environmental impacts of hydroelectric projects on fish resources in china
TRANSCRIPT
REGULATED RIVERS: RESEARCH & MANAGEMENT, VOL. 12, 81-98 (1996)
ENVIRONMENTAL IMPACTS OF HYDROELECTRIC PROJECTS ON FISH RESOURCES IN CHINA
YIGUANG ZHONG AND GEOFF POWER* Department of Biology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1
ABSTRACT
China has embarked on a programme to vastly expand its hydroelectric generating capacity and this is certain to alter its freshwater and anadromous fish communities. To provide some insight into the direction and consequences of the likely changes, four (> 250 000 kW) existing facilities were selected for review. The Gezhouba Dam, on the Changjiang River, commissioned in 1981, is a low-head run of the river facility. The Xinanjiang Dam (1959) is a high-head dam and the Fuchunjiang Dam (1968) is a low-head, run of the river dam, both sited on the Quiantang River. The Danjiangkou Dam (1968) is a high-head dam in the Han River, a tributary of the Changjiang River. Impacts on fish were classified as those caused directly by the structures, those resulting from changes in physical and chemical factors in their environment and those induced through biotic changes in their habitat.
Migrations of anadromous and semi-migratory fish were blocked by the Gezhouba Dam, although some species adapted to the new environment by reproducing downstream. Below the Xinanjiang and Danjiangkou dams spawning was delayed 20-60 days by lower water temperatures. Reduced water velocities and less variable discharges caused spawning grounds below the dams to be abandoned. Marked changes in the hydrological regime caused the extinction of Macrura reevesii, a highly valued fish, in the Qiantang River. The fish communities in the Qiantang estuary were affected by the regulated discharge. Freshwater species fell from 96 to 85, whereas marine species increased from 15 to 80. Loss of habitat eliminated torrential habitat species from the areas inundated by Xinanjiang and Danjiangkou Reservoirs; lentic fish replaced lotic species and now dominate the reservoir fish communities. The expanded aquatic habitat was beneficial for fishery production. Catches from the two reservoirs continue to increase 20 years after impoundment, but are supported by extensive artificial propagation and stocking. There is no doubt that, when the expansion of China’s hydroelectric facility network is complete, the fish communities in its rivers will be markedly changed.
KEY WORDS China; fisheries; hydropower
INTRODUCTION
In China, hydro power is usually considered a better source of energy than fossil fuels due to its low cost over the long term and lack of perceived environmental problems. Since the 1950s, approximately 62 000 hydro- electric projects have been constructed; most are small, < 12 000 kW, and almost all the major rivers in the country are today regulated (Fang, 1993).
In recent years, the construction of hydroelectric projects has been further encouraged to meet the demand of the booming economy of the country. Some large, > 250 000 kW, and medium-sized hydroelectric pro- jects have been finished and more projects are being planned, designed or are under construction in the major rivers. In Fujian Province, more than 40 large and medium projects are being designed and built in the 60992 km2, 584 km long Min River basin (Lian et al., 1987). In December 1994 construction started on the Three Gorges Project, Changjiang River (Yangtze), which will have a capacity of 18 200 MW and will be the largest hydropower station in the world (Lu, 1994). A number of other large projects will be developed later in the upper reaches of the Changjiang River (Chao et al., 1987). A 30-year plan for hydroelectric devel- opment in Sichuan Province, located in the upper reaches of the Changjiang basin, has been proposed (CRDI, 1989). According to this plan, a number of new hydropower stations will be constructed in the pro- vince, with a potential capacity of 35720MW by the year 2015. The Longtan Hydropower Station in
* To whom correspondence should be addressed
CCC 0886-9375/96/01008 1 - 18 0 1996 by John Wiley & Sons, Ltd.
Received 25 February 1995 Accepted I7 July 1995
82 Y. ZHONG AND G . POWER
I DANJIANGKOU DAM
0 t do N SCALE Km
HAN RIVER
QIANTANG RIVER
Figure I . Locations of the major hydroelectric dams discussed in the text. The black scale bars on the detailed maps represent 100 km
Guangxi is to be built soon (Dansie, 1995). The project is one of 10 hydropower stations planned for construc- tion along the Hongshui River and it will be the second largest in the country (China Daily, 17 February, 1994). In Chma the total capacity of large projects under survey, design and scheduled for construction in the near future and in the early 21st century will exceed 100 000 MW (Pan and Zhang, 1993). However, although hydro- electric projects play an important part in the economy and development of society, there are many environ- mental effects on fish and aquatic ecosystems which need to be considered (Brooker, 1981; Chen, 1984a; 1984b; 1985; Saltveit et af., 1987; Ward and Stanford, 1987). The tendency has been to neglect the ecological costs and emphasize only the economic benefits when making decisions about the hydroelectric developments.
This paper reviews the environmental impacts of hydroelectric development on fish in China. It describes the hydrological changes and the primary, secondary and tertiary impacts on fish. Four large hydroelectric projects in central and eastern China (Figure 1) were selected as the main focus of this review, namely the Xinanjiang, the Fuchunjiang, the Danjiangkou and the Gezhouba projects. These were chosen because the dams vary in location, height and effects on fisheries and they provide insights into the overall cumulative effect on fish resources of China’s massive hydroelectric development plans.
DESCRIPTION OF THE RIVERS AND THE PROJECTS
Table I summarizes the main technical details of the four hydroelectric projects considered. A description of their setting and type of operation follows.
The Qiantang River (Figure 1) is a major river in Zejiang Province, with a length of 494 km. It flows from west to east through the north of the province before entering the East China Sea. Annual precipitation in the basin is 1500-2000 mm, half falling between June and August. The mean discharge before regulation was 1038m3 SKI, with 49% occurring during May to July (Chen et al., 1990). Four large and medium hydro- electric projects have been constructed on the river and its tributaries since the late 1950s. The Xinanjiang
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84 Y . ZHONG AND G . POWER
Dam is the largest. It was completed in October 1959 and is situated in the Xinan River, an upper tributary of the Qiantang River. The dam crest is 105 m as1 and it creates a reservoir of 580 km2 in which the water level fluctuates annually between 85 and l00masl. Discharge through the turbines is between 200 and 1000m3 s-'. The water transparency (Sechi disc readings) is normally 5 m. Fuchunjiang Dam, another large dam in the river, is situated on the main stem of the middle reach of the Qiangtang River, only 60 km below the Xinanjiang Dam. It was constructed in December 1968, with a controlled drainage area of 31 300 km2. The dam is a low-head, run of the river dam. The water level in the reservoir is normally 23 m as1 with an effective storage of 440 x lo6 m3, and the reservoir is regulated daily according to demand. The maximum discharge through the turbines is 2500 m3 s-'.
The Han River (Figure 1) is the largest tributary of the Changjiang River. The headwaters of the river are in the south of Shaanxi Province and it enters the middle reach of the Changjiang River at Wuhan, Hubei Province. The river is 1532 km long, with a drainage area of 173 621 km2. Annual precipitation in the basin is between 700 and lOOOmm, about 40% of which falls in July and August. Before dam construction, the mini- mum discharge was 250m3 sC1 in January and February and peak flows of 2300-3300m3 s f l occurred between July and September (Yu et al., 1981). The river section above Danjiangkou is called the upper reach, with a length of 890 km. The Danjiangkou hydro project, with a high-head dam, was finished in 1968. The reservoir formed by the dam is about 100 km long, 1000 km2 and is, at present, the largest reservoir in China.
The Changjiang River (Figure 1) flows from the Qing-Zhang Plateau in the west to Shanghai in the east to join the East China Sea. With a length of more than 6300 km it is the third largest river in the world and the longest in Asia. Its 1.94 x lo6 km2 drainage basin is the home for nearly half of China's billion inhabitants. The mean annual discharge in the Yichang section of the river is about 14 300 m3 s-'. The period June to October is the flood season when about 72% of the annual runoff occurs, with peak flows concentrated in July and August (Yu et al., 1985a). The Gezhouba hydroelectric project, 4 km above Yichang City, Hubei Province, was the first dam constructed on the main stem of the Changjiang River. It is a low-head, run of the river hydroelectric project and was completed in January 1981 and impounded in May 1981. The generating capacity is about 2700 MW, which makes it the largest generating station now operating in China. The maximum difference in water level between the reservoir and the river below the dam is 27 m. The project creates a reservoir with a length of 110-180 km and an area of 63 km2. Most of the reservoir is in steep- sided gorge areas and its width is only 300-1000m.
HYDROLOGICAL EFFECTS
The downstream hydrology is modified by the regulated discharge from operational hydroelectric projects. Factors affected inciude water temperature, water level, discharge and current velocity.
Water temperature After the Xinanjiang Dam was built on the Qiantang River in 1959, the mean water temperature below the
dam decreased from 19.0 to 13.5"C. Peak temperatures 2.5 km downstream from the dam decreased from 34.8 to 23.2"C and minimum temperatures increased from 1.9 to 6.3"C. The cooler discharge reduced water temperatures as far as the mouth of the Qiantang River, a distance of about 260 km (Li, 1987). In the Han River, water temperatures below the Danjiangkou Dam generally decreased by 4-6°C from March to Sep- tember and increased by 4-6°C from October to February (Yu er al., 1981). In contrast, water temperatures downstream from Fuchunjiang and Gezhouba Dams both low-head structures, did not change significantly after construction (Chao et al., 1989; Chen et al., 1990) (Table 11).
Downstream discharge Frequent and large variations in water levels in rivers are reduced after dam construction and discharge
regulation. Yu et al. (1981) reported that before Danjiangkou Dam was built, the lowest mean monthly water level in the middle reach of the Han River in July was 88.8masl and the highest level was 91-6masl. After construction, water levels varied from 88.6 to 89-6m. In the Qiantang River after the con- struction of the Xinanjiang Dam, water levels in the flood season over the spawning grounds were about 3 m
Tabl
e 11
. Mea
n m
onth
ly w
ater
tem
pera
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s bef
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and
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ario
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Befo
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Be
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7.0
8.0
8.4
8.6
8.4
8.6
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5.2
8.2
8.3
7.6
9.6
9.7
9.0
9.0
12.5
18
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21.2
26
.8
11.8
15
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19-6
22
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15.5
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17.1
20
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21.7
14
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15.2
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16.9
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Aug
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Nov
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Mea
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z !2 0 z >
* XD
, Xin
anjia
ng D
am; F
D, F
uchu
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D, D
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nd G
D, G
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2 t S
ampl
ing
site
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ater
tem
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ture
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at t
he F
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eser
voir
bef
ore
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truc
tion
of th
e Fu
chun
jiang
Dam
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as m
oved
bel
ow t
he d
am in
196
8
§Dat
a fr
om C
hen ef
al. (
1990
). T
he d
ata
wer
e co
llect
ed b
etw
een
1960
and
196
8 qD
ata
from
Che
n et
al.
(199
0). T
he d
ata
wer
e co
llect
ed b
etw
een
1968
and
197
3 an
d be
twee
n 19
78 a
nd 1
980
II Dat
a fr
om Y
u ef
al. (
1981
). T
he d
ata
wer
e co
llect
ed in
196
2 an
d 19
74, r
epre
sent
ing
befo
re a
nd a
fter
dam
con
stru
ctio
n, r
espe
ctiv
ely
** D
ata
from
Cha
o ef
al. (
1989
). T
he d
ata
wer
e co
llect
ed b
etw
een
1977
and
198
1 an
d be
twee
n 19
82 a
nd 1
984,
repr
esen
ting
befo
re a
nd a
fter
dam
con
stru
ctio
n, r
espe
ctiv
ely
* Data
from
Che
n et
al.
(199
0). T
he d
ata
wer
e co
llect
ed b
etw
een
1957
and
195
9
86 Y. ZHONG AND G. POWER
Table 111. Changes in downstream hydrological factors after dam construction
Parameter River Before dam After dam
Water level (elevation, m) Lowest Highest Difference in flood Season Lowest Highest
Winter Summer Percentage of annual flow May to June Lowest discharge (February) Highest discharge (July)
Velocity (ms-') Spawning grounds April-June
Discharge (m3 s-I)
Wan
Qiantang Changjiang
Han
Quiantang Changjiang
Qiantang Changjiang
88.8 91-6 4.08
39.83 47.95
250 2300-3300
545 3406
24 275
1-1.5 0'89-1.77
88.6 89.6
1 -0 39.64 50.1 1
750-900 1000- 1500
27.1 4203
39 200
0.5 0.78-1.65
lower (Chen et al., 1990; Zhu, 1992). There was no noticeable change in water levels in the Changjiang River after construction of the low-head Gezhouba Dam (Chao et al., 1989) (Table 111).
Reservoir storage is important in diminishingpeak flows. Chen et al., (1990) reported that discharge below the Xinanjiang Dam in the period May to July 1968- 1976 decreased from 54.5 to 27.1 % of the mean annual discharge. The peak discharge in the middle reach of the Qiantang River, which was 29000m3 s-' before 1960, decreased to 13 800 m3s-' after 1960 when the Xinanjiang Dam was finished, and was further reduced to 8290 m3 s-' after 1974 when the Fuchunjiang Dam was completed. The monthly mean rate of flow in the Han River after the Danjiangkou Dam was built was increased from 250 to 750-900m3 s-' in the winter and decreased from 2300-3300 to 1000- 1500 m3 s-' in the summer. Peak discharges basically disappeared as well (Yu, et al., 1981). The monthly mean discharge in the Changjiang River below the Gezhouba Dam increased slightly, except in April (Chao et al., 1989) (Table 11).
In May to July, outflow from the Qiantang River decreased by 6.9% as a result of hydroelectric develop- ment (Chen et al., 1990). Not only are flows regulated, but annual discharge may be reduced after dam con- struction. When 12 years of pre-impoundment data were compared with a similar period after dam construction in the Huaihe River, annual discharge decreased by 15% from 1028 to 874m3 s-l (NIGAS, 1981).
Chen et ul. (1990) indicated that water velocities in the main spawning grounds in the Qiantang River were reduced from 1 - 1.5 to approximately 0-5 m sC1 because the discharge had been regulated by the hydroelec- tric projects. However, in the Changjiang River, after construction of the Gezhouba Dam, there was no noticeable change in downstream velocities (Chao ei al., 1989) (Table 111).
In the Han River, after construction of the Danjiangkou Dam, there was a significant reduction in the silt content of the discharge water due to silt deposition in the reservoir. Just below the dam silt loads were 1.2% of those before construction (Yu et al., 198 1). This effect was not as evident in the Gezhouba Dam. There was a slight increase in the period July to October, which may have been associated with serious earth erosion in the upper reaches of the Changjiang River during the flood season. Silt loads below the dam were lower during the rest of the year (Chao et al., 1989).
IMPACTS OF HYDROELECTRIC DEVELOPMENT ON RIVERINE FISH
Three orders of impacts of hydroelectric projects on fish can be considered according to the characteristics of the causal factors affecting the fish. First are the primary impacts, which are caused directly by the project. Examples include interruption of the migration route by the dam and the expanded habitat created by the reservoir. The second order comprises secondary impacts which act directly on the fish through changes in
HYDROPOWER AND FISH IN CHINA 87
their physical and/or chemical environment. The most obvious parameters are water temperature, velocity, discharge and total dissolved solids. More subtle, long-term geomorphic effects such as channel degradation and other consequences of altered sediment transport are also included. Third-order tertiary impacts are induced by biotic responses in the ecosystem the fish inhabit to changes brought about by hydroelectric development. These include changes in prey availability or predators and parasites. Both secondary and tertiary impacts can be thought of as indirect impacts. The generally accepted English common names for fish are used in the text. When these are not available, binomial scientific names are used. A complete listing of the common, scientific and authority names is given in the Appendix.
Primary impacts As no fish passage facilities are provided at these Chinese hydroelectric dams (except the Fuchunjiang
Dam where a 15 m high fish pass did not help fish past the dam and was abandoned; Chen, 1984a), move- ments of anadromous and so-called ‘semi-migratory fish’ were blocked (Zhou et al., 1980; STSGDFCR, 1982; Yu et al., 1981; 1985a; 1986a; 1988a,b; Liu et al., 1986; 1990; 1992; Yuan and Huang, 1989; Chen et al., 1990). In China, ‘semi-migratory fish’ migrate between the upper reaches and the lakes adjacent to the middle and lower reaches of rivers for reproduction, feeding and overwintering. After the Han River was blocked by the Danjiangkou Dam and connections between the river and lakes were obstructed, these fish modified their behaviour and continued to live in the river. Among them, Rhinogobio typus and Coreius heterodon reproduced and overwintered very well in the isolated river section and the stock of the latter increased significantly (Yu et al., 1981). Some well-known rare fish, such as Chinese sturgeon Acipenser sinensis, Chinese sucker Myxocyprinus asiaticus and white sturgeon (a paddlefish) Psephurus gladius, were threatened by the Gezhouba Dam (Yu et al., 1985b; 1986b; Zhou et al., 1985; Liu et al., 1992). These fish previously ascended the main stem of the Changjiang River from the sea or the middle and lower reaches to spawn in tributaries in upper reaches (more than 2000 km above the river mouth). Spawning runs were detained below the dam and became the main target for a local fishery. In this section of the river the annual catch of Chinese sturgeon increased from tens to hundreds of fish and the Chinese sucker, which was rarely caught before dam construction, made up 5% of the total catch (Ke et al., 1986; Wu et al., 1988a). Stocks of these rare fishes were endangered by overfishing. In addition, many Chinese sturgeon were observed severely damaged or dead below the Gezhouba Dam, apparently wounded trying to ascend the dam (Yu et al., 1986a).
The question of whether anadromous and semi-migratory fish could reproduce naturally below the dam in the Changjiang River has been a focus of research on the environmental impacts of hydroelectric develop- ment on fish in China. It used to be thought that the gonads of these fish matured gradually while the fish were ascending to the upper reaches of the Changjiang River. However, the gonads of several fish species, including Chinese sturgeon, Chinese sucker and white sturgeon detained downstream by the Gezhouba Dam could develop to the late stage 4, considered to indicate sexual maturity (Zhou et al., 1985; Yu et al., 1986b; Liu et al., 1992). There is no evidence that white sturgeon and Coreius guichenoti are able to spawn in this section of the river (Yu et al., 1986b; Liu et al., 1990; Xia, 1993). In contrast, eggs, fry and juveniles of the Chinese sturgeon and Chinese sucker were often collected between the dam and the estuary, which con- firmed natural reproduction (Zhou et al., 1985; Yu et al., 1986a; 1988a; Zhao et al., 1986; Liu et al., 1992). Furthermore, artificial reproduction was performed successfully on Chinese sturgeon (Fu et al., 1985; Yi et al., 1986) and Chinese sucker (Yu et al., 1988a), which were collected below the dam. However, the sexual maturity index of Chinese sturgeon caught below the Gezhouba Dam is less than that of those caught further upstream before the dam was constructed (Hu et al., 1992). The scale of artificial breeding of sturgeon and sucker later expanded and many juveniles of both species are now released into the Changjiang River each year (Chao et al., 1987; Deng et al., 1987).
Fish communities in rivers are directly affected by hydroelectric projects. Li (1987) reported that the num- ber of fish species in the area of the Xinanjiang Reservoir decreased from 107 to 83 because the migration of fish was interrupted by the dam. Another survey, conducted by the Inland Waters Fisheries Resources Survey Team of Zhejiang Province in 1983, caught only 66 species in the reservoir (Zhou et al., 1989). The reduction of fish biodiversity occurred not only in the flooded section of the river forming the reservoir, but also in the river below the dam. Several species of torrential habitat fish disappeared
88 Y. ZHONG AND G. POWER
from the Yichang section of the Changjiang River below the Gezhouba Dam during a six-year survey, and this was thought to be caused by the dam (Wu et al., 1988a). Yu et al. (1981) also reported that some species of torrential habitat fish had not been seen in the middle and lower reaches of the Han River since the Danjiangkou Dam was built. In addition to these examples, by 1970, migratory fish had disap- peared from the East River, a tributary of the Pearl River, fol1owi;ig the construction of five dams in the lower reaches and many reservoirs in the upper parts of the river (Liao et al., 1989).
Eggs, fry, juveniles and even some adult fish were killed or seriously damaged when they passed through the turbines of the Gezhouba hydroelectric station because of sudden current shear stress and water pressure (Yu et al., 1985b). In addition to mechanical damage, gas-bubble disease caused by dissolved nitrogen in the water was also discovered below the dam in fry of four domestic carp species: grass carp Ctenopharyngodon idellus, black carp Mylopharyngodon piceus, silver carp Hypophthalmichthys molitrix and bighead carp Aris- tichthys nobilis (Chen, 1984a; Liu et al., 1986). Wu (1987) reported that, in two observations, the mortalities were 38 to 60% for grass carp and 19 to 59% for black carp, respectively, after passage through the Gez- houba Dam.
One of the most significant changes fish must adapt to, if they are to survive after the construction of hydroelectric projects, is alteration to the spawning grounds. Above the reservoirs, new spawning grounds may be established when raised water levels in the impoundment make previously unavailable tributaries accessible and when fish are displaced from impounded areas and move elsewhere to spawn (Yu et al., 1981; Wu et al., 1988b; Chen et al., 1990). In the Han River there was an obvious trend for spawning grounds to move down to the lower reaches, where the contribution of some large tributaries provided hydrological factors which better met the reproductive requirements of the fish (Zhou et al., 1980; Yu et al., 1981). Simi- larly, the spawning grounds of the Chinese sturgeon, Chinese sucker and Coreius heteroden were re-estab- lished below the dam when their migration routes were interrupted by the Gezhouba Dam in 1981 (Xu et al., 1984; Yu et al., 1986a; Liu et al., 1990; 1992; Hu et al., 1992). Table IV summarizes the primary impacts of these hydroelectric projects on fish.
Secondary impacts Lower summer water temperatures below hydroelectric dams can have serious consequences for some fish.
In the Han River below the Danjiangkou Dam, spawning was delayed by 20-30 days. Late hatching and lower water temperatures reduced the first year growth compared with growth of the same species of fish in the Changjiang River (Zhou et al., 1980; Yu et al., 1981). In the Qiantang River below the Fuchunjiang Dam, spawning was retarded by 30-60 days as the result of cold water discharge from Xinanjiang and Hunanzhen Dams (Figure 1) located upstream (Chen et al., 1990; Zhu, 1992). Hunanzhen Dam, constructed in 1979, is 129 m high. In the approximately 15 km section of river between Xinanjiang Dam and the upstream margin of Fuchunjiang Reservoir, the water temperatures are generally less than 17°C and most warm water fish species have disappeared (Li, 1987; Chen et al., 1990).
Table IV. Documented primary impacts
River Location Causal factors Impacts
Changjiang, Quiantang Upstream River blocked Migratory fish are incapable of accessing
Changjiang Powerhouse Damaged turbine Mortalities increase when fish pass below the upstream spawning grounds
Downstream passage and nitrogen the dam supersaturation
Changjiang Downstream Detained by dam Reproductively mature upstream
Changjiang, Han Downstream River blocked Torrential habitat fish disappear in the migrants, overfished below the dam
river below the dam
HYDROPOWER AND FISH IN CHINA 89
In China, 15°C is considered the threshold temperature at which warm water fish start to grow. Although the mean annual water temperatures downstream of the Xinanjiang and Danjiangkou Dams only decreased by 1.9 and 1-6"C (Table I), the annual sum of degree days > 15" between April and November, effective for gyowth, decreased by 36.5 and 40-0%, respectively. In contrast, there was no notable change in the tempera- ture accumulations below the two low-head dams (Figure 2).
Many fish spawn in running water and need a sudden increase in current velocity to stimulate them to spawn (Yi and Liang, 1964; Zhou et al., 1980; NIGAS, 1981; Xu et af. , 1981; Yu et al., 1981; STSGDFCR, 1982; Yi et al., 1988; Chen et al., 1990). Zhou et al. (1980) reported a close correlation between spawning intensity and an increase in water velocity. With the regulation of discharge, peak flows downstream from the Danjiangkou Reservoir decreased and there was less variation in water level. As a result, some of the spawning grounds below the dam were abandoned and there were fewer spawners. In contrast, in the Changjiang River below the Gezhouba Dam, reproduction by the four domestic carp species was not affected, apparently because discharge regulation through the hydroelectric facility is limited (STSGDFCR, 1982; Yu et af . , 1985a; Liu et al., 1986). High discharge is important for inducing anadromous fish to ascend rivers to spawn. Zhong (1983) reported that, after the construction of the Fuchunjiang Dam, Qiantang River, there was a significant correlation between the captures of an anadromous fish Coifia ectenes ascending the river to spawn and the amount of the discharge from the project (Table V).
The numbers of Chinese shad (Macrura reevesii) migrating upstream were also correlated with runoff in
7 APR MAY JUN JLJL AUG SEP'OCTNOV
C
APR MAY JUN JLJL AUG SEPOCTNOV
550
450
350
250
150
50
-50
350
300
250 200
150
100
B
PR MAY JUN JLJL AUG SEPOCT"0V
D
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0 APR MAY JUN JLJL AUG SEPOCTNOV
Figure 2. Monthly variations in accumulated degree days > 15°C (effective temperature accumulation downstream of the four hydro- electric reservoirs). (A) Xinanjiang Reservoir; (B) Danjiangkou Reservoir; (C) Fuchunjiang Reservoir; and (D) Gezhouba Reservoir
90 Y. ZHONG AND G. POWER
the Qiantang River (Li, 1987; Chen et al., 1990). Wu et al. (1988a) reported that several anadromous fishes such as Chinese shad, Coilia ectenes and Fugu obscurus would ascend the Changjiang River to near Yichang (more than 1600 km above the mouth) only in years when the peak runoff was very high.
Spawning grounds in the rivers and floodplains are destroyed in areas flooded by hydroelectric reservoirs. About 40% of the spawning grounds in the Qiantang River above the Fuchunjiang Dam were lost in this way (Chen et al., 1990). At least eight spawning grounds used by the four domestic carp species disappeared in the upper reaches of the Han River when the Danjiangkou reservoir was filled (Zhou et al., 1980). Riverine species are replaced in reservoirs by lake-inhabiting fishes and these increased rapidly in the Xinanjiang Reservoir (Chen et al., 1990). Similarly, in the Danjiangkou Reservoir, lentic fish dominate the community and 70% of the catch between 1982 and 1986 consisted of Erythroculter mongolicus and Elopichthys bambusa (Xiong, 1988).
After filling, the water currents in reservoirs are slight. Fish which normally live in torrential habitats dis- appeared from river sections inundated by the Xinanjiang and Danjiangkou Reservoirs. Some still survive in torrential reaches of rivers above the reservoirs (Yuan and Huang, 1989; Chen et al., 1990). Zhou et al. (1980) reported that there were 25 species of fish reproducing by surface drifting eggs in the Han River above the Danjiangkou Reservoir. Where currents decreased to less than 0.15 m3 sC1, no egg was caught drifting at the water surface. It was presumed that most eggs sank and were unable to continue development when they entered the reservoir because the currents were inadequate to maintain them in suspension (Zhou et al., 1980). A laboratory experiment showed that a water velocity of 0.25 m s-' seemed to be minimal. At this velocity, 89.1, 89.3 and 81.0% of eggs of grass carp, silver carp and bighead carp remained in suspension (Tang et al., 1989).
Conditions for successful reproduction of Chinese riverine fish are exacting. For example, the Chinese shad requires a water temperature between 26 and 30°C, peak floods, a current velocity between 0.6 and 0*8msC' and a transparency less than 30cm (Chen et al., 1990). After construction of the Fuchunjiang Dam in 1968 and the Hunanzhen Dam in 1979, the hydrological conditions in the lower reaches of the Qiantang River changed considerably and spawning requirements of the fish were rarely met. The Chinese shad was drastically reduced and finally became extinct in the river (Li, 1987; Chen et al., 1990; Zhu, 1992). Chen et al. (1990) found that conditions in the Qiantang River below Xinanjiang Dam changed to a slow-running river with cooler water, and fish dependent on torrential habitats and also some warm water species decreased greatly in abundance or were extirpated. The cumulative effect of diminished peak discharges, stabilized water levels, reduced current velocities and water tem- peratures diminished or eliminated spawning grounds below the dams on the Qiantang and Han Rivers (Yu et al., 1981; Li, 1987; Chen et al., 1990). Six migratory fish and five species favouring torrential habitats declined severely in the middle and lower reaches of the Qiantang River, whereas small-sized, coarse fish of low market value gradually increased in the catches in this section of the river (Chen et al.,
Table V. Acclimatization of fish to changed environments
River Changed environment Exhibited acclimatization
Changjiang Former spawning grounds Han, inundated and hydrological Qiantang factors changed
Changjiang Migration route blocked
Han River section blocked both in upper and lower reaches
Qiantang River flow regulated artificially
New spawning grounds may be formed both above the reservoir and below the dam
Some migratory fish which used to ascend to the upper reaches of the river now reproduce naturally below the dam
Many fishes which used to migrate between upper reaches and lakes adjacent to middle and lower reaches of the river have become stationary or restricted their movements
The number of anadromous fish ascending the river to spawn is related to the amount of the discharge from the hydroelectric project
HYDROPOWER AND FISH IN CHINA 91
1990). Liao (1980) reported that the numbers of juvenile Chinese carps, especially mud carp Cirrhinus moli- torella, diminished in the lower reaches of the Pearl River after the construction of a hydroelectric station on the middle reach of the river in 1958.
Regulation of river discharge for the production of hydroelectricity can modify estuaries. There has been a significant change in the fish community in the estuary of the Qiantang River since hydro development. Chen et al. (1990) found that, once the river flow was regulated and floods reduced, salt water intrusion into the estuary greatly expanded. As a result, the number of species of freshwater fish found in this region decreased from 96 to 85, whereas marine species increased from 15 to 80.
In China, as in many countries, marine mammals are the responsibility of the fisheries administration. The Baiji dolphin Lipoles vexillgeer is an endangered freshwater mammal found only in the middle and lower reaches of the Changjiang River. The discharge of relatively silt-free water from the Gezhouba Dam, which picks up bedload as it moves downstream, appears to have altered its habitat. By 1985-1986 the river bed between Yichang and Yunchi (40 km below the dam) had deepened by about 40 cm and become coarser. By 1990- 1991 the channel in this reach was 100 cm deeper and the zone of erosion extended 160 km downstream to Sashi. As a consequence, the distribution of the dolphin had receded from Yichang to Sashi and the numbers of dolphin in the river section between Ouchikou and Chenglingji (approximately 158 krn) had declined from nine groups and 43 individuals in 1986 to three groups and 11 individuals in 1991 (Hua and Chen, 1992). Reasons for the decline are complex and many factors may be involved. The main causes were believed to be changes in the prey fish community, habitat loss and disturbance, including direct injuries from contact with boats and fishing gear (Chen and Hua, 1987, 1989). Table VI summarizes the secondary impacts of hydroelectric projects on fish.
Table VI. Documented secondary impacts on fish
River Location Causal factors Impacts
Han, Qiantang Downstream Lower temperature
Han Downstream Lower temperature
Han, Qiantang
Qiantang
Changjiang Han, Qiantang Han, Qiantang, Changjiang Qiantang Han, Qiantang
Downstream Lower water velocity and
Downstream Lower temperature and
Downstream River bed washed out Reservoir Lower flow velocity
Reservoir Impoundment
lower temperature
reduced discharge
Reservoir Impoundment Downstream Changed hydrological factors
Han Reservoir Lower flow velocity
Qiantang Estuary Reduced discharge from the river
Fish reproduction delayed 20-30 days in the Han and 30-60 days in the Qiantang; warm water fish disappeared below the Xinanjiang Dam Delayed reproduction and age-1 fish grew
Anadromous fish and torrential habitat fish reduced or disappeared An important anadromous fish, Chinese shad, became extinct Population of river dolphin greatly reduced Torrential habitat fish disappeared Spawning grounds in the reservoir inundated
slowly
Fish community in the reservoir simplified Some spawning grounds were discharded or used less; reduced stimulus for spawning A great quantity of drifting eggs produced upstream from the reservoir sank and were lost Species of freshwater fish were reduced from 96 to 85 and marine fish species increased greatly
92 Y. ZHONG AND G. POWER
3000 i I -xR. I
1960 1965 1970 1975 1980 1985 1990
YEAR
Figure 3. Trends in fishery production in two hydroelectric reservoirs after impoundment. X.R., Xinanjiang Reservoir; and D.R., Danjiangkou Reservoir
Tertiary impacts Biotic communities respond to changes in the physical and chemical factors in rivers by adjustments in
abundance and species composition. Below the Xinanjiang Dam food sources for fish have decreased con- siderably because nutrients are retained in the reservoir and water is discharged at reduced temperatures. Since 1963 grass carp, black carp, silver carp and bighead carp have almost all disappeared from the 15 km section of river below the dam (Li, 1987).
In the Han River, Yu et al. (1981) found that the filamentous algae Cladophora and the freshwater mussel Limnoperna lacustris were among the most abundant aquatic biota benefiting from the stabilized water levels, reduced silt content, increased transparency and less variable water temperatures after the river was dammed. Coreius heterodon, which feed on freshwater mussels, and grass carp, which consume filamen- tous algae, did very well and became the dominant fish species. Yu et al. (1981) reported that the feeding habit of grass carp shifted from vascular plants to filamentous algae as a result of changes in the availability of these food organisms in the middle and lower reaches of the Han River. The species composition of the economically important fish in the middle and lower reaches of the river responded to the change in food organisms. Dominant fishes were herbivores and benthivores (Yu et al., 1981). The grass carp grew more slowly in the Han River than in the warmer Changjiang River, in part because the biomass of the filamentous algae was at a minimum between June and August, when the fish usually achieve most of their growth.
HYDROELECTRIC DEVELOPMENT AND FISHERIES
Reservoir jisheries In China, hydroelectric projects are usually constructed in steep, narrow river sections which cut through
mountain areas. Narrow river sections are replaced by much wider reservoirs after dam construction. Hydrological conditions in the reservoirs generally tend to vary between rivers and lakes. In the upper reser- voir in the former river stem they are river-like, so that most riverine fish are able to live there. In contrast, in inundated reservoir bays, slow circulation, low water exchange rate and nutrients provide suitable living and growing conditions for lacustrine fishes. Populations of lacustrine species increase as a result of expanded habitat and the nutrients trapped in the reservoir. In Fuchunjiang Reservoir, wild lacustrine fishes accounted for 30.7% and artificially stocked carp 61.5% of the fish harvest according to catch statistics (Chen et al., 1990). In the Danjiangkou reservoir, when some lotic fish disappeared and others became less common,
HYDROPOWER AND FISH IN CHINA 93
lacustrine fish dominated the yields, accounting for 70% of the catches between 1982 and 1986 (Xiong, 1988). Although both the Xinanjiang and Danjiangkou reservoirs have been impounded for about 20 years, fishery yields remain high (Figure 3). Catches reached 3500 t in the former in 1995 and 2780 t in the latter in 1990, representing an increase of 33.3 and 32.2 times, respectively (Li, 1987; Xiong, 1993). There is no evi- dence of the trophic upsurge and decline displayed in temperate reservoirs. A linear correlation was reported between annual fish catches and the annual turnover of water in the Danjiangkou reservoir. The explanation offered was that large volumes of inflowing water stimulated fish to assemble and ascend tributaries, thus making them vulnerable to capture (Xiong, 1988).
Catch compositions differ between the Xinanjiang and Danjiangkou reservoirs. In the Danjiangkou reser- voir before 1985 catches consisted mainly of wild fish, especially predators. These accounted for about 70% of the harvest (Xiong, 1988). On the other hand, a large number of yearling silver carp, bighead carp and a few other species were released in the Xinanjiang reservoir to use plankton and other natural food organ- isms. The annual numbers of stocked yearlings reached 9.5 x lo6 between 1959 and 1982 and these contrib- uted the largest proportion to the catches, around 69.6-73.4'/0 in 1980-1982 (Chen et al., 1990). A higher yield was achieved from a smaller water area in the Xinanjiang reservoir as a consequence of aquaculture in the reservoir.
However, in Fuchunjiang reservoir, the mean annual yield during a 10 year post-impoundment period only increased 34.6% compared with catches over a similar period before dam formation, although 5.7 x lo6 yearling fish were released into the reservoir in the period 1969-1973 (Chen et al., 1990). The reason probably relates to the hydrological parameters of the run of the river reservoir, which did not change significantly after construction of the dam. The turnover time in the reservoir was too short to stimulate productivity.
Downstream river -fisheries As discussed earlier, downstream fisheries are affected by hydroelectric development. The fisheries may
benefit at least temporarily from blocked migration routes. Chinese sturgeon, Chinese sucker and Coreius guichenoti, which used to ascend to the upper reaches of the Changjiang to reproduce, now contribute a higher proportion to catches immediately downstream from the Gezhouba Dam which makes capture of these fish easier than before (Wu et al., 1988a; Huang and Deng, 1990). In winter, habitats are improved due to increased flows and warmer water temperatures in the river section below the Danjiangkou Dam
NAllVE FISH
"1 0 COARSE FISH
z 050 E 2
FOUR CARPS
MIGRATORY FISH
a PREDATORY FISH
TONGLU FUYANG HANGZHOU
Dam 4-b Figure 4. Catch compositions in different river sections downstream of the Fuchunjiang Dam. The order of river sections from the dam
to the estuary of the Quiantang River is Tonglu, Fuyang and Hangzhou
94 Y. ZHONG AND G. POWER
and a large number of fish ascend and congregate in this reach for overwintering. This has provided a new fishing period and high yield (Yu et al., 1981; Liu and Yu, 1992). Although low water temperatures caused warm water fishes to disappear from a 15 km section of river downstream from the Xinanjiang Dam, intro- duced rainbow trout, Oncorhynchus mykiss, grew very well there. Production reached 42.2 kg m-3 in mesh cages and the total yield was 100 t in 1985 (Li, 1987; Zhou et al., 1989).
Li (1987) reported the annual catch in the Qiantang River decreased from 1750t in 1954-1960 to about 230-250 t in 1981-1985. One of the best known and economically valuable migratory fish, the Chinese shad, used to be an important target for the river fisheries. After Fuchunjiang Dam construction, catches in the river collapsed from 39 000 kg in 1962 to only 463 kg in 1981 (Chen et al., 1990) and no fish has been caught in recent years (Zhu, 1992). Low water temperatures, decreased spawning areas and blocked migration caused the decrease. Furthermore, with a drastic reduction in this economically important fish, small-sized native and coarse fish gradually increased and now account for a large proportion of the catches in the lower reach of the Qiantang River (Xia et al., 1989; Chen et al., 1990). The closer to the Fuchunjiang Dam, the higher the proportions of native and coarse fish (Figure 4). In contrast, after construction of the Danjiangkou Dam in the Han River, data indicate that annual catches increased in the middle reaches of the river below the dam (Yu et al., 1981; Liu and Yu, 1992). This increase was apparently correlated with increased fishing effort (Yu et al., 1981).
DISCUSSION AND CONCLUSIONS
Decisions to construct hydroelectric projects are driven by many factors-the need for energy, the need to create employment, political expediency related to the first two factors, water storage for irrigation, domestic and industrial use, even aesthetic and recreational interests. In developing countries, need for energy is fore- most and the biological consequences of projects may not be fully considered or appreciated. As China modernizes its economy, the emphasis is likely to shift from the more technical aspects of hydroelectric project construction to a broader viewpoint. Such a perspective will attempt to weigh all aspects of each development to ensure the true costs are recognized and all benefits realized.
Fishery interests must be considered in planning hydroelectric projects in China and, in doing so, the type and location of the dam becomes important. High-head dams cause greater changes to the aquatic environ- ment than low-head run of the river projects and have more effect on fish and fisheries. The hydrological factors downstream from the Gezhouba Dam were similar to those before dam construction (Tables I1 and 111) due to the low storage capacity of the run of the river dam. Several workers have reported that grass carp, black carp, silver carp and bighead carp were reproducing normally below the dam and there was no significant change in the number of spawning grounds or their locations (Yu et al., 1985a; STSGDFCR, 1982; Liu et al., 1986). This is in sharp contrast with what happened to these fish below the Danjiangkou Dam, Han River (Zhou et a[., 1980; Yu et al., 1981).
The Xinanjiang and Danjiankou Dams are both high-head dams, but they differ in their impacts because the turbine intakes are from different depths in the two reservoirs. The changes in the Han River below the Danjiangkou Dam are less serious than those in the Qiantang River below the Xinanjiang Dam and some are even beneficial to fish. Surface discharge from the Danjiangkou reservoir entrains plankton and nutrients. Yu et al. (1981) reported that the phytoplankton biomass in the middle and lower reaches of the Han River increased slightly and the zooplankton increased significantly. The nearer to the reservoir, the greater the increase in phytoplankton and zooplankton. In contrast, there were few organisms or nutrients in the dis- charge from the Xinanjiang Dam, where the turbine intake is 17-30m below the water surface (Li, 1987; Chen et al., 1990).
The impact on anadromous fish of a hydroelectric project near an estuary is more severe than that of one far from an estuary. For the former, there are a few tributaries joining the river below the dam and the effects of changed hydrological factors are difficult to alleviate, so that the hydrological conditions in the lower reach and estuary are modified by discharge from the project. For the latter, there is a long distance from the dam to the river mouth and many tributaries may join the river downstream of the dam. These combine with the river and provide a more natural environment. The distance between the Fuchunjiang Dam and the
HYDROPOWER AND FISH IN CHINA 95
mouth of the Qiantang River is just 200 km, whereas both the Danjiangkou Dam, Han River and Gezhouba Dam, Changjiang River are more than 1600 km from their common estuary. After construction of the Fuchunjiang Dam, Chinese shad became extinct in the Qiantang River and there was a significant change in the fish community in the estuary (Li, 1987; Chen el al., 1990; Zhu, 1992).
The impacts of a project built in a tributary on the fish community of a river are localized and may be modified by other tributaries, whereas a project on the main stem of a river will affect fish and the aquatic ecosystem over a much larger area, not only in the main stem, but also in many upstream tributaries. For example, as only one migratory fish, the eel Anguillajaponica which descends to the sea to spawn, lives in the Han River, the Danjiangkou Dam has no obvious impact on migratory fish. In contrast, the Gezhouba Dam affected a number of migratory and ‘semi-migratory’ fish whose spawning grounds were located in upper reaches of the Changjiang River.
In summary, in China, although there are a few beneficial impacts of hydro development for fish, the nega- tive impacts far exceed the positive impacts and fish resources may be severely damaged. Nevertheless, an increasing national demand for energy is being directed towards the installation of increasing numbers of hydropower facilities. To mitigate the impacts on fish, the best option is to make the changed environment as similar to the former river as possible. We suggest that, where possible, hydroelectric projects should be built in tributaries of large rivers, but not on the mainstem. If dams must be built on the mainstem, low-head dams sited as far from the estuary as possible are the least damaging. There is no practical means of mitigat- ing the impacts of high-head dams built near the sea. The most important consideration is that multilevel intakes should be used to draw turbine water primarily from the surface, regardless of the height of the dam. Chao et al. (1987) also proposed that, during the normal spawning season, several large water releases should be built into the operational schedule for the Three Gorges Project to stimulate fish reproduction. Maintaining species ability to reproduce successfully is essential to minimize harm to fish communities. However, with the scale of hydroelectric development planned in China, the riverine fish communities are going to be severely perturbed and, after the year 2020, will be represented by a very different species mix from today.
ACKNOWLEDGEMENTS
We are grateful to Dr R. A. Bodaly (Freshwater Institute, Winnipeg, Department of Fisheries and Oceans) for his helpful comments on the original manuscript.
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98 Y. ZHONG AND G. POWER
Appendix. List of species names of fish discussed in this paper
Common name Scientific name Family
Chinese sturgeon Chinese sucker White sturgeon
Acipenser sinensis Gray Myxocyprinus asiaticus (Bleeker) Psephurus gladius (Martens)
Acipenseridae Catostomidae Pol yodontidae
Four domestic fish Grass carp Ctenopharyngodon idelhs (Cuvier et Valenciennes) Cyprinidae Black carp Mylopharyngodon piceus (Richardson) Cyprinidae Silver carp Hypophthalmichthys molitrix (Cuvier et Valenciennes) Cyprinidae Bighead carp Aristichthys nobilis (Richardson) Cyprinidae
Common carp Chinese shad Mud carp
Eel
Rainbow trout
Erythroculter mongolicus (Basilewsky) Erythroculter ilishaeformis (Bleeker) Elopichthys bambusa (Richardson) Cyprinus carpio Linnaeus Macrura reevesii (Richardson) Cirrhina molitorella (Cuvier et Valenciennes) Coilia ectenes Jordan et Seale Fugu obscurus (Abe) Coreius heterodon (Bleeker) Coreius guichenoti (Sauvage et Dabry) Auguilla japonica Temminck et Schlegel Rhinogubio typus Bleeker Salmo gairdneri Richardson
Cyprinidae Cyprinidae Cyprinidae Cyprinidae Clupeidae C yprinidae Engraulidae Tetraodontidae C yprinidae C yprinidae Anguillidae Cyprinidae Salmonidae