Java’s protective mangroves smothered in plastic waste

A natural ally against coastal erosion in Java is slowly suffocating in plastic waste. The mangrove forests on the Indonesian island’s north coast cannot be restored without better waste management, warns new research.

On the forest floor of mangroves along the north coast of Java, it is hard to find a square metre without plastic. There is an average of 27 plastic items per square metre, says new research.

NIOZ researcher Celine Van Bijsterveld, who has monitored the accumulation of plastic waste in Indonesian mangroves over years, explained that mangroves – which form a natural coastal defence by breaking waves – also form a perfect plastic trap.

She said: “For the mangrove tree, this trap can become quite lethal. The most common mangrove tree on Java’s coast, the grey mangrove, has upward-growing roots to get oxygen flowing during high tide. When plastic waste accumulates in these forests, the snorkels are blocked. In areas completely covered by plastic, trees suffocate.”

The problem isn’t only the plastic on the surface, says the statement. The team found plastics buried as deep as 35 cm inside the sediment. Plastic stuck in these upper layers further decreases the trees’ access to oxygen.

Although the roots change course when they are obstructed, the prospect of survival gets much gloomier once the threshold of 75% is reached and plastic in the sediment pushes it towards 100%, writes the statement.

The Indonesian government is investing in mangrove restoration in an attempt to recreate a green-belt along the coast, but restoration is slow and existing forests are stressed, says the research.

Van Bijsterveldt warns: “Replanting mangroves without tackling the plastic problem is like trying to try to empty the ocean with a thimble. Successful restoration needs to go hand in hand with sustainable waste management.”

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