| 4.3.4.1 |
Pollution of habitats and environments is undoubtedly a significant impact for ecological resources, although it is often difficult to irrefutably document a cause and effect relationship. A number of impacts are attributable to pollution (WWF 1999):
- at the community level, pollution eliminates sensitive species, changes species composition and decreases species diversity;
- at the ecosystem level, pollution can hamper the recycling of nutrients and upset the natural balance of the system; and
- effects may be long term (chronic) as is typically the case in Hong Kong, or more immediate and unpredictable in the case of accidental pollution events like oil spills.
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| 4.3.4.2 |
Habitats which have a limited capacity for self-cleansing are likely to be in the most precarious situation with regard to pollution impacts. Such habitats may include enclosed bays and harbours, watercourses with limited natural flows, or areas of airshed inversions. Further discussion of the assimilative capacity of marine waters, freshwaters and airsheds for pollutants is provided in Section 5. When considering impacts of pollution on species, it is likely that sedentary organisms, or those which are already severely restricted in their habitat range, are most vulnerable. In some cases, pollution contributes to but does not cause the ultimate impact to the species, for example when a population weakened by pollution impacts succumbs to an outbreak of disease. |
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| 4.3.4.3 |
Several local examples of the effects or suspected effects of pollution on habitats or species illustrate the range of potential concerns. Pollutant impacts to the Deep Bay mudflat fauna, the Lam Tsuen River, molluscs in Victoria Harbour, the Chinese White Dolphin and corals in Tolo Harbour are discussed below. |
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| 4.3.4.4 |
As described earlier in this section, the intertidal mudflats of inner Deep Bay host an abundant community of invertebrate organisms and thus provide an important feeding ground for many wintering birds. In recent years an increase in pollutant-tolerant capitellid polychaetes near the mouth of the Shenzhen River has been observed suggesting that the mudflat communities have been impacted by pollution from this source (McChesney 1997). In addition, a substantial reduction in the number of crabs feeding in the area's mudflats was observed in 1996 (Ng and Hopkinson 1997). Given that these mudflats are already considered to be at their carrying capacity for shorebirds (McChesney 1997), any further changes in species composition or abundance may have considerable impact on migratory waterbird populations. |
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| 4.3.4.5 |
Research on the Lam Tsuen River (Dudgeon and Corlett 1994), located west of Tai Po, has indicated that the stream invertebrate community has been altered and the normal functioning of the ecosystem has been disrupted by the input of domestic and agricultural waste. The resulting degradation of water quality has eliminated certain taxa, while concomitantly increasing the abundance of a few tolerant species and creating an environment ripe for the introduction of exotic species (see Loss of Terrestrial Habitats and Species above). |
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| 4.3.4.6 |
Another potential example of the effect of pollution on terrestrial environments concerns the pinewood nematode that causes pine wilt disease in the native pine tree species, Pinus massoniana, discussed above under Loss of Terrestrial Habitats and Species. There is evidence from Japan that air pollution can greatly increase the susceptibility of pine trees to nematode infection and thus it is possible that pollution will also be a factor in the deaths of vast numbers of pine trees in Hong Kong (Dudgeon and Corlett 1994). |
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| 4.3.4.7 |
A growing body of scientific literature concerning the effects of pollutants on the disruption of endocrine systems has resulted in increasing levels of public concern. A local example is the discovery of four species of gastropod molluscs exhibiting varying degrees of imposex development (Proud and Richardson 1997). Imposex is a condition whereby male sexual characteristics are imposed on female organisms. The organisms displaying this condition were collected from Cape d'Aguilar, Tolo Harbour and southeastern subtidal waters. |
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| 4.3.4.8 |
As discussed above (see Paragraph 4.2.2.18), the apparently increasing rate of strandings of Chinese White Dolphins may be attributable to high concentrations of organic contaminants (Parsons 1997). While data clearly show that the organic contaminant body burdens were high in stranded individuals, a recent review found that contaminant body burdens in Sousa chinensis are well within the range of values recorded from other parts of the world (ERM 2000b). It is possible that pollution may have weakened these individuals and made them more susceptible to viral or bacterial infections. |
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| 4.3.4.9 |
The effects of marine pollution on coral communities in Tolo Harbour have been documented in a series of studies (Scott and Cope 1982; Scott and Cope 1990). |
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