Wetlands – the Key to a Sustainable Northern Metropolis
Dr. Michael LAU, Founder and Executive Director, Hong Kong Wetlands Conservation Association
The Northern Metropolis with a total land area of some 30,000 ha will cover the largest expense of flat, lowland areas in the Hong Kong SAR along the Shenzhen River and Deep Bay. Much of these flat areas were fertile plains and had settlements even during the Sung Dynasty, with large areas under rice cultivation. Later settlers were forced to settle near mangrove swamps at the edge of Deep Bay. They resorted to draining the marsh and turning them into brackish rice paddies, and later freshwater rice paddies. In the 1940’s more mangrove swamps along the shore were turned into tidal shrimp ponds called gei wais. In the 1970’s many of the agricultural fields and gei wais were turned into fish ponds to supply freshwater fish to the increasing urban population in Hong Kong.
The people living in the area were wise enough to take advantage of the fertile land, the ample water supply and productive estuary. The landscape was modified, towns and villages were built and the human population grew. Despite the long and profound man-made changes, nature was only modified, not destroyed. Various types of new wetlands were formed and actively managed, not only for the benefits of the people, but also helped wildlife, including migratory water birds which adapted to these man-made wetlands.
Importance of wetlands for nature conservation
The importance of these wetlands to biodiversity conservation is well known as exemplified by Mai Po & Inner Deep Bay Ramsar Site (a wetland system of international importance) especially as waterbirds habitats. There are over 600 ha of commercial fish ponds raising freshwater fish to satisfy the local demand for affordable healthy proteins. In 2021, over 2,900 tonnes of fish amounting to HK$73 million were produced. The traditionally managed fish ponds are not only an intangible cultural heritage but also provide plenty of small fish and shrimps for the egrets, herons and the endangered Black-faced Spoonbills when they are drained during fish harvest.
Under the Northern Metropolis Development Strategy, a comprehensive system of some 2,000 ha of wetlands and coastal conservation will be formed. This will include five wetlands conservation parks which will be proactively managed. The major functions of the proposed parks would be for ecological conservation, preservation and promotion of modernized aquaculture industry, scientific research, and education plus recreation opportunities. These are all worthwhile aims but the aquaculture should be expanded to cover the traditional pond fish culture which is exemplary of the wise use of wetlands. Another aim should be added with respect to climate resilience.
Function as coastal protection
The Deep Bay wetlands are of particular importance in terms of climate adaptation and reducing disaster risk. Super typhoon Hato struck Hong Kong in August 2017 and caused a tidal surge of 4.56m, i.e. 2.42m above astronomical tide. It did not cause serious flooding in the villages and residential developments in the area because of the over 1,000 ha of fish ponds and gei wais at the seaward side. These took up the storm surge water and many got flooded but then protected the homes and properties of people living further back. With climate change, sea level is rising and there is likely to be more extreme typhoons. These wetlands will play an increasingly important role in the climate resilience of the area.
Hence, when designing the future wetlands conservation parks in the Northern Metropolis, it would be opportune to consider how to retain and even increase the climate adaptation role of the wetlands, in particular prevent flooding of both existing developed areas and the new developments from heavy rains and storm surge. The hydrology and landform of the area have been modified by humans for hundreds of years. A review is needed to gather the historical changes and the most up-to-date information on the hydrology of the whole area. With this information and the knowledge and experience in restoring and managing wetlands, we can work with Nature to come up with nature-based solutions to alleviate flooding threats. These will provide benefits to both human and biodiversity.
A carbon-storage reservoir
There are also around 600ha of mangroves along the shore and lower reaches of rivers and channels in Deep Bay. They are important carbon stock. According to a recent study by the Chinese University of Hong Kong, an average of over 450 tonnes of carbon (in living and dead biomass plus sedimentary organic and inorganic carbon) can be found in one hectare of mangroves.
Although mangroves restoration is found to be the second most efficient at capturing and storing CO2 from the atmosphere, from 6.7 to 23.1 tonnes of CO2 ha-1 year-1, Deep Bay is constrained by size. WWF-Hong Kong estimated that the mangroves have advanced 15-20 m per year between 1990’s and 2000’s. This has caused a big loss of the inter-tidal mudflat which is very important feeding ground for the many migratory water birds. The potential for expanding the mangroves lies at the landward side in which mangroves were cleared decades ago for gei wais and fish ponds. In addition to the active fish ponds, there may be 200-300 ha. of inactive fish ponds in Deep Bay, some being abandoned for many years. Those along the coast or rivers can be considered for mangrove restoration which will help carbon sequestration.
Knowledge and experience transfer across the GBA
The wetlands system outlined in the Northern Metropolis is key for climate change mitigation and adaptation, disaster risk reduction, human health, food security, and support incredible biodiversity. It also has great potential to support further social and economic development. The benefits are not confined to the HKSAR. The future wetland conservation parks will provide plenty of opportunities to study and experiment wetlands restoration and management, running education and public engagement programme and how to manage visitors in biodiverse wetlands. The knowledge and experience gained should be shared with wetland practitioners across the Greater Bay Area to facilitate biodiversity conservation, climate action, education and sustainable aquaculture.
To this end, apart from climate change, biodiversity loss also poses a serious threat to Earth’s life supporting system. The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) latest assessment report showed nature has been deteriorating worldwide with extinction rate tens to hundreds of times higher than the average rate over the past 10 million years. The wetlands in Deep Bay can help combat both climate change and biodiversity loss and is key to the sustainable development of Northern Metropolis.