Estuary Processes and Managment - River Dynamics and Integrated River Management - page 532

Pearl River Estuary, with 418 species of zooplankton, 515 species of benthos and more than 302 species
of main fishes (Chen et al., 2005). Similar bio-diversity is found in the wetlands in Guangxi Zhuang
Autonomous Region (Hong, 1992) and Hainan Province (Zou et al., 1999). In particular, mangrove wetlands
are of particular interest because they are the most productive ecosystems along the South China's coastlines.
A healthy mangrove wetland is helpful to maintain coastal food webs and provide habitats for various
living creatures. For example, the Mai Po mangrove wetland of Hong Kong (Fig. 8.75, 8.76) was listed as a
'Wetland of International Importance Especially as Waterfowl Habitat' under the RAMSAR Convention
in September 1995, serving as an important area for internationally important numbers of wintering and
migrating water birds. Over 200 bird species can be found in the Mai Po Nature Reserve; about 13 globally
threatened species of birds and 17 species of invertebrates new to science are found in this site.
Fig. 8.76 Waterbirds (Black-faced Spoonbill and Egret) in Mai Po Marshes, Hong Kong (See color figure at the
end of this topic)
However, under increasing pollution threats and other anthropogenic influences (e.g., wastewater
discharges, change of hydrology, coastal reclamation, sand mining), mangroves are among the most threatened
wetlands with global loss exceeding 35% (mangrove ecosystems covered up to 75% of the tropical coastlines
on earth in the 1990s). For instance, Deep Bay at the mouth of the Pearl River delta had the sixth largest
mangrove forest in China (Fig. 8.75). However, since the 1980s, due to rapid industrialization and
urbanization, mangroves around Deep Bay including Mai Po in Hong Kong and Futian in Shenzhen have
suffered from excessive discharge of untreated domestic, livestock and industrial wastewater. At present,
the mangrove in Shenzhen is the only one located in the heart of a modern city in China.
8.6.2 Wetland Evolution, Degradation and Restoration
8.6.2.1 Costal Wetland Evolution
Coastal wetland evolution is closely related to the dynamic interplay between natural erosion and accretion.
The erosion factors are mainly from sea water, and the accretion factors are mainly from fresh water and
sediment transportation by rivers. Wetlands will enlarge seaward if fresh water and sediment overwhelm
erosion effects, and consequently a strong salinity gradient could be formed from fresh water at the
landward end toward the coastal waters. For instance, the Yellow River is the second-longest river in