River Ecology

Apart from the main stream originating from Kau Keng Shan, all tributaries of Tuen Mun River are very short. In addition, the headwater areas are seriously weathered and perennial rivers only form in the lower elevations because there is little soil to act as a sponge. The river ecosystems are more susceptible to interference and destruction.

River habitats of Tuen Mun River can be broadly divided into several sections: the upstream outside the lowlands, the downstream in Tuen Mun New Town and the lowland rural areas, and the "river" created by reclamation of the original bay. The upper part of the main stream is within Country Park, while most of the other upstream tributaries are flowing through rural areas or urban fringe, affecting the water quality and river ecology. Most upstream still retain their natural status, apart from a few reaches that have been channelized. Most of the downstream have been channelized; some sections have even been converted into underground drains. Originally natural former estuarine, coastal landscapes and the ecosystem, have been destroyed beyond recognition.



Downstream of Tuen Mun River is destroyed beyond recognition

Upper course

Clumps of Chinese Lipocarpha (Lipocarpha chinensis) and Six-angular Pipewort (Eriocaulon sexangulare) grow in numerous channels along the valley, there's a small population of insectivorous Spoon Leaf Sundew (Drosera spathulata), Blue Bladderwort (Utricularia caerulea) and Small Yellow Bladderwort (Utricularia bifida) grow on stones along the river bank, Pitcher Plant (Nepenthes mirabilis), which also feeds on insects, can also be found among rock crevices on the banks. In slow-flowing water, one can occasionally spot clusters of blue green algae. Begonia hongkongensis can be found in the valley of Kau Keng Shan.

In the upper course of the main stream, Flat-headed Loach (Oreonectes platycephalus), Rhinogobius duospilus and Bee Shrimp (Caridina sp.) can be found. In addition, sometimes one can spot Backswimmers and Water Skater (Limnogonus fossarum) on the water surface. On the banks of river besides villages, there are dragonflies including Common Red Skimmer (Orthetrum pruinosum), Common Blue Skimmer and Orange-faced Sprite (Pseudagrion rubriceps). Chinese Pond Heron (Ardeola bacchus), Grey Wagtail (Motacilla cinerea) and White Wagtail (Motacilla alba) love to forage along catchwater and channelised rivers besides villages.


Orange-faced Sprite (Pseudagrion rubriceps)

Blue Bladderwort(Utricularia caerulea

 


Rhinogobius duospilus

 


Backswimmer

Lower course

Primrose Willow (Ludwigia octovalvis), Hairy Knotweed (Polygonum barbatum), Umbrella Plant (Cyperus flabelliformis), Common Day-flower (Commelina communis) and Mile-a-minute Weed (Mikania micrantha) grow in the lower channelised rivers at the north of Tuen Mun River basin. Shade trees were planted by the pedestrian walkways along the riverbanks of Tuen Mun River Channel, including Queen Crape Myrtle (Lagerstroemia speciosa), Camel's Foot Tree (Bauhinia variegate), Lebbeck Tree (Albizia lebbeck) and Chinese Banyan (Ficus microcarpa). These trees are mostly for ornamental use, with little connection to the river ecology.

Among animals, Mosquito Fish (Gambusia affinis) and Apple Snail (Pomacea canaliculata), both exotic species, can be found in northern part of downstream. In polluted stretches of slow flowing water, Midge (Chironomous sp.) larvae abound. Gunther's Frog (Rana guentheri) can be found in the streams near the villages, and Yellow Featherlegs (Copera marginipes), Wandering Glider (Pantala flavescens), and Common Blue Skimmer (Orthetrum glaucum) are frequently spotted on aquatic plants.

Rock oysters and barnacles are plentiful in the tidal areas flanking the river mouth, which is adjacent to the typhoon shelter. Fiddler Crabs (Uca arcuata) and Sesarmine Crabs (Perisesarma bidens) can be found on riverbanks in these tidal areas. Mullet (Liza sp.), Spottail Needlefish (Tylosurus strongylurus), Rabbit Fish (Siganus oramin), and Mozambique Tilapia (Oreochromis mossambicus), can be spotted in Tuen Mun River. Waterbirds like Great Egret (Egretta alba), Little Egret (Egretta garzetta), Chinese Pond Heron (Ardeola bacchus), Common Kingfisher (Alcedo atthis) might also be seen foraging near the river.


Primrose Willow(Ludwigia octovalvis

 


Apple Snail (Pomacea canaliculata

 


Barnacles

 


Little Egret (Egretta garzetta

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