Biological diversity in rivers, lakes and reservoirs

 

1 Species richness in the inland waters of China

2 Impact of human activities on the biodiversity of inland waters

3 Conservation of inland water biodiversity

 

1 Species richness in the inland waters of China

       There are many rivers, lakes and reservoirs in China with abundant biotic resources and many different species. There are around 800 species and subspecies of freshwater fish, some 348 species of rotifers, about 206 species of freshwater copepods and some 162 species of cladocerans (about 40% of the known species in the world). A comprehensive investigation of freshwater algae has not yet been completed, but it is already known that there are 253 species of Chroococcophyceae (Cyanophyta), i. e., 80% of the known species of the class; 347 species of Zygnemataceae (Chlorophyta), i.e., 40% of the known species of the family; 301 species, 81 varieties and 33 forms of Oedogonium and Bulbochaete; and some 437 species and varieties of hydro-vascular plants and macroalgae.

       The biota and species diversity are apparently different in different rivers, lakes and reservoirs. Generally, large rivers and lakes have a favorable environment and a long history, resulting in a bigger biodiversity.

       (1) Rivers

       Biodiversity in rivers generally tends to increase progressively from the upper to the lower reaches. In upstream reaches, rheophilus freshwater fishes predominate, whereas anadromous and estuarine fishes also enter the middle and lower reaches. Of the four large river systems in China, the Heilongjiang River, which represents a cold temperate water system, is inhabited by about 100species of fish, including cold water species such as Campetra reissneri and Coregonus ussriensis and northern endemic species such as Acipenser schrenckii. The Yellow River, which represents a warm temperate water system, is inhabited by about 190 species and subspecies of fish. The numbers of species are few in the upper reaches, and all belong to the Schizothoracinae and Nomacheiliae. In the middle reaches, the species increase and include endemic species such as Coreius septentrionalis. The lower reaches have many more species, most of them belonging to the flood-plain category, as well as some migratory fishes. The Yangtze River, which represents a mid-subtropical water system, has 332 species and subspecies of fish, of which 291 are freshwater, dominating the flood-plain category and around one half belong to the Cypriniidae. Migratory species, such as Macrura reevesi and Anguilla japonica, are rich in the lower reaches. Chinese endemic and rare fishes, such as Psephurus gladius and Myxocypxinus asiaticus, chiefly occur in the Yangtze River. The Pearl River, which represents a south subtropical water system, has 313 species and subspecies of fish, of which 270 are freshwater and more than 100 are endemic, such as Carassioides cantonensis and Luciocyprinus longsoni.

       In the other the water systems, the fauna of the Liaohe and Haihe water systems is situated between the Heilongjiang and Yellow River and each have 100 species of fish. The Huaihe water system, whose fauna is situated between the Yellow and Yangtze Rivers, has 120 species of fish. The Qiantangjiang water system is inhabited by 157 species of fish, of which 123 are freshwater. The Minjiang water system has 160 species of fish, of which 118 species are freshwater and chiefly belong to the Cyprinidae, but with other common fishes. The water systems in Taiwan and Hainan Islands have 97 and 122 species of fish, of which 81 and 105 species are freshwater, respectively. Their pisci faunas are similar to that of mainland China. The Lancangjiang, Nunjiang and Yaluzangbujiang water systems are all plateau rivers with abundant fish species, chiefly members of the Schizothoracinae and Barbinae. In these rivers, large numbers of endemic species exist and their faunas are complicated. The Talimuhe water system has only about 10 species of fish, including a few endemic ones such as Carassius carassius and Tinca tinca.

       (2) Lakes

       The biological resources of lakes are, typically, extremely abundant. In the shore zone there are emergent plants, floating plants, submerged plants, and adnascent peribiota on the stems and leaves of such hydrophytes, with abundant plankters and benthic animals. In the middle and hypolimion, hydrophytes are scarce and the benthos decreases whereas the plankton and fish remain abundant.

       According to their geographical distribution, lakes in China can be divided into five major districts:

       a. The Eastern Plain Lake District (including lakes in the middle and downstream of the Yangtze and Huaihe Rivers and downstream of the Yellow and Haihe Rivers), mostly has mesotrophic and eutrophic, shallow-water, lakes with abundant species (Table 1), and where most Chinese common freshwater biota occur. For example, in Taihu Lake, there are 134 genera of phytoplankton, 122 species of zooplankton, 68 benthic species, 66 species of aquatic plants and 106 species of fish; in Poyanghu Lake, there are 14 genera of phytoplankton, 112 species of zooplankton, 102 species of aquatic plants, 65 species of shellfish and 122 species of fish.

       b. The North-eastern Plain and Upland Lake District, mainly comprises eutrophic, shallow water lakes, and has fewer species than that of the Eastern Plain Lake District. For example, in Jingpohu Lake there are 92 genera of phytoplankton, 66 species of zooplankton, 22 species of benthos, 29 species of hydrophytic grasses and 53 species of fish. In Zhalonghu Lake, there are 50 genera of phytoplankton, 62 species of zooplankton, 6 benthic species 26 species of aquatic plants and 21 species of fish. In addition to some cold water fish, there are also some endemics, such as four species of Mollusca, i. e., Cipangopalvdina uosuriensio, Semisulcospira amurensio, Viviparus chui and Margaritiana daburica, four species of Cladocera, i. e., Limnosida frontosa, Dnaphanosoma chankensis, Moina chankansis and Daphnia cristata, and twelve species of Copepodta.

       c. The Yun-Gui Plateau Lake District has various types of lakes with numerous species. For example, in Dianchi, there are 205 species and varieties of phytoplankton, 171 species of zooplankton, 112 benthic species, 22 species of fish. In Fuxianhu, there are 74 genera of phytoplankton, 57 species of zooplankton, 30 benthic species, and 28 species of fish. There are also some endemics such as 2 species of aquatic plants, i. e., Ottelia vunnansis and O. esquiralii, 4 species of Mollusca, i. e., Margarya melanodes, M. mansuyi, M. yangtsunghaiensis and Bellamya limnophila, 1 species of shrimp, i. e., Macrobrachium yui, 3 species of Cladocera, i. e., Lurzia yunnanensis, Simocephalus aculirostratus, and Daphnia lamgdtzi, 11 species of Copepoda and some species of fish dominated by Cyprinus and Anabarilius.

       d. The Meng-Xin Plateau Lake District, mostly comprises inland salt water lakes, and is poor in species. For example, in Bositenghu Lake (total dissolved solids (TDS), 1.90g¡¤L-1), there are 54 genera of phytoplankton, 39 species of zooplankton, 5 benthic species, 21 species of fish and 11 species of aquatic plant. In Nulanghu Lake (TDS 3.1 g¡¤L-1) there are 23 species of phytoplankton, 59 species of zooplankton, 69 benthic species and 18 species of fish. There are also some endemics such as 5 species of Cladocera, i. e., Bythotrephes longimanus, Pleuroxus sinkiangensis, Leydigia leyaigii, Camptocercus serratunguis and Diaphanosoma mongolinum, 10 species of Copepoda and some fishes chiefly belonging to the Louciscinae and Nemachilinae.

      e. The Qing-Zang Plateau Lake District has deep water and mainly comprises oligotrophic and salt water lakes, and is poor in species. For example, in Qinghaihu Lake, the biggest lake in China, with a salinity of 1.22%, there are only 53 genera of phytoplankton, 24 species of zooplankton, 8 benthic species and 6 species of fish. In oligotrophic Lake Namucuo, there are 49 genera of phytoplankton, 12 species of zooplankton and 3 species of fish. There are also a number of endemic and new species, e. g., there are 3 new species and subspecies and 93 endemic species of rotifer, 3 new species (Diaphanosoma peramatum, Simocephalus himalayensis and Alona aliensis) and 4 endemic species (Scapholeberis aurita, Daphnia pamirensis, Chydorus undulatus and Cornuella annandalei) of cladocerans, and 2 endemic species (Arctodiaptomus stewarfianus and Acanthodiaptomus tibetanus) of copepods.

Table 1 A comparison of the species numbers in five lake districts of China

 Lake district

Aquatic plants

Benthic species

Zooplankton

Fish

Eastern Plain

tens¡«100 upwards

20¡«100 upwards

40¡«120 upwards

>100

Northeastern Plain and Upland

<50

<50

30¡«70

<60

Yun-Gui Plateau

£­

10¡«110 upwards

30¡«70 upwards

<30

Meng-Xiin Plateau

¡Ý10

<60¡«70

<60¡«70

<30

Qing-Zang Plateau

4¡«5

8¡«22

12¡«40

3¡«8

       (3) Reservoirs

       A reservoir is an intermediate habitat between a river and a lake, but usually has less species than similar lakes. For example, in 8 lakes within the Heilongijang drainage area, there are 143 genera of phytoplankton and 101 species of zooplankton while the corresponding figures in reservoirs are only 93 and 95. Fluctuations in water level result in poor aquatic plants which, in turn, results in a poor peribiota and benthic community. Species diversity in reservoirs tends to increase progressively from the upper to the lower reaches. The fish fauna of Chinese reservoirs is mostly dominated by cultivated species such as Hypophthalmichthys molitrix and Aristichthys nobilis.

2 Impact of human activities on the biodiversity of inland waters           

       (1) Impact of fisheries

       Fish production in China has been increasing year by year since the 1980s, but now fishing is so excessive and indiscriminant in rivers and large lakes, especially the intense fishing of spawners, larval fish and immature fish, that it has resulted in the deterioration of fish resources. For example, in the 1980s, fish production in the upper reaches of the Yangtze was only 20% of that in the 1960s, and commercial fishes have decreased from more than 50 to about 20 species over the same timeframe. About 70 species of fish have disappeared from Honghu Lake, Hubei Province, from 1959 to 1987 and 97% of the catch comprised small individuals. Some rare Chinese aquatic animals such as Andrias davidianus and Pelochelys bibroni have also become fewer as a result of over-fishing. Inappropriate stocking and the introduction of exotic fish into lakes also threaten the survival of endemic resources.

       (2) Impact of large-scale water conservancy works

       Hydraulic structures have been increasing continuously in streams, rivers and lakes, adversely affecting the spawning and fattening of migratory fish and crabs and severely threatening the survival, or drastically decreasing the quantity, of many important aquatic organisms such as Acipenser sinensis, the Chinese paddlefish, Myxocyprinus asiaticus and Corieus heterodun (also see Section 3.12.3).

       (3) The impact of excessive felling of forests and reclaiming farmland from lakes

       Since the 1970s, the excessive felling of forests and the exploitation of steep upland slopes in many places, have resulted in serious soil erosion, sharp increases in water turbidity, siltation of lakes and reservoirs, and a decrease in both species and the quantity of aquatic biota. Excessive silt in flood seasons even results in ¡°fish flows¡±, i. e., large numbers of choked fish floating downstream in the middle reaches of the Yellow River. There has been massive reclamation of farmland from lakes since the 1950s, which has resulted in the extermination of flora along the coast. The peribiota and benthic animals have also decreased greatly, and the spawning grounds of fish destroyed. In some places, the lake bed has been turned into farmland and, as a result, hydrobionts have lost their habitats.

       (4) Impact of water pollution and eutrophication

       With the development of industry, agriculture and urbanization, large quantities of industrial effluents, urban domestic wastewater, pesticides and chemical fertilizers have run into surface waters, and heavy metals and other toxic elements have killed hydrobionts and affected their growth. The decomposition of large amounts of organic matter consumes oxygen, produces toxic gases and greatly deteriorates aquatic living conditions.

       Rivers in the north have small runoffs and low capacities for self purification and, therefore, the impact of pollution is especially serious. Since 1959, sugar refineries and paper mills have discharged large quantities of effluents into the Nenjiang River. As a result, a large number of fish die periodically in winter when the river is covered with ice and oxygen levels are depleted. Recently, in the middle reaches of the Yellow River, mercury, phenol and lead have been discovered to be accumulated within the bodies of fish.

       The discharge of urban sewage has greatly promoted the eutrophication of surface waters, resulting in a simplification of the plank tonic species, and a drastic decrease in aquatic plants, benthic animals and fish. In the last twenty to thirty years, Donghu Lake in Wuhan City has, owing to the discharge of domestic wastewater and the impact of fishing, seen the zooplankton decreased from 203 to 171 species, and benthic animals from 113 to 26 species. More than 60 species of original fish, except stocked ones, are seldom seen in the catches.

       (5) Impact of water body salinization

       Salinization of water bodies is quite common in northern China. In salinized waters, many intolerant freshwater bionts have gradually disappeared, and a small number of halobionts, or salt-tolerant species, have increased. In sodium-carbonate lakes, the rise in total alkalinity and Ph often happens prior to the increase in salinity and threatens the existence of the biota. With the same level of salinity, species richness is far lower than that of other types of saline lakes. The salt-tolerances of aquatic plants and fish are lower than those of algae and invertebrates and, in the course of alkalization, their species numbers will decrease first. Huangqihai Lake in the Inner Mongolia Autonomous Region was freshwater in the 1950s. Later, owing to the diversion of run-off into the lake, salinization and alkalization have been intensified, aquatic plants have decreased and fish production dramatically declined. In 1972, when the salinity was 7.8gL-2,total alkalinity 0.53 gL-2 and pH 8.9, a considerable number of fish began to die. By the 1980s, there was no fish.

3 Conservation of inland water biodiversity

       The Chinese government has paid attention to the conservation of inland fishery resources and the protection of the aquatic environment since the late 1970s. An investigation of inland water fishery resources, chiefly in the four large water systems, Heilongjiang, Yellow, Yangtze and Pearl River, was launched in 1980. Extensive investigation of environmental quality in rivers and lakes has been carried out since the 1980s. Water source protection zones have been delineated and effluent standards have been proposed. The ¡°Conservation of Aquatic Resources and Fishery Laws¡± were enacted in 1979. The ¡°Environmental Protection Law¡± and ¡°Water Pollution Prevention Law¡± were widely publicised and enforced rigorously. The negative impacts of hydraulic structures on biotic resources have been decreased to a minimum. Ecological effects have also been studied and counter-measures taken during the planning and engineering of large-scale irrigation projects. The indiscriminate felling of forests and the opening up of wastelands have been prohibited. Reclaiming farmlands from lakes and the draining of paddy fields have also been stopped. Attention has been paid to protect rare and endangered animals. So that, in 1981, a series of stations were set up along the Yangtze River to protect Acipenser sinensis. Anhui and Zhejiang Provinces have, respectively, set up natural reserves and breeding farms for Alligator sinensis. Fishery authorities have investigated and practiced the exploitation and management of inland fishery resources according to ecological principles, and now recommend and determine stocking standards and reasonable introductions according to potential fish productivity and the character of the water body. The relationship between the increase in production and eutrophication of water bodies has also been properly determined and scientific fishing standards and quotas have been worked out. All of these measures have played an important role in the protection of the nation¡¯s water body biodiversity.