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  • Aug 1, 2014
  • Updated: 5:20am

Spring in the air means algal blooms in the water

PUBLISHED : Saturday, 13 March, 2010, 12:00am
UPDATED : Saturday, 13 March, 2010, 12:00am

Spring is finally in the air, and in the Yangtze River Delta that means one thing: algal blooms.

Yes, it's nearly that time of year again, when lakes, canals and other waterways will start to burst out in a proliferation of stinking green gunge.

All environmentally conscious eyes are now on Lake Tai - the highest profile victim.

For centuries, the lake has been famed throughout China as a scenic spot. In recent years it has achieved worldwide infamy as an ecological disaster zone.

Three years ago, the water supply had to be cut off for two million residents in Wuxi , the city on its eastern shore, after levels of toxic algae reached unprecedented levels. This brought glares from the central government and a mammoth clean-up effort has been under way ever since. The scale of the task is daunting, however, and the results so far have not been overwhelming.

The huge, roughly semi-circular lake measures some 70 kilometres across, covering around 2,250 square kilometres. But the water is only an average of two metres deep, meaning its temperature quickly builds up once winter is over.

The topography of the region is unbelievably flat. Rainfall and groundwater simply have nowhere to go, so what is left of the countryside is criss-crossed with barely flowing drains and stagnant ancient canals. These are now loaded up with nitrates from sewage and agricultural run-off from fields treated with too much fertiliser. Coupled with industrial pollutants from factories in the highly developed surrounding area, the resulting soup is a near-ideal environment for algae.

Jurisdiction surrounding the lake is shared between Jiangsu and Zhejiang provinces, and the cities of Suzhou , Wuxi and Huzhou . Inter-administration collaboration has never been one of the mainland's strong points, and local environmental protection officials admit that communication and mutual trust are a problem.

Despite the talk of sorting out the problem, water tests carried out by Greenpeace last year found nitrogen levels were actually still going up, and 20 out of 25 samples were unfit for human consumption. They weren't even suitable for industrial purposes.

But local officials believe they have hit on a solution: fish.

The Taihu Lake Fisheries Management Committee is releasing silver and green carp into the lake to suck up the blue-green algae. Not too many: just 20 million, double the number introduced last year. The 8.6 million yuan (HK$9.7 million) cost of the project is being funded by a mixture of government money and public donations.

Using carp to cut down on algae is not a new idea, but it is a controversial one. Carp have a voracious appetite; Lake Tai fishery officials boasted how they each eat 50kg of algae while only gaining a single kilo of body mass. The trick is down to the fact they have no stomachs; they simply siphon the microscopic organisms through their gut in a continuous cycle.

Whether you would want to eat something that has been fattened up on toxic algae is another matter.

Recent studies have also found that the use of algae-eating carp may be based on a misconception. Just because the fish swallow a lot of algae doesn't necessarily mean they remove it from the water.

Algae are hardy types, and the US Fish and Wildlife Service has discovered that a number of species are able to pass right through carp intestines, unharmed. Other studies in the US since the late 1980s have found that carp can actually increase algae levels.

It may be a surprise to some city folk, but fish don't normally get out of the water to go to the bathroom.

Hearing about the Lake Tai carp project, a childhood nursery rhyme sprang to mind: 'There was an old woman who swallowed a fly'. Her strange choice of diet is never explained in the song, but it is hinted that it could prove fatal. To get rid of the fly the woman swallows first a spider, and then progressively larger animals to deal with the creature that came before. It all gets too much when she ultimately reaches a horse, and dies (of course).

Boosting Lake Tai's fish stocks may keep the blue-green algal bloom in check enough to stop it appearing on the national news, but it will do nothing to solve the underlying problems.

Authorities around the lake will only be able claim success when they have managed to stop the pollutants getting into the lake in the first place. Lip service and superficial measures won't achieve that; it can only be done by getting tough with farmers and industry, and by improving waste-water treatment systems. They might even have to talk to one another.

Otherwise, it's like taking painkillers to sort out a brain tumour.

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