Contamination of mangrove swamps, China

Mangrove sample locations

Mangrove forests, the intertidal wetlands of the tropics and subtropics, are key ecological habitats that link terrestrial (land) and marine (sea) environments. Mangrove forests and adjacent mudflats are increasingly impacted by urban and industrial development in the tropical coastal zone. They suffer pollution from multiple sources including but not limited to municipal waste, aquaculture, mariculture and shipping as well as onshore industries and run-off from urban centres.

Mangroves in China

BGS coastal geochemists undertook a screening survey of selected persistent organic pollutants (POPs) in mangrove surface sediments from mainland China in the south-west (Beihai, Zhanjian) south (Shenzhen) and south-eastern coast (Xiamen) as well as Hainan Island (see map below).

Research aims

The primary aims of this study were:

  • to ascertain whether mangrove sediments in close proximity to urban industrial areas have higher concentrations of organic pollutants than those in rural areas
  • to identify the source of pollution
  • to establish the natural background of biogenically-sourced (from plants or animals) PAHs in mangroves

Results

To the sampling sites

In combination, the total non-volatile hydrocarbon, PAH, PCB as well as mercury in the surface sediments from nine mangrove swamps indicate low pollution levels.

The highest pollutant levels were detected from sites in Shenzhen and Xiamen confirming the hypothesis that mangroves in close proximity to urban, industrial areas receive greater hydrocarbon sourced pollution than those adjacent to rural, non-urbanized areas such as those on the Island of Hainan.

Results suggested combustion-related PAH sources for the Xiamen and Shenzhen mangroves.

None of the sediments analysed in this study exceeded published threshold effects concentration levels, suggesting that they would not harm sensitive biota or humans; although the possibility that certain lipophilic pollutants could accumulate via biomagnification at higher trophic levels cannot be entirely discounted.

The low amounts of organic pollutants from anthropogenic (human) activities from Haikou, Wengchang, Beihia and Zhanjiang mangroves showed what is most likely a combination of natural biogenic (from plants or animals) and aeolian transported (wind-blown) background pollution. The evidence for this is large amounts of phenanthrene, perylene and naphthalene relative to other PAH compounds.

This observation supports recently developed theories on the source and alteration of PAH in terrestrial soils from tropical and subtropical zones.

Reference

Vane, C H, Harrison, I, Kim, A, Moss-Hayes, V, Vickers, B and Hong, K. 2009. Organic and metal contamination in surface mangrove sediments of South China. Marine Pollution Bulletin, 58 (1). pp134–144.

Contact

Contact Dr Christopher Vane for more information.