Natural recolonization of a chronically oil-polluted mangrove soil after a de-pollution process

The authors discuss the results of a restoration operation at a mangrove site polluted by hydrocarbons. This site is a swamp usually planted with Avicennia sp. mangroves but which was totally destroyed after chronic oil spillings. A special programme has made it possible to prevent pollution of the site, and to bring clean marine water, thereby assisting its natural cleansing. The natural recolonization of the site by small Avicennia plants began rapidly (3 months) once the restoration equipment was operational. The density and the growth of these small plants seemed to be more influenced by the substrate nature than by the hydrocarbon concentrations in the soil. The results showed that fresh oil was the real cause of the mortality of small plants rather than the concentrations of a soil-aged product. In the case of chronic pollution of a site, to stop the regular arrival of a pollutant can be sufficient in itself to restore a site, and it is not necessary to consider costly cleansing and restoration operations.