Environmental Engineering Reference
In-Depth Information
nitrogen cycle, and the microbial activities in mangrove sediments can increase as a result of the addition
of nutrient-rich sewage. With continuous losses of nitrogen from the system, mangrove ecosystems are
maintained as a sustainable wastewater treatment facility without saturation. The Futian field study also
showed that the species diversity and abundance of macro-algae and benthic invertebrates colonizing the
mangrove floor were not affected by sewage discharge (Tam, 2006); only the surface sediments in the
first two meters from the discharged points had 20% increases in total Kjeldahl nitrogen and 38% increases
in phosphorus concentrations, while no significant change in nutrient concentrations was found in other
sediments.
Fig. 8.75 Mangrove swamps in Hong Kong, Macau, Taiwan and Mainland China (from Tam, 2006)
Although the mangrove ecosystem has a high potential to act as a sink for organic pollutants, the long
term capacity to assimilate pollutants depends on both the hydraulic and organic loading. For example,
the Futian experiments involved application of sewage onto a 180 m × 10 m mangrove strip three times a
week, and only 20 m 3 for each discharge—to allow the wastewater to be soaked into the sediment within 50 m
of the discharge points. The dynamic nature of mangrove ecosystems is also strongly influenced by factors
like tidal flow, wave action, climate, salinity, redox potential, and various biotic components—which may
cause the retained pollutants to be re-suspended back to the aquatic environment. In general, coastal wetlands
may offer practical and sustainable alternatives to wastewater treatment mainly for relatively small coastal
communities that can provide the required mangrove area.
8.6.1.3 Bio-Diversity Conservation
Wetlands exhibit different characteristics that are influenced by freshwater flow, water level change, waves
and tidal flow, salinity intrusion, sediment transport and the general climate. In general the rich variety of
natural hydrologic and geologic environments lead to high biological diversity. Apart from serving as
spawning and rearing areas and shelter for fish, wetlands support the food chain for the feeding, nesting and
substrate of mammals, reptiles, amphibians and birds, including those endangered and threatened species.
Healthy wetlands are of great importance for biodiversity conservation of coastal ecosystems—i.e.,
maintenance of the rich and balanced variety of plants, animals and microbes.
There are more than 300 species of birds in China's wetlands, accounting for one-third of the total
number of birds found in China (Lu and Wang, 1995). The major wetlands in South China include the
Search WWH ::




Custom Search