Large Lakes of China

J. Great Lakes Res. 13(3):235-249 Internat. Assoc. Great Lakes Res., 1987

FEATURE ARTICLE LARGE LAKES OF CHINA

William Y. B. Chang Great Lakes Research Division The University of Michigan Ann Arbor, Michigan 48109

A BSTRA CT: China contains 28 of the world's large lakes (> 500 km 2). Information on these lakes is considerably limited. This paper describes in greater detail the origin, location, and the physical, chemical, and biological characteristics of the Chinese lakes and discusses the prevalant lake fish management methods in China. Elements which have influenced changes in Chinese large lakes are discussed. Climatic condition and tectonic uplift have strongly influenced the large lakes in the TibetQinghai-Sinkiang region while sediment loading and human impacts continue to be the major concern for the large lakes in the Pacific basin. ADDITIONAL INDEX WORDS: China, large lakes, sediment loading, climate, human impacts.

TABLE 1. The number and total area in each lake size category (Academia Sinica 1981).

INTRODUCTION China is the most populous country in the world and ranks third in territory. It contains 28 of the world's largest lakes (> 500 km 2), 25 of which are within the Chinese territory, and 3 of which form part of its borders. The number of large lakes in China is exceeded only by the number found in Canada and the Soviet Union. Information on the Chinese lakes, however, is considerably limited. Herdendorf (1982) presented an overview of large lakes of the world, which included information on the formation, distribution, and physical attributes of the large lakes in China. Melack (1983) discussed the limnological characteristic of Lake Qinghai (Lake KoKo), which is the largest lake in China. This study will expand the database on large lakes in China and describe in greater detail the formation, distribution, and the physical, chemical, and biological characteristics of these lakes. The problems and prevalent lake management methods will also be discussed.

Lake Size (km 2)

No

Total Area (km 2)

1-10 10-50 50-100 100-500 500-1,000 > 1,000

2,383 234 107 96 15 13

9,129 4,932 7,365 19,830 10,082 29,307

Total

2,848

80,645

lakes in China (Fig. 1), with a total area of 39,389 km 2 , represent 48.8% of the total national lake area. Of these large Chinese lakes, all eight situated in the Pacific drainage basin are freshwater lakes including one in Manchuria forming the border between China and the USSR. The remaining large lakes are situated in the Tibet-Qinghai plateau and in the Mongolia-Sinkiang area (Table 2). Many of the last group are saline, being the final destiny of rivers. The formation of large lakes in China has been primarily attributed to tectonic movement, to river action, or to some combination of the two. Studies have shown that there were once two major river systems in China, one flowing to the Pacific Ocean

DISTRIBUTION, FORMATION, AND GENERAL CHARACTERISTICS China has more than 2,800 lakes > 1 km 2 occupying approximately 80,000 km 2 (Table 1) and constituting 0.8070 of the entire territory. The 28 large

235

236

w. Y. B. CHANG I

110 0

SOVIET UNION

i

N

FIG. 1. Locations and distributions of large lakes of China. The name and physical attributes of each lake code can be found in Table 2. I indicates the Pacific drainage basin while 11 shows the Tibet-Qinghai-Sinkiang region.

and the other draining to the Indian Ocean. Plate tectonic movement caused the Indian subcontinent to collide with Eurasia in the Tertiary, resulting in the formation of the Himalayan mountain ranges in the southwestern part of China and the highest Tibet plateau, which in turn blocked the flow of the rivers which had originally emptied into the Indian Ocean. Many large lakes in the TibetQinghai region were formed as a result of the uplift process. The collision of subcontinents not only blocked water flow, but also created barriers which lessened the monsoonal rains that provided most of the freshwater input for the regions of Tibet,

Qinghai, and Sinkiang. The region became increasingly arid, evaporation far exceeded precipitation, and many of the large lakes became saline with high mineral contents. Geological instability has caused the formation and disappearance of a few large lakes in the region even in recent time, and has produced extensive changes in size, configuration, and water depth as new outlets are formed or old rivers become blocked. The desert climate exaggerates the contrast between wet and dry periods, with lake size and depth following this general seasonal cycle. Many of the large lakes situated on the Tibet-Qinghai plateau have an eleva-

237

LARGE LAKES OF CHINA

TABLE 2. Distribution, location, origin, and general characteristics of large lakes in China. (F) - fresh water, (S) saline water, and (F/S) - fresh and saline water. I - Pacific drainage basin and II - Tibet-Qinghai-Sinkiang region. Location Code Lake

Zone

Lat

Long

Geological Origin

I 2

Chao (F) Hongtze (F)

31°31'N 117°33'E Fluviatile 33°18'N 118°41'E Fluviatile

3

Kaoyu (F)

32°50'N 119°15'E Fluviatile

4

45°00'N

5 6

Khanka (F) (Xingka) Poyang (F) Tai (F)

7

Dongting (F)

8

II

42°00'N 87°00'E

10

Weishan (F) (Nanse) Bosten (S) (Baghrash) Buyr (F)

11

47°48'N

II 12 13

Ebi (S) Har Hulun (F/S)

II II II

44°55'N 82°55'E 38°18'N 97°35'E 49°00'N 117°27'E Fluviatile

14 15

Kyaring (F) Lop (S)

II II

31°IO'N 88°15'E 40 30'N 90 30'E

16 17 18 19

Nam (S) Ngoring (F) Oling (F) Pangong (S/F)

II II II 11

30 45'N 34°55'E 34°52'N 33°45'N

20 21

Porno (F) Qinghai (S) (Koko) Shalimo* (S) Tangra (S) Terinam (S) Ulan UI Ulungur (S) Yamdrok (S) Ziling

II II

28°35'N 37°00'N

11 II II II II II II

31°00'N 31°06'N 34°50'N 47°20'N 29°00'N 31°50'N

9

22 23 24 25 26 27 28

Province

132°24'E

29°00'N 116°25'E Fluviatile 31°15'N 120 1O'E Fluviatile & Coastal Lagoon 29° 18'N 112°45'E Fluviatile 0

34°35'N 117° 13'E Fluviatile

0

0

Jiangsu & Shantung Sinkiang

Tectonic

I 17°42'E

Tectonic Tectonic (Block-Faulting) 90 30'E Tectonic 90 00'E Tectonic 97°30'E Tectonic 78°43'E Tectonic (Graben) & Glacial (Scour) 90 20'E Tectonic 100 20'E Tectonic (Uplift) Tectonic 86°22'E Tectonic 86°35'E Tectonic 90 30'E 87° IO'E 90 40'E Tectonic 90 00'E Tectonic 0

0 0

0

0

0

0 0

Anhwei Anhwei & Jiangsu Anhwei & Jiangsu China & USSR Jiangsi Chekiang & Jiangsu Hunan

China & Mongolia Sinkiang Qinghai Inner Mongolia Tibet Sinkiang

Area (Km)

Elevation Depth (M) Volume (M) Mean Max (Km) 15 12.5

4.4 1.4

5.5

3.6 3.1

775

7

1.3

3.2

2.2

4,400

69

3,583 2,420

21 3

820 2,069

10.

18.5

2.1

16. 5.

24.9 4.9

34.5

6.7

31.

17.8

15

4.2

7.

5.4

1,019

1,048

9.7

15.7

9.9

610

583

2,74012,000 1,260

1,070 602 2,315

189 4,078 545.5

670 3,010

II. 26.6 5.7

8.

16. 13.1

4,708 768

2.

5. 10.7 4.7

Tibet Qinghai Qinghai Tibet & India Tibet Qinghai

1,940 611 618 600

4,627 4,269 4,285 4,248

6.9

30.7 13.1 43.

880 4,460

4,936 3,197

18.6

26.

Sinkiang Tibet Tibet Qinghai Sinkiang Tibet Tibet

464 1,400 1,000 610 745 678 1,640

464 4,724 4,613 4,859 468 4,441 4,530

50.

85.6

23.2

59.

5.9 16.

7.9

105.

"Lake area fluctuates around 500 km, the area indicated is shown from the most recent survey.

tion of more than 4,000 m and are certainly among the highest large lakes in the world (Table 2). The large lakes situated in the Pacific drainage basin, in contrast, are primarily a result of river action. They are shallow and eutrophic. The elevation of these lakes is low, less than 40 m (Table 2). Changes in river courses (primarily that of the Yellow River) and large deposits of river sediment contributed extensively to the formation of the large lakes in this region. For example, when the

Yellow River changed its course from 1194 to 1845 A.D. to run along the old course of the Huai River as it drained into the sea, large amounts of sediment were deposited at the mouth of the Huai River (Wong et al. 1984) Eventually these deposits blocked access to the sea. The Yellow River pushed out yet another outlet to the sea, while the sediment-blocked Huai River basin gave rise to Lakes Chao, Kaoyu, Nanse, and Hongtze. In a similar fashion, the sediments brought down by

238

W. Y. B. CHANG

the Yangtze River contributed to formation of Lake Tai, which was an ocean bay in 6,000 B.c., and Lakes Dongting and Poyang. The Pacific basin is the most populous area in China. These lakes are not only important for fishing, but also provide water for agriculture and aquaculture (Chang 1987). The area surrounding the lakes has long been a major population and culture center in China. The large lakes in this region are affected by seasonal flows in the major river systems. Lakes Poyang and Dongting, which receive water from Yangtze River tributaries and drain into the Yangtze River, vary in depth and size according to conditions in these tributaries. At the same time, Lakes Poyang and Dongting, which have capacities of 24.9 billion m 3 and 17.8 billion m3, respectively, serve an important role in regulating river water and in reducing water level fluctuations in the river. During the high water period, these lakes offer a storage place for river floodwaters; whereas, during the dry period, they provide water to the river, thereby enabling river transportation to continue without major interruption. HYDROLOGY Rivers are the primary means by which replenishment water reaches the large lakes in China. Seasonal monsoons and melting snow are two major water sources. The moisture brought by the seasonal monsoon is the principal source of water for the large lakes situated in the Pacific drainage basin. The Yangtze and Huai rivers are the major water carriers to the large lakes in this region except for Lake Khanka. Precipitation directly onto the lake surface constitutes a relatively small percentage of the total input of water « 5070) (Academia Sinica 1981). Annual evaporation is generally balanced by annual precipitation onto the lakes in the Pacific basin. The major water output is by way of river outflow (Table 3). In contrast, the large lakes situated in the TibetQinghai Plateau and Mongolia-Sinkiang area are often the final destiny of rivers with no outlets to the oceans. Evaporation far exceeds precipitation (Table 3). Direct precipitation to the lake basin is minimal and rivers are the major source of water input. A deficit in the annual water budget has been observed in many of these lakes, which are in the process of becoming smaller, shallower, and more saline. Lake Qinghai lost an entire meter in average depth between 1959 and 1966. As a result

TABLE 3. Water budget in percentage for lakes in the Pacific drainage basin and the Tibet-Qinghai-Sinkiang region (Modified from the Academia Sinica 1981 report).

Region Lakes

Pacific Basin

Tibet-QinghaiSinkiang Basin

Poyang

Hongtze

Bosten

3 97

3 97

99

7 93

2

3 97

60 40

100 0

Ebi

Input Precipitation onto lake River input

1

Output Evaporation River output

98

of this water deficit, the mineral content of the water has increased and water has become more saline. In the Pacific basin, high lake levels correspond with the monsoonal rains in June, July, and August; whereas, for the Tibet-Qinghai and Sinkiang areas, the high water levels correspond with both snow melting in the spring and precipitation in summer. Seasonal water level fluctuations are not particularly marked in the Tibet-Qinghai and Sinkiang regions, since evaporation is the major source of water output. For example, seasonal water level fluctuations for Lake Qinghai are within 1 m, whereas, fluctuations in both water level and size can be over 10 m in lakes which drain directly into the Yangtze River. In Lakes Dongting and Poyang, the annual differences in levels are 13.6 and 7.3 m, respectively. The size of these lakes also varies greatly with the seasons. For example, Lake Dongting varies in size from 2,740 to 12,000 km 2 depending on time of year. The extent of fluctuation in water level and size has been found to be related to the catchment basin and lake surface ratio. Lake Dongting has a ratio of 86.6: 1 and Lake Poyang has a value of 46.1: 1 (in both of these statistics, the catchment basin of the Yangtze River is not included) (Academia Sinica 1981). In contrast, the value for both Lakes Chao and Tai is 16:1, while the water level differences are only 2.5 and 1.3 m, respectively.

239

LARGE LAKES OF CHINA WATER QUALITY Pacific Drainage Basin Large lakes in the densely populated Pacific drainage basin are shallow and rich in nutrients and organic matter. They range from mesotrophic to eutrophic, with average Secchi disk transparencies between 0.2 to 0.5 m. The major sources of turbidity are sediments, organic solids, and algal biomass. Nuisance algal blooms (primarily bluegreens) are found in summer in all large lakes in this region except Lakes Dongting, Poyang, and Khanka. Little information is available for Khanka Lake, but this lake is situated in the sparsely populated part of Manchuria and has low nutrient inputs. The high flushing rates for Lakes Dongting and Poyang, which are expansions of large rivers receiving water from tributaries of the Yangtze River and then emptying into the Yangtze River, are the major reason for the absence of extended growth of phytoplankton despite the fact that these lakes receive loadings from extensive catchment basins. The peak flows through the lakes during summer for Lakes Poyang and Dongting are 22.4 x 103 m 3/s and 41.6 x 103 m 3/s, which correspond to a flushing rate of 13 and 6 days, respectively. The flushing rate and human population density are greater in the Lake Tai basin than in the basins of Lakes Dongting and Poyang (Table 4). The denser population in the Lake Tai basin has contributed to the more eutrophic conditions in that lake. Statistics on human population density compared with lake water volume appear to be useful indices of eutrophication since these measurements are correlated significantly with the nutrient loadings into lakes. Higher population density produced the larger loadings to lakes and higher nutrient concentrations (Figs. 2 and 3) (LECS'84 1984). This way of measuring levels of eutrophication is useful since nutrient measurements are often not available for large lakes in many third world countries. Because the lakes in the Pacific basin are shallow, wind and seiche provide sufficient turbulence to mix water vertically. The large lakes in this region are polymictic, and seasonal thermal and oxygen stratifications are not observed. In Lakes Dongting and Poyang, additional turbulence is found as a result of the large flow of water through these lakes. The dynamics of strong flows of water through these expansions of large rivers generate considerable turbulence in the stratum where the

TABLE 4. Comparison of total human population and trophic condition in Lake Tai and Lake Dongting basins in China. Parameters Total Population/ Lake Basin

Tai

Dongting

30,000,000

11,754,000

825

381

Human Population Density/Water Volume (no/1O'm 3)

5,000

671

Trophic Condition

Eutrophic

Mesotrophic

Yes

No

Transparency (m)

0.15-0.5

0.2

Dissolved Oxygen (mg/L)

6

7.9

Total-Phosphorus (mg/L)

0.06

0.002

263

13

Population Density/ km 2

Occurrence of Algal Bloom

Flushing Rate (days)

10

0

CD

•

~b

~

0

..J .. - I t )

. --

CD_ 0.1

0

• • • • • •

-

01 >.

c: '0 0 0

..J Q.

... I

N

0

0

.

• • •

• III • • • ••• • •• ••

10 10~ 10 4 105 106 T01al Population of Drainage Basin FIG. 2. Relationship between T-P loading per lakes and total population of drainage basin (LECS'S4 1984).

w. Y. B. CHANG

240 N

Tibet-Qinghai-Sinkiang Region

Q

-0 c'~ 0-

.o,? .3ECD ~

z· .0 ~

I

~

CD

0::

-_I

_0

-

~

o ,

• I

• I

• I

10-3 10-2 10-1 I Relative T-P LoadinQ (t 10-6 m-3 yr- I )

I

10

FIG. 3. Proportional relationship between relative loadings (per lake water volume) of total nitrogen and total phosphorus (LECS'S4 1984).

inflowing and generally colder water levels out in the region of the metalimnion. As a result, the metalimnion increases greatly and is not characterized by a climbing temperature gradient. The salinity for all these lakes is less than 5010 and pH values range from 7.5 to 8.5. The dissolved oxygen concentrations exhibit a diel cycle having its peaks at 4-6 p.m. and the lowest points at 2-6 a.m. The free carbon dioxide concentrations of these lakes show the reverse of the diel oxygen cycle. Photosynthetic activity can be attributed to these diel oxygen and carbon dioxide cycles, which have been observed in many ponds and shallow impoundments (Chang 1986). The oxygen concentrations for the pelagic part of large lakes are rarely below 5 ppm even at the bottom, except at the locations where direct untreated wastes enter the lakes and where circulation is limited, such as bays or arms of large lakes. The shallowness of these lakes and strong mixings by wind and currents are contributing factors to the absence of anoxic conditions in the lakes.

This region encompasses one half of the Chinese territory but is home to less than one tenth of the Chinese population. It has little or no major industry, but this may change soon, because several major industrial developments are being undertaken in Qinghai and Sinkiang provinces. The large lakes here are low in organic solids and nutrient loadings, and could be classified as either oligotrophic or mesotrophic. Population densities in the lake basins are low. Water transparencies (> 1 m) here are greater than those in lakes situated in the Pacific basin. Lake Qinghai, for example, has a water transparency betwen 5 and 10m in the deeper portions of the lake while those in the Tibet Plateau are 7-8 m. Many large lakes in this region are land-locked with water flowing into them but with no outlets. Evaporation is the major source of water loss. The proportion of salts in solution changes as strong evaporation causes the less soluble ones to precipitate. Mineral contents are high for these lakes, and mineral crystals have reportedly been found at the shore line and along the bottom of many saline lakes. Nine of these large lakes are always saline, while two others, Lakes Hulun and Pangong, alternate between saline and fresh water depending on the major seasonal water input. Three types of major ions are found in the lakes in this region: chloride, sulfate, and bicarbonate. Sodium and chloride ions predominate in the chloride waters of Lakes Eibe, Lop, and Qinghai; sodium sulfate and sodium chloride in the sulphate-chloride waters of Lake Ziling; and sodium and magnesium ions in the bicarbonate-chloride waters of Lake Hulun (Academia Sinica 1981). Borax lakes are also found in this region, but no information is available as to whether any of the large lakes included in this study are borax lakes. This is the most important region in the world for salt lakes. The lakes are generally deeper than those of the Pacific basin, and stable thermal oxygen stratifications occur in summer in the lakes with a depth greater than 20 m. Temperature profiles from most of the lakes are not available, but based on available information, those lakes having a depth greater than 20 m, such as Lake Qinghai, are dimictic since isothermal conditions occur during spring and autumn. Lakes with depths of less than 10 m (e.g., Lop Lake) are polymictic in summer. In addition, a few deep saline lakes situated on the Tibet Plateau can be meromictic in view of the

241

LARGE LAKES OF CHINA

seasonal air temperature and water input, but no report has yet described these high-altitude, deep, saline lakes. Surface ice can be found 5 to 6 months of a year. It usually begins to form in October or November and continues to be present through the following April or May. The thickness of the ice on lakes in the Tibet-Qinghai-Sinkiang region varies with the elevation and the location of the lakes, but in general it is around 1 m. Many of the deeper lakes in this region not only stratify vertically but they also manifest substantial differences between the nearshore and offshore areas; such differences were also found in lakes from other parts of the world (Beeton 1984). For example, water is generally isothermal in the nearshore zone of Lake Qinghai where there is a higher biomass of organisms, while water is stratified in the offshore zone of the lake, which is characterized by lower biological activity. The dissolved oxygen concentration differs with lake and season. Dissolved oxygen in the surface water of Lake Qinghai varies from 2 to 10 mg/L. Nuisance algal blooms (blue-greens) are not found in the lakes in this region. Diatom-predominant assemblages have been reported from Lake Qinghai during the ice free season. The average pH for these lakes ranges between 7.8-9.2 with high pHs in Lakes Qinghai (9.1-9.3) and Ziling (9.1), and low pHs for Lakes Lop (7.8) and Bosten (7.8).

HYDROBIOLOGY

All biological research and surveys of the Chinese lakes aim directly at providing information which can be used to increase aquatic food production. As a result, the available data primarily address issues related to the use of lakes in connection with aquaculture or aquatic food prodution. These data bases are available mostly for the lakes in the Pacific drainage basin, because the Tibet-QinghaiSinkiang area is sparsely populated and because natural conditions there, such as temperature and maturation period, are not suitable for aquaculture. There are also religious counterindications to the development of aquaculture in the Tibet-Qinghai-Sinkiang regions since many of the minority peoples who live there regard fish as the incarnations of gods, and do not eat them. Only limited information has been collected for this area. The data included here deal primarily with the large lakes in the lower Yangtze River and the Huai River basin; limited data from Lake

TABLE 5. Most common forms of phytoplankton found in lakes in the Pacific drainage basin. Chlorophyta Eudorina Pandorina Chlorella Pediastrum Coelastrum Westella Oocystis Ankistrodesmus Crucigenia Scenedesmus Ulothrix Cladophora Spirogyra Mougeotia Closterium Euastrum Cosmarium

Bacillariophyta Cye/otella Melosira Fragilaria Navicula Amphora Cymbella Surirella Nitzschia Diatoma Cyanophyta Chroococcus Aphanocapsa Microcystis Merismopedia Lyngbya Oscillatoria Aphanizomenon Anabaena

Qinghai (Koko) in the Tibet-Qinghai area are also included. Phytoplankton

More than 125 genera of algae have been reported from the large lakes in the Pacific basin (Nanjing Institute of Geography 1982). They include 7 families and 28 genera of Cyanophyta, 5 families and 6 genera of Pyrrhophyta, 20 families and 33 genera of Chrysophyta (including 3 families and 3 genera of Xanthophyceae and 14 families and 26 genera of Bacillariophyceae), 2 families and 5 genera of Euglenophyta, and 20 families and 60 genera of Chlorophyta (including 1 family and 4 genera of Charophyceae). Common forms of phytoplankton are shown in Table 5. The blue-greens appear in late spring and bloom in summer when the temperature is high. The blooms occur in the lakes where the flushing rate is slow and where nutrient inputs are high, such as Lakes Tai, Hongtze, and Kaoyu. The blooms are often found on the surface of the water and are comprised of Microcystis and Anabaena. The diatoms contribute a major proportion of the total assemblage in all seasons; in some lakes, however, spring and sometimes autumn have relatively higher diatom assemblages. Lack of clear seasonal diatom cycles may be a result of the absence of a stable seasonal thermocline, since the

242

w. Y. B. CHANG

lakes are shallow and diel vertical mixing occurs whenever wind is strong, and nutrients from sediments are resuspended in the water column. Difference in spatial distribution of diatoms is more noticeable; the diatom assemblages of sheltered bays and open waters have been found to differ substantially from each other in forms and numbers. The dominance of diatoms in these lakes is due to the high silica concentration (Nanjing Institute of Geography 1982) which at its lowest point is above 1 mg/L. The lowest concentrations of silica are often found during or immediately after diatom peaks, and silica concentration changes inversely with the density of diatom population in these lakes. The lowest silica concentrations in July and August were 7.92 mg/L (Hongtze), 13.6 mg/L (Kaoyu), and 3.2 mg/L (Tai). The green algae are transitory species. The population density peaks in spring and decreases in summer in these lakes. Blooms are found on the surface of sheltered bays and in the littoral zone of the large lakes. The groups Chrysophyta (Xanthophyceae and Chrysophyceae), Pyrrhophyta, and Euglenophyta are rarely found in major proportions and are important only in small lakes in this region except for Ceratium, which is the only species in Pyrrhophyta found in major proportions in Lake Dongting. The major percentage of the phytoplankton assemblage in the large lakes in the Pacific drainage basin is composed of the blue-greens (30-90070), the diatoms (10-35070), and the greens (10-35070). The high percentage of the blue-greens may be more a reflection of the time of sampling, since all the phytoplankton surveys were done in July and August. However, the blue-green blooms have become more frequent in recent years. The density of population assemblages varies with lakes and location within a lake. Lake Hongtze has the highest counts (> 110,000 individuals/L), while the counts for Lake Kaoyu (5,000-10,000 individuals/L) and Lake Tai (20,000 individuals/ L) are much lower (Nanjing Institute of Geography 1982). The difference in counts can be attributed as much to the difference in survey time as to the aquatic environments since the survey for Lake Hongtze was conducted in 1973, whereas the other two studies were made in 1960 and 1961. Since phytoplankton are viewed as the major food source for silver carp (Hypopthalmichthys molitrix), increases in the production of phytoplankton as a result of eutrophication have not been considered a major environmental problem

by the Chinese. Some large lakes and bays of large lakes, in fact, had been intentionally enriched to increase algal production. The increased eutrophication results in the dominance of blue-greens, which can be toxic in aquatic food webs and to birds and mammals (Nizan et al. 1986) and which were once considered of no food value for fish. However, studies have shown (Shi 1976, 1984) that silver carp can digest Anabaena spiroides which is the major species of blue-greens in the Pacific basin area. Increase in the stocking of silver carp has been proposed as a solution to reduce the nuisance blue-green bloom, but it is not known whether this program has been carried out since many Chinese lakes already have an extensive carp stocking program. Another method used to reduce the blue-green population is to collect the surface bloom of blue-green algae when they are concentrated in bays by wind and to use the collected algae as fertilizer in fields. This method has been adopted very extensively by the Lake Chao farmers, who use fermented blue-green algae to enrich the nitrogen content of the soil for agricultural crops. Phytoplankton assemblage data for the large lakes in the Tibet-Qinghai-Sinkiang area are limited. The data presented here are from Lake Qinghai (Koko), which is the largest lake in China and has been studied more extensively than other lakes in this region. The data were collected in 1961 and 1962 (Academia Sinica 1979, Melack 1983) and show phytoplankton counts as follows: winter, 76,000 individuals/L (Pyrrhophyta 50070, Bacillariophyta 30070); spring 32,000 individuals/L (Bacillariophyta 60070); summer, 71,000 individuals/L (Bacillariophyta 90070); and autumn, 57,000 individuals/L (Bacillariophyta 65070). Diatoms predominantely consisted of Cyclotella, Navicula,

Surirella, Cocconeis, A mphiprora, Epithemia, Diatoma, Pinnularia, Amphora, Gomphonema, Gyrosigma, and Achnanthes (Li 1959). Cladophora jracta and Rhizoclonium sp. cover large areas in the littoral zone near river inflows to water depths of 2 m; the wet weights often exceed 50 g/ m2 and reached as high as 2,400 g/m 2 • Zooplankton The groups of zooplankton found in the large lakes of the Pacific basin are protozoans, rotifers, cladocerans, and copepods. There are 28 families, 43 genera, and 68 species of protozoans, 13 families, 34 genera, and 52 species of rotifers, 7 fami-

LARGE LAKES OF CHINA TABLE 6.

Common forms of zooplankton.

1. Pacific Drainage Basin

Protozoa Sarcodina Difflugiidae Ciliata Colepidae Didiniidae Tetrahymenidae Paramaediidae Pleuronematidae Voricellidae Epistylidae Stentoridae Halteriidae Strobilidiidae Tintinnidae Codonellidae

Rotatoria Rotaria tardigrada Lepodella ovalis Trichotria pocillum Keratella cochlearis Keratella quaolrata Lacare luna Asplanchna priodonta Scaridium langicaudum Diurella parallus Polyathra trigla Synchaeta pectinata Pedalia mira Filinia longiseta

243

TABLE 7. Common forms of benthic organisms found in lakes in the Pacific drainage basin. Annelida Nereis japonica Limnodri/us hojjmeisteri Whitman is pipra Crustacea Neodaridina denticulate sinensis Palaemonetes sinensis Palaeman modestus Macrobrachium nipponensis Potamon denticulatus Neorhynchoplax introversus Eriocheir sinensis

Mollusca Cipangopaludina Bellamya Anadonta Hyriopsis Cristaria Lepidodesma Unio Corbicula

II. Tibet-Qinghai-Sinkiang Area Cladocera Moina Copepoda A rctochiaptomus Eucyclops Bryocamptus Acanthocyclops

Protozoa Arcella Vorticella Strombidium Centropyxis Rotatoria Pedalia Notholea Keratella

lies, 19 genera, and 32 species of cladocerans, and 9 families, 23 genera, and 31 species of copepods reported for these lakes. Common forms of zooplankton are shown in Table 6. The lakes in this region are shallow with extensive littoral zones; as a result, protozoans are most common zooplankton. The proportion of protozoans frequently exceeds 70070 of the total assemblage. Rotifers are the second-most common group of zooplankton including both benthic and planktonic forms (see Table 6). Cladocerans and copepods are low compared to the number of protozoans and rotifers and constitute less than 10% of the total assemblage in Lakes Tai, Hongtze, and Kaoyu. In the Tibet-Qinghai-Sinkiang area, the only zooplankton data available are from Lake Qinghai and are listed in Table 6. Since an increase in fish production is one of the principal functions in lake management, and since zooplankton is a major source for fish, a high abundance of zooplankton is viewed as insufficient utilization of natural resources. Higher stocking

rates of bighead and/or silver carp are often suggested. Benthos The groups of benthic organisms commonly found in the large lakes in the Pacific basin are annelidans, molluscs, and arthropods. There are 9 families, 17 genera, and 20 species of annelidans, 10 families, 28 genera, and 46 species of molluscs, and only 7 families, 9 genera, and 9 species of arthropods reported. Common forms of benthic organisms are presented in Table 7. Among them, insects are the principal arthropods. The crustaceans documented are those which serve as food, such as shrimps and crabs. The distribution and abundance of benthic organisms usually vary with water depth, sediment type, and aquatic macrophyte abundance. Abundance of benthic organisms in this area is inversely related to water depth. For example, Cipangopafudinas are most common between 1-1.5 m, few or none are found in depths greater than 2 m; Corbicufa are most often located in 1.5-2.5 m, and decrease substantially beyond 4 m. The higher densities of organisms are found in mud or sandy substrates, the number is low in clay substrates. The density of annelidans and insects increases with the macrophyte biomass, while the number of molluscs decreases as macrophytes become dense. The biomass of zoobenthos varies with lakes and regions of the lakes, ranging between 45 and 80 g/ m2 in Pacific basin lakes. The high biomass is attributed to the shallow depth, well oxygenated

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water, organic-rich sediment, and extensive growth of macrophytes. Benthos are considered an important part of the food web in terms of increasing aquatic production. Molluscs are harvested for food and animal feed, and are the primary food for black carp (Mylopharyngodon piceus), which is a major fish stocked in the large lakes in the Yangtze River delta. Crustaceans, such as shrimps and crabs, are also considered important and account for about 10070 of the total aquatic production from large lakes. The construction of weirs and dams substantially reduced the crustaceans in Lakes Tai, Hongtze, Kaoyu, and Nanse, but stocking wild larvae to the lakes has improved the total production of shrimps and crabs. As for the Tibet-Qinghai-Sinkiang area, the Chiromid, Tendipes reductus, is the most abundant benthic organism in Qinghai Lake. Biomass of the zoobenthos is low (ca. 1.2 g/m Z) (Academia Sinica 1979). The low abundance and number of zoobenthos is a combination of high HzS concentration, sandy substrate, and scarcity of macrophytes. Fish Distribution and Management The major mission of aquatic research in China is to increase food production, since the pressure is great to provide sufficient food for nearly 1 billion people. Added to this consideration is the significant increase in demand for staples such as fish, crab, and shrimp in recent years, particularly after the implementation of new economic initiatives which allow limited free trading. This increased need has provided a strong impetus to increase aquatic production, including a substantially higher fish yield from natural waters. Aquatic researchers and all levels of government have devoted major efforts to increasing aquatic production from usable water bodies, including extensive aquaculture and extended stocking programs in large lakes. In China, this basic concern has guided the development of fishery management and research in recent years. The waters of China contain approximately 700 species of fish, which belong to 33 families (Table 8). Twenty two of the 33 families are found in the Pacific drainage basin, while 7 families of fish are reported in the Tibet-Qinghai area. Only four families are recorded from the waters in the Mongolia-Sinkiang area, where climate is arid, and water temperature, water levels, and water salinity

TABLE 8. The distribution of fish families by genus/ species in regions in China. Region

Family Petromyzonidae Acipenseridae Polyodontidae Salmonidae Thymallidae Osmeridae Esocidae Engraulidae Catostomidae Cyprinidae Gyrinocheilidae Cobitidae Homalopteridae Siluridae Clariidae Pangasiidae Bagridae Amblycipitidae Sisoridae Akysidae Gadidae Gasterosteidae Cyprinodontidae Ophiocephalidae Symbranchidae Serranidae Percidae Anabantidae Eletridae Gobiidae Cottidae Mastacembelidae Tetraodontidae

MongolianSinkiang Basin

Tibetan Qinghai Plateau

Pacific Basin

2/3 1/1

III

5/9

12/36

2/5

1/7 1/1

1/1 1/4 1/2 1/1 1/2 1/1

Total

1/2 2/6

III 5/8 1/1 1/1 1/2

1/1 III 1/1 1/1 64/140 118/396 1/1 12/82 6/16 8/13 16/36 1/1 5/8 1/1 1/6 2/2 7/44 3124 1/8 1/3 2/6 5117 1/2 1/1 1/1 2/2 1/1 III 2/5 2/10 1/1 III 1/8 1/11 2/3 3/4 112 4/7 4/9 6/7 2/8 2/5 1/1 1/3 1/2

fluctuate remarkably between seasons and years. Among all fish, Cyprinidae is the most important and common family in China, and many species of this family are used for lake stocking programs and aquaculture. Of the indigenous species, about 16 species are economically important and have been used for major stocking programs and in freshwater aquaculture (Table 9). Among the 16 species, grass carp, black carp, silver carp, and bighead carp are the most important and most extensively used in both lake stocking programs and aquaculture. They are called the "four major household fish," and are the major economic fish species in China. They are used with the second major group of fish, called the "principal species" (Table 9), and are

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TABLE 9. Economically important fish species used for stocking and in fish culture in China. Species

Common Name

A. Major (Household Species) Ctenopharyngodon idella Mylopharyngodon piceus Hypophthalmichthys molitrix Aristichthys nobilis

Grass carp Black carp Silver carp Bighead carp

B. Important Cirrhina molitorella Cyprinus carpio Carassius auratus Parabramis pekinensis Megolobrama amblycephala

Mud carp Common carp Crucian carp White Amur bream Wuchang bream

C. Less Important

Megalobrama terminalis Xenocypris argentea Misgurmus anquillicaudatus Plagiognathops microlepis Ophicephalus argus Siniperca chautsi Siniperca scherzeri

Black bream Freshwater yellowtail Loach Small scale Snakehead Mandarin fish Spotted mandarin fish

stocked and raised according to natural environmental conditions and local preference. A third group of fish is rarely used in stocking and is primarily found in pond aquaculture and cage culture. The fish management of large Chinese lakes focuses on the followings aspects: 1) stocking, 2) establishing and improving spawning environments, 3) regulating the fishing period, 4) regulating water levels by weirs and dams, and 5) controlling fishing boats. The major purpose of stocking programs is to increase the total fish yield. The approach is to stock fish which can utilize all aspects of natural food resources in lakes. A balance in number and types of fish is usually stocked, each of which has a different diet and uses different parts of the natural resources. This stocking and management concept resembles a polyculture approach in pond cultures. Depending on the ecology and natural productivity of lakes, the number and the type of fish stocked in a lake are also different. For example, planktonic feeders such as bighead carp and silver carp generally prefer the upper layers of the pelagic zone, while the grass carp and Wuchang bream inhabit the coastal zone

TABLE 10. The natural diets of stocked species of fish in China. Species

Natural Diets

Foraging Zones

Silver carp

Mainly phytoplankton & some zooplankton

Surface and mid-water

Bighead carp

Mainly zooplankton & some phytoplankton

Pelagic zone

Grass carp

Aquatic vegetation

Mid-water and bottom

Wuchang bream Aquatic vegetation

Coastal zone

Mud carp

Refuse

Benthic zone

Common carp

Benthos

Benthic zone

Crucian carp

Benthos

Benthic zone

Black carp

Molluscs

Benthic zone

(Table 10). Mud carp, black carp, common carp and crucian carp feed in the deeper benthic zone. In general, grass carp, silver carp, and bighead carp are stocked in all lakes, while black carp is stocked in those lakes with a high mollusc population such as Lake TaL Wuchang bream, common carp, and crucian carp are stocked depending on natural habitats, climatic conditions, and local preference (Chang 1987). However, no ichthyophagous species are stocked in Chinese lakes. Predator control programs are often carried out in small lakes to reduce the ichthyophagic fish population; nevertheless, these programs have been found to be impractical for large lakes and are no longer undertaken there. Fingerlings are usually stocked in spring. In Lake Tai, for example, 10 million fingerlings of "household fish" (size 10 cm) in combination with other species (3 cm) such as common carp, Wuchang bream, and crucian carp are generally stocked every year. The stocking program is not restricted only to fish; in some lakes in the Pacific basin, crab and shrimp larvae are also stocked. Aquatic plants are also seeded in the littoral zone of the lakes as a part of an integrated program for providing and improving spawning environments for fish. The planting of aquatic vegetation provides not only the environments for fish spawning, but also food for grass carp and sheltered places for many species of fish young. In

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Y. B. CHANG

some lakes, areas are fenced off for spawning and clumps of floating grass are anchored in designated areas to provide additional spawning environments and to increase spawning success. During the spawning season, areas for fishing are regulated; for example, 20 areas are closed off in autumn in Lake Tai to protect the newly hatched young. Additional regulations also limit the number of fishing boats and fisherman allowed to fish in the lake and control the type and size of gill nets used in the lake. Weirs and dams are used for water control primarily in the lakes in the Pacific basin. These weirs and dams were constructed for flood control but they are also used to regulate water level in order to control spawning habitats. The selective openings of weirs and dams during larval fish migration from rivers to lakes have been shown to improve the total harvesting of fish, shrimps, and crabs in the year that follows. Total fish production in lakes varies with the size and richness of the natural water. In general, unit productivity declines as surface area increases (Chang 1987). While the total annual fish production from small lakes or embayments of large lakes « 10 km 2) can exceed 750 kg/ha, the average total annual production for large lakes in the Pacific basin is far below that level. Lakes Poyang and Tai have average annual production levels between 52 and 60 kg/ha. Lakes Dongting and Hongtze are about 45 kg/ha and Lake Chao is around 15-20 kg/ha. The average production in the lakes in the Pacific basin is higher than those in the TibetQinghai-Sinkiang area. Lake Hulun has an annual production of 30 kg/ha and Lakes Bosten, Ulungur, and Qinghai have an annual production of 16, 15, and 11 kg/ha, respectively. A brief period of higher production for Lakes Bosten, Ulungur, and Qinghai was observed in the 1960s when a major stocking and fish enhancing program was conducted in these lakes, but the higher yields were sustained only for a few years before returning to current levels of production, which are believed to be the capacity of the lakes in the area (Wong et al. 1984). The major explanation for low fish yield in the lakes of the Tibet-Qinghai-Sinkiang area is slow growth rate and long maturation time. As a case in point, the major fish harvested in Qinghai Lake is Gymocypris grzewalskii (Cyprinidae). The oldest of these fish captured from this lake was 21 yr old, but only weighed 2.7 kg and was 59 cm long. The average instantaneous growth rate, G, (Beverton-Holt model) for this species of fish is

only 0.07 (Zhang and Chan 1984). It is estimated that it takes 10 yr for this species of fish to reach 1 kg. The low nutrient inputs and short growth period contribute to the slow fish growth and low fish production in this lake. However, this level of production may not be considered low if compared with the catch statistics per unit area from the North American Great Lakes. The prodution increase due to aggressive stocking programs in China has been documented, but the extensive stocking of Cyprinidae can have major impacts on lake fishery. No data on this are available for large Chinese lakes. Liu (l984b) indicated from his 20-yr study on Dong Lake « 10 km 2), Wuhai, that such stocking programs substantially reduced the diversity of indigenous fish species in the lake. LAKE EVOLUTION Large lakes in China evolved differently depending on their geographical location, climate, and the extent of human inhabitation. In their early stages these lakes were mostly oligotrophic freshwater lakes, low in nutrients and organic matter. The distribution of aquatic vegetation was limited. As the aging process continued, lakes in the Pacific basin gradually became more eutrophic and shallow with an extensive growth of aquatic vegetation; lakes in the Tibet-Qinghai-Sinkiang area became saline with a high mineral content and a continuous reduction in water levels. The main factors which have been responsible for these changes in China are climatic conditions, tectonic uplift, sediment loads, and human population patterns. Climatic Condition and Tectonic Uplift Climate has been the most significant factor shaping the condition of large lakes in China, while tectonic uplift is the force that shapes the large lakes in the Tibet-Qinghai-Sinkiang area. Both factors have influenced changes in the physical, chemical, and biological conditions of lakes, including size, shape, volume, chemical composition, and types of organisms which live in the lakes. Tectonic uplift is the primary factor in the formation and shaping of the lakes in the TibetQinghai-Sinkiang area and is also the major element shaping the regional climate. Together, climate and tectonic uplift have created in this region one of the world's largest clusters of saline lakes and have produced water draw-downs as

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great as 80-213 m in some lakes in the Tibet plateau, based on estimations from watermarks on the shoreline (Wong et al. 1984). Increased precipitation in Manchuria close to Inner Mongolia has resulted in an increase in the water levels for Lakes Hulun and Bosten. The water level for Lake Hulun rose 3 m between 1939 and 1956, and another 3.5 m between 1956 and 1962; surface area has nearly doubled. Historically, the prevailing monsoons have significantly impacted the large lakes in the Pacific basin; the water levels and lake sizes vary according to the amount of monsoon rain available to the area. Records indicate that Lake Tai was completely dry in 1545, 1568, and 1589, and the water level was low during 1635-1644 when the monsoon rain was weak. On the other hand, floodwater ravaged the nearby towns and cities in 1670 and 1769, when the monsoon rain was strong (Nanjing Institute of Geography 1982). Sediment Loads

Sediment loads have been responsible for the formation and, more recently, for the significant reduction in size and volume of the large lakes in the Pacific basin. As discussed earlier, when the Yellow River changed course to run along the old course of the Huai River, large amounts of sediment were deposited at the mouth of the Huai River resulting in the formation of Lakes Chao, Kaoyu, Nanse, and Hongtze. The sediment load from the Yangtze River resulted in the formation of Lake Tai. The amount of sediment loads to the various lakes differs with the location and physical relation of these lakes to the river systems which drain into them. Lakes which receive water from tributary rivers and then empty into large rivers usually have higher sediment loadings than lakes with limited tributary inputs. The net sediment load to Lake Dongting (a river expansion lake) is 140 x 106 m 3 y-l, which raises the lake bottom about 5 cm/yr. Over a period of only 152 yr (1825-1977), this large amount of sediment loading reduced the lake size from 6,300 km 2 to just 2,740 km 2 (Liu 1984a, Wong et al. 1984). Lake volume was reduced from 293 x 108 m 3 in 1949 and 178 x 108 m 3 in 1977. Sediment loads have reduced not only lake size and volume but also their capacity to regulate floodwater. Since the average rainfall in this area has not changed significantly, the reduction in lake volume has exacerbated the annual fluctuation of

water levels and lake size. During the high water season (in summer), lake size may be several times the level characterizing the low water season. This water level fluctuation has a remarkable effect on aquatic vegetation, fish habitats, and other aspects of aquatic ecology. On the positive side, the seasonal floods have created a fertile lake sediment plain which lends itself to high yields in agriculture production. The successful utilization of this land has historically contributed great wealth to China and has stimulated progress and civilization. Human Impact

Sediment loading is a natural process which has contributed to major changes in Chinese lakes. The utlization of lakes by humans has further accelerated many changes in these lakes. Since 90070 of the population in China lives in the Pacific basin, most changes due to human impact are also seen in this basin. Cultivation of lakefront land in the Pacific basin, for example, has substantially affected lake environments. This activity began in China about 3,000 B.C., when inhabitants used flat lakeshore sediment plains for agriculture and aquaculture. The farmers used the soil surrounding their farms to build levees to prevent flooding at their newly claimed lakeshore farms. The construction of levees produced a network of waterways surrounding the farming field, forming a checkerboard pattern still visible today with canals neatly laid out every 2 to 5 km. The process of using lakefront land has contributed to the reduction and disappearance of lakes in China, particularly in the last 30 yr when the population in the Pacific basin has increased more than 2.5 fold. As a result, the process of cultivating the fertile lakefront land has also been accelerated. For example, the total lake area in the five provinces situated in the lower reaches of the Yangtze River diminished from 28,859 km 2 in 1950 to 18,695 km 2 in 1984, a reduction of more than 10,000 km 2 in less than 35 yr (Wong et al. 1984). While sediment loading has been an important factor in lake size reduction, the major factor responsible for the disappearance of many lakes, especially lakes smaller than 10 km 2 , has been human cultivation. In Jiangsu province, for example, 42 lakes have disappeared since 1957 as a result of agricultural activities. The large increase in human population and rapid development in industry have contributed to the deterioration of water quality in the lakes in the

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Pacific basin. The total human population increased from 400 million in 1950 to more than 1 billion in 1985. Most of this increase occured in the Pacific basin, where the population was historically dense. The rapid increase in the human population resulted in an increase in household wastes and agricultural runoff which drain into the waterways and lakes. Untreated household waste and the waste from agriculture and animal husbandry accelerate substantially the process of cultural eutrophication. This process is further affected by organic fertilization of lakes used to increase fish production, which has increased due to this practice, but the extensive lake fertilization has led to nuisance algal blooms, particularly blue-greens. Reductions in fish yields due to extensive nutrient loadings have been reported in some small lakes but not in the large lakes. Furthermore, in 1980 the government began the new economic initiative program, which stimulated the growth of industry and resulted in an increase in wealth and availability of goods. Among the improvements is the increase in the use of household detergents, in part because washing machines became available to Chinese households. The phosphorus detergent has begun to have a visible impact on the water quality. With increased cultural eutrophication, nuisance bluegreen algae blooms are now frequently noted in large lakes in areas where population density in the basin is high and water exchange rate is low. The new economic initiatives have stimulated major industrial development, which has also greatly increased industrial effluents. As a result, a large number of new contaminants and high levels of pollutants have begun to appear in Lakes Tai, Hongtze, and their tributaries. These contaminants include mercury, arsenic, phenol, copper, cyanide, zinc, lead, and chromium, and can be readily associated with the nearby major industrial sources (Nanjing Institute of Geography 1982). The highest concentrations of these pollutants are found in the tributaries which carry the industrial outflow from the cities where the factories are located. A decreasing concentration gradient is usually noted from the pollutant sources to the lakes. Among all the industrial pollutants, mercury poses the greatest concern and has been on the increase in both water and sediment samples from Lakes Tai and Hongtze. The presence of pesticides in the lakes has also increased substantially as more pesticides are used in this region to increase agricultural output. These increased industrial effluents and agricultural runoffs have resulted in

major changes in fish species. For example, when Lake Chao was surveyed in 1960, it had more than 90 species of fish; a similar survey conducted in 1970 found only 62. If a survey were made now, it is expected that the number would be even further reduced. Construction of extensive weirs and dams to regulate flood water by controlling water levels in lakes is another major change for which man is responsible in altering lake environments. The most notable biological consequence of this construction is the reduction in fish (finfish and crustaceans) production in lakes in the Pacific basin, since many species which use riverine spawning grounds are not able to return to lakes after these constructions. Reduction in recruitment of larval fish is the major explanation for this decrease in yield. FUTURE CONCERNS

Predominant factors influencing large lakes in China differ depending on the region in which a given lake is situated. In the Pacific basin, sediment load and human impact have been the most important influences, since these factors have brought about major changes in the lakes of the region and are expected to play an increasing role in shaping lake environments in the future. On the other hand, climatic conditions and tectonic uplifts have been the predominant factors influencing the lakes in the Tibet-Qinghai-Sinkiang area. Here, new patterns of human habitation and new priorities in terms of economic development may bring about significant changes in large lakes environments. In the decades ahead, human impact will be the major element to be considered, since major industrial centers are planned in this region. ACKNOWLEDGMENTS

The study was supported by the CSCPRC, National Academy of Sciences, and the faculty grant program to augment international academic partnership of the University of Michigan's Rackham Graduate School. Helpful comments from Drs. A. M. Beeton, L. S. Chang, D. J. Jude, R. Moll, R. Rossmann, and Mr. J. Barres are gratefully acknowledged. The author wants to thank Dr. C. E. Herdendorf and Mr. J. Lin for reviewing this paper and providing comments to improve this manuscript, and is particularly indebted to the scientists at the Nanjing Institute of Geography, Academia Sinica, for providing valu-

LARGE LAKES OF CHINA able information and data on lakes in China and useful discussions on matters concerning the management of Chinese lakes.

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on conservation and management of world lake environments. The Secretariat, LEC'84, Otso, Japan. ____ . 1984b. Dong Lake. In Data Book of World Lakes. Proceedings of SHIGA Conference 84 on conservation and management of world lake environments. The Secretariat, LEC'84, Otso, Japan. Melack, J. M. 1983. Large, deep salt lakes: a comparative limnological analysis. In Saline Lakes, ed. U. T. Hammer, pp. 223-230. The Hague: Dr. W. Junk Publishers. Nanjing Institute of Geography. 1982. Lakes in Jiangsu Province. Nanjing, Jiangsu: Jiangsu Scientific and Technical Publisher. Nizan, S., Dimentman, c., and Shilo, M. 1986. Acute toxic effects of the Cyanobacterium Microcystis aeruginosa on Daphnia magna. Limnol. Oceanogr. 31(3):497-502. Shi, Z. 1976. Comsumption and assimilation of Anabaena Spiroides by silver carp Hypopthalmichthys molitrix. Acta Hydrobiologica Sinica 6: 89-95. ____ . 1984. Fish culture experiment with the filtrate of Anabaena spiroides. Acta Hydrobiologica Sinica 3:357-362. Wong, H. T., Tao, H. S., Woing, S. 1., and Zhang, L. 1984. Chinese Lakes. Beijing, China: Commerce Publisher. Zhang, Y. S., and Chan, N. 1984. Population estimation of Gymnocypris przwalskii in Qinghai Lake. In Aquatic Science & Technology 1:63. Beijing, China: Agricultural Publisher.