Planted mangroves cap toxic oil spill

Mangroves are known to provide many ecosystem services, however there is little information on their potential role to cap and immobilise toxic levels of total petroleum hydrocarbons (TPH). Using an Australian case study, we investigated the capacity of planted mangroves (Avicennia marina) to immobilise TPH within a small embayment subjected to multiple oil spills throughout the 1980s. Mangroves were planted on the oil rich strata in 1984 to rehabilitate the site, with 2% surviving to form a dense forest. Sediment core examination down to 1 m deep, revealed mangroves have formed a thick (up to 30 cm) organic layer above the TPH spill (39.5 tonnes/hectare) accumulating on average 6.6 mm of sediments a year. TPH levels below this organic layer are extremely toxic (30,441.6 mg/kg), exceeding safety thresholds up to 220-fold. This research shows that mangroves can play a valuable role in capping highly toxic oil spill material.