SECTION 4 ECOLOGICAL RESOURCES CAPITAL STOCK
4.2 Existing Capital Stock and Trends
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| Inland Watercourses |
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| 4.2.1.27 |
Two categories of watercourses have been defined based on whether the watercourse has been anthropogenically modified. Natural watercourses are rivers and streams experiencing natural flow patterns in unchannelised beds and banks. Modified watercourses include channelised rivers, streams and other waterbodies, which are often without natural banks and beds, and are not subject to natural flow patterns. Rivers with substantial abstraction of water for irrigation or domestic use are also regarded as modified watercourses. Examples of modified watercourses include drainage channels, nullahs, reservoirs and rivers and streams modified for flood protection or through abstraction. Natural watercourses are likely to support higher levels of biodiversity than modified watercourses although this may vary considerably from case to case. |
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| 4.2.1.28 |
Findings from recent field surveys (ERM 1999, unpublished data) indicate that some local freshwater streams, eg the upper reaches of the stream near Tsing Tam Village in the New Territories, are rural and support a high faunal species diversity and dense riparian vegetation. The habitat provides an ideal breeding ground for such insects as dragonflies and mayflies. Despite despoilation by man, various other Hong Kong streams, eg Lam Tsuen River, supports a diverse fauna, including animals of various habits from a range of phyla. |
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| 4.2.1.29 |
The watercourse sections located at Pat Heung, Lam Tsuen and Tai Po Kau in Northeast New Territories and Tai Ho Wan in North Lantau were established through surveys to be of high* ecological value due to their relatively intact and undisturbed conditions, and high biodiversity. The protected plant species, Nepenthes mirabilis (Pitcher Plant) was recorded in a large colony near seepage immediately adjacent to the main river at Tai Ho Wan during the field visit. Sightings of the rare fish Ayu (Plecoglossus altivelis) have also been reported in the streams at Tai Ho Wan (Chong and Dudgeon 1992; Chong 1993). |
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| 4.2.1.30 |
Some of the natural watercourses (eg those at Shap Pat Heung and Pat Heung) appear to have been disturbed by some form of pollution as refuse and highly turbid waters were observed during the field surveys. Disturbance due to development was also observed in some of the surveyed habitats where channelisation or modification to stream banks to reduce flooding has occurred. |
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Mangroves, Fishponds and Gei Wais
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| 4.2.1.31 |
Mangroves are characteristic of the tropics and mostly are found on intertidal to high shore areas in the estuarine waters of sheltered bays, and seawards of salt meadows. The mild winter climate and the massive freshwater influence of the Pearl River (especially during summer) promote the development of mangrove communities in Hong Kong, particularly the western region (eg Deep Bay). The local distribution of the mangrove community is governed by the salinity regime and the availability of sheltered, depositing shores (Morton et al 1996) and mangroves have been characterised and mapped recently by Tam and Wong (1997). Apart from the largest mangroves established in Mai Po, much smaller patches of mangrove are scattered in areas such as Three Fathoms Cove and Ting Kok in Tolo Channel. Mangrove habitats are generally highly productive areas that support high biological diversity and which are known as breeding and nursery grounds for a range of fauna. They can also serve to reduce coastal erosion. |
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