improvements

Mostly the green algae are non-toxic (unlike blue-green and some red algae). But when these green marine plants die, their decomposition consumes the oxygen in the water and creates stinking dead zones – conditions that are harmful to aquatic life. Encouragingly, recent research has found an absence of any widespread increase of such events over the early 21st century in China Seas.

One of the key factors causing these algal outbreaks is excess amounts of nitrogen and phosphorous entering coastal waters as run-off from land. Agricultural fertilizers are the main source of these excess nutrients.

Large algal “blooms” are an annual phenomenon offshore for China, but 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 kilometres of coastal waters.

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.

More than 500 major algal bloom regions have been mapped by scientists – from the East China Sea to the Baltic and the Black Sea to the Gulf of Mexico. Since 1950, their extent in coastal waters has increased tenfold.

Excess nitrogen fertiliser in the ocean and other aquatic environments has become a global epidemic. Worldwide, some 120 million tonnes of synthetic nitrogen – fixed from the atmosphere by the Haber-Bosch process – 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.

The UN Environment Program has launched a global strategy for reducing nitrogen waste and environmental pollution, known as the International Nitrogen Management System. It is set to report in late 2021. Among other things it is likely to call for more treatment of human sewage, more recycling of manure, reductions in food waste and a major assault of nitrogen efficiency on farms.

The last of these will involve a combination of breeding strains of major crops such as rice and wheat that use nitrogen more efficiently and replacing the current scattergun approach to dosing fields with fertiliser. Instead, the world needs more precision agriculture that delivers fertiliser at a time and place where the plants need sustenance. This involves both in-field monitoring of crops so farmers know exactly when and how much fertiliser to apply, and greater precision in placing that fertiliser close to crop roots.

China’s government has recognised the urgency of reducing over application of fertiliser, particularly nitrogen. At the end of 2017, scientists calculated that a government target to halt further growth in the use of fertiliser on Chinese fields by 2020 – through more targeted use of more effective fertilisers – had been achieved three years early. Meanwhile efforts to curb emissions of nitrogen and phosphorus into vulnerable watersheds from large fixed sources were announced in April.

Over the past few decades, coastal waters of China Seas have experienced a significant increase in the occurrence of major algal bloom events, in common with the vast majority of coastal waters of the world.

Encouragingly, research reported in 2019 ( Marine Pollution Bulletin, Volume 139, February 2019) found an absence of the widespread increase over the early 21st century in China Seas.

The scientists found that “both frequency and coverage area of annual algal bloom events have decreased at statistically significant rates for the 2000–2017 period. Despite the multiple factors determining the outbreak of algal bloom events, the improvement of water quality in the marginal sea off China and changes in the sea surface temperature in the early 21st century may play an important role in the decrease in the algal bloom events.”


CGTN, Enteromorpha algae invades waters off E China’s Qingdao City, 16 June 2021.

Marine Pollution Bulletin, Significantly decreasing harmful algal blooms in China seas in the early 21st century, 2019.

China Dialogue Ocean, Algal blooms endangering China’s seas, June 2018.

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