urban jungle

PUBLISHED : Friday, 02 March, 2007, 12:00am
UPDATED : Friday, 02 March, 2007, 12:00am

This week: Pollution in Deep Bay

A report by WWF on pollution in Deep Bay and its threat to Mai Po and the Inner Deep Bay makes disturbing reading. The Mai Po marshes in Yuen Long are an important site for migratory birds.

In winter, about 70,000 water birds transit through the area, including some rare species.

Under the management of WWF and the Agriculture, Fisheries and Conservation Department, the area is probably the best bird-watching spot in Asia. Not to mention that the government has spent millions of dollars to promote the area for ecotourism.

It is a commendable effort, not only to stimulate the economy but also to educate the public about the natural beauty of our own backyard - but it's only going to be a tourism site if it remains pristine and full of life.

With so many birds that visit the area daily, especially in winter, the area's ecosystem is complex, very rich and diverse. The food chain is delicate and a problem anywhere along its links can have major ramifications for complex predators.

The WWF report is concerned about the deterioration of water quality in the area despite a 40 per cent fall in effluent discharge since 1996.

This change has coincided with a fall in the numbers of birds, such as the rare and vulnerable Saunder's gull that feed on the more delicate organisms, which are sensitive to pollution, like small crabs. There is also a parallel increase in the number of birds that feed on tougher organisms that are more tolerant to pollution.

There has been a deterioration in all the parameters that alter water quality, such as a reduction in the level of dissolved oxygen, which directly affects both micro and macro marine life, and extremely high nutrient content, which causes eutrophication, a process by which the wildlife diversity in an area is reduced by slow-growing species of plants being overtaken by rapid-growing species that use up excess nutrients.

These high nutrient levels also promote growth of unwanted bacteria that affect marine life at all levels and can sometimes lead to toxic algal blooms that would be devastating if they were to occur in the marshes.

Deep Bay has some of the most polluted waters of Hong Kong and the causes are complex. One of the main factors is the development of Tin Shui Wai that led to the destruction of parts of the wetland.

With 4 million people living in both the Hong Kong and Shenzhen Deep Bay catchment areas, the monitoring and control of effluent discharge is crucial to the area's survival.

The other major source of pollution is agricultural waste. Although there is a legal requirement for farms to process their waste, many farms break the law as there is a lack of enforcement and penalties for those caught are low.

Ironically, the Shenzhen government has moved livestock farms from the catchment area, so they do not contribute to the pollution. Heavy metals due to industrial waste and run-off from roads between Hong Kong and Shenzhen contribute to the toxins that are killing the bay.

A feature of the Deep Bay wetland area is its tidal mud flats, where birds feed when the tide recedes. The tides bring in micro life from the sea and stimulate the ecosystem in the mud, which feeds the birds. It has been found that the mud flats are rising due to sedimentation and this means the birds have increasingly smaller areas to feed from. The rising of the mud flats could be due partly to reclamation projects on the Shenzhen side.

What is happening in Mai Po concerns me deeply. It reminds me of what happened to another spectacle back in Australia on an island off the coast of Victoria called Phillip Island. Every evening on the island massive flocks of fairy penguins, numbering in the thousands, would waddle up the beach to their homes on the shore.

Like Mai Po, it is a major ecotourism attraction, but the last time I went, about six years ago, the numbers of penguins had visibly dropped, with only small groups of the birds.

It's still a sight to see but it's not what it use to be and I hope that conservation efforts in Mai Po will be supported by the public so that it can remain the spectacle it is today and not a memory of what it was like yesterday.