Analysis of eutrophication state and trend for lakes in China

Papers from Bolsena Conference (2002). Residence time in lakes:Science, Management, Education

J. Limnol., 62(2): 60-66, 2003

Analysis of eutrophication state and trend for lakes in China

JIN XIANGCAN

Chinese Research Academy of Environmental Sciences, Beijing, China

ABSRACT

The article analyzes the present state and trend of eutrophication of lakes in China and concludes that lakes throughout the country are commonly undergoing the process of eutrophication: most of urban lakes are facing hypertrophication, many medium-sized lakes are of eutrophic state, some lakes even approaching to hypertrophic level. The five large freshwater lakes are in the con-dition of eutrophication, especially Lake Caohu and Lake Taihu are already in the state of eutrophication, water quality is deterio-rating and ecosystem is destroyed. According to domestic and foreign experiences of the successful demonstrations in eutrophication and pollution treatment, this article puts forward the theory of combining source control with ecological restoration, which as the guidance for eutrophication control of lakes in China.

Key words: lake, eutrophication, countermeasure

1. GENERAL SITUATION OF LAKES IN CHINA

AND ITS MAIN ENVIRONMENTAL

PROBLEMS

China is a country boasting of many lakes, with over 24,880 lakes, 2300 of them with a surface higher than 1 km2. The total area of all the lakes reaches 70,988 km2, accounting for about 0.8% of the total area of the coun-try, and most of lakes distributes in the East Plain, Qingzang Altiplano, Mengxin Altiplano, Yungui Alti-plano, and Northeast Plain-hills, also called Five Big Lakes Zone. All lakes are with a total storage capacity of 707.7 billion m3, of which freshwater storage capac-ity amounts to 225 billion m3. Besides, there are 86,825 reservoirs, with a total storage capacity of 413 billion m3. The two add to a total freshwater capacity of 6380 × 108m3, forming one of the most important freshwater resources in the country, playing a major role in sup-plying drinking water for the people as well as water for industrial and agricultural production, and aquaculture, travel industry, improving climate, generating electricity etc.

Owing to various natural geography and climate condition of Chinese lakes, in the recent several decade years discharge of large quantities of pollutants and hu-man activities of irrational exploitation, environmental problems of lakes shows complexity and diversity. There are five main environmental problems: eutrophi-cation, pollution of organic pollutants, salting of lakes in the west of China, shrinking of area and reduction of water quantity of lakes and destruction of ecosystem. But at present eutrophication is the most important envi-ronmental problem in many lakes and thus brings a tre-mendous influence on sustainable development of soci-ety and economy in lake regions. 2. PRESENT STATE OF TREND

EUTROPHICATION OF LAKES

Investigation of 1980s and 1990s shows eutrophic lakes was mainly located in the middle and lower stream of Changjiang River, Yungui Altiplano, part of Northeast Plain-hills and Mengxin Altiplano. But all the urban lakes almost have been in the eutrophic level be-cause the urban lakes are small and seriously destroyed by the domestic wastewater.

Owing to the fact that people have not realized the frailty of the lake ecosystem and lack of environmental awareness, human activities such as land reclaimation and destruction of plants around lakes, discharge of large quantities of industrial and agricultural waste water into lakes, and irrational development and utiliza-tion of natural resources of lakes, and so on have greatly affected the environment of lakes, which now face many environmental problems. And lakes throughout the country are commonly undergoing the process of eutrophication. As a result, the cycling of the ecosystem of many lakes is damaged, causing great losses to pro-duction and people's life in lake regions. Figure 1 shows trophic state of over 50 Chinese lakes. Eutrophic and hypertrophic lakes account for 66% and hypertrophic lakes amounts to 22%. Therefore, lake eutrophication has become an important environmental problem now.

Investigation shows that many freshwater lakes, even some lakes in the district where people seldom lived have accounted to the eutrophic state and most of them have been in the high trophic level. The charac-teristics of trophic state of lakes follow as:

1) The five largest freshwater lakes have been in the

eutrophic level, they have been generally facing eu-trophication with high nutrients (Tabs 1a, 1b), for

Eutrophication in China 61

example, concentration of TN is above 10 times higher. Now Lake Taihu and Lake Caohu are al-ready in the eutrophic state, with some waters even approaching to hypereutrophic level. And the other three lakes may also enter into eutrophication in the condition of higher nutrient load.

2) The urban lakes are facing serious eutrophication. According the investigation of many years, the ur-ban lakes have been facing serious eutrophication with extremely high concentration of TN, TP, Chl-a and low transparency (SD) in water bodies and mainly in the hypertrophic level accompanying the serious organic pollution with very high concentra-tion of COD Mn and BOD 5 in waters, exceeding the Grade V water(GB3838-88) (Tab. 1).

3) Most of medium-sized lakes are already of the eutro-phic state. Lots of medium-sized lakes are already of

the eutrophic state with TN and TP approaching or

Fig. 1. Trophic state of main lakes in China.

Tab. 1a . Trophic state and estimation of over 50 Lakes in China. **Biggest freshwater lakes.

Index (C i ) TSI G Trophic conditions Chl-a TP TN SD COD Mn BOD 5DO Py NH 3-N pH Estimated Practical

μg l -1mg l -1 mg l -1 mg l -1 mg l -1mg l -1 mg l -1 East Plain Lakes Zone

**Poyang L. 1.34 0.094 0.67 0.65 2.05 2.39 8.43 47.60 39.31Meso-eutrophic Meso-trophic **Dongting L. 1.68 0.119 1.168 0.39 2.13 0.78 9.71 39.14Meso-eutrophic Meso-trophic **Taihu L. 5.35 0.052 1.11 0.70 3.16 1.69 9.00 41.57Meso-eutrophic Meso-eutrophic **Hongze L. 0.130 1.39 0.38 2.85 7.11 46.00Meso-eutrophic Meso-eutrophic **Caohu L. 15.010.088 1.43 0.25 3.76 2.33 46.06Eutrophic Eutrophic Qiandao L. 3.72 0.057 0.40 5.83 1.85 0.81 35.6 Meso-trophic Meso-trophic Gucheng L. 4.05 0.055 1.73 0.34 2.65 1.03 7.27 42.93Meso-eutrophic Meso-eutrophic Nansi L. 3.73 0.21 3.38 0.50 21.38 6.79 51.40Eutrophic Europhic Dianshan L. 5.98 0.088 1.95 0.57 4.30 1.73 8.90 50 43.26Meso-eutrophic Meso-eutrophic Baiyangdian L. (80s)

0.082 2.30 5.00 4.24 11.68 0.396

47.79Eutrophic Eutrophic

Yangui Altiplano Lake Zone

Dianchi Lake Caohai L. 77.410.504 0.40 14.74 61.84Hypertrophic Hypertrophic Inner L. 101.74 1.401 0.28 16.58 67.00Hypertrophic Hypertrophic Average of Dianchi L. 49.700.270 0.60 8.40 56.43Hypertrophic Hypertrophic Average (except for InnerL. and Caohai L.) 16.760.123 0.65 7.07 50.26Eutrophic Eutrophic

Erhai L.(1995) 0.03 0.29 3.00 0.57 127 34.52Meso-trophic Meso-trophic Cibi L. in Dali (1995) 0.02 0.29 1.40 0.53 135 35.07Meso-trophic Meso-trophic Xihu L. in Dali (1995) 0.02 0.46 1.00 1.51 148 38.88Meso-eutrophic Meso-trophic Haixihai L. in Dali (1995) 0.01 0.56 1.20 0.90 218 37.31Meso-trophic Meso-trophic Tianchi L. in Dali (1992) 0.02 0.51 2.30 1.55 133 37.30Meso-trophic Meso-trophic Jianhu L. in Dali (1993) 0.03 0.33 1.20 1.37 72 37.56Meso-trophic Meso-trophic Mutunhai L. in Dali (1994) 0.02 0.28 0.8 0.86 254 37.90Meso-trophic Meso-trophic Dayindian L. in Dali (1995) 0.02 0.49 1.70 1.50 611 39.54Meso-eutrophic Meso-eutrophic Xinyun L. (1990) 0.045 0.67 1.50 3.98 2.16 418.3 41.96Meso-eutrophic Meso-eutrophic Yilong L. (1988) 0.122 0.62 22.18 7.18 5.22 1.23 8.93 55.39Hypertrophic Hypertrophic The east of Yilong L. 0.08 0.70 18.92 9.24 6.25 1.06 8.91 54.09Hypertrophic Hypertrophic The middle of Yilong L. 0.154 0.65 20.51 6.59 6.18 1.34 8.95 55.32Hypertrophic Hypertrophic The west of Yilong L. 0.133 0.50 27.31 11.15 3.24 1.30 8.92 58.54Hypertrophic Hypertrophic Qilu L. 0.09 2.187 0.40 8.29 3.55 7.30 0.59 8.98 52.09Hypertrophic Hypertrophic

Fuxian L.1988) 0.0098 0.15 7.10 0.80 0.57 18.02 25.98Oligo-trophic Oligo-trophic Qionghai L. (1988)

0.6490.137 1.21 2.13 1.488 0.50 6.70 14.440.003 32.12

Meso-trophic Meso-trophic

Jin Xiangcan 62

exceeding the eutrophication transition concentra-tion and some waters even reaching hypertrophic level (Lake Dianchi and Lake Erhai).

The concentration of COD Mn, BOD5, TP and TN is high in eutrophic lakes. Secchi disk transparency is lower than 1.0 m, and in most of them even lower than 0.5 m. Water quality is more and more deteriorating and the lake ecosystems appear to be greatly damaged.

Also the problem of nutrient elements released from sediment is serious. For example, 29% area of Lake Taihu is coverd with 0.1 m or more of highly contami-nated sediment. The total storage capacity amounts to 69.1 million m3. Algal nutrients (especially phosphorus) are the most important elements released from sedi-ments, together with the refloating of small organic granule. There are so much nutrient elements in sedi-ments that Lake Tajihu can still maintain an high level of eutrophication, even if all the external loading is re-duced to zero.

As a consequence of the extremely high trophic condition, ecosystem in many lakes is commonly dam-aged due to deterioration of water quality, lowering of transparency, and destruction of lakeshore vegetation and wetland. The change of biological community ac-companying the raising of pollutants and nutrients level is hereafter briefly summarized.

Phytoplankton densities largely increase, diversity of phytoplankton community declines, and dominant spe-cies of phytoplankton community change into species characteristic of eutrophic environments as cyanobacte-ria, which dominate in almost all the lake.

In eutrophic lakes phytoplankton produce high blooms and seasonal changes are reduced. In the hyper-trophic and eutrophic lakes average yearly densities of phytoplanktonic algae vary between 1,000,000 and 10,000,000 ind l-1 and in the urban lakes the average algae per year amounts to between 10,000,000 and 100,000,000 ind l-1 (Tab. 2).

Diversity of phytoplankton community decrease. In eutrophic lakes seasonal change of composition of phytoplankton community tends to simplicity and the general tendency is that the higher is the concentration of nutrients in lakes simpler is the species composition

Tab. 1b. Trophic state and estimation of over 50 Lakes in China.

Index

(C i) TSI G Trophic conditions

Mn53

μg l-1 mg l-1 mg l-1mg l-1mg l-1mg l-1 mg

l-1

Quingzang Lake Zone

Qinghai L. 0.02 0.08 8.00 1.41 5.6329.27Oligo-Meso-trophic Meso-trophic Namucuo L. 0.042 0.031 0.411 9.00 27.70Oligo-Meso-trophic Oligo-trophic Mengxin Altiplano Lake Zone

Boshiteng L. 5.22 0.018 0.92 1.74 6.02 1.207.3036.3 38.00Meso-trophic Meso-trophic Caiwobao L. 0.099 5.93 0.27 5.21 1.58 7.7622.00 1.32 51.05Eutrophic Eutrophic Wulungu L. 0.031 1.98 3.30 13.36 1.41 8.868.100.55 43.89Meso-eutrophic Meso-eutrophic Hulun L. 0.140 1.88 0.47 13.36 1.419.19230 46.41Eutropjhic Eutrophic Wuliangsuhai L. 4.45 0.067 1.873 1.21 6.44 1.86 6.43121844.70Meso-eutrophic Meso-eutrophic Hasuhai L. 15.51 0.090 1.21 0.88 7.68 2.317.35138746.89Eutrophic Eutrophic

Dihai L. (1989) 32.56 0.22 2.25 0.61 132.472.187.18111.750.025 51.55Eutrophic Eutropic

North-East plain hills Lake Zone

Songhua L. 0.024 0.543 0.85 5.28 292 41.87Meso-eutrophic Meso-eutrophic Tianchi L. (in Jilin) 0.78 1.208.90 0.064 7.7

23.82Oligo-trophic Oligo-trophic Xingkai L. 0.10 0.55 0.60 5.54 1.968.50 3.11 40.43Meso-eutrophic Meso-eutrophic Jingpo L. 9.62 0.40 0.98 1.32 7.00 1.218.890.170 46.25Eutrophic Eutophic Wudalianchi L. (90) 0.419 1.67 1.15 7.97 7.97225.1547.92Eutophic Eutophic Urban Lakes

Luhu L. 86.40 0.22 3.04 0.38 9.68 8.719.6655.75Hypertrophic hypertrophic Liuhua L. 239.530.530 6.38 0.20 23.3616.5111.4463.80Hypertrophic hypertrophic Dongshan L. 132.000.420 6.15 0.29 11.7414.266.9360.71Hypertrophic hypertrophic Liwan L. 149.650.620 8.53 0.31 14.4317.504.7444.70Hypertrophic hypertrophic

Xihu L. (in Hangzhou) 64.80 0.17 3.06 0.53 7.18 4.8410.15 0.76 54.43Hypertrophic hypertrophic Cihu L. 11.20 0.090 2.20 0.67 3.94 3.687.2046.87Eutrophic Eutophic DongHu L. (in Wuhan) 15.5 0.125 2.50 0.80 12.56 3.50100051.52Eutrophic Eutophic Moshui L. (in Wuhan) 156.590.740 16.05 0.15 13.6 25.714.2662.87Hypertrophic hypertrophic Xuanwu L. (in Nanjing) 103.000.478 3.50 0.25 8.95 10.708.64476758.53Hypertrophic hypertrophic Gantang L. (in Jiujiang) 37.60 0.240 1.73 0.56 26.17 6.418.0354.00Hypertrophic hypertrophic Nanhu L. (in Changchun) 113.110.529 5.45 0.19 78.289.768.5863.30Hypertrophic hypertrophic Mogu L. (1988) 32.12 0.21 2.33 0.62 9.88119352.09Eutrophic Eutophic Dianchi L. (Caohai) 77.41 0.504 0.40 14.7461.84Hypertrophic hypertrophic Reservoirs

Miyun R. (1990) 3.02 0.0175 0.115 2.15 2.41 1.687.9858.180.063 33.02Meso-trophic Meso-trophic Yuqiao R. 6.56 0.02 1.24 1.97 3.36 3.0210.269950046.49Eutrophic Eutrophic Dahuofang R. (88-91) 5.433 0.06 1.09 2.10 4.20 7.40267.650.153 41.37Meso-eutrophic Meso-eutrophic Gaozhou R. 0.739 0.022 0.369 2.11 1.64 32.60Mesotrophic Mesotrophic

Eutrophication in China

63

of phytoplankton community and lower bio-diversity. In some lakes such as Gantang Lake composition of phytoplankton community is very simple and only one of algae species takes absolute advantage all over the year. In some lakes such as Luhu Lake, Liuhua Lake and Xuanwu Lake etc. only one of algae take advantage in most seasons (Tab. 4).

Dominant species change to the species indicating the eutrophication. Table 4 shows that in eutrophic lakes the dominant species are species characteristic of the eutrophic waters. In many lakes the quantities of the dominant species increase sharply, which leads to "waters bloom" (Tab. 3).

Tab. 2. Yearly average concentration of Chl-a , number of individuals and biomass of phytoplankton for some lakes in China.

Chl-a n. ind. Biomass Trophic state

(μg l -1) (×104 l -1

) (mg l -1) Luhu L. (Guangzhou)

86.40 9695.7 Hypertrophic Liuhua L. (Guangzhou) 239.53 1561.0 51.94 Hypertrophic Dongshan L. (Guangzhou) 132.00 4505.1 Hypertrophic Liwan L. (Guangzhou) 150.00 5664.0 Hypertrophic Xihu L. (Hangzhou) 64.80 4319.8 Hypertrophic Moshui L. (Wuhan) 157.00 9692.7 Hypertrophic Donghu L. (Wuhan) 15.50 322.4 Eutrophic Xuanwu L. (Nanjing) 103.00 4767.0 Hypertrophic Gantang L. (Jiujiang) 37.60 5316.3 Hypertrophic Nanhu L. (Changchun) 113.11 1237.4 Hypertrophic Caohai in Dianchi L. 139.00 6467.0 Hypertrophic U r b a n l a k e s

Outer of Dianchi L. 23.80 1364.9 Eutrophic Poyang L. (Jiangxi) 1.34 65.45 Meso-trophic Taihu L. (Jiangsu) 5.35 32.1 5.86 Meso-eutrophic Caohu L. (Anhui ) 15.01 214.1 Eutrophic Erhai L. (Yunnan) 562.3 4.66 Meso-trophic Qilu L. (Yunnan)

290.9 Hypertrophic Bositeng L. (Xinjiang) 5.22 340.9 1.36 Mesotrophic Wulungu L. (Xinjiang) 0.031 630.3 1.34 Meso-eutrophic Xika L. (Heilongjiang) 3.67 Meso-eutrophic Jingpo L.(Heilongjang)

9.62 376.1 9.80 Eutrophic Wudalianchi L. (Heilongjiang) 211.7 6.17 Eutrophic Gucheng L. (Jiangshu) 4.05 162.9 Meso-eutrophic Nansi L. (Shandong) 3.83 232.4 Eutrophic Dianshan L. (Shanghai) 7.05 55.2 Meso-eutrophic Fulun L. (Neimeng)

3430.5 8.10 Eutrophic Wuliangsuhai L. (Neimeng) 4.45 1218.0 2.69 Meso-eutrophic Daihai L. (Neimeng) 32.56 1127.3 1.19 Meso-eutrophic Qionghai (Sichuan)

0.70

12.4

Mesotrophic

Tab. 3. Seasonal succession of dominant species of phytoplankton in some of eutrophic lakes in China. Legend: Ana = Anabaena ; Ank = Ankistrodesmus ; Aph = Aphanocapsa ; Apha = Aphanizomenon ; Ast = Asterionella ; Bin = Binuclearia ; Chla = Chlamydomonas ; Chlo = Chlorella ; Cho = Chodatella ; Chrc = Chrcoococcus ; Chrm = Chromulina ; Chro = Chroomonas ; Clo = Closterium ; Coe = Coelastrum ; Cos = Cosmarium ; Cru = Crucigenia ; Cry = Cryptomonas ; Cyc = Cyclotella ; Dac = Dactylococcopsis ; Din = Dinobryon ; Epi = Epithemia ; Eug = Euglena ; Fra = Fragilaria ; Lyn = Lyngbya ; Mel = Melosira ; Mer = Merismopedia ; Mic = Microcystis ; Nav = Navicula ; Ooc = Oocystis ; Osc = Oscillatoria ; Ped = Pediastrum ; Pho = Phormidium ; Pla Planktosphaeria ; Rap = Raphidiopsis ; Sce = Scenedesmus ; Sch = Schroederia ; Syn = Synedra ; Tra = Trachelomonas ; Eud = Eudorina ; Anop = Anabaenopsis ; Chl = Chloroccum ; Nos = Nostoc .

Lake Spring Summer Autumn Winter Trophic state Cihu L. Nav,Frg,Cyc,Sce,Ped Sch,Chro,Osc,Mer,Dac Osc,Mer,Ooc,Ped,Chla Cry,Nav

Eutrophic

Gantang L. Mer,Dac Mer,Dac Mer,Dac Mer,Dac Hypertrophic Moshui L. Sce,Mer,Cyc Mic,Sce,Mer Mic,Cys Cyc,Mer,Chlo Hypertrophic Xihu L. Osc,Syn,Apha Lym,Sce Lyn,Ose Osc Eutrophic Nanhu L. Mic,Mer Mic Mic Hypertrophic Luhu L. Osc,Chro Osc,Dac Rap,Osc Rap,Osc Hypertrophic Liuhua L. Mic Mic Mic,Osc Mic,Osc Hypertrophic Liwan L. Cyc,Sce Sce,Cyc Sce,Eug Sce,Cyc,Cry Hypertrophic Dongshan L. Cyc,Cry Cyc Cyc,Chro Cos,Osc Hypertrophic Honghu L. Chlo,Eug,Ank,Eud Chlo,Chro,Eug,Chl Cos,Osc Chl Eutrophic Caohu L. Chro,Mic,Cry Mic,Ana Mic,Chro Cyc,Mic,Chro

Eutrophic Hulun L.

Mic,Ana,Chrc,Apha,Mer,Coe Mic Mic

Eutrophic Wuliangsuhai L. Chla,Sce,Mer,Chlo Mer,Chrc,Mic,Coe,Ana Mic,Sym,Ana,Lym,Coe,Sce Sce,Mic

Eutrophic Dianchi L. Osc,Mic,Cyc,Syn Osc,Chrc,Cyc,Cry,Sce,Eug Cyc,Cry,Chla,Mica,Apha Osc,Mic,Apha,Mica,Eug

Eutrophic Mogu L.

Osc Osc,Dac Osc Osc

Hypertrophic

Jin Xiangcan 64

Accompanying the evolution toward hypertrophic status of lakes, the area of macrophyte gradually shrink. For example, before 1970s Lake Dianchi showed a good water quality with 100% coverage of aquatic vascular bundle plants, and in outer of Lake Dianchi with SD of over 2 m and 90% coverage of various aquatic vascular bundle plants. But after the middle of 1970s, due to gradual intensity of human activities, Lake Dianchi changes to eutrophication and water quality rapidly de-teriorated, leading some species to die out, community composition became more simple. In 1990s the area covered by aquatic plants accounted for only 1.8% of the total lake area.

In 1950s Lake Dianchi have multiple community types: Chara vulgaris community, Ottelia acuminata community, Vallisneria spiralis community, Myrio-phyllum spicatum community, Potamogeton malainus community, Acorus calamus community, Scirpus validus community, E. crusgallia community, Phrag-mites communis community, and Potamogeton crispus + M. spicatum + Hydrilla verticillata + C. demersum community etc. After 1970s Ottelia acuminata commu-nity died out, in succession C. vulgaris community died out, owing to inning and repairing of lake shore A. calamus and S. tabernaemontani community deraci-nated too, V. spiralis community, P. malainus commu-nity and P. cripus + M. spicatum community were died gradually, P. pectinatus community with high tolerance for pollution evolved, and E. crassipes community took advantage. In 1990s in Caohai of Lake Dianchi P. pectinatus community of submerged macrophytes dis-tributed in one or two sites; As for hydrophyta natantia, E. crassipes community took advantage with big bio-mass, and Alternanthera sessilis, Oenanthe japonica, A. imbricate and L. minor etc. distributed sporadically in E. crassipes community (Tab. 5).

During the oligotrophic state, there were 44 species of submerged macrophytes in Lake Dianchi and 18 spe-

Tab. 4. Composition and succession of aquatic plants community in Caohai of Lake Dianchi. Y =

yes; numerical value in the bracket means percent which this community accounts for all the area

of all the aquatic plants.

Community

type 1950s 1960s 1970s 1980s 1990s

Emerged macrophytes community

Phragmites communis Y(1.1)

Y(1.2)

Y(0.2)

Y

Y Zizania caduciflora Y(1.1)

Y(1.1)

Y(0.3)

Y

Y Shoenoplectus tabernaemontani Y(1.7)

Y(1.2)

Y(0.1)

Acorus calamus Y(1.1)

Y(0.1)

Y(0.01)

Echinochloa crusgallia Y(1.1)

Y(0.6)

Y(0.01)

Hydrophyta natantia community

Lemna minor Y(1.1)

Y(0.4)

Y(0.004)

Y(0.001)

A. imbricata Y(0.2)

Y(0.001)

Y(0.01) Eichhornia crassipes Y(1.2)

Y(18.6)

Y(57.6) Nymphaeoides peltatum Y(4.3)

1

Y(0.02)

Submerged macrophytes community

Ottelia acuminata Y(40.4)

Y(46.9)

Vallisneria spiralis Y(14.2)

Y(19.4)

Y(6.9)

Chara vulgaris Y(17.1)

Y(16.2)

Ceratophyllum demersum Y(2.8)

Y(2.5)

Y(0.02)

Myriophyllum spicatum Y(9.1) Y(14.1) Y(2.1) Y(1.4) Y(14.1)

Potamogeton malainus Y(7.1)

Y(3.4)

Potamogeton maackianus Y(3.4)

Y(4.8)

Y(3.5)

Potamogeton pectinatus Y(10.4) Y(10.1) Y(15.3)

Potamogeton cripus Y(1.1)

Y(2.5)

Y(1.39)

Y(0.01)

Total communities Y(14) Y(15) Y(16) Y(6) Y(4)

Tab. 5. Main composition and change of submerged macrophytes community in various trophic state in Dianchi and Erhai lakes.

n. species Dominant species Trophic state

Dianchi Lake

1950s 44

O. acuminata, C. vulgaris, V. spiralis, M. spicatum, P. maackianus, D. demersum, P. cripus Oligotrophic

1960s

O. acuminata, V. spiralis, C. vulgaris, M. spicatum, P. malainus, P. maackianus, D. demersum,

P. cripus

Oligotrophic

1970s 30

P. pectinatus, V. spiralis, P. maackianus, P. malainus, M. spicatum, P.cripus, C. demersum Mesotrophic

1980s 20

P. pectinatus, M. spicatum, P. cripus Eutrophic

1990s 12

P. pectinatus, M. spicatum Hypertrophic

Erhai Lake

1950s

P. pectinatus, N. marina, O. acuminata Oligotrophic

1960s Oligotrophic

1970s 18

H. verticillata, C. demersum, P. maackianus, P. lucens Oligo-mesotrophic

1980s 15

H. verticillata, V. spiralis, P. maackianus, C. demersum Mesotrophic

1990s 13

P. maackianus, V. spiralis, Z. palustris, H. verticillata, C. demersum Mesotrophic

Eutrophication in China 65

cies in Lake Erhai. In the mesotrophic state the number of species declined to 30 species in Lake Dianchi and 13 species in Lake Erhai. Such species as O. acuminata and C. vulgaris disappeared. In the hypertrophic state the number of species of Lake Dianchi declined to only 12, sporadically distributed in a few areas of the lake shore and with small scale (Tab. 6).

Some species with strong tolerance for pollution rapidly increased in density and biomass, while other species gradually declined and, in general, the distribu-tion area of aquatic plants becoming small. For exam-ple, P. pectinatus come into being only one dominant species community with absolutely preponderant bio-mass, distribution area and high frequency, leading to P. pectinatus covering all the lake.

Frequent emergency of "water blooms" in many ur-ban lakes of China may do serious harm to the lake. First it may produce obstacle to water function of lakes, then it will have impacts on aquaculture and scenic tourism, and algae toxin will endanger the health of people in the lake basin. In early 1980s microcystin (one of the algae toxin) was separated from Lake Donghu in Wuhan. The microcystin was also detected in the drinking water on Tongan (Fujian province) where has high rates of liver cancer. The highest concentration of microcystin in Lake Taihu was 38.5 μg l-1 in 2001.

The trend of the eutrophic lakes in China is quite rapid. Table 7 shows trophic state of 34 lakes in China. Most of lakes were of in middle- trophic state, account for 91.8%. Eutrophic lakes account for 5.0% (Tab. 6). In only ten years, oligo-trophic lakes change to be middle-trophic lakes. The percent decrease from 3.2 to 0.53. Middle-trophic lakes change to be eutrophic lakes, the percent increase from 5.0 to 55.01 (Tab. 7). In 1996, Eutrophic and hypertrophic lakes account for 85%. Therefore, lake eutrophication in China has become an important environmental problems at present.

Excessive discharge of pollutants into lake is one of the important causes of eutrophication of lakes in China. Table 8 shows that now the ratio between present pol-lutant discharge and the maximal allowable load of the lake are of 3 to 10 in many lakes, and the value is even higher in urban lakes, which lead to deterioration of water quality and eutropohication of lake waters gradu-ally.

3. COUNTERMEASURE FOR LAKE

EUTROPHICATION CONTROL

All kinds of irrational activities and excessive nutri-ent load into the lake are the main causes of lake eutro-phication and ecological disorder. Therefore, we should stop all kinds of irrational activities first, then take ef-fective measures to restore lake ecosystem gradually.

Taking into consideration the domestic and foreign experience, the strategy to control eutrophication is hereafter described.

1) To combine source control with ecological

restoration

Pollution sources are obviously the most direct rea-son of lake eutrophication, so control pollution sources is regarded as the preliminarily step. But lake is a lived waterbody and we could not control eutrophication ef-

Tab. 6. Trophic state and estimation of 34 lakes in China

(1978-1980).

Oligotrophic

Mesotrophic

Eutrophic Number 4 16 14

% 11.76

47.06

41.2

Area (km2) 3354.6 95929 5220.6

% 3.2

91.8

5.0

Tab. 7. Trophic state and estimation of over 50 lakes in China

(1987-1989).

Oligotrophic

Mesotrophic

Eutrophic Number 1 7 14

% 4.5

31.8

63.6

Area (km2) 29.5 2493 3084.9

% 0.53

44.45

55.0 Tab. 8. Pollutant load (t y-1) of some lakes in China.

Present pollutant discharge Maximum allowable load

Cr Cr Dianchi L. 1021 8981 41,672 356 5012 5754 Taihu L. 5168 72,017 224,032 587 2167 59,532 Caohu L. 2677 26,802 66,773 225 5400 36,036 Erhai L. 122 1154

Yuqiao L. 228 4458 28 888

Jin Xiangcan 66

fectively with the single measure of source control. Lake eutrophication treatment requires to take not only source control measures but also ecological restoration measures. Ecological restoration mainly pay attention to rehabilitation of aquatic plant in the shallow waters, restoration of lakeshore in the water-land crisscross area, and replantation of terrestrial ecological zone in erosion area. Only by ecological restoration measures, lake ecosystem could be restored to normal cycle and eutrophication could be controlled basically.

2) To protect lake from the point of view of the whole

catchment

Lake is only part of a ecosystem of the whole lake catchment. Therefore to maintain normal ecosystem re-quires to control and protect lake from the point of view of the whole catchment.

3) The synthetical treatment and management

Synthetical treatment and managementis proved to be more rapid and effective measure in prevention and treatment of lakes. CONSULTED LITERATURE

Jin Xiangcan et al. 1995. Lakes in China - Research of their environment (I). China Ocean Press.

Jin Xiangcan et al. 1990. Eutrophication of lakes in China.

China Environmental Science Press.

Nanjing Institute of Geography and Lake, CAS. 1989. Survey of Chinese Lakes. Science Press.

Wuqinglong, Wangyunfei. 1999. Analysis on succession of bio-community in Lake Erhai. Lakes Sciences, 3: 267-273. Yuguoying et al. 2000. Relation between succession of aquatic plants and change of water environment. Lakes Sciences, 12(1): 73-79.

Sea and Lakes Society in Prefecture Jiangsu. 1987. Sea and Lake Science Paper Collection. Agriculture Press, Beijing, China.

Jin Xiangcan, Tuqingying et al. 1990. Investigation of the En-vironment of Lakes and Reservoirs in China. Chinese En-vironmental Science Press, Beijing , China.

Morikiro Aizaki & Harukuni Tachibana. 1990. Limnlogical Comparison of Characteristics of Water Quality in Chi-nese and Japanese Lakes, Proceedings of Symposium on "Limnological Comparison of Chinese and Japanese Eu-trophic lakes" at Hokkaido University: 95-96.