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August 10, 2011

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Home » Metro » Environment

Rotting weed problem for city

THE city's water authority has managed to clear a duckweed outbreak on an upstream portion of the Huangpu River but has a new headache: how to deal with the tens of thousands of tons of plants now rotting in the hot sun.

The river in Jinshan District was facing the most serious duckweed outbreak in a decade, and workers controlled it by pulling out more than 55,000 tons of the plant, said a senior official of the Jinshan District Water Authority surnamed Yu.

The plant feeds off nitrogen and phosphorous from sewage and river runoff. As the plant dies and rots, it absorbs oxygen, killing fish.

The authority has set up 14 fences along the river to stop the plants from drifting downriver into the downtown areas, Yu told Shanghai Daily.

However, the authority found it could neither burn nor bury all of the salvaged plants because of the sheer quantity. As a result, large amounts of duckweed are being piled along the river in the district. Some has rotted and begun to smell, prompting many residents living nearby to complain to the authority, Yu said.

"The authority can ensure the low stream of the river will not be affected, but is worried about the increasing number of weeds being salvaged from the river," he said.

In previous years, when the outbreak was less severe, workers gave some plants to local farmers to feed ducks and the city's public sanitation authorities would bury the rest in local landfills, said an official with the Shanghai Greenery and Public Sanitation Administrative Bureau. Because of the volume this year, the bureau may buy farmland from farmers living along the river to bury the duckweed right after salvaging it from river.

The serious drought along the middle and lower beach of the Yangtze River, combined with hot sunshine in the first half of the year, is the main cause of the outbreak, Yu said.

More than 70 percent of the plants come from neighboring Zhejiang Province.

After the duckweed, an outbreak of water hyacinth is expected in the Huangpu River in October, Yu said.


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