Biodiversity changes in the lakes of the Central Yangtze

Global biodiversity is decreasing at an unprecedented rate, in parallel with the rapid growth of the human population (DeFries et al. 2004). Among ecosystems that support high biodiversity, wetlands occupy only about 1% of the Earth's surface, but provide habitat for about 20% of the world's species (Dugan 1993), especially endangered and endemic species. For example, approximately 50% of the endangered bird species in China inhabit wetland ecosystems (Wetland International China 1998). However, these biologically rich ecosystems have undergone dramatic reductions. The ecological consequences of these changes to wetlands, and the resulting loss of biodiversity, have elicited considerable concern (Gibbs 2000). The Central Yangtze refers to the section of the Yangtze River Basin that extends from Yichang in Hubei province to Hukou in Jiangxi province (Figure 1), and includes a number of ecologically and economically valuable lakes and wetlands. Dongting Lake, Poyang Lake, and the lakes in the Jianghan Plain and Anqing region, together with the Yangtze River and its tributaries, provide important habitats for aquatic animals and plants. This area is also an important stopover and breeding ground for birds migrating through Eurasia (Kanai et al. 2002). More than 300 species of waterfowl, about 200 fish species, and approximately 95% of the world's wintering Siberian crane (Grus leucogeranus) depend on these wetlands (Wu and Ji 2002). It is also an important habitat for the endangered Baiji (or Chinese river) dolphin (Lipotes vexillifer), a freshwater cetacean that inhabits the Yangtze River. Because of its many vital ecological functions and unique biodiversity, the Central Yangtze has been designated by WWF as one of the Global 200 priority ecoregions for conservation (Olson and Dinerstein 1998). Distribution of lakes in the Central Yangtze region in 1998, produced from eight non-cloudy Landsat Thermatic Mapper (TM) images in the dry season of 1998 (∼October to December). Numbers 1 to 33 represent major lakes, where detailed information on lake size (water surface area) was documented in the 1950s and the late 1990s (most for the year of 1998). 1. Dongtinghu (Dongting Lake); 2. Datonghu; 3. Niulanghu; 4. Guhu; 5. Changhu; 6. Honghu; 7. Paihu; 8. Laoguanhu; 9. Diaochahu; 10. Futouhu; 11. Luhu; 12. Guanlianhu; 13. Wangmuhu; 14. Qinglinghu; 15. Huangjiahu; 16. Nanhu; 17. Donghu; 18. Beihu; 19. Wuhu; 20. Liangzihu; 21. Yaerhu; 22. Zhangduhu; 23. Huamahu; 24. Dayehu; 25. Wanghu; 26. Taibaihu; 27. Longganhu; 28. Huangdahu; 29. Pohu; 30. Wuchanghu; 31. Poyanghu; 32. Banghu; and 33. Dahuchi. Nevertheless, intensive land reclamation over the past several decades has replaced floodplains and lakes with agricultural areas and urban settlements. For example, in the 1930s, the surface area of Dongting Lake covered 4955 km2, but had decreased to ∼2500 km2 by the late 1990s, and the lake was divided into three sublakes (East, West, and South Dongting Lake; Zhao et al. 2005). In the 1950s, there were 414 lakes with surface areas greater than 1 km2 in the Jianghan Plain, but by 1998 this number had fallen to 258 (Fang et al. 2005). Wetland degradation has resulted in serious negative ecological consequences, including increased flooding, a decline of biodiversity, and extinction of a number of endemic species (Zhao et al. 2005). Several studies have documented the changes in aquatic biodiversity patterns and community structures in various rivers and lakes in the Central Yangtze at different periods since the 1950s (eg Fu et al. 2003); however, an integrated analysis on the status of biodiversity changes is not yet available. Here, we review biodiversity changes at the community, population, and species level for aquatic plants, fish, and waterfowl in the Central Yangtze. The objectives of this review are to: (1) provide basic information on the changes in the lakes over the past 50 years using historical land cover information and remote sensing data; (2) review the changes in biodiversity based on analyses found in the literature; and (3) summarize major factors that have led to the changes in biodiversity. Although our review focuses on a period beginning in the 1950s, some of the biodiversity data were available only from the 1960s, as a result of changes in China's policy on restriction of information and investigation methods during that period. In addition, we did not perform statistical analyses on some aspects of biodiversity changes because of insufficient data. The data sources used in this review were gathered from different publications and reports and are listed in WebTable 1. In order to understand the effects of the changes in lake size on biodiversity, we documented the current distribution of lakes in the Central Yangtze, using Landsat Thematic Mapper (TM) remote sensing data (Figure 1). Figure 1 was generated from eight non-cloudy Landsat TM images in the dry season of 1998 (mostly from October to December). The satellite images were classified into six land-cover types (settlement, cropland, shrub, forest, water body, and barren land) on the basis of the multispectral classification algorithm (maximum likelihood), using Erdas Imagine 8.4. Only data on water body type was exported to ArcView GIS software for data analysis (Zhao et al. 2005). Figure 2 illustrates changes in water surface area (lake size) for some of the major lakes in the study area between the 1950s and the late 1990s. Information on the size of the lakes in the late 1990s was taken from Figure 1, and data for the 1950s was obtained from land-cover maps made during that period (scale of 1:200 000). For further details on the data and on data processing, see Fang et al. (2005). Comparison of the surface area of 33 major lakes in the Central Yangtze region between the 1950s and the late 1990s. Lake sizes were much smaller in the late 1990s than in the 1950s for most lakes. Among the 33 major lakes, the size of 14 lakes decreased by 50–100%, that of 10 lakes by 25–50%, and of seven lakes by 0–25%. Only two lakes (Changhu and Huamahu) increased due to aquaculture (inset). The numbers 1–33 represent major lakes and correspond to those listed in Figure 1. The results showed that the surface area of most of the lakes shrank dramatically in the late 1990s, as compared to the 1950s: 31 of 33 lakes experienced a marked decline in size, while only two (Changhu Lake and Huamahu Lake) showed an increase (Figure 2). The term “changing rate of lake size” was used to evaluate the magnitude of lake degradation, and was obtained by dividing the difference in lake size in the 1990s and in the 1950s by the lake size in the 1950s. This revealed that 14 lakes had decreased in size by 50–100%, another 10 lakes had been reduced by 25–50%, and a further seven by 0–25% (Figure 2 inset). These reductions in surface area were mainly the result of the practice of impoldering (a type of land reclamation that encroaches on lakes and their associated wetlands for agricultural purposes, through the construction of dikes and drainage structures; Zhao et al. 2005). Natural processes, such as sedimentation and interannual changes in climate may also cause reductions in lake surface area (Du et al. 2001), but the contribution of natural silt deposition to the decrease in water surface of Dongting Lake, the second largest lake in the region, was estimated as < 7% over the past 70 years (Zhao et al. 2005). According to Fang et al. (2005), variations in annual rainfall were also not a major factor in the size decreases of lakes in the Jianghan Plain area. Over the course of many decades, the number of aquatic vascular species has tended to decrease in six of the eight major lakes in which species were well documented (Figure 3). This was mainly due to loss of certain species which are sensitive to environmental pollution and other habitat changes. For example, at Donghu Lake, formerly dominant species, such as sago pondweeds (Potamogeton maackianus and Potamogeton cristatus), Indian fern (Ceratopteris thalictroides), duck lettuce (Ottelia alismoides), ivy leaf duckweed (Lemna trisulca), Eriocaulon buergerianum, water celery (Oenanthe javanica), Asian marshweed (Limnophila sessiliflora), and dwarf bladderwort (Utricularia exoleta), have mostly disappeared since the 1970s, primarily as a result of increasing pollution (Liu 1995; Yu 1995). Eight plant species have disappeared from Honghu Lake during the past 50 years (Peng et al. 2004). At Liangzi Lake, which suffers less human disturbance, plant richness did not show any significant change and has fluctuated between 87 and 92 species over the past 30 years, while the number of species at Poyang Lake (the largest lake in this area) has tended to increase since the 1980s, most likely due to the establishment in 1983 of the Poyang Lake National Nature Reserve (Poyang Lake National Nature Reserve 1993). Changes in species richness of aquatic vascular plants in eight large lakes in the Central Yangtze. The inset figure illustrates averaged relative species richness of all the lakes for each decade; they show a significant decrease (r2= 0.93, P = 0.007) over the study period. (See text for inset details.) Not only did the number of species change, but so to was species composition within aquatic plant communities altered (Table 1). The dominant aquatic vegetation species at Donghu Lake were common reeds (Phragmites communis), wild rice (Zizania latifolia), and sago pondweed (P maackianus) in the 1950s (Zhou et al. 1963), but these were replaced by P maackianus, holly-leaved naiad (Najas marina), and Hydrilla verticillata in the 1960s (Chen and He 1975). P maackianus disappeared during the 1970s–1980s, and N marina became predominant (Yao et al. 1990). Submersed plants, such as N marina, spiked water-milfoil (Myriophyllum spicatum), and American eelgrass (Vallisneria spiralis), were dominant in the 1990s (Yan et al. 1997), but were supplanted by emergent plants such as bulrushes (Typha orientalis) and Indian lotus (Nelumbo nucifera) by 2001 (Wu et al. 2003). The dominant species at Honghu Lake in the 1960s included floating-leaved plants such as water chestnut (Trapa bispinosa) and submersed ones such as P malaianus, V spiralis, and H verticillata), but these were replaced by other submersed plants (P maackianus, M spicatum, and Ceratophyllum demersum) and emergent plants (Hydrilla and Zizania latifolia) in the 1980s (Li 1982). By the 1990s, they were further replaced by submersed plants, such as P maackianus, and hornwort (C demersum; Li 1997). The dominant species of aquatic vegetation at Liangzi Lake also underwent major changes. The original vegetation consisted primarily of V spiralis, H verticillata, N marina, and brittle naiad (Najas minor) in the 1950s, but had changed to P malaianus, P maackianus, Potamogeton crispus, and C demersum by the 1980s (Jin 1992). In the 1990s, areas covered by P malaianus were greatly reduced and largely replaced by P maackianus (Jin 1999). During the study period, substantial changes were also seen in fish diversity at community, population, and species levels (Figure 4). The species richness of fishes in Donghu, Honghu, and Liangzi lakes has tended to decline since the 1960s (Figure 4a). In Donghu Lake in the 1960s, for example, there were 67 species of fish, but this number had fallen to 38 by the 1990s; nearly half the fish had disappeared, including some rare species, such as Reeve's shad (Tenualosa reevesi), Chinese banded shark (Myxocyprinus asiaticus), the Yangtze grenadier anchovy (Coilia brachygnathus), and bream (Megalobrama skolkovii; Fang 1991; Huang et al. 1995). The number of fish species in Honghu Lake declined from 74 in the 1960s to 57 in the 1990s (Chang et al. 1995; Song et al. 1999). Similarly, fish species in Liangzi Lake dropped from 75 in the 1970s to 54 in the 1980s. Changes in species richness and population structures of fish in some lakes in the Central Yangtze. (a) Changes in species richness in three large lakes (Donghu, Honghu, and Liangzi). (b) Frequency distribution of mean age of T reevesii. (c) Frequency distribution of mean individual size (weights) of T reevesii. An important characteristic of the changes in fish species composition is that the proportion of migratory and semi-migrant species decreased, while that of resident species increased in the fishing yield. Most importantly, the percentage of typical migrant species, such as Chinese sturgeon (Acipenser sinensis), Yangtze sturgeon (Acipenser dabryanus), Tenualosa reevesi, Japanese eel (Anguilla japonica), and Myxocyprinus asiaticus, declined dramatically, and some have not been observed at all in recent years (Qiu et al. 1998; Yi et al. 1999; Zhang et al. 2000). At Dongting Lake, the yield of four carps (well-known migrant and semi-migrant species in China) –black carp (Mylopharyngodon piceus), grass carp (Ctenopharyngodon idellus), silver carp (Hypophthalmichthys molitrix), and bighead carp (Aristichthys nobilis) – declined steadily from 21% of the total fishing yield in 1963 to 14.1% in 1981, and to 9.3% in 1999. At the same time, the yield of resident fish species, such as common carp (Cyprinus carpio), goldfish (Carassius auratus), and catfish (Silurus asotus), have increased from 63% in the 1960s to in et al. 2002). At Honghu Lake, the yield of semi-migrant species approximately 50% of the total yield in the 1950s, but to only in the 1980s (Chang et al. 1995; Song et al. 1999). The changes seen in these fish have been in body size and age of some species. For example, for T a important migrant fish in the Yangtze fishing yield showed that in only in of the total yield of this species, while the was of fishes years However, in the percentage of fish increased to while of years were seen at all (Figure In to this decrease in numbers of fish, mean individual size also decreased in the with a number of < while in of < made of the total and there were (Qiu et al. 1998; Figure in the Central Yangtze region are important stopover and breeding for migrant birds in Eurasia (Kanai et al. 2002). Figure the changes seen in the waterfowl species at Honghu Lake, Dongting Lake, and Lake, where interannual changes in bird have been well waterfowl at Honghu Lake decreased from species in the 1960s to species in the 1990s (Figure and duck species declined from to (Figure while in Lake species disappeared between the 1980s and the 1990s (Figure and at Dongting Lake declined from 31 species at the of the 1950s to species in and increased to in the period (Figure Zhao 2002). The increase seen over the past 10 years was most likely due to the establishment of the Dongting Lake in (Zhao 2002). However, seven rare species, including and javanica), which were in were not observed in four bird species and (Zhao 2002). Changes in species richness of (a) waterfowl and (b) and in three lakes and in the Central Yangtze. The changes in waterfowl in the Central Yangtze lakes are seen in the variations in of Siberian (Grus leucogeranus) at Poyang Lake and the at Dongting Lake (Figure These were as species for these two lakes, because approximately 95% of the endangered Siberian crane at Poyang Lake and and about half of the population of the at Dongting Lake 2000). data on waterfowl is available for these two lakes. Changes in population size of two (a) Siberian crane (Grus leucogeranus) from 1983 to 2001 at Poyang Lake, and (b) from to at Dongting The population of Siberian at Poyang Lake increased steadily from in the wintering period of to during and from to which the population to The much smaller numbers for the wintering periods of and (Figure were by in these years (Zhao 2002). At Dongting Lake, the population of increased between the wintering period of and (P = and in with a total of (Figure The total population of is estimated to et al. 1999). The Baiji also as the Chinese is endemic to the Yangtze and is to a than However, its numbers have declined over the past several decades (Liu et al. was observed in the Yangtze River and in Poyang and Dongting lakes. However, population size over the past 50 years from in the 1950s to in to in Most has not been observed at Poyang Lake and Dongting Lake since that may et al. 2000). and land-cover change habitat and to in biodiversity (DeFries et al. 2004). Over the past 50 years, the Central Yangtze region has experienced and land-cover changes. For example, impoldering land reclamation through drainage in this region resulted in a decline in biodiversity and extinction of some endemic species (Zhao et al. 2005). levels of impoldering have a substantial loss of areas for the common carp at Poyang Lake, from in to in greatly decreasing population size has on most wild including and lake to in lake size, of water and and loss of biodiversity (Li et al. pollution is one of the to biodiversity in the Central Yangtze region and 1999). The used to the of in the Yangtze River the of between and the 1980s to the of the and while this led to a serious in water and biodiversity et al. 2002). For example, at Poyang Lake, waterfowl numbers between and the was (Poyang Lake National Nature Reserve 1993). Donghu Lake, a urban was classified as of and in water in the 1950s, but to by major and water by the 1980s, due to levels of greatly through the water This is one of the major aquatic vascular submersed declined disappeared (Yan et al. et al. 2003). pollution also classified as a of environmental has greatly the growth and of the Baiji and may a factor in the decline of its population size et al. 1995). The increasing of aquaculture in the Central Yangtze has also had serious negative effects on biodiversity. et al. that fish in Honghu Lake on aquatic especially submersed decreasing aquatic vascular plants and vegetation At Donghu Lake, the loss of P maackianus, a dominant submersed vascular was associated with of grass carp (C of fish is another major cause of the dramatic in the number of wild fish species in most lakes in this area. The of certain fishing such as and has breeding and of fish species in some lakes cause habitat the of some species, and to a substantial decline in biodiversity and et al. 2004). The construction of the in the Yangtze River in led to a decline in the of three endangered and endemic fish species, Chinese sturgeon sinensis), Yangtze sturgeon dabryanus), and Chinese which are from their areas in the River the of the Yangtze by the et al. 1997). The the largest in the from have for fish, most especially to the migrant species in the and of Yangtze by the and the and the of fish 2003). These large not only fish, but many other aquatic and species as well (Wu et al. 2004). The Central Yangtze is by an of water including the and its tributaries, and a large number of lakes. The and dikes to from the 1950s through to the of the 1970s all of the lakes to from the Yangtze only Poyang Lake and Dongting Lake The of the lakes from the and its has the migratory of many fish and the species between the lakes and the which is another cause of the decline in fish species in the lakes et al. 1995; Song et al. 1999). The of China's and a of environmental and biodiversity conservation in the Central Yangtze, a biodiversity have considerable within the past years, and have been in this area and are an important in biodiversity (Fang et al. For example, since the establishment of the Poyang Lake and Dongting Lake have the most important for the Siberian crane and (Figure impoldering was in the Central Yangtze to support a human population, and of this land reclamation practice increased from the 1950s to the late 1970s The negative together with a of the of wetlands, have to the establishment of to and lakes and associated wetlands. The Chinese a policy to impoldering from the of the have some to to the original lakes because they are to dikes 1998). unprecedented in 1998, the Chinese a lake in the Central Yangtze which the impoldering and degradation of the lakes to some For example, the area covered by Honghu Lake, the largest lake in the Jianghan Plain, increased in size between and 1998 (Zhao et al. 2003). changes have been observed in aquatic biodiversity in most of the Central Yangtze lakes. These changes are the result of the of three of as in Figure (1) lake degradation (eg loss of wetlands, water pollution and and by a human population and increased (2) the construction of large primarily at water for and (3) the establishment of and lake to habitats for plants and Natural as lake sedimentation and climate are also factors for the changes in lake and biodiversity in this region, but these were not included because their are likely much smaller than those by intensive human (Zhao et al. 2005). changes and their with human in the Central Yangtze lakes. in human population result in and land-cover changes and environmental which to degradation of lakes (eg loss of wetlands, water pollution and and together with the construction of large establishment of and lake are the major of changes in aquatic biodiversity in the Central Yangtze. biodiversity changes at levels community population size and age and individual body and in Figure lake degradation and the construction of large have led to a substantial decrease in species richness within plant and as well as changes in population size, age and individual size of fish species. the other the establishment of a number of and lake since the late 1980s and 1990s has habitats and biodiversity to some of this is seen in the increase in the numbers of waterfowl at some lakes (Figure by policy and to negative human the of and lake and to and the wetland biodiversity of this area. This was a of the on in the Yangtze River Basin in Lake in This study was by the and the National Natural of China and and The is not for the of any information by the than to the for the