NATIONAL SCIENCE FOUNDATION
TOKYO REGIONAL OFFICE
The National Science Foundation's (NSF) Tokyo Regional Office periodically receives and disseminates reports on research developments in Japan that are related to the Foundation's mission. It also provide occasional reports on developments in other East Asian Countries.
These reports present information for the use of NSF program officers and policy makers; they are not statements of NSF policy.
Special Scientific Report #02-08 (September 19, 2002)
The following report was prepared by William Y.B. Chang, Senior Program Manager, East Asia and Pacific Program in the National Science Foundation's Office of International Science and Engineering. Dr. Chang was an Embassy Fellow at the American Consulate General in Shanghai, China from July 29, 2002 to October 8, 2002. Dr. Chang may be reached at wychang@nsf.gov.
Introduction
Lake Tai (Tai Hu)
Lake Tai is the third largest freshwater lake in China, covering an area of 2,350 km2 and situated in the center of the 35,000 km2 Yangtze River Delta. This delta is one of the major lake districts in China, with 189 lakes (>0.5km2) covering 3,159 km2. Much of the delta is flat, below 30 m in elevation. It currently serves more than 33 million people in the Yangtze River Delta for drinking water, flood control, shipping, waste disposal, fisheries, aquaculture, and farming.
The Yangtze River Delta is an area where the most rapid urbanization has been taking place in China. It has entered a period of accelerated urbanization, in which urban renovation, infrastructure development, and social, economic and spatial structures are experiencing great changes. Population density has been increasing greatly as the rural population enters this delta for employment. Urban spread and construction have been taking over what once were farmlands, as industrial enterprises gradually replace farming as the key sector for providing employment. Uncontrolled and untreated wastes have increased substantially in regional waterways and have been carried into the lake. Lake Tai is now facing pressures as never before, as it struggles to survive in the face of rapid regional urbanization.
Physical Environment
Lake Tai is shallow and has a mean depth of 1.86 m, a maximum depth of 2.6 m, and a volume of 4.4 x 109 m3. It is a lake with no seasonal stratification and no sustained oxygen deficit. It takes 309 days for water exchange to take place. Strong wind-driven current circulation prevails in the lake. This circulation is closely related to wind direction and seasonal monsoons. Because of this wind-driven circulation, the lake basin has a circular outline with a hard bottom and steep shore; there is no delta from the streams on the southern side of the lake, where erosion is strong. Areas with sediment deposits are usually found in the areas on the eastern and northern side of the lake, in holes or in ancient creek beds.
Major Environmental Changes
Lake Tai is a multi-use water body. The lake was once home to many species of endemic fishes, but dam construction, littoral conversion, and over-fishing since the 1950s led to the disappearance of many of these species and resulted in major changes in the ecology of the lake. Lake Tai had low nutrient inputs in the 1950s, and this continued to be the case into the 1960s. The subsequent increased use of the lake has resulted in the increased level of eutrophication and deteriorated water quality. Signs of advanced culture eutrophication have developed in recent years in many parts of the lake, especially at the northern end of the lake where the river carries large amounts of untreated effluent into the lake. Eutrophication conditions are serious in Lake Tai, particularly during the peak of the low water period in March.
Three major types of activities since 1950 have had a significant impact on the ecology of the lake: (1) ) increased anthropogenic inputs to the lake as a result of regional urbanization, (2) the construction of dams and weirs in the waterways connecting the lake, and (3) increased use of wetland and littoral zones. Untreated effluents from the watershed draining into the lake have increased substantially in recent years. The total amount of untreated effluent in 1987 was estimated at 33.83x106 tons per year. (No new figures are available.) This untreated effluent began to change the degree of eutrophication in Lake Tai rapidly, and affected the water quality of the lake. As the lake became more eutrophic, seasonal changes in nutrient concentrations also became greater. The concentrations of total inorganic nitrogen (TIN) and total phosphate (TP) change inversely with the dry and wet periods. By 1988, TIN and TP concentrations were three times higher during the low water dry period than during the high water wet period. Many areas in the lake showed the effects of advanced culture eutrophication during the dry period, while eutrophic conditions improved during the wet period. In recent years, the highest nutrient concentration has usually been found in March, before the onset of monsoon rain, while the lowest in situ concentration is in September, at the end of the monsoon period. Precipitation plays a significant role in water quality conditions in this lake.
Dams and weirs have been constructed in the waterways connecting the lake for the purpose of water resource management and flood control. While these constructions have brought benefits in terms of flood control, they have had deleterious effects on water quality, fisheries resources and aquatic life, especially with respect to those species which migrate from lakes to rivers in order to spawn. Recruitment is prevented by dam construction, and reductions in fisheries stocks have become apparent. Fish-stocking programs are now the major means of maintaining lake fisheries in Lake Tai. These programs also led to changes in trophic relationships in fish communities and significantly affected the indigenous lake species. The primary commercial species affected by the construction are grass carp, black carp, silver carp, and bighead carp, all riverine species which need to spawn in the streams and rivers, but are unable to migrate to Lake Tai for maturation. The dam constructions also reduced water exchanges and increased the frequency of water reuse; these activities directly contribute the increased level of eutrophication.
Increased use of wetland and littoral zones beginning in the 1950s has significantly reduced the lake size. The total area of the littoral zone converted to farmland and ponds between 1950 and 1980 was 160 Km2. The highest annual rate of conversion was in the 1970s. Such conversion was halted in the early 1980s when the Chinese government recognized that many small lakes were disappearing as a result of this activity, and that the floodwater holding capacity of the large lakes had been severely reduced. The conversion of lake area for rice and fish farming also had major ecological effects on this lake. The conversion reduced the area covered by aquatic vegetation, which has been important to many littoral species for spawning, foraging and protection during maturation. As a result, many species that depend on this environment have been declining, most notably fish species such as common carp and Crucian carp. With the reduction in carp species, the families of fishes which prefer open water and prey primarily on large zooplankton quickly become dominant in the lake. These opportunistic fish species are small in size (adults have an average size of 7-10 cm), with a short maturation period of about one year. There is an inverse relationship between the population of these fish species and the zooplankton population in the lake. The large increase in these fish populations has had a major effect on the zooplankton population. The depressed zooplankton population in turn results in a relatively high density in the phytoplankton population. The combined effects of littoral conversion and construction of dams and weirs have thus significantly changed the trophic dynamics and the fish population in Lake Tai over the last 40 years.
Key Research Institute: Tai Hu Laboratory for Lake Ecosystem Research
The Nanjing Institute of Geography and Limnology of the Chinese Academy of Sciences (CAS) is a key Chinese institute focusing on issues related to lake ecosystems and environmental change, and lake resource planning and utilization. The Tai Hu Laboratory for Lake Ecosystem Research of the Nanjing Institute of Geography and Limnology is a major institute focusing on issues related to Lake Tai. It was founded in 1988, and is the major field station of the Chinese Academy of Sciences for long term ecological monitoring of Lake Tai. The major focus of research carried out by the Tai Hu Laboratory includes (1) monitoring the physical, chemical, and biological processes in the lake, (2) studying the mechanisms and controls of the eutrophication process, and (3) developing integrated lake management for sustainable use of aquatic resources. The principal research scientists include the following members:
Prof. Chen Weimin, Algal and Ecosystem Dynamics
Prof. Fan Chengxin, Environmental Chemistry and Sediment Interaction
Prof. Qin D. Q, Water Resources and Environment
Prof. Yang Longyuan, Water Chemistry and Nutrient Dynamics, including
sediment-water interaction on nitrogen cycles.
Major Control Programs for Lake Tai Pollution
(in the Wuxi portion of the watershed)
1. Establish programs for controlling point source inputs into the lake.
2. Establish phosphorus control program for detergents, replacing the use of phosphorus detergents with non-phosphorus detergents.
3. Establish programs for controlling industrial effluents to the lakes.
4. Establish integrated pollution monitoring and reduction remedial programs to treat 50-75% of the total untreated effluents.
5. Establish programs to reduce the non-point sources of phosphorus and nitrogen inputs, and to reduce inputs from fertilizers and pesticides as a result of agricultural uses. The program includes the establishment of wetland and riparian zones to reduce non-point source inputs into the Lake Tai watershed.
6. Research the sedimentary ecology, in order to better implement the lake sediment dredging program.
7. Establish programs to increase water exchanges in the lake.
8. Encourage international cooperative projects to secure the needed environmental technologies for pollution control.
New National Program: the Lake Tai Restoration Program
The Chinese Ministry of Science and Technology (MOST), in cooperation with the Jiangsu Provincial Government, embarked upon an impressive Lake Tai Restoration Program in August, 2002. This is a five year, 210 million yuan (8 yuan = 1 dollar) initiative. MOST will provide 70 million yuan through its 863 New Science & Technology Project Office, while the Jiangsu Provincial Government will provide 140 million yuan in support. The project encompasses four areas: (1) removal of contaminant sediment; (2) protection and improvement of drinking water resources (guarantying that the water quality will reach level 3 (the highest water quality is level 1)); (3) control of non-point source pollution; and (4) development of an integrated lake management plan. The Restoration Program will be overseen by the Wuxi City Environmental Protection Bureau, and managed by a consulting firm (administratively related to the Wuxi City Environmental Protection Bureau (EPB)). This is the largest investment by the Chinese Government in any restoration program for Lake Tai. The notification of the Request for Proposals (RFP) for the various components of this project has been sent to many official research institutes and to the firms associated with provincial and city EPBs.
Conclusion
This is an impressive initiative for combating pollution and reducing the rate of culture eutrophication in Lake Tai. However, the source of the problems associated with this lake is the surrounding watershed. As long as untreated household and industrial wastes, uncontrolled major construction along the water’s edge, aggressive conversion of wetland and littoral zone, and uncoordinated dam and weir management continue in the surrounding watershed as a result of rapid regional urbanization, we can expect that the Chinese government will have to invest additional funds in such restoration programs at this lake.