Managing the environment at Three Gorges16 February 2006
Dai Huichao and Wang Rushu discuss the effects of the Three Gorges project on the regional ecology and environment, and investigate impacts on water quality, rare species and landscape and cultural heritage
The Three Gorges project can play a key role in improving the ecological and atmospheric environment of the Yangtze basin. However, reservoir inundation and project construction will also bring about adverse impacts on the ecological environment. As a result, systematic studies of these impacts were conducted during verification of the scheme and at different phases of the project design.
Since the 1950's, the State Science and Technology Commission, the Chinese Academy of Sciences, the State Planning Commission, the Yangtze Valley Water Resources Protection Bureau and the National Environment Protection Agency have successively carried out monographic studies on ecological and environmental factors related to Three Gorges, such as: reservoir inundation and resettlement; sedimentation; seismology; reservoir bank stability; underground water level; soil erosion; forest vegetation; rare flora and economic flora; wild animal and rare animal; public health; schistosomiasis and epidemic diseases. These studies led to the ‘Report on the Key points of the Yangtze Valley Planning and the Preliminary Design of the Three Gorges Project’, ‘Report on the Environment Impacts of Construction of the Three Gorges Project’ and ‘The Environment Impact Report for the Three Gorges Project’.
In June 1986, a panel consisting of 55 experts from the fields of ecology, environment and water conservancy examined and reviewed the available findings and conducted supplementary investigation and verification on specific subjects. In January 1988, the ‘Verification Report on the Environmental Impact of Three Gorges Project and its Countermeasures’ was completed. In February 1992, the ‘Environmental Impact Statement for the Three Gorges Project on the Yangtze River’ was officially approved by the National Environment Protection Agency.
In the reports mentioned above, ecological and environmental issues concerning Three Gorges have been systematically investigated and verified; with countermeasures proposed to deal with any adverse impacts. The studies found that the positive impacts of Three Gorges on the ecological environment outweigh the negative, and that most of the negative impacts could be avoided or alleviated if necessary measures are implemented.
Regional rare species
Of the rare plants found in the Three Gorges area, 47 species were listed as Chinese protected rare and vanishing plants. Four of these were of first class protection, 21 were of second class protection and 22 were of third class protection. The Three Gorges project has had an effect on rare and vanishing plants but will not lead to their extinction. The original growing areas of some species will be submerged and the quantities of individual plants will be affected. For example, Myricaria laxiflora will be totally submerged and Adiantum reniforme will be partially submerged.
According to the National Key Protected Wild Animal List, of the various vertebrate species living on land in the project area, four species were of first class protection, and 22 species were of second class protection. After the start of the Three Gorges project, the horizontal ranges of distribution of rare animal species were reduced, the vertical ranges of distribution moved higher and the species density decreased. In the areas affected by the project, there were six rare water-habitating animal species, consisting of Chinese River dolphins, Chinese paddlefishes, Chinese sturgeons and Yangtze sturgeons that belong to first class protection animals, and Finless porpoises and Chinese suckers that are second class national protection animals. After the construction of the Three Gorges, the distribution area of Chinese River dolphins would be reduced by 155km, the probability of accidental death would increase, and the decrease of fish resources below the dam would negatively affect food provision.
Chinese sturgeons lay their eggs upstream and swim back; however, as the construction of Gezhou dam blocked their way back, measures such as artificial breeding and release have been taken to protect them, and a new spawning field downstream of Gezhou dam was adopted. After construction of Three Gorges, the spawning field area of Chinese sturgeons has been reduced, and the development of fish eggs will be adversely affected. With the increase of regular boats, parent Chinese sturgeons could also be further disturbed by the noises, and the chance of being hurt by boat screws will increase.
The construction of Three Gorges will not affect the spawn field of Yangtze sturgeons; or Chinese sucker species living in the upper reaches. It would be difficult to keep stable numbers of species living in the middle and the lower reaches, however, due to the lack of replenishment of young Chinese suckers from upstream.
In order to protect the biodiversity of the Yangtze, a series of species resources protection measures have been taken by the Three Gorges project. Starting from 1996, research work on the inspection and protection of the species has been carried out by the land plant observation and experimentation station, the key station for land plant and animal inspection, as well as for water animal floating inspection and the special fish experimentation station.
Many natural reserve areas have been built or are being built. For example, three natural reserve areas (Yichang Dalaoling national forest park core reserve area, Wushan miniature Three Gorges landscape ecological natural reserve area and Xingshan Longmenhe ever-green arbor forest natural reserve area), three rare plant reserve areas (natural reserve areas of Myricaria laxiflora, Adiantum reniforme and Chuanminshen), and four rare water animal reserve areas (Yangtze upstream rare and special fishes natural reserve area, Yangtze Hubei Yichang Chinese sturgeons natural reserve area, Yangtze Swan Land and Newluojiangduan Chinese River Dolphin national natural reserve) have been established. Also built are one rare water animal semi-natural reserve (below dam rare water animal and their ecology), three rare water animal artificial breeding and release stations (Yangtze upstream Yangtze sturgeons and Chinese suckers artificial breeding and release station, Yangtze middle stream Chinese paddlefishes and Chinese suckers artificial breeding and release station, Yichang Gezhou Dam Chinese sturgeons artificial breeding and release station), Yangtze middle and upstream rare and special fishes protection and breeding centre (under construction), and new research projects of species protection measures.
Migration measures have reserved 35 species of rare and vanishing plants distributed in the reservoir area, and nine species of rare and vanishing plant distributed in other areas. Research has also been carried out to breed and release Myricaria laxiflora, Adiantum reniforme and Chuanminshen artificially on a large scale; many species of rare and vanishing plants have been successfully bred. From 1995 to 1998, research and protection work on 44 old trees that would be submerged first in the Three Gorges area in Hubei province has been completed; and research and protection work for rare and special fishes such as Chinese sturgeons has continued over the past few years.
Up to the end of 2003, five million artificially bred young Chinese sturgeons had been released into the Yangtze river. According to statistics from marker release sampling, survival rate is around 1%. Among the population of young sturgeons in the Yangtze river, around 10% of them are artificially released Chinese sturgeons. Work in these areas was mainly carried out by the following institutes: Chinese Academy of Science Institute of Hydrobiology; Institute of Oceanograph; Institute of Botany and Chengdu Institute of Mountain Hazards and Environment; office of Yangtze River Fishery Resources Management Committee; and National Forestry Bureau Main Station of Ecological Environment Monitor.
The quality of river water can be affected by a number of natural and artificial factors. Although the construction of water resources projects will not produce any pollutants, it will change the hydrological regime and hydraulic characteristics of the river, leading to an indirect impact on water quality. The extent of the impact varies with the scale and type of reservoir, the location of dam and the reservoir operation regimes. The main impacts of Three Gorges construction on water quality in the reservoir and downstream of the dam are as follows:
Water quality in the reservoir
Presently, the river water quality in the reservoir region is generally in good condition. However, due to effluents of the industrial wastewater and sewage discharged from the cities and counties, pollution belts have formed along the river in some reaches.
After the Three Gorges reservoir is formed, pollutant concentration will increase in the water body near the shoreline due to the decrease of water flow velocity, and, as a result, the turbulent diffusion ability of the water body. It is expected that the near shoreline pollution belt will develop to a certain extent, particularly at the reaches of Chongqing and Wanxian cities, where the amount of discharged pollutants are the highest in the region.
Biochemical oxygen demand (BOD)
After impoundment, flow velocity will decrease, meaning water will stay in the reservoir for a longer period. This will benefit the degradation and purification of degradable organic pollutants. The degradation amount of BOD is expected to be more than that under natural conditions. Conversely, the decrease of the flow velocity will weaken the re-oxygenation ability, thus diminishing the assimilative capacity for BOD. Therefore, whether the impact of the reservoir impoundment is beneficial or adverse to the degradation of BOD will depend on the role of the factors that control the BOD processes. Presently the inflow of BOD loading is far below the predicted future reservoir's assimilative capacity. Therefore, it is expected that with good management and control measures, the water quality in the reservoir will not significantly deteriorate in the near future.
After impoundment, hazard substance and nutrients will be leached and released from soil into the water, which will degrade the reservoir water quality. According to field observation at existing reservoirs, when the ratio of the inundation area to the annual runoff is small, the inundation of land is unlikely to have significant impact on the deterioration of water quality. In the case of Three Gorges, where the ratio is rather small, the possibility of land inundation aggravating water pollution will be relatively small too. However, in some tributaries and bays where the ratio is large, land inundation impact on water quality could be significant.
It should be noted that inundation impact on water quality mainly occurs at the early stage of reservoir impoundment. The impact is temporary and short-term.
It is expected that concentrations of suspended solids and heavy metals in the reservoir water body will decrease significantly due to sediment deposition. The gross concentration of heavy metals in water phase will decrease by about 63-70% while the contents of pollutants and heavy metals in the reservoir sediments are expected to increase. The absorption capacity of the suspended solids in the reservoir is very large, meaning that heavy metals in sediments are unlikely to be released.
After the construction of the dam, some nutrients such as nitrogen, phosphorus and potassium will be intercepted in the reservoir. The increase of nutrients will promote the growth of algae and other plankton, causing an adverse effect on water quality. However, the flow velocity in the reservoir will restrict the growth to a biologically productive amount. Because the pH of the Yangtze water is rather high, usually more than eight, the phosphorus in the water can easily be converted into insoluble compounds and combined with fine sediments. Most of them will be flushed out of the reservoir with the releasing flow. Therefore, the concentration of soluble phosphorus, which is absorbed by algae, will remain very low in the reservoir. As a result, nutrients are unlikely to be accumulated, and eutrophication of the reservoir water body should not occur. However, in the bay areas of the reservoir, where the flow is slow, the growth of phyto-plankton eutrophication could possibly occur. Monitoring is necessary to discover the extent of the problem.
It has been estimated that about 70-80% of the nutrients flowing into the sea from the Yangtze come from the reaches below the Three Gorges dam site. Coupled with the fact that the amount of nutrients trapped by the reservoir is rather limited, the project has little effect on the concentration of nutrients in the downstream reaches of the dam and the estuary.
Water quality in the downstream reaches
The impact of reservoir operation on water quality in the downstream reaches of the dam is related to both the quality and the quantity of sluiced water – if the quality of the water sluicing from the reservoir is poor, then the water quality downstream will be bad. If the quantity of released water is decreased, the diffusion capacity for pollutants downstream will be weakened. Because of the reservoir settling and biochemical function, clear water will be sluiced downstream, its transparency will increase and water quality will be improved.
It is anticipated that the average amount of sluiced water will remain the same as that in the natural condition for most months of the year. In dry seasons the discharge will slightly increase, only decreasing slightly in October due to water storage needs. During the low water and normal years, after regulation, flow will still be more than 10,000m3/sec in October. In dry years, although decreased to a certain extent, it will still be larger than the minimum average discharge in the month.
Following approval of the state council, the Three Gorges Area Water Pollution Prevention Guidance Group, sponsored by the State Environmental Protection Administration, was founded in August 2001. The group published the ‘Three Gorges Area Water Pollution Prevention and Treatment Strategies’, which has been approved by the State Council. Over the next few years, China will invest approximately 39.2B yuan (US$337.3M) to prevent and treat water pollution in the Three Gorges reservoir and its upstream drainage area, and water quality on the whole is to reach the third grade of national surface water environmental quality standard by the year 2010.
Currently, 26 sewage treatment factories and 21 garbage treatment factories have been built, with many already commissioned. Main stream water quality of the Three Gorges reservoir has stayed between the second and the third grade, basically remaining unchanged as compared to the water quality before water storage.
Natural landscape and cultural relics
The total length of the Three Gorges project is 192km, with the dam located in the middle of Xilingxia. The storage of water will affect the 158km section from the dam upward to Baidicheng, while the release of water will affect the east section of Xilingxia from Sandouping to Nanjinguan, which amounts to 34km. After the construction of Three Gorges, the natural landscapes will of course change, especially in the project site area. Distant and midway landscape will not be significantly affected by the ebb and flow of water levels. The rapid stream and canyon landscapes of the Yangtze tributaries will be affected by the rise of the water level; this is likely to include part of the canyons and cliffs on the Daning river and the miniature Three Gorges. The change in released water volumes will not significantly affect natural landscapes downstream of the dam, and it may offer new tourist attractions for the area: the various huge architecture of the Three Gorges irrigation project and the stunning artificial waterfalls formed from the water releases would become grandiose landscapes on the Three Gorges tourism route.
With the combined efforts of culture heritage specialists nationwide and the culture heritage protection programme authorised by the State, 1087 culture heritage protection projects (335 projects in Hubei province, 752 in Chongqing) in the submerged and migration areas of the Three Gorges project were established. Of these, 364 projects were located above ground, with the remainder underground.
Up to the end of 2003, 845 culture heritage protection projects (78% of the planned projects) in the Three Gorges area had been completed. Of these, 544 were underground culture heritage salvage projects. A total area of 9.8668Mm2 has been probed, and 1.1041Mm2 has been exhumed. Of the 301 above-ground projects, 89 were protected by migrating them to other locations (22 projects have been completely rebuilt), 49 were saved by on-site protection, and 163 projects involved reserving documents. A further 680 culture heritage protection projects related to second stage migration (located below the 135m water level) have all been completed. In addition, key culture heritage protection projects (in Baiheliang Peiling, Shibaozhai Zhongxian, Zhanghuanhou Temple in Yunyang) have been carried out successfully. By the end of 2003, basic engineering of underwater protection and main channel repair in Baiheliang Peiling had been completed; the revised and supplemented design of Shibaozhai on-site protection had been submitted to the State Administration of Culture Heritage for approval and implementation; and the Zhanghuanhou Temple (popularly known as Zhangfei Temple) was been migrated and rebuilt before water storage started at the dam in June 2003. The whole migration project has been completed and it has already been reopened to tourists.
More than 60,000 specimens of culture heritage have been excavated in the Three Gorges area. Of these, more than 6000 specimens were rare culture heritages, and many important achievements have been made: the archeological culture chronicle of the whole Three Gorges area is gradually being uncovered. An outline of pre-history archaeology of culture development from 7500 to 4000 years ago was discovered, and important documents useful to the exploration of the origin and distribution of ancient Ba culture and the relationships of Ba with Shu and Chu were obtained. Important achievements were also made in various aspects such as the study of the Paleolithic culture in Southern and Northern China. New knowledge was also obtained concerning the cultural heritages of the Han and Tang dynasties in the Three Gorges area.
Culture heritage protection specialists from 30 institutes nationwide have participated in the culture heritage work at Three Gorges, including: China Culture Heritage Research Institute, Beijing Culture Heritage Research Institute, Hubei Culture Heritage and Archaeology Research Institute.
Three Gorges dam completed