GeoJournal 40.1-2: 39-44. © 1996 (October) Kluwer Academic Publishers. Printed in the Netherlands.

The water quality of Lake Tailhu and its protection

Huang, Yiping, Nanjing Institute of Geography and Limnology, Academia Sinica, Nanjing, P.R. China

Zhu, Min, Centre Station of Monitoring Lake Taihu Water-Quality, Wuxi, Jiangsu Province, P.R. China

Received 28 September 1995; accepted 28 December 1995

Abstract: Lake Taihu, the third largest fresh water lake of China, with a surface area of 2338 km 2, is located in the Changjiang River Delta, the most advanced economic zone in China. It is a typical saucer-like shallow lake in its depth and shape. During the last decade, the rapid economic development of local agriculture and industry both in the urban and rural areas of the Taihu region has made great advances. Great quantities of pollutants have been discharged into the lake, its nutrient content has increased continuously, and phytoplankton blooms have occurred in some areas. Water quality protection in Lake Taihu is very impor- tant because of its close relation with economic development and people's daily life. It is urgent to have comprehensive pollution control in Lake Taihu. Based on water quality mon- itoring data in Lake Taihu from 1986 to 1993, the dynamic variations of water quality and eutrophication trends have been analyzed, showing obvious spatial and temporal variations. The main water quality factors were compared with the standards for drinking water and indicate considerable change with the seasons. Basic srrategies to protect water quality and prevent eutrophication are discussed.

1. In troduct ion

Lake Taihu, located in the south of the Changjiang River delta, is one of the f ive famous and largest freshwater lakes in China (Figure 1). The catchment area of Lake Taihu is 36500 km 2, the surface area of lake is 2338 km 2, its m ax i m um depth is 4.0 m, the mean depth is 2.0 m, and the total water storage is 52 × 108 m 3. It is a typical saucer-like shallow lake in its depth and shape. More than 200 rivers enter into Lake Taihu at present. Located on the northern border of the subtropical broad-leaved forest region, it belongs to the southeast monsoon climate area. The rainy season (Plum Rains) always appears in summer, and typhoons and rainstoms have considerable impact on the area. The annual mean temperature is 15- 16 °C, average precipitation is 1000-1400 mm, and there are over 2000-3000 hours of insolation.

The Taihu region is not only an agricultural center but also one of the most flourishing economic regions in China with abundant natural resources. The population in the Taihu region is 33 million. The lake usually receives its inflow from the southwest

and discharges to the northeast due to the catchment 's topographic features. Because of the rapid develop- ment of local agriculture and industry, human activ- ities have exerted much influence and pressure on the ecological environment:, and a large number of pol- lutants have been discharged into the lake, leading to an increase in lake nutrients and a deterioration of its ecology and environment for many years. Investiga- tion and research on eutrophication evaluation have been carried out for a long time on this lake (Carlson; 1977; Jorgensen 1980; Huang 1993).

2. Water qual i ty eva luat ion

Lake Taihu serves as a source for drinking water, irrigation, aquatic production, navigation and tourism. The annual average water quality in Lake Taihu is described in Table 1. During the five surveys in the period of 1987-1988, data from 37 sampling locations were obtained. The results of the analysis of the various water quality parameters were compared with the standards given by the Chinese

40 E Huang and M. Zhu

Nantong City

,Wuxi city

, q

/ t l

Lske Taihu

" • ~ . - .11, Dianshan

Figure 1. Catchment area of Lake Taihu.

Table 1. Annual average water quality data in Lake Taihu* (as mg/L except pH)

Item 1986 1987 1988 1989 1990 1991

Water temperature (°C) 18.2 16.9 17.0 17.4 18.2 17.3 Transparency (m) - 0.55 0.35 0.40 0.40 0.40 Chlorophyll-a - 0.007 0.012 0.006 0.043 0.012 pH 7.88 7.73 8.06 7.75 7.90 8.10 Dissolved oxygen 8.88 9.15 8.97 8.60 8.66 9.0 Susp. solids 62.3 21.6 70.2 59.1 41.5 53.6 Total hardness(CaO) 44.4 48.2 47.9 48.3 52.2 54.5 CODM° 3.23 3.30 4.20 3.86 3.89 3.70 BOD 5 1.37 1.77 2.66 2.38 2.96 2.60 Ammonia N 0.267 0.274 0.306 0.525 - - Nitrite N 0.009 0.023 0.025 0.042 - - Nitrate N 1.021 0.991 1.192 1.207 - - Volatile phenols 0.002 0.001 0.003 0.002 0.002 0.001 Cyanide 0.001 0.001 0.002 0.002 0.001 0.001 Arsenic 0.003 0.001 0.001 0.001 0.001 0.004 Mercury-Tot 0.00003 0.000025 0.000025 0.000029 0.000025 0.000025 Chromium-hex 0.002 0.002 0.002 0.002 0.002 0.002 Lead 0.012 0.006 0.005 - 0.005 0.005 Cadmium 0.0024 0.0001 0.0001 - 0.0001 0.0005 Nitrogen-Tot - 1.542 2.772 2.447 2.349 1.89 Phosphorus-Tot - 0.029 0.055 0.070 0.058 0.051

* 23 sample points for 1986 to 1991; 37 sample points in 1987 to 1988.

National Environment Protect ion Bureau (CNEPB) for dr inking water (Table 2). The results of this evaluation of water quality for drinking water stan- dards change with the seasons. The average water quality in 1987-1988 was near the standards state,

but after September every year it deter iora ted and by March was worst (Table 3). For the geographical distribution of average water quality in Lake Taihu (1987-1988) see Figure 2. General ly speaking, water quality in Lake Taihu is slightly polluted, however,

Water quality o f Lake Taihu

Table 2. Results of water quality surveys in Lake Taihu (1987-1988)

41

No. Parameter Item

Appar. Min. Max. Average III Typ. Standard Number Exceeding rate value of surface exceeding rate (%) (%) (mg/1) (mg/1) (mg/1) water for drinking

1 pH - 6.40 8,99 7.71 6.5-8.5 4 2.5 2 DO - 0.69 14.20 9.00 > 5 mg/L 6 3.6 3 CODM. 100 1.39 6.82 3.16 < 6 mg/L 7 4.2 4 BOD 5 99 0 6.99 1.69 < 4 mg/L 3 1.9 5 NO3--N 100 0.007 5.80 1.04 < 20 mg/L 0 0 6 NO2--N 99.4 0 0.460 0.028 < 0.15 mg/L 6 3°6 7 NH 3 86.7 0 0.102 0.0082 < 0.02 mg/L 10 6,3 8 KN 100 0.02 5.832 1.112 < 1 mg/L 70 41.7 9 TP 76.0 0 0.608 0.0579 < 0.05 mg/L 68 40 10 TOC 93.2 0 15.90 7.84 < 10 mg/L 41 23.3 11 PHN 6.1 0 0.0146 0.0002 < 0.005 mg/L 1 0.6 12 CN 24 0 0.004 0.0006 < 0.2 mg/L 0 0 13 As 10.2 0 0.004 0.00018 < 0.05 mg/L 0 0 14 Hg 4.2 0 0.00075 9 × 10 -6 < 0.0001 mgJL 1 0.6 15 Cr 6+ 9.5 0 0.002 0.00014 < 0.05 mg/L 0 0 16 Cd 44.7 0 0.0015 0.00014 < 0.005 mg/L 0 0 17 Pb 100 0.002 0.018 0.0075 < 0.05 mg/L 0 0 18 Cu 100 0.003 0.022 0.0092 < 1.0 mg/L 0 0 19 Escherichia coli 100 20 240000 < 10000/L 10 7.1 20 Total bacteria 100 5 17400 < 10000/L 1 0.7

Table 3. The spatial distribution and evaluation of surface water quality in Lake Taihu

Year Month TYPE percentage of area (%) Mean water Main pollutant quality

I II III IV V

1987 May 0 28.3 43.5 28.0 0.2 III (3.0) TP, TOC, KN, NH3 July 8.3 43.7 40.0 6.8 1.2 II-III (2.48) KN, TOC, TP Sep. 7.5 24.6 56.3 10.7 0.9 II-III (2.72) TOC, KN, COD Dec. 0.4 0.6 20.1 78.8 0.8 III-IV (3.78) KN, TP, TOC

1988 Mar. 0 0 0 87.8 12.1 IV-V (4.12) KN, TP, TOC

1987-1988 0 0 81.2 18.4 0.4 III (3.19) KN, TP, TOC, NH 3

major pollutants such as nitrogen, phosphorus, related nutrients, organic substances and eutrophica- tion are already serious. This change in water quality apparently took place over the recent thirty years. For instance, total inorganic nitrogen increased from 0.12 mg/1 in 1960 to 1.12 mg/1 in 1987 (Figure 3) (Fan 1993). Heavy metal pollution almost does not exist.

3. Trends in Lake Taihu water qual i ty

The variations of total nitrogen (TN), total phos- phorus (TP), chlorophyll-a in different areas of Lake Taihu are shown in Figures 4 to 6. In Lake Wuli, TN and TP increased by 23.6% and 62.1% respectively, from 1988 to 1989, and chlorophyll-a increased by 340.6% from 1988 to 1990. Lake Wuli is already a serious eutrophied water body. In Meiliang Bay, TP

increased by 46.5% from 1988 to 1990. TN in Meiliang Bay has already been higher than eutroph- ication standards, so it too can be placed in the higher eutrophicated grouping. The sudden blooming of plankton in July, 1990 ('Table 4) greatly affected the drinking water supply and caused an enormous loss of RMB 130 million. The water of the central lake body belonged to the middle-degree category of eutrophication. Along the lake shores, because of the pollution discharge from nearby areas, BOD 5 had an increasing trend (% -- 0.886) during the year. This indicated that pollution discharges along the shores were increased year by year. Organic pollution in main tributaries and the outlet of the lake was increasing, and the lake shore areas were classified as a eutrophied water body.

From 1988 to 1990, TN, TP, CODMn, BOD5 and chlorophyll-a were all increasing at different degrees

42 Y. Huang and M. Zhu

I II IiI I%' V

Figure 2. The spatial distribution of seasonally averaged water quality type (1987-1988) in Lake Taihu.

1.0'

0.S'

1960

~ A / ~ -TIN ",..` ,.~.k~j././/'" "'NOi-N . .//

II ,,x rx. k" / \ ! x, ¢ 11 "~" " ~ / / " ' - - - - - - . p NH,-N L ~ " . ~ ~ ' " NO" N ...... : ...... .'"'" ":'"":"",,:,'" "".'"- --. ..... ; ..... : ..... ; .... . I~--

77 78 79 80 81 82 83 84 85 86 87 J

Figure 3. Annual changes in inorganic nitrogen in Lake Taihu.

in the different areas of Lake Taihu. Meanwhile, recent monitoring in Lake Taihu shows that the all cell numbers and coverage areas of algae have con- spicuously increased. The biomass of phytoplankton in Lake Taihu has increased rapidly in the past thirty years, especially since the 1980s. In the 1960s, the average count of algal cells was 22000/1 in western Taihu. In 1980s it reached 92000 cells/1 and 28.4 million cells/l in 1991, a hundred times more than that in 1960s. The composition of dominant species has changed. The ratio of blue-green and green algal species exceeded diatoms, and now formed the dominant species. The change in the zooplankton community has been characterized by a reduction of

(rag / I) " IN Lake Wuli . . . . L a k e open ~aters

. . . . . . . Meiliang Ba) . . . . . . . Lake shoreline areas 5

I standards I mg~i

I i I /917 19~85 19~89 1990 1991 year

Figure 4. Nitrogen-tot. yearly variation in different regions of the Lake Taihu area.

• rP(mg / I)

t ~ I aim Wuli O J 4 A Meiliang Bay

0.08 / / ~'~.

0.04 ~ - ~ ' - ~ " = ' = - - " : ' : . . . . . . . O,O$mg/I

f * 0.02 J

I ! |

19a7 i m , 89 , ;9 , , . ,

Figure 5. Phosphorus-tot. yearly variation in different regions of the Lake Taihu area.

0.10

0.08

i 0.06 0.04 I

0.02

Lal~ Wu~

1997 19Sa

-'~----~1989

' ~ - "~1990

__ ~ 1991 year

MeiliangBay l.ak¢open~aters Lake shoreline areas

Figure 6. Chlorophyll-a variation from 1987 to 1991 in different regions of the Lake Taihu area.

the number of species and an increase of individuals. There were 91 species belonging to different genera of zooplankton in 1991. The peak quantity was 1184 ind./1 in western Taihu. The composition and biomass of benthos and macrophytes were also undergoing a significant change. All these phenomena show that the level of eutrophication in Lake Taihu is getting more serious, and the areas affected are becoming enlarged.

Water quality of Lake Taihu

Table 4. Algae concentration near the inlet pipe of the Meiyuan Water Supply Plant in July 1990

43

Depth from surface(m) 0.0 1.0 3.0 4.0 Average

Algal cell numb. (10 s i/l) 13.2 4.8 5.7 6.5 7.6 Biomass (mg/1) 10.8 43.8 48.5 50.6 38.4

4. Water quality protection and eutrophication prevention strategies for Lake Taihu

Water quality protection in Lake Taihu is a very important need which has close relations with economic development and people's daily life. It is very urgent to have comprehensive pollution control in Lake Taihu. The basic strategies to protect Lake Taihu and prevent eutrophication are as follows:

1. Control the total quantity of pollutants entering the lake According to our data (Huang 1990), the annual amount of nitrogen and phosphorous entering Lake Taihu is 21,806 tons and 1,988 tons, respectively. In more detail, the amount of nitrogen and phosphorous brought into the lake by its tributaries entering rivers are 20,241 tons and 1,552 tons separately, accounting for 72% of TN and for 78% of TR The amount of nitrogen from non-point sources is 7,823 tons and that of phosphorous is 422 tons, constituting 28% of TN and 21% of TR The amount of nitrogen and phosphorous delivered from point sources only accounts for 1% of their total load. Therefore, in order to limit the input of nitrogen and phosphorous, the prime objective is to reduce the nutrient loading carried by rivers that enters Lake Taihu. Because this pollution is by non-point sources, including inflowing rivers, it is much more serious than that by point sources, and it is essential to control this pollution pathway. In order to reduce non-point pollution, the following measures should be taken: Waste water treatment plants should be set up in the cities around the lake, especially in those situated around the upper reaches such as Huzhou, Changxing amd Yixing. The waste of large-scale animal husbandry, fowl and fish farms should be controlled, Innovated technologies of using fertilizers and pesticides, reform of the farming system, afforestation, control of pollution from navigation and tourism must all be undertaken as soon as possible.

2. Reduce the nutrient load from internal sources The rapid increase of phytoplankton, the reduction of zooplankton and the decrease of macrophytes caused by trawling and suction dredging to collect snails as well as pen-culture, lead to the destruction of the ecosystem's nutrient balance. In 1991, the amount of nitrogen in the lake water was 1.7 times more, and the amount of phosphorous was 3.5 times more than

that in 1980. Therefore, it is important to alleviate the impact of internal nutrient loading on Lake Taihu.

Some water plants such as water hyacinth can grow in the eutrophic areas to utilize the nutrients and absorb detritus. From 1991 to 1994, some ecological engineering (biological, chemical and physical) experiments were carried out in several pumping regions of the drinking water plants around Meiliang Bay of Lake Taihu, and some good results were obtained. The ecological engineering not only protected the quality of the water supply, but also took nutrients out of the lake by removing the water plants, and also restraining the growth of algae.

Eutrophication of Lake Taihu has intensified the destruction of its ecosystem, therefore, reducing internal loading through ecological engineering and developing means to collect the algae is worth con- sideration.

3. Set up and complete planning for Lake Taihu environmental protection The Lake Taihu basin covers an area of 36,500 square kilometers, including seven cities, and 35 counties and 989 townships (towns) with a population of 33 million. Its environmental and ecological factors are quite complicated, and therefore, it is necessary to have an integrated authoritive organization. The two provinces (Jiangsu, Zhejiang) and the municipality (Shanghai) within the Lake Taihu basin should work together to provide capable manpower to form a Lake Taihu resource protection committee, charged with organizing and co-ordinating pollution control in Lake Taihu. Then a master plan,with a phased pro- gramme and practical implementation schemes should be worked out. A developmental strategy which can coordinate the development of the economy, society and environment also should be established by means of various incentives, con- strained and co-ordinated measures including policy, planning, technology, engineering, economy, admin- istration and legislation. The balance of the "resource, environment and sustainability" can be kept at a desirable level so as to maintain the good circulation of Lake Taihu's natural ecological system by reasonable resource use, reuse and various man- made ecological systems. The ability to control environmental pollution depends on the economic and technical capacities as well as on environmental consciousness of the whole society and of its man- agement. There is a possibility that through the

44 Y. Huang and M. Zhu

adjustment of economic-social development strate- gies and the reform of economic-environmental policy and management system, correct policies and counter measures for the following items should be given high priority: (1) integrated and co-ordinated local development plans, (2) reasonable layout of industries and energy production, (3) technical progress of proposed new projects and old enter- prises, and (4) pollution control of main cities, towns, and natural resources protection. Thereby the objec- tive can be reached, which is to alleviate the conflicts between economic-social development and environ- mental protection, and to avoid the occurrence of a vicious circulation of the lake's ecosystem.

4. Use appropriate legislation to strengthen the public consciousness for environmental protection. It is very important to draw up authoritative laws and policies and to strengthen public consciousness for environmental protection. If the managers of enter- prises and relevant authority sections have no solid appreciation of environmental protection, it would be very difficult for them to pursue the environmental policies. Also the public with a low level of eduction will not understand the real harm of pollution. So it is very important to popularize the knowledge of environmental problems. The public's consciousness and supervision will give the vital go ahead for envi- ronmental protection.

Regulations regarding the control of water quality in the Lake Taihu basin have to be formulated so as to harmonize the relations among the two provinces and one municipality in respect to the management

of water quality of the drainage systems. In order to reduce the phosphorus concentration below 0.03 mg/1 in Lake Taihu, appropriate policies and legislation should be established. The laws and regulations have to be in agreement with the practical water quality protection in the Lake Taihu water areas and should be worked out in the localities. Those which have been confirmed as appropriate through practice could turn gradually into regional laws and regulations so as to guarantee their validity in this lake basin.

References

Carlson, R. E.: Atrophic state index for lakes. Limnol. Oceanogr. 22, 361-369 (1977).

Fan, C. X. et al.: Variations in nutrient elements and evolution of plankton in Taihu Lake. Mon. of Nanjing Institute of Geography and Limnology, Academia Sinica.No. 9, pp. 37-47. Science, Press. Beijing, China 1993.

Huang, Y. P.: Study on the water quality status in Taihu Lake and its future trends, Men. of Nanjing Institute of Geography and Limnology, Academia Sinica. No.9, pp. 27-36. Science Press, Beijing, China 1993.

Huang, Y. P.: Lake Taihu in Jiangsu province. In: Jin, C. X. (ed.), Eutrophication of lakes in China, pp. 185-194. China Science of Environment Press Beiiing, China 1990.

Jorgensen, S. E.: Lake Management: Water development, Supply and Management, Volume 14, pp. 11-21. Pergamon Press 1980.

Sun, S. C.; Huang, Y. P.: Lake Taihu, pp. 1-3; 250-261. Ocean Press, Beijing, China 1993.

Sund, H.; Yu X. G. et al.: Environmental Protection and Lake Ecosystem, pp. 159-166; 178-179; 269-270. China Science and Technology Press, Beijing, China 1994.