Let’s bring the rivers alive
28 Dec 2018
In Hong Kong, there are hundreds of rivers, streams and open nullahs. They have different roles including irrigation, prevention of flood, preservation of aquatic life and the passage of storm water. Thus, polluted waterways may cause a number of different kinds of ecological issues.
The Environmental Protection Department (EPD) has run a comprehensive river water quality monitoring programme in Hong Kong since 1986, which covers 82 stations at 30 main rivers and streams running through urban areas. According to River Water Quality in Hong Kong 2017, 87% of the river monitoring stations were graded “good” or “excellent”. Although the majority of the monitoring stations were awarded high grades, some stations in the Northern and Western New Territories were graded "fair" or even "bad".
Speaking about water quality in Hong Kong, Dr Karen Chow, a lecturer in the Department of Geography, says: "Over the past two decades, the water quality of watercourses has significantly improved due to the relocation of local production industries to the Mainland and the implementation of different pollution control measures by the Government. However, the water quality of some watercourses, especially those located in the Northwest New Territories such as Kam Tin River, Yuen Long Creek and Tuen Mun River, is not good enough. It is probably the results of discharge from unsewered village houses, small industries and livestock farms as well as some human activities including farming, and illegal discharge of polluted water."
Dr Chow says that bacteria, excess nutrients and toxic chemicals such as metals are common pollutants in Hong Kong watercourses. The harmful levels are determined by the type and concentration of the pollutants. Excess nutrients, including nitrogen and phosphorus in water, cause algae populations to grow rapidly and block sunlight. As a result, they can affect vegetation along watercourses and thus the food chain.
In addition, some studies have found that pollutants such as cadmium will be accumulated in fish body and may also have an adverse effect on their growth. Once pollution affects feeding, shelter and reproduction of animals, it may jeopardize the well-being of species and may even harm the food chain. On the other hand, if we use polluted water for agriculture and fish farming, our food may also become polluted. In addition, contacting with polluted water may also bring along potential health risks to human beings.
Dr Chow says: "The Government has implemented different measures to improve water quality over the years. In addition to bio-remediation and dredging, constructed wetlands have been shown to be effective worldwide in removing a wide range of pollutants." Dr. Chow and Prof. Wong Ming-hung, Emeritus Professor in Hong Kong Baptist University and Advisor (Environmental Science) in The Education University of Hong Kong, are now conducting a research study on “Selection of wetland plants for wastewater treatment of persistent toxic substances by constructed wetlands in Hong Kong” supported by the Environment and Conservation Fund.
Constructed wetlands are an artificial system using soil, vegetation and microorganisms to treat domestic and municipal wastewater. When wastewater flows through the system, suspended solids and phosphorous are retained by the filtration media, such as gravels and oyster shells. To further purify wastewater, vegetation and reeds provide roots, stems, and leaves, which can absorb pollutants such as nutrients, and organics. Apart from wastewater treatment, wetlands can also attract and provide food and shelter for wildlife such as birds, insects and frogs. As a result, this can enrich the biodiversity and develop sustainable ecosystems, as well as serve the purpose of environmental education.