Potential impacts of a water control structure on the ......Potential impacts of a water control structure on the abundance and distribution of wintering waterbirds at Poyang Lake

Potential impacts of a water control structure on the abundance and distribution of wintering waterbirds at

Poyang Lake By Jeb Barzen1*, Mike Engels1, James Burnham1, Jim Harris1 and Guofeng Wu2

1 International Crane Foundation, E-11376 Shady Lane Road Baraboo, Wisconsin 53913 USA

*Corresponding Author Email: [email protected]

2 School of Resource and Environmental Science, Wuhan University No.129 Luoyu Road (430079) Wuhan City, Hubei Province, P.R.China

Poyang Lake Assessment (cont.) p. 2 of 54

1. Summary of conclusions Poyang Lake is a dynamic wetland ecosystem that provides critical habitat to a variety of waterbirds, many of which are threatened. Over 98% of the world’s Siberian Cranes (Grus leucogeranus), for example, depend on Poyang Lake for their survival each winter. The goal of this report is to assess the impact on waterbirds of a dam that is proposed for construction at the outlet of Poyang Lake. Specifically, this report assesses the three minimum winter water elevations that are proposed for the dam’s operation: 12 m, 14 m and 16 m (Wu Song Elevation). These elevations were compared to current conditions at Poyang and to other lake systems in the region. A ‘no dam option’ was also considered. The potential impact of the proposed dam was assessed only in respect to waterbirds and their primary food sources, not for other native fauna or flora in the system. Additionally, this document does not assess potential impacts to human communities or land uses within the lake basin. Other aspects of a full assessment are essential but beyond the scope of this report.

Potential impact from the construction of a dam at the outlet of Poyang Lake to wintering waterbird populations is significant. If minimum water levels were maintained at 16 m (Wu Song) most shallow water areas historically used by wintering waterbirds would be inundated so deeply that they would be lost as waterbird habitat and consequently many species would no longer have access to food resources. Second, of the remaining shallow water areas at 16 m, plant communities would be forced to shift extensively across elevation gradients where historically they were not found. With submerged aquatic vegetation these changes would be expected to occur rapidly when compared to other vegetation. Re-establishment or movement of plant communities dominated by emergent sedges or warm season grasses, however, would take several years, if at all; it cannot be assumed that these important vegetation communities would re-establish and hence ensure the survival of many waterbird species. During this period of vegetation change, whole populations of birds that depend upon communities (e.g. grazers) would be severely impacted, and may be extirpated.

Finally, changes in the plant communities, which filter river water and control resuspension, would also alter water quality, primarily through increased water turbidity. The magnitude of this alteration might reduce productivity of submerged aquatic plants substantially, or even shift the system to one dominated by phytoplankton and algae. Given the size of Poyang Lake, this change in ecological character might be too costly to reverse for the whole lake. Other studies of wetlands in the Yangtze River drainage, such as at Tai Hu, demonstrate the prohibitive costs associated with restoration of ecological services once they are lost. The isolation of Tai Hu from the Yangtze River, and the stabilization of water levels within that lake, greatly contributed to the loss of many ecosystem services traditionally provided by the lake.

The potential impact of a minimum water elevation maintained at 14 m (Wu Song) would be similar to that of 16 m. Reduction of foraging habitat for tuber-feeding birds would be less severe as would changes in the emergent plant communities for grazing birds. Still, at a 14 m


minimum water elevation, the impacts to waterbird habitats would be so dramatic as to closely resemble the scenario at 16 m as described above.

Maintaining a minimum water elevation of 12 m (Wu Song) would approximate the average winter water elevations that have naturally occurred in the main basin of Poyang Lake over the last 50 years. Important differences between a no dam option and maintaining a minimum water level of 12 m, however, still occur. At 12 m emergent plant communities would not be inundated in winter and submerged aquatic vegetation communities would not be altered in most years. Importantly, if water elevations can go no lower than 12 m then important foraging habitats for waterbirds that become available in low water years might be lost. In addition, the dynamic nature of water level fluctuation is a key component of overall health of Poyang Lake. Stabilizing water levels, even at 12 meters, would likely undermine the entire ecosystem.

Most of the world’s Siberian Cranes and Oriental White Storks (Ciconia boyciana) depend upon Poyang Lake while significant populations of Greater and Lesser White-fronted Geese (Anser albifrons and A. erythropus), Swan Geese (A. cygnoides), Tundra Swans (Cygnus columbianus), and White-naped Cranes (Grus vipio) depend on Poyang Lake during winter months. Although appropriate habitat may be available in most years when water is maintained by a dam to go no lower than 12 m, insufficient habitat in only a few years each decade could still cause significant population declines or extirpation. Many waterbird species that depend upon Poyang Lake during winter do not have alternate habitats outside of Poyang Lake.

A cost/benefit analysis for using a dam to mitigate impacts arising from development projects located outside the Poyang Lake basin is beyond the scope of this report. The benefits of a dam, regarding protection against altered flows from outside of Poyang Lake, are not certain and management of outflows from projects like Three-Gorges Dam need detailed assessments to reduce potential impacts on highly productive ecosystems like Poyang Lake.

Changes to the hydrology of natural wetland systems in other lakes connected to the Yangtze River provide useful comparisons to the Poyang system. Primary among these changes is the damming of shallow lakes and an artificial dampening of their seasonal fluctuations. Though Poyang Lake is a unique ecosystem, changes to these neighboring ecosystems illustrate what might happen to Poyang Lake if a dam is constructed. In all cases where comparisons can be made, substantial negative impacts of these systems were documented. Waterbird foraging habitat was lost, ecosystem services were compromised and benefits to human communities accruing from the development project were not proven worth the costs in remedial action forced by changes within these systems. These changes can cost billions of dollars, and wetland restoration has yet to be completely successful.

Our understanding of the Poyang Lake ecosystem remains limited. Many gaps in our knowledge and our analytical ability still exist. Filling these gaps will improve our ability to predict changes


for a variety of development projects, better quantify the ecosystem services Poyang Lake provides and help create alternative development projects where management of the ecosystem can benefit waterbirds, fish, mammals and people who depend upon this dynamic and unique environment.

2. Acknowledgments Though the authors are solely responsible for any errors included in this report, the information presented reflects the work of many scientists and managers. Contributing scientists include, but are not limited to: Dr. Mark Barter (Hefei University of Science and Technology), Dr. Lei Cao (Hefei University of Science and Technology), Dr. Jan de Leeuw (International Livestock Research Institute, Narirobi, Kenya), Weitao Ji (Poyang Lake Nature Reserve), Dr. Wei Li (Laboratory of Aquatic Plant Biology, Wuhan Botanical Garden), Dr. Herve Yesou (University of Louis Pasteur), Yuan Zheng (International Institute for Geo-Information Science and Earth Observation) and Nanjing Zeng (Poyang Lake Nature Reserve). Their contributions to this report have been extensive and very productive. Careful effort in creating this document in both English and in Chinese has been provided by Xiuxiu Hou (Wuhan University) as well as Liying Su and Fengshan Li, both of the International Crane Foundation. Though this document is written in both languages, the English version is the primary source.

3. Introduction

Poyang Lake is a dynamic wetland system where water depths are deep during the summer rainy season and shallow during the winter dry season. How deep or how shallow water becomes varies greatly each year. Poyang Lake is also one of the largest wetlands in Asia with an area of approximately 4,000 km2 (Shankman 2006). In addition to the five main tributaries that drain into the lake, Poyang also has a seasonal, reverse-flow system which greatly contributes to the complexity of its yearly hydrological variation. This variation, both within and among years, directly contributes to the large biomass of plant life (Li et al. 2004), which provides a wide range of foraging options for many waterbird species (Cao et al. 2008). Siberian Cranes, which depend solely on the lake for wintering habitat, are one example. As a key winter area for waterbirds, an analysis of how various impacts from development can alter this ecosystem is critical because mismanagement of this ecosystem can lead to extirpation of species, such as Siberian Cranes, from the wild.

This report evaluates the estimated impact of artificially raising minimum winter water levels, and reducing the seasonal and annual variability of water levels at Poyang Lake by building a dam at the outlet of the lake. To fully assess the impact of a development project such as a dam, water level is not the only important characteristic to measure at Poyang Lake. The timing of when, and the location of where, water occurs in the ecosystem is also important. So is quality


of water. Though these additional hydrological aspects are addressed in our report, we focus primarily on water elevation because few other data are available. Significant data gaps still exist regarding other aspects of the dynamic hydrology in Poyang Lake and these data will be important to gather in the future. At the request of the Wuhan Hydro-ecology Institute, we compared the maintenance of three minimum water levels through operation of a dam at the outlet of Poyang Lake with the option of maintaining the natural hydrology.

Though many alterations of the ecosystem may occur from building a dam, this report evaluates only the impact to waterbirds and their habitats at Poyang Lake and relies on other reports to assess impacts to other components of the system. Our process of assessing impacts from the proposed dam follows an unpublished report where various waterbird species are sorted into foraging guilds and direct or indirect impacts of altering winter water levels are explored (Barzen 2008). In addition to these considerations, variation in the Poyang Lake ecosystem over time, independent of foraging guilds, was also evaluated.

Specifically, we describe here-in the waterbird habitat conditions at Poyang Lake with unaltered winter water elevations (represented as an average of 11.98 m in the Wu Song Elevation System), and the natural deviations above and below the mean elevation. We also estimate how waterbird habitats might directly change if minimum winter water elevations were managed at 12 m, 14 m and 16 m (Wu Song) by an outlet dam. Unlike natural water levels, it is assumed that a dam will not allow water elevations to be lower than the designated elevation. After 1) assessing the direct impacts of altered water levels on plants that provide winter waterbird forage in this ecosystem, we will 2) assess indirect impacts caused by higher winter water levels on waterbird foods produced by this wetland ecosystem, 3) examine how elevated water levels may alter the dynamic nature of this wetland ecosystem, 4) evaluate the potential for alternative habitats to exist away from Poyang Lake, and 5) compare the Poyang Lake system that currently exists (i.e., the ‘natural state’) to other lake ecosystems in the Yangtze River floodplain that have been isolated from the Yangtze River by water control structures. We will also compare the effects of changing the Poyang system with the effects of altering dynamic aquatic systems in other countries.

4. Study Area Poyang Lake covers 4,000 km2 and is characterized by a broad, flat landscape that is dominated by gradual slopes typical of floodplain areas. Within Poyang Lake, however, a variety of slopes still occur that range from a relatively steep 1:1 ratio of natural levees or river cut banks to the more gradual slopes of 1:100 that typify flat floodplain basins. Outside of river channels and natural or man-made levees, steeper slopes generally occur along the north edge of the lake while the more gradual slopes exist along the southern and western edges of the lake. Many sub-lakes also occur in these latter regions of the lake. Sub-lakes are often connected by sheet flow of


water during summer floods. These lakes become separated from one another and are connected to Poyang Lake only by channel flows (man-made or natural) during winter.

Biological productivity within these wetlands is often concentrated in areas where slopes are shallow because relatively flat gradients allow for the accumulation and presence of water over time. Steeper slopes allow for quicker water run-off and cause water depths to occur in a relatively narrow band, thereby reducing habitat availability for wetland plants and animals. Accurately mapping water depth and the length of time that water persists in a particular area is therefore critical to understanding how these wetlands function and how that function can be altered through artificial dampening of hydrological variation. The geographic basis for our assessment thus depends upon a precise elevation map of the basin. For this report we attempted to utilize several datasets that covered the whole Poyang Lake Basin but concluded they did not have sufficient precision for our assessment. The only data available for assessing water depth in a precise enough manner to guide our evaluation of impacts is a Digital Elevation Model (DEM) that exists for the northwest portion of Poyang Lake (Fig. 1).

Our conclusions in this report depend upon a successful extrapolation from this smaller area of Poyang Lake to the lake as a whole. As a result, some uncertainty will exist in our conclusions but the DEM for the entire basin was not available at the time of this report. The northwest corner of Poyang Lake represents a microcosm of the entire lake with diverse land-uses focusing on smaller-scale agricultural production in the uplands and the grazing of domestic animals in the seasonally accessible lowlands. This range of land use is influenced by the complex hydrology of the area giving rise to a variety of water features including sub-lakes, artificial polders and rivers. Not represented in this DEM is the inland delta found at Nanjishan Nature Reserve and steeper gradients found in the outlet channel and along the northern shore of Poyang Lake (Fig. 1). Importantly, the entire Poyang Lake Basin has a much higher proportion of main lake, as compared to fringe areas, than does our study area (Fig. 1). The significance of this discrepancy will be discussed in the results below.

Data presented for the northwest portion of Poyang Lake include all of Poyang Lake Nature Reserve and represent an area of 572 km2, comprising 12.7% of Poyang Lake Basin (Fig. 2). To aid in the modeling process, elevation data were overlaid on a LANDSAT image, taken on December 10, 1999. This image was chosen as a base image because it represented average low water conditions for Poyang Lake (see below for calculation, 11.98 m Wu Song).


5. Methods 5.1 Different elevation scales Three vertical elevation datums are commonly found in data obtained at Poyang Lake: Wu Song, Huang Hai, and National Vertical Datum 1985. Huang Hai elevation systems were used as the basis for reporting elevations on topographic maps whereas water levels were often recorded in Wu Song or National Vertical Datum 1985 elevation systems. We were asked to evaluate the impact of minimum water levels in the Poyang Lake Basin, to be maintained in winter by the proposed dam, as expressed in the Wu Song datum. Conversions to the other two datums are provided (Table 1). In this report, any given elevation is assumed to be measured in the Wu Song datum unless otherwise noted. Table 1. Water elevations measured in three datums used at Poyang Lake (Wu Song, National Vertical Elevation 1985, and Huang Hai) and their conversion factors to the Wu Song system. A water elevation of 12 m (Wu Song) approximates the average low water elevation at Poyang Lake (11.98 m Wu Song) as measured for the combined months of December, January and February 1955-2006.

Conversion Table of analysis water levels for the 3 elevation datums (m)

Water Level Water Level Water Level Conversion

Wu Song 11.98* 14.00 16.00

National 85 10.14 12.16 14.16

National 85 Elevation =

Wu Song Elevation ‐ 1.84 m

Huang Hai 9.72 11.74 13.74

Huang Hai Elevation =

Wu Song Elevation ‐ 2.26 m

*Historic Mean Low Water Level. Based on water elevation from Water Gauge Data of Gan and Xiu Rivers averaged for the months of December, January and February 1955‐2006.

5.2 Describing the Sedge Zone Identification of the sedge zone is an important element in this study. The sedge zone is dominated by cool season graminoid vegetation, with species that are predominantly in the sedge genus Carex. These species are perennial and grow when soil temperatures are cool. At Poyang Lake these sedges grow and flower in the winter when moisture (mostly fog and mist) is abundant and soil temperatures are low (0-20oC) but not below freezing. This is the first


emergent vegetation zone that extends above average low winter water and mud zones where submerged aquatic vegetation occurs. The sedge zone of emergent vegetation is sensitive to water elevation in both summer and winter (Liu et al. 2006) and would be the first zone affected by permanent alterations of water elevation. This zone also provides critical foraging habitat for many bird species in the grazing guild that winter at Poyang Lake (Barzen 2008). Identification of the Sedge Zone for the study area was an iterative process. In the first step, polygons representing sedges were created using a LANDSAT ETM pan-sharpened image (15 m resolution). Only sedge areas that had ground-truthing available and that were distinctly characterized in the satellite image were used. In the second stage, the polygons were overlaid on the DEM and elevation data were extracted. Extracted DEM data were then analyzed to identify areas within the polygons with elevations outside what would be expected based on past research. The polygons were then modified to exclude these areas. Finally a slope calculation was performed on the DEM and the sedge polygons were overlaid. Polygons were then modified to exclude any locations with a slope greater than 30% because sedges would not likely grow on steeper slopes. The overall mean elevation for sedge areas was calculated for representative areas of seven sub-lake basins (Northwest Poyang Hu, Bang Hu, Sha Hu, Da Hu Chi, Da Cha Hu, Chang Hu Chi and Zhong Hu Chi). Of these sub-lake basins, four sub-lakes were examined for variations in sedge zone elevations. Specifically, Da Hu Chi and Chang Hu Chi were chosen as relatively isolated lake basins while Bang Hu/Sha Hu was selected as a partially isolated lake basin and Da Cha Hu as an example of a basin that is more fully connected to the main Poyang Lake basin. 5.3 Elevation Models Water elevations were estimated and overlaid in the Wu Song datum by using the DEM for the study area. The DEM, however, used the National 85 elevation datum; therefore, elevation data were first converted to the Wu Song datum (Table 1). An elevation model was built using a simple reclassification of the converted DEM for each of the specified elevations (12 m, 14 m, 16 m) depending on the water depth in question. For example, to display areas having 10 cm water depth when winter water levels are held at 12 m, the DEM was classified into three ranges: 1) less than 11.90 m, 2) from 11.90 m to 12.00 m and 3) greater than 12.00 m. Percentages of the water area at a specified depth were then calculated by taking the total number of pixels representing each depth and dividing by the total number of pixels in the DEM. An assumption of these elevation models is that all sub-basins were hydrologically linked at any elevation. This is not true. Except for a drainage canal, sub-lakes such as Da Hu Chi (Fig. 2) have higher basins than Poyang Lake or adjoining rivers. When gates to drainage canals are closed, it is possible to manage water in the sub-lakes independently from Poyang Lake at some water elevations. Sub-lakes can be higher or lower than Poyang Lake until Poyang Lake


surpasses approximately 15.8 m when sub-lakes like Da Hu Chi will be flooded by sheet flow, nullifying control at water structures located on drainage canals at the lake. Water in Da Hu Chi may be held above the Xiu River by closing the water control structure that links Da Hu Chi with the Xiu River. In Fig. 2, the satellite image (taken on December 10, 1999) depicts water in Da Hu Chi but the elevation of the Xiu River on that day was 12.21 m, an elevation lower than the entire basin of Da Hu Chi. If Da Hu Chi was fully connected to the Xiu River on December 10 it would be dry. On December 1, 1999 (the closest datum), actual water elevations in Da Hu Chi were 14.61 m, 2.4 m above the Xiu River. Once water is released from Da Hu Chi, however, it cannot be returned until sheet flow or excessive rainfall occurs or until water in the Xiu River exceeds water levels in Da Hu Chi and the water control structure can be opened. Conversely, water in Da Hu Chi can be held at lower levels than the Xiu River by keeping the water control structure closed as the Xiu River rises. The relative difference can be maintained, if rainfall is minimal, until Poyang Lake elevations surpass 15.8 m and sub-lakes like Da Hu Chi become linked with Poyang Lake through sheet flow. Other basins, like Bang Hu and Da Cha Hu do not have water control structures that can be manipulated by people but still can impound, or isolate, bodies of water creating uneven elevations of water bodies in the sub-lakes for limited periods. Bang Hu has high soil ridges that constrict outflow to the north while Da Cha Hu has high soil ridges that constrict outflow to the east (Fig. 2). 5.4 Poyang Lake Database The Poyang Lake database contains historical water elevation data, water clarity data, bird observations and plant data for four study lakes (Mei Xi Hu, Sha Hu, Da Hu Chi and Si Xia Hu) within Poyang Lake Nature Reserve (Fig. 2). This database also contains weather data for the region and water elevation data for the Gan and Xiu Rivers. In this report daily elevation data for the two rivers were used and ranged from January 1955 to December 30, 2006. We also used daily elevation data for the lakes ranging from October 2, 1999 to December 31, 2006 although some gaps occurred. Tuber samples for each of the four study lakes were collected in October 1999-2006 along two perpendicular transects that bisected the entire basin for each of the four study lakes. Sampling points were located at approximately every 50 m and four soil samples were taken from each collection point. Tubers were extracted by washing soil from the samples in a screen mesh (Li 2001, Li 2002). Bird abundance was recorded at least three times per month for the four study lakes in October-March, 1999-2007. For each census, the birds counted at each of the four study lakes were summed to estimate the total number of birds seen in the study lakes (note that birds were not


counted in all lakes of the reserve). To estimate annual bird use of the reserve, bird censuses were then averaged for the entire winter season. To estimate the proportion of Siberian Cranes using the entire nature reserve we averaged number of cranes in the four study lakes and divided this average by the entire Siberian Crane population, estimated to be 3,500 (Li et al. 2005). These data were gathered cooperatively by Poyang Lake Nature Reserve and the International Crane Foundation.

6. Results and Discussion

6.1 Direct effect of water levels in winter A. Elevation and ecology of the sedge-dominated plant community:

The average elevation of the sedge zone that we identified was estimated at 14.50 m from the DEM (Table 2). The location of these sedge zones occurred in distinct bands surrounding sub-lake basins (Fig. 3). Not all sedge zones were mapped in our analysis because insufficient ground-truthing has been done to date. The communities that we did map, however, appeared representative of sedge zones within Poyang Lake Nature Reserve. Importantly, within the four selected lake basins the average elevation of the sedge community varied from a low of 14.1 m in Da Cha Hu to a high of 15.3 m in Da Hu Chi (Fig. 4) even though the variation of elevation within individual sub-lake basins was lower. The overall narrow range in elevation of this representative sedge community, 14.1-15.3 m, suggests that this community is very sensitive to water elevation either in summer, in winter, or during both seasons and this conclusion matches other studies (Liu et al. 2006). Evidence also suggests that the sedge zone can vary in elevation among lakes but is predominantly within the overall range of 14.1-15.3 m because the basin profile within different sub-lake basins varies. Factors that influence this variation between sub-lake basins are unclear but may be linked to different use patterns by local human populations or to sediment composition of different sub-lakes as well as to variations in hydrology. Our estimates of 15.3 m Wu Song (13.5 m; National 85) for the elevation of the sedge zone in Da Hu Chi are also consistent with measures of the sedge community elevation of 14.8-15.8 m Wu Song (13-14 m; National 85) reported in Wu et al. (2008). Collectively, the sedge zone represents a plant community adapted to the lowest basin elevations of any emergent vegetation community at Poyang Lake. The submerged aquatic vegetation community occurs at elevations below the sedge zone. By mapping the sedge zone it is possible to identify the relative impacts of changing water levels because the sedge zone identifies the transition between plant communities dominated by submerged aquatics and those dominated by


emergent species. The submerged aquatics tend to be able to adapt quickly to changing water levels whereas the emergent species, most of which are perennial, take longer (presumably several years) to adapt to changing water levels. Liu et al. (2006), for example, reported that although Vallisineria spp. seeds would germinate in the sedge zone, the plant would not persist during the drawdown phase of the annual water cycle. Vallisineria seeds were found throughout the system but could only persist where conditions were appropriate. In contrast, the sedges did not move appreciably even though water levels varied considerably. This sedge zone provides fodder for grazing ungulates and for critical populations of waterbirds (Cao et al. 2008a) and it functions to reduce re-suspension of sediments which, in turn, improves water clarity (Wu et al. 2008a). Mapping the sedge zone thus provides an ecological basis for assessing changing water levels at Poyang Lake and is referenced in subsequent water elevation maps in this report.

Table 2. Mean elevations (in meters) of sedge areas in specified sub-lakes within Poyang Lake Nature Reserve and for the entire estimated zone encompassing seven sub-lake basins measured in different datums and their standard deviation.

Mean Elevations of the Sedge Zone at Selected Lakes (m) Lake National 85 Wu Song Huang Hai Standard Deviation

Bang Hu/Sha Hu 12.89 14.73 16.99 0.95 Da Hu Chi 13.50 15.34 17.60 0.70 Chang Hu Chi 12.98 14.82 17.08 0.99 Da Cha Hu 12.24 14.08 16.34 0.47 Entire Zone 12.66 14.50 16.76 1.18

B. Elevations and ecology of submerged aquatic vegetation (SAV) community: From an intensive sampling of tubers in Da Hu Chi during November, 2004, vegetation zones that occur at elevations lower than the sedge zone were mapped. Above the sedge zone was a warm season grass-dominated vegetation community that is not used extensively by waterbirds in winter but likely improves water clarity as does the sedge community during summer by preventing re-suspension of sediments (Wu et al. 2008a). Unlike the sedge community, the warm season grass community also filters sheet flow of water when water is above 16 m Wu Song.

The sedge community was discussed above. Below the lower boundary of the sedge zone there was a zone with few tubers extending into the main basin of Da Hu Chi and existing between 14.6 and 14.3 m (Fig. 4). This zone likely supports submerged aquatic plant species but not


those that produced tubers. This zone is also used by annual plants (e.g. Polyganum spp.) that grow during drawdown conditions. In 2004, tuber-producing submerged aquatic vegetation (as evidenced by tuber presence) first were sampled in low numbers at elevations as high as 15.68 m but did not become prevalent until 14.30 m. From 14.30 m and into the deepest part of the lake (13.93 m) tubers were sampled at moderate frequency in Da Hu Chi (Fig. 5). The minimum elevations where Vallisineria spp. tubers could occur during 2004 were unclear because the Da Hu Chi basin was not low enough to exclude Vallisineria spp. in 2004.

Tuber production of Vallisineria spp. varies among lake basins (Yuan and Li 2008) which also differ in elevation (see above) and therefore water depth. Vallisineria spp. tuber production also declined dramatically or ceased with summer water depths greater than 2 m in Xi Ling Lake (Yuan et al. 2007). In 2003 at Da Hu Chi, however, deeper water conditions were tolerated by Vallisneria spp. (Table 3). In addition, summer water levels at Poyang Lake varied by up to 1.5 m, between 2000-2006, with mean summer (June-September) water levels that ranged from 16.12 m (in 2001) to 17.63 m (in 2002). In Da Hu Chi this meant that mean water depths during summer ranged from 1.82 m to 3.33 m among years while tuber production varied by almost two orders of magnitude (Table 3).

In a given year, the submerged aquatic vegetation zones of this map of wetland vegetation at Da Hu Chi likely vary extensively in response to water levels, the timing of when water fluctuations occur, or water clarity. This is presumably the same for Poyang Lake as a whole. Certainly, changes in water clarity for the entire lake can influence tuber production (Wu et al. 2007).

In years where tuber abundance in Da Hu Chi is low because of very high or very low water, tubers are likely found elsewhere in the Poyang Lake ecosystem. The ability of Vallisneria spp. to move rapidly throughout a large ecosystem like Poyang Lake is poorly documented but evidence that Vallisneria spp. can recover rapidly in one place following abnormal floods or droughts has been documented (Li et al. 2004) as has the ability of Vallisneria spp. to move extensively throughout the ecosystem by water-born seeds or to persist in the seed bank (Liu et al. 2006). For Vallisneria spp. to persist at an abundance sufficient to support the large populations of waterbirds at Poyang Lake that feed on it (see below), these species of submerged aquatic plants must thrive in such variable environments. Removal of such variability through increasing water permanence may result in lower tuber production in some, if not all, years.


Table 3. Number of tubers for all samples collected in October (mostly Vallisneria spp.), mean water elevation (Wu Song in meters) during summer (June-September) and summer water depth at Da Hu Chi 2000-2006.

Da Hu Chi Summer Water Levels and Tuber Data Year 2000 2001 2002 2003 2004 2005 2006 Mean Water Elevation 16.78 16.12 17.63 16.77 16.52 17.15 16.25 Mean Water Depth (m) 2.48 1.82 3.33 2.47 2.22 2.85 1.95 Total # Tubers in samples 121 105 350 980 80 38 11

C. Average elevation of water during winter under natural conditions: Under natural conditions, the average winter (December–February) elevation of water in Poyang Lake, 1955-2006, was 11.98 m as measured at the Gan River station near Wu Cheng. Standard deviation of this mean water level was 0.95 m. At an elevation of 11.98 m the main Poyang Lake Basin would be covered by water in the northeastern part of the study area but not the eastern section of the study area near Da Cha Hu (Fig. 6). The standard deviation of 0.95 m means that fluctuating water levels one meter above and below this average occur frequently both within and among years. This fluctuation is likely a major driver to the Poyang Lake ecosystem and is therefore very important. As an example, Da Cha Hu, and the portion of Poyang Lake associated with Da Cha Hu, does not become hydrologically connected to the main part of Poyang Lake until water reaches 12.93 m, almost a full meter above the average winter elevation. In isolation from Poyang Lake, Da Cha Hu alone would have standing water in it at elevations beginning at 12.4 m a full half meter below the point where Da Cha Hu is connected directly to Poyang Lake.

Isolated pools of water can form in Da Cha Hu because summer water levels are high and then water levels drop, typically from August to April. As water elevations drop, water becomes separated from the main lake. Once separated, other than through natural or artificial water channels, water loss only occurs through evaporation in winter because the soils have aquatards in them so ground water outflow is minimal. In addition, no plants are growing in the water, making transpiration negligible. Isolated water bodies will decline through evaporation over winter and can be moved within the basin by wind (called seiches). Seiches are described below in the report.

The large change in the surface area of standing water between 12 m and 13 m suggests that the basin profile of Poyang Lake is very flat and minor alterations of water level will result in major changes in area of water coverage of the lake. We have no data to evaluate how coverage of the Poyang Lake basin would change at water elevations below 11.98 m because our study area does not include much of the basin at these lower elevations. We only know that lower elevations occur frequently.


At 11.98 m, assuming complete connection between Poyang Lake and the sub-lakes, none of the sub-lakes would contain water. Because of the isolation of the sub-lakes from Poyang Lake during the winter months, however, these lakes may hold water even though their basin elevations are higher than the average water elevation. Some isolated water bodies in the Poyang Lake ecosystem are managed by water control structures while other basins have only natural barriers to water movement.

Distinguishing between a wetland ecosystem where water elevations can go no lower than 12 m because of an outlet dam (or other constraint), as compared to an ecosystem that can frequently fluctuate up to a meter below an elevation of 11.98 m, is important. If critical habitats for birds occur at elevations below 11.98 m during some years, these habitats would be eliminated when water levels were managed by an outlet dam to go no lower than 12 m. For species that are found only at Poyang Lake, if critical habitat was lost during infrequent hydrological events, populations would still decline or be eliminated because the species lifecycle is broken. Siberian Cranes are one species with few other viable habitats remaining outside of Poyang Lake (see below, Barter et al. 2005). Over 98% of the world’s wild Siberian Cranes depend upon habitats found within the Poyang Lake ecosystem alone. Importantly, Siberian Cranes have likely used habitats at elevations lower than 11.98 m in years where tuber production in higher elevation areas was poor (e.g. Fig. 10). In some years, if Siberian Cranes could not feed in habitat located below 12 m, they would no longer have habitat available in Poyang Lake. Lacking appropriate habitat, so many birds might die that the population could be lost or severely reduced. This would be true even if poor habitat conditions occurred only once every 10 years.

D. Water elevations controlled to go no lower than 12 m, 14 m, and 16 m: Two important questions exist if water levels are managed at Poyang Lake with minimum elevations occurring at 12 m, 14 m, and 16 m: Would there be a reduction in the amount of area available to foraging birds that need specific water depths to find food? If so, how severe might that impact be? The first approach is to examine the direct impact of foraging depths as they might affect birds. At 12 m how much area in the study area exists that has a water depth that ranges from 0 (i.e. mud) to 10 cm? Within the study area, 0.7% is composed of foraging habitats with this water depth (Table 4). At a managed level of 14 m and 16 m 2.6% and 1.3% of the study area would have a foraging depth of 0-10 cm. For water depths of 0-10, 0-20, 0-30, 0-50, and 0-100 cm the proportion of foraging area increased between 12 and 14 m. The proportion of areas containing these foraging depths between 14 and 16 m decreased. Even with the decrease in the uniform proportion of foraging area within each foraging depth from 14 m to 16 m, the proportions of foraging depths at 16 m were still greater than those at 12 m (Table 4).


Table 4. Proportion of the study area, within specified water depths, occurring at three different minimum winter elevations of water (12 m, 14 m, 16 m, Wu Song). Water depths can be compared to depths at which different guilds forage. These minimum elevations represent proposed elevations at which water would be maintained by water control structures at the outlet of Poyang Lake.

Lake Water Elevations (Wu Song) Water Depth (cm) 12 m 14 m 16 m0-10 0.7% 2.6% 1.3%0-20 1.8% 5.0% 4.7%0-30 2.0% 7.0% 6.0%0-50 4.0% 11.0% 9.0%0-100 7.0% 19.0% 15.0%

Will managing minimum water levels at Poyang Lake increase the amount of foraging habitat for birds at water depths ranging from zero to 100 cm? Where water occurs can be as important, ecologically, as how deep it is and how large an area occurs at a specified water depth. Foraging depths determine access to foods but they do not produce the foods themselves. Production of food relies on other ecological aspects that can be related to water depth or be independent of it. To be beneficial to any bird species the appropriate water depth must be found that will facilitate feeding but so must the ecological conditions occur that produce the food in the first place. A discussion on the role of variation in these ecological systems occurs below.

A minimum water elevation of 12 m

At 12 m, water occurs primarily in the main body of the lake (Fig. 6) and is closely associated with the main river channel that courses through the lake. The coverage of water occurs well below the elevation of measured sedge communities. At 12 m of managed minimum elevation, appropriate water depths chiefly occur in close association with this river channel at all foraging depths (Appendix A.). Near the river channels the slope of the substrate is steeper than in the main body of Poyang Lake, much of which would be dry.

At this elevation water can be captured in isolated basins and managed by man-made structures such as the ones at Da Hu Chi and Sha Hu or it can be isolated naturally in basins like Bang Hu and Da Cha Hu (Fig. 2). Within Poyang Lake Nature Reserve, negative impacts arising from an outlet dam that controls water to go no lower than 12 m can be mitigated by proper management of water within these basins. In more open parts of Poyang Lake, such as at Nanjishan Nature


Reserve, this situation may be less easy to control. Without access to a DEM for the entire lake and sub-lake areas, however, this impact is impossible to assess.


At 14 m, water levels in the main body of Poyang Lake have increased (Fig. 7). Some sedge areas are inundated including a third of the sedge community in Bang Hu, half the sedge community in Da Cha Hu and all of the sedge community in the northwest corner of Poyang Lake. Sedge communities in Da Hu Chi, Sha Hu or other sub-lakes would not be inundated. Sedge communities can tolerate flooding during part of the year, usually during the summer months. If these communities remain inundated permanently, however, they will not persist (Liu et al. 2006). Sedge communities within the study area permanently inundated by minimum water levels of 14 m would, therefore, die.

Since the sedge community did occur at elevations of 14.0 – 15.3 m it is possible that sedges would adjust to new elevations of water by moving up the elevation gradient. Unlike the submerged aquatic plant community described above, however, the sedge community is dominated by perennial species and it would take time (perhaps a few years) to adjust to a new elevation with the same biomass that occurred prior to the change in water levels. The lag between changes in water level and plant community adjustments could cause problems for bird species that depend heavily upon grazing in this community. For example, if the adjustment in the plant community occurs slowly and food is limiting for grazing species like White-fronted Geese (Cao et al. 2008a) then populations for these species may decline. Many grazing geese are already in decline (Wetlands International 2006) and this impact could be serious.

At a managed water level of 14 m foraging areas at all water depths would move primarily into the sub-lakes and the narrow fringe of the main body of Poyang Lake (Appendix B). Except for birds that can forage at water depths of 0-50 and 0-100 cm, the bands of appropriate water depth at this managed water elevation are narrow.

Importantly by concentrating birds at the fringes of Poyang Lake, or at the fringes of many sub-lakes, birds are concentrated close to places where human activity in winter is greater. At lower water levels birds often find appropriate foraging depths in areas that are well away from human activity because they are surrounded by extensive mud flats that make human access difficult. In such an isolated environment birds not only have suitable habitat but they are much less vulnerable to human disturbance or to poaching. While the illegal harvest of cranes is unlikely significant, many species of geese, swans, and shorebirds are likely poached (i.e. killed illegally) but to an unknown extent. Increasing human access to bird populations, either through traditional activities (e.g. herding) or through novel activities (e.g. ecotourism in the form of bird watching), might cause serious problems for wildlife populations.


At 14 m lakes like Bang Hu and Da Cha Hu are no longer isolated from the main lake so seiches are less likely in these basins. With proper management, lakes like Da Hu Chi, Mei Xi Hu and Sha Hu could still be managed for water that responds to seiches. Allowing seiches to occur maintains the complexity of available foraging habitat, especially for species that forage at shallow depths (Appendix B). With a minimum water elevation of 14 m many (possibly a majority), but not all, areas capable of supporting seiches would be removed.

Wetlands like Bang Hu would have water depths that are very appropriate for foraging swans (a water depth of 100 cm, Appendix B). Even if tubers were present and with suitable foraging depths, however, wetlands like Bang Hu may not provide suitable habitat because of human use. The number of fishing nets erected in winter at Bang Hu is very large, making the density of human use so high that much of the apparent habitat for species like swans at Bang Hu is not available, being excluded by human use. Previous efforts to significantly curtail fishing intensity in lakes like Bang Hu have not been successful because fisherman still own fishing rights while the nature reserve controls only wildlife rights.


With minimum water levels managed at no less than 16 m, all of the current known sedge community would be permanently inundated (Fig. 8) and would not persist at the elevation where they are currently located because of the permanent water conditions. The ability of sedges in this plant community to shift to higher elevations, where drying in winter might still occur at higher water levels, is unknown because sedges would be forced to grow at elevations where no known sedge communities currently occur. It is unknown how quickly, and to what extent, this community would move under a minimum water elevation of 16 m. If sedges took several years to re-establish at a higher elevation, a logical prediction for perennial species, then there would be a gap in food availability that could be catastrophic for grazing species that depend on the sedge community during the intervening period of adjustment.

With water levels as high as 16 m all of the foraging depths would occur in areas that currently support warm season grass communities (Wu et al. 2008a, Appendix C). These plant communities do not support aquatic benthic invertebrates or submerged aquatic plants. Few data exist to suggest how much or how quickly lands currently covered by warm season grasses can shift to benthic zones. Certainly, these shifts, if possible at all, would take several years or more during which time the thousands of individual birds (Cao et al. 2008a) that forage in benthic environs would have few alternative habitats within the Poyang Lake ecosystem to utilize. If these species could not find alternative habitats located outside of Poyang Lake then dramatic population declines would ensue. The extent to which alternative habitats exist outside of Poyang Lake is discussed further below.


Should species survive the initial impacts of this large change in water level, these species would be again concentrated near areas of human use. Human disturbance would therefore further suppress any ability of varied waterbird species to recover.

In short, at a minimum water level of 16 m the impact to waterbird species using Poyang Lake would likely be catastrophic.

E. Can sub-lakes be managed separately from the river or from Poyang Lake levels under any of these elevation scenarios?

The ability of varied sub-lake basins to hold water that is hydrologically isolated from water elevations in the main body of Poyang Lake is important. Both satellite images (Fig. 2) and water monitoring data (Fig. 9) illustrate that sub-lake basins can function separately at some water levels. Once water levels in the sub-lake basins are isolated the elevations can still change through precipitation and through evaporation or drainage. Once water is isolated, variations in wind direction and wind speed can move shallow sheets of water around within these relatively flat basins (e.g. see Fig. 2 in Wu et al. 2008a for a bathymetric map of Da Hu Chi). As water becomes shallower the relative influence of wind becomes greater. This variability increases the complexity of available foraging habitats for birds, especially for those species that forage in shallow water depths (i.e. <30 cm), by varying habitat availability in both space and time within a winter. Seiche influence on benthic invertebrates, an important food for bird species that feed in shallow water, is unknown: it likely increases invertebrate availability by maintaining larger areas suitable for organisms that require soil to be moist at least some of the time during winter.

With natural, average water levels at Poyang Lake, the benefit of seiches occurs to its greatest extent. With any managed water level the influence of seiches will decline but to different degrees. At 12 m, there will be an impediment on the ability of the seiches to form and move through the system, but less so than for other impact scenarios. At 14 m, many basins that can become isolated at lower water levels will no longer do so. The positive influence of seiches would be reduced greatly under this scenario but the degree to which this would occur in the main body of Poyang Lake is unknown since our DEM does not cover a large portion of the main lake. At 16 m, virtually no seiches would be possible in the lake basin because shallow foraging depths would occur at places where slopes were relatively steep.

Though natural water conditions provide the greatest range in water elevations, and therefore foraging habitat, allowing water levels to fluctuate can result in some bird habitats at Poyang Lake being temporarily eliminated. Abnormally low water levels at Poyang, such as those that occurred in the winter of 2007/2008, may have failed to provide some birds shallow foraging habitats in the system. These abnormally low water levels did provide critical foraging or roosting habitats for some endangered species like cranes, however. Maintaining constant water levels at 12 m may provide more stable habitat availability, especially in such extreme weather events. In contrast, stable water levels tend to reduce wetland productivity (e.g. Swanson and


Duebbert 1989, LaBaugh et al. 1998). The trade-off between habitat that is created as opposed to habitat that is lost in extreme weather events, as well as trade-offs between wetland productivity versus predictability, are important questions to address and no data currently exist to evaluate this dynamic at Poyang Lake. The negative impacts of an outlet dam (even if managed at a low level), however, may outweigh the benefits of constructing a dam for the system. The ecological, social, and economic costs of creating a barrier to fish or dolphin movement between Poyang Lake and the Yangtze River, for example, may outweigh the potential benefit of the outlet dam. This analysis would also depend heavily upon other, more economical solutions that could be found to prevent un-natural reverse flow. Alternative solutions might include timing water releases from Three Gorges to more closely mimic natural downstream flows. Such a cost/benefit analysis is beyond the scope of this assessment because we focus only on impacts to waterbirds in winter. 6.2 Indirect impacts by foraging guild

Variations of water in elevation, timing, permanence, and quality can influence the distribution and abundance of foods in Poyang Lake. This variation can subsequently determine a significant portion of habitat quality for most of the 250 bird species at Poyang. When evaluating the impact of any proposed development on the range of bird species at Poyang Lake, it is difficult to separately consider each individual species that uses the ecosystem. Instead, it is helpful to group these species into guilds that rely on similar foods or foraging behavior and describe how these different guilds utilize the lake. It is then possible to assess how impacts may affect representative species within that guild. Importantly, most of the threatened bird species at Poyang Lake fit within the six foraging guilds listed below. Though other foraging guilds exist at Poyang Lake in winter (e.g. upland seed gleaners, raptors or frugivores) most bird species that have a significant proportion of their population winter at Poyang are grouped within these six, distinct foraging guilds:

1. Tuber feeding birds (e.g. Siberian Cranes) 2. Sedge/grass eating birds (e.g. Greater, and Lesser White-fronted Geese) 3. Seed eating/dabbling birds (e.g., puddle ducks like Spot-billed Ducks, Anus poecilorhyncha) 4. Benthic insect larvae eating birds (e.g. Spotted Redshanks, Tringa erythropus) 5. Large fish eating birds (e.g. Oriental White Storks) 6. Zooplankton/small fish eating birds (e.g. Eurasian Spoonbills, Platalea leocorodia) Direct impacts that might result from proposed managed water levels, such as changes in the area of various water depths available for foraging, have been addressed earlier in this report. This section focuses on water level impacts to foods of various foraging guilds.


A. Tuber feeding guild

Tubers and winter buds are plant organs that store energy as starch. Tubers fuel growth of new plants after a period of stress, such as the winter drawdown period, is over. For birds that feed on them, tubers provide good energy during a portion of the annual cycle where birds increase their fat stores in preparation for the long spring migration and breeding.

Some tuber feeders, like Siberian Cranes, dig for tubers directly with their bills. Swan geese also dig extensively. For tuber feeding birds to forage efficiently, soil conditions must be moist enough to allow digging yet water cannot be so high as to prevent the benthic zone, where the tubers are, from being accessed by wading birds. If standing water exists, water levels must be low enough (less than 40-60 cm) for cranes to wade or for swan geese to float and tip up so that they can reach the benthic zone with extended necks. At the other extreme, when dry, the soil cannot be so hard that it becomes impossible to manipulate with the bird’s bill.

The sub-guild of shallow-water tuber feeders is represented by Siberian Cranes, Hooded Cranes (Grus monacha), White-naped Cranes, Eurasian Cranes (Grus grus) and Swan Geese but also includes other bird species. Almost all of the world’s wild Siberian Cranes, approximately 60% of the world’s White-naped Cranes, and about 50% of the world’s Swan Geese winter at Poyang Lake. Importantly, few data describe tuber-feeding diets fully. For the purposes of this report, it is pertinent to assess the importance of tubers to this foraging guild.

Winter foods of Siberian Cranes at Poyang Lake

Foods of Siberian Cranes wintering in India have been studied better than in other regions. As early as the mid-1800’s, Hume reported that stomachs (likely proventriculi and gizzards) of at least 20 Siberian Cranes consisted entirely of vegetable matter -- in contrast to other crane species, where animals (reptile and insect), as well as plants, were found (Hume 1868). Hume described the food as, "rush-seeds, bulbs, corms, and even the leaves of various aquatic plants." Also in India, Sauey (1979 and 1985) and Spitzer (1979) were able to observe foraging Siberian Cranes from distances as close as 20-30 m, and with use of a spotting telescope, could identify food items consumed. The dominant food was tubers. When the birds were not present, researchers dug in bird foraging places and identified tubers of Cyperus rotundus as the primary food, although it is probable other tubers were eaten as well.

In addition to observing foods consumed, Sauey quantified foraging behavior of 21 Siberian Cranes over a 15-week period, recording behavior of a pair or family group for 2-3 hours at a time. He described three foraging behaviors: 1) begging of the juveniles to elicit food from the parents, 2) adult birds walking about and picking food from the water surface or other substrate ("walk-foraging"), and 3) adults standing stationary and immersing beak or head in shallow water or wet mud and probing vigorously ("dig-foraging"). In 725.8 hours of observation, dig-foraging comprised 96% of foraging behavior of adults, and walk-foraging 4%. Food secured in


dig-foraging was invariably tubers. Sauey observed invertebrates being consumed on only a few occasions.

Although a vegetarian diet was documented for this species in India during winter, the Siberian Crane consumes animal foods during summer more commonly than at other times of year in the far north of Russia (Uspenski 1961, Vorobiev 1963, and Perfilyev 1965), likely due to food availability and dietary needs of growing chicks during the breeding season.

Direct observation of foods for Siberian Cranes at Poyang Lake is much more difficult because birds are more wary of people there than in India. At Poyang Lake, foraging occurs in shallow water or wet mud (Liu and Chen 1991) and consists primarily of dig-foraging. Liu and Chen observed Siberian Crane behavior through spotting scopes for two winters, 4-5 hours/day, and found that over 90% of food consisted of ”stems and roots of such aquatic plants at Potamogeton malainus and Vallisneria spiralis together with small amounts of snails, small fish, clams and grit”. They examined one stomach (likely a proventriculus and gizzard) that contained 37 g sand, 1.5 g small snails, and 14.5 g plant roots, feathers, fibers and mud.

Wu (2005) reported that digging was the most common way for Siberian Cranes to obtain food; mostly tubers and roots at the depth of 20 cm. In the early morning, Siberian Cranes could be seen grazing leaves of Eleocharis yokoscensis, Polygonum criopolitanum, Myriophyllum vericillatum and other plants. This kind of grazing is not very common. In captivity, Siberian Cranes also eat fish, shrimps and clams, but in the wild, they were not observed chasing fish.

Zeng et al. (2002) reported that a group of Siberian Cranes in January of 2000 foraged in shallow water, and some newly grown parts of leaves of Polygonum were eaten; the color of the droppings were green. In winter 1986, one stomach (likely a proventriculus and gizzard) was examined, which contained 27 g tubers, 2 g snails, 5 g sand, and 9 g mud.

Additional vegetation transects were established within Da Hu Chi and Mei Xi Hu during the 2004/2005 winter to compare Siberian Crane foraging locations with tuber densities. Tuber density alone explained 51% of the variation in Siberian Crane locations (Table 5). Adding an interaction term between tuber density and water depth explained 75% of the variability in the multiple regression model (Burnham 2007).


Table 5. Results of Linear Regression Models from Burnham (2007). Models 1-2 are simple linear regression models that fit the observed number of Siberian Cranes to measured tuber densities and projected water depths of foraging birds within Da Hu Chi. Models 3-4 are multiple linear regression models fitting the observed number of Siberian Cranes to both average tuber densities and projected water depths. Adjusted R2 values indicate how much variability in the data the model explains. AIC is a common tool to evaluate different models against one another. Lower AIC values indicate a better overall model (Burnham and Anderson 1998).

Model Adjusted R2 AIC Value

1. Total Number of Observed Birds Vs. Average Tuber Densities 0.51 308.9

2. Total Number of Observed Birds Vs. Projected Water Depth 0.18 321.4

3. Total Number of Observed Birds Vs. Average Tuber Densities + Projected Water

Depth0.49 310.6

4. Total Number of Observed Birds Vs. Average Tuber Densities + Projected Water

Depth + Tuber/Water Interaction 0.75 294.6

In summary, Siberian Crane foraging locations correlated very well to the density of Vallisneria tubers provided the birds can access the tubers. These results provide corroboration of the importance of tubers in the diet of this species. Importantly, access to these benthic resources is heavily influenced by the water depth where birds forage, and once water depths exceed ~50cm, the Siberian Cranes do not appear able or willing to forage for tubers within Da Hu Chi (Burnham and Engels, unpublished data).

Beyond data presented here, the only way that complete dietary analysis can be made is to observe feeding Siberian Cranes for entire foraging bouts and then shoot them so that contents of the esophagus can be accurately made (Bartonek and Hickey 1969). If this is not done, differential digestion occurs that results in animal materials being under-represented in the diet because digestion of soft-bodied animals (e.g. insect larvae) is often completed by the time that food enters the proventriculus and gizzard. Due to the wary nature of the birds at Poyang Lake, the usefulness of direct observational data pursued in India is limited. Nevertheless, all available evidence indicates that cranes in winter feed primarily by digging tubers and can access only those tubers that are found in appropriate habitats (i.e. in water that is not too deep or on soils that are not too dry). Conversely, no data suggest animal materials are important in the winter diet. Most conclusions through the remainder of this report will focus on water depth and availability of suitable foraging habitat. The extent to which the cranes forage on Vallisneria


tubers, as opposed to tubers of other submerged aquatic plants, has little bearing on the conclusions that we present in this report because these foods are all found in the benthos.

Other tuber feeders

Tundra Swans are also tuber feeders but can forage in deeper water than can the shallow water tuber feeders like cranes. Swans can feed in water as deep as 1.5 meters and reach the benthic zone with their long necks. They can also dig in deep water by creating erosive water currents. This behavior, called treading, occurs when swans move their large webbed feet up and down in the water, creating convectional water currents. This water movement erodes the soil directly under the swan and allows tubers underneath to be exposed or to float to the water surface and be eaten. Tundra Swans represent a deep water tuber feeding sub-guild at Poyang Lake. Approximately 1/3 of the world’s Eurasian subspecies of tundra swan winters at Poyang Lake.

Collectively, tuber feeders utilize the areas of lowest elevation at Poyang Lake and follow the moving water so that new tuber resources are exploited over winter (Fig. 4). This behavior predisposes swans to be affected through direct loss of appropriate water depths caused by artificially raising water elevations at Poyang Lake as discussed above. With Siberian Cranes, though tuber abundance explained a significant amount of crane use of foraging habitats, water depth was also an important explanatory variable (Burnham 2007). Presumably, this would be the same for other tuber feeding species as well.

Burnham and Barzen (2007) and Burnham (2007) reported on intensive sampling of tubers at Da Hu Chi together with regular counts of swans during six winters (1999/2000-2004/2005). Except for the winter of 2004/2005 (noted as 2004 in Fig. 10), Tundra Swan use-days (Fig. 10) correlated strongly with Vallisneria tuber numbers within the study lakes (Burnham and Barzen 2007). No correlation between Siberian Crane use-days and tuber numbers occurred among years but, within a year, the relationship between tuber density and water depth with Siberian Crane numbers was strong (Burnham 2007).

Indirect loss of foods of tuber-feeding birds may also occur through the impact of changing hydrology on the ecology of submerged aquatic vegetation like Vallisneria spp. Increasing water depths to 14 and 16 m would force submerged aquatic plants to grow in areas of the reserve that have not traditionally produced tubers as discussed above. In addition, higher water levels could result in greater boat traffic and sand dredging on Poyang Lake which will increase water turbidity and negatively affect plant growth (de Leeuw et al. in prep, Wu et al. 2007).

B. Sedge/grass eating birds

Birds that graze on the sedges and grasses at Poyang Lake utilize a zone that is at a higher elevation than the tuber zone but still at a relatively low elevation when compared to the rest of the basin (Fig. 4). In contrast to the tuber zone, where plant abundance varies greatly in any one


location among years and can occur across wide expanses of the lake basin, the sedge/grass zone is often relatively narrow in width (Fig. 3) and it varies little in spatial distribution from one year to the next. The plant community in this zone is dominated by sedges that grow in cool weather and by some grasses. As such, this plant community is short in stature and produces the highest growth rates during autumn, winter, or spring. Plants that grow during winter are essential for wintering grazing birds because it is the new growth of plants that contain enough protein and energy to sustain wintering grazing birds. Warm-season plant species, both dormant in cool weather and which constitute the common grassland vegetation at this latitude, cannot provide adequate nutrition.

Zheng (2009) linked grazing waterfowl with the sedge community by analyzing plant species composition in the grasslands and using stable carbon isotopes (12C and 13C) ratios to discriminate C3 (ratio ~ -29) from C4 (ratio ~ -13) species. Sedges and some short stature grasses are predominantly C3 (cool season) species whereas the taller grasses are warm season (C4) species. Next Zheng analyzed the droppings of geese that were collected from sedge communities at Poyang Lake. Goose droppings had an isotope ratio of -29, confirming that geese were feeding heavily on sedges and cool season grasses and not the tall C4 grasses. Zheng next developed a model which demonstrated that the relative abundance of C3 species is positively related to duration of submergence as well as to maximum temperatures during peak biomass production in winter. For the sedge community the peak productivity (thus nutrition for grazers) was concentrated in early winter.

Within the entire Lower Yangtze Floodplain, there appear to be more sedge community areas available than grazing species that feed on them (de Leeuw et al. 2006). Poyang Lake and Dongting Lake, however, provide a majority of these habitats. If sedge communities at Poyang Lake were eliminated by maintaining higher water levels, availability of sedge communities could become limiting to species in the grazing guild.

Typical bird species in this foraging guild include Greater White-fronted Geese, Lesser White-fronted Geese, Greylag Geese (Anser anser), Bean Geese (A. fabalis), and often Swan Geese as well. Of these species, a large proportion of Asia’s Bean Goose, Swan Goose, Greater White-fronted Goose and Lesser White-fronted Goose populations winter at Poyang Lake (Cao et al. 2008a) and their populations are vulnerable to further loss of habitat.

This more permanent zone of vegetation is very susceptible to changes in water level during winter because it cannot tolerate deep inundation during the winter growing season. At the other end of the gradient, shallow summer inundations may also cause greater competition from grasses that dominate vegetation zones at higher elevation. The grass/sedge zone thus occurs between submerged aquatic and tall grass zones and presumably requires moderate water levels during summer as well as low water levels during winter to persist. Given that many of the sedge species in this zone are long-lived, this zone likely will not shift rapidly in response to


proposed water levels. Elimination of these important sedge communities, even if for just a few years of transition, would have large impact on grazing geese which are already in decline (see below).

C. Seed eating/dabbling birds

The seed eating and dabbling species are represented by birds that forage along the water surface on foods that are floating or found just beneath the water surface. Often the foraging areas that are best for these species occur at, or near, the edge where open water ends and mudflats begin because seeds and invertebrates are concentrated there. The foods eaten can be plant (primarily seeds) or animal (e.g. insects or benthic organisms). Generally these foods have been produced elsewhere in the system and are concentrated along edges of water by water currents or wind.

The shape of wetland basins that produce good quality habitat for these species are areas where the basin slope is very shallow (a profile of 1:100 or more). With gently sloping surfaces subtle changes in water level during winter can create large new foraging areas for the birds. As wind direction and speed vary through the winter, these habitats can shift dramatically throughout the basin. With this guild, habitat quality within the year is highly variable and determined by minute changes in water level. Open systems, such as at the inland delta found at Nanjishan, are areas where these habitat conditions occur in great abundance at a large scale. Ecologically, broad open areas differ in quality for species in the seed eating/dabbling guild from the sub-lake basins like Da Hu Chi because lake basins are more closed than are the open deltas. Raising water levels, to the extent that they would reduce seiches, would markedly change habitat conditions for this foraging guild of species. In addition, if seeds consumed are produced primarily by sedges, proposed water levels could also decrease overall seed production. Few data exist to guide this assessment further.

Characteristic species within this foraging guild include mallard, gadwall, spot-billed duck and common teal. Areas where these habitats occur at Poyang Lake are variable both within and among years but are similar to the submerged aquatic plant zone except that birds in this guild need shallower water levels (e.g. < 30 cm) than do tuber feeding birds. The inland delta of Nanjishan Nature Reserve (Fig. 2) is likely a key area for this guild.

D. Benthic insect larvae eating birds

The habitats utilized by shorebirds in this foraging guild are similar to seed eating/dabbling birds but their range of water conditions is narrower. The maximum water depth for tall foraging shorebirds like Black-winged Stilts (Himantopis himantopis)is approximately 20 cm whereas maximum water depth for medium foraging shorebirds like Spotted Redshanks is around 7 cm. Because of their size (Marchant et al. 1986), smaller shorebirds (e.g. Little Ringed Plover, Charadrius dubius) have maximum foraging depths of about 3 cm. In most cases, optimal foraging depths are 50% lower than maximum foraging depths.


Most of these species can also feed on mudflats but are less likely to feed in these areas as they dry out. Foods of benthic feeders consist of invertebrates (usually insect larvae, crustaceans or gastropods). Birds probe to capture them and thus cannot forage on dry soils. Factors that influence productivity of invertebrates are not well understood but are likely improved by having occasional dry periods which allow aerobic decomposition (relatively fast) to occur compared to slow decomposition rates under anaerobic conditions (caused by water inundation). Thus, though dry conditions can often prevent foraging, they may be necessary to maintain high productivity. In the Poyang system the variable nature for water levels, and the large spatial scales over which these variable water levels occur, allows a heterogeneous patchwork of both wet and dry patches to occur simultaneously. As with the dabbling guild above, benthic foraging guild species would be especially sensitive to changes in areas that are affected by seiches because these variable conditions create collectively large areas of moist soil habitat as sheets of water move within the basin, altering where invertebrates can be accessed.

Thousands of shorebirds utilize Poyang Lake each winter but estimates of their numbers are poor because the many, relatively small species are difficult to count over such broad and variable areas.

E. Fish eating birds

There are two basic groups of fish eating birds, those that forage on predominantly live, healthy fish (e.g. herons (Ardea spp.), egrets (Egretta spp.), bitterns (Ixobrynchus spp.)), or large crustaceans like crayfish and crabs, and those that feed on dead or stressed fish (e.g. storks, Ciconia spp.). Herons, egrets and bitterns feed by stealth, standing in water and waiting for animals to come to them. These birds are able to feed on large expanses of water as long as water levels are not so deep as to prevent wading. Maximum water levels that birds could forage in would range from approximately 15 cm for small bitterns like the Little Bittern (Ixobrychus flavicollis) to 40 cm for larger birds like Grey Herons (Ardea cinerea). For this group, areas of suitable water can be large. Important habitats are also not as sensitive to change as are habitats for tuber feeders (for example) because they only require standing water of variable quality and animal prey densities. Prey species can be produced anywhere and migrate to feeding areas. Abundant presence of several egret and heron species in both summer (when water levels are high) and winter (when water levels are low) illustrate the flexible habitat requirements of members of this sub-guild.

No species of heron, egret or bittern that utilize Poyang Lake is threatened and no major concentration of a population for any heron, egret, or bittern resides at Poyang Lake.

For storks that feed on dead fish or fish that are incapacitated or stressed in some way, the habitat requirements differ from herons, egrets and bitterns. Storks can physically forage in deeper water but require water areas to be more segregated and shallow so that they can seek out prey


species rather than waiting for fish to swim near them as egrets and herons do. Though physical maximum water levels are likely 60 cm for storks in this sub-guild, the normal foraging depth is less than 30 cm. Accordingly, the area of foraging habitat available to storks is likely influenced by seiches. Changes that influence zones that are influenced by seiches would be detrimental to this foraging guild.

Approximately 90% of the world’s endangered Oriental White Storks winter at Poyang Lake. Other birds that belong to this group include Black Storks (Ciconia nigra).

F. Zooplankton eating birds

Represented by Eurasian Spoonbills and Pied Avocets (Recurvirostra avocetta), members of this foraging guild have very specialized feeding habits. They sift through water, and perhaps benthic materials, for zooplankton like ostracods and daphnia while opportunistically feeding on small fish found in isolated pools. Maximum water levels are not known but likely do not exceed 25 cm (Swennen and Yu 2004) and are considerably less for avocets (i.e. < 10 cm). Typically spoonbills forage at water levels that are 13 cm deep. As with benthic systems mentioned above, little is known about what factors influence the abundance or distribution of prey species for this guild but overall primary wetland productivity may play an important role.

Black-faced Spoonbills (Platalea minor) have wintered at Poyang Lake and are threatened but their use of Poyang has not been extensive. Besides Black-faced Spoonbills, no species in this foraging guild is endangered but a significant proportion of Eurasian spoonbills in the Asian Flyway utilize Poyang Lake.

6.3 Other considerations A. Importance of variation in water levels

The hydrological models developed so far for this assessment do not accurately reflect the importance of intra-annual variation in water levels even though this variation may be a key abiotic driver of the entire ecosystem. More habitat is available than predicted by surface elevation alone because of the ability of water pools to become separated from the main lake and because of the effect of seiches. These two factors create a vastly more dynamic hydrological system than we can model with the data currently available. Both birds and their foods respond favorably to these conditions.

Compared with the option of allowing natural water levels, management action to maintain more constant water levels, as would occur in all three scenarios of dam construction, would reduce the dynamic characteristic of this wetland system and therefore have a negative impact on bird species. Of the dam options proposed, raising water to a minimum of 16 m would have the greatest impact because it would eliminate all of this variability since few water bodies could become isolated or could be moved over flat surfaces by wind in a way useful to foraging birds. At 14 m some variation due to seiches would still occur at Poyang Lake but this residual


variation would be minimal and not likely sufficient to maintain all important foraging guilds. Without a precise and accurate water elevation model for the whole lake basin, it is not possible to model the importance of seiches, nor the impact of raised water levels on seiches further. Finally, at 12 m variation in the system would still be large and likely adequate in most years. Whether it could be adequate in years of extreme flood or drought as well as in abnormally cold years is questionable (see below).

Importantly, though variability can reduce food accessibility in small areas, the large region encompassing the greater lake basin ensures sufficient habitat is available for these foraging guilds under a variety of circumstances over the entire winter period. This unique fluctuation of water levels at Poyang over the course of the winter, and between years, provides a fluid mosaic of habitat availability to over 250 species of birds. No other wetland like Poyang remains in China or Asia.

Hydrological conditions at Poyang Lake vary greatly among years as well (Table 3), leading to large variation in food abundance and distribution from one year to another. In Da Hu Chi, tuber production varies among years (Table 3) and so does the number of tuber feeders such as Siberian Cranes in all four study lakes (Table 6). In some winters, as much as 15% of the world population of Siberian Cranes foraged in the four study lakes over the entire winter. In other years less than 1% of the Siberian Crane population foraged in the same four lakes.

Table 6. Average number of Siberian Cranes seen in four study lakes of Poyang Lake Nature Reserve during eight winters (Average # of cranes) in comparison to the total estimated world population (% of Total Population). The total population of Siberian Cranes for this period was estimated at 3,500 birds (Li et al. 2005).

Annual Mean Daily Winter Siberian Crane Observations (November-March)

1999-2000

2000-2001

2001-2002

2002-2003

2003-2004

2004-2005

2005-2006

2006-2007

Average # of Cranes 80.43 394.74 536.58 108.77 92.72 137.81 33.93 158.29 % of Total Population 2.30% 11.28% 15.33% 3.11% 2.65% 3.94% 0.97% 4.52%

If cranes were not foraging in Da Hu Chi, Mei Xi Hu, Sha Hu and Si Xia Hu then where were they? The vast expanse of Poyang Lake makes this simple question difficult to answer. When Siberian Cranes were tracked with satellite transmitters, however, they spent their entire winter within the Poyang Lake basin (Kanai et al. 2002). Multiple aerial surveys of the Poyang Lake


basin found 57-88% of the known population of Siberian Cranes within the Poyang lake basin (Li et al. 2005) and more recent coordinated ground surveys found 77% of the world’s Siberian Cranes wintering at Poyang Lake (Barter et al. 2005). In each of the winters where counts have been done, Siberian Cranes were using markedly different areas of Poyang Lake. With the limited data available, therefore, the collective areas of Poyang Lake that have been used sum to an area far larger than the known areas of use from within any one year.

One last consideration about variability in water depth and distribution: in our assessment of the extent of areas with water at 12, 14 and 16 m (see appended figures), our data reflect a fixed minimum water depth calculated for the entire winter. These data do not provide a comparison of how much area, cumulatively over the course of the entire winter, would have appropriate water depths for different foraging guilds. When comparing 14 m to 16 m scenarios, the cumulative area available to the birds during the winter for the 14 m scenario would be much larger than for the 16 m scenario because the water would be falling throughout the winter over a two-meter range of foraging depths. For the 12 m scenario, the water would be falling over a four-meter range, in comparison to the 16 m scenario, so that during the course of the winter vastly larger areas would be accessible to the birds. This changing choice of location could be particularly important during years when food supplies were low – e.g. because high summer flooding had reduced growth of Vallisneria or production of tubers -- as birds would be constantly changing where they fed and thus less likely to exhaust food sources that might be limited at any one location.

Importantly, slowly changing water levels would increase the diversity of habitat available because of the very gradual slopes found throughout the Poyang Lake Basin. Under these conditions, a minor change in water elevation results in dramatic changes in the distribution of that water. These changes can then be made more complex through the influence of seiches which redistribute water coverage even when water elevation does not change. Sub-lakes can also be managed with different water levels than occur in the main Poyang Lake basin (Fig. 9) and these lakes can further add to the hydrological heterogeneity in the entire system. With management capabilities of the sub-lakes, between year patterns of water level during summer highs and winter lows can differ greatly as well (Fig. 9).

B. Importance of water quality

Apart from water levels in winter, which influence the availability of food, water levels and water clarity in summer can influence the productivity of food by altering how much light penetrates the water column. Light is needed for photosynthesis and submerged aquatic vascular plants, as well as algae, are strongly affected by light availability (Yuan et al. 2007, Yuan et al. 2008). Deeper water can reduce the amount of time light reaches benthic layers but shallower water can also increase the probability of re-suspension of benthic sediments. Both situations cause deterioration of water clarity (Wu et al. 2008a). Examining non-point pollution or specific


toxins, as well as other aspects of water quality, is beyond the scope of this assessment but may be important to examine elsewhere. Dams, for example, can change water retention time in the basin which, in turn, affects sediment loads and accumulation rates of non-point pollution or nutrient input.

Generally, water clarity was largely explained by seasonal water levels with the clearest water occurring in summer when water levels were high (Wu et al. 2008a). In water depths of up to 2 meters, clearer water typically improves plant growth and tuber production (Yuan et al. 2007). If an outlet dam alters this pattern of water change by altering either the timing or the overall elevation of water in the basin this change could have a large impact on plant growth. With 14 m and 16 m elevation scenarios, the impact of the dams might provide better water clarity, at least as it relates to re-suspension of sediments, and would increase productivity of submerged aquatic vascular plants. Wu et al. (2008b) predicted that Three Gorges dam, if it extended the high water period in Poyang Lake, might increase tuber production for submerged aquatic plants. In contrast, however, lake basins elsewhere in the Yangtze basin that have altered flow regimes via impoundment have not seen an increase in submerged aquatic plant production (see section D. below), perhaps because dams also increase retention of pollutants in addition to raising water levels.

With higher and more constant water levels in the Poyang Lake basin there would likely be an increase in boat traffic. Currently, boat traffic and direct extraction of sand have caused dramatic declines in water clarity at Poyang Lake (Wu et al. 2007). Since the management of the outlet dams is designed to increase navigation, this negative impact is expected to increase. Thus, though maintaining higher water levels could have a positive influence on water quality through decreasing the re-suspension of sediments via wind action, the net impact to water quality would be a general decline because of turbidity caused by boat traffic, sand dredging, and nutrient retention (see below).

C. Existence of alternative habitat areas outside of the Poyang Lake system.

If available habitats at Poyang Lake were reduced through dam construction or other development projects, would birds belonging to different foraging guilds have alternate habitats that could be used? Few species are well-known enough to answer this question. Perhaps the best known species where this question can be addressed is the Siberian Crane. The most recent waterbird surveys of the lower Yangtze River floodplain (Fig. 11) have found less than 0.5% of the world’s Siberian Cranes utilizing wetlands outside of Poyang Lake (Barter et al. 2005).

If habitats for Siberian Cranes at Poyang Lake were lost, how likely would it be that the population could persist in other habitats located outside of Poyang Lake? Tundra Swans, another tuber feeder, occur in other areas of the lower Yangtze River (Fig. 11) so tubers are likely available elsewhere. Most of these wetland areas, however, have water depths that are too


deep for Siberian Cranes to forage efficiently. Further, since winter areas of Siberian Cranes were described in 1981, few records have ever occurred outside of Poyang Lake (Cheng 1987). It is unlikely that alternative habitats sufficient for this population of Siberian Cranes to persist would occur if Poyang Lake was no longer available to provide them. Extirpation of Siberian Cranes in the wild would be a likely event if Poyang Lake were lost as a wintering habitat for this species.

Poyang Lake and the other wetlands in the Yangtze River floodplain have extraordinary importance for other species of cranes, waterfowl, and related species. Recent counts indicate that about 1.1 million individuals of 24 species of Anatidae winter in China, with about 80% in the Yangtze floodplain (Cao et al. 2008a). Poyang Lake is by far the most important of these wetlands for waterbirds. Over five years (1997-2001), Poyang Lake had the largest winter count in East Asia, according to the Asian Waterbird Census – its 1997 count of 353,737 birds was 73% higher than any other location during this five-year period (Li et al. 2004).

Yet waterbird numbers in China have declined dramatically (see Cao et al. 2008a and 2008b), possibly indicating threats on both winter and breeding grounds. Lu (1996) estimated Anatidae numbers in China in the early 1990s at 3-4 million, as compared to a current estimate of 1.1 million (Cao et al. 2008a). Goose populations in particular have declined. All five goose species (Lesser White-fronted Goose, Greater White-fronted Goose, Bean Goose, Greylag Goose, Swan Goose) wintering regularly at Poyang Lake reflect these trends (Wetlands International 2006). Since the mid 1980s, breeding populations of Greater White-fronted Geese and Bean Geese– that migrate from the Arctic to China -- have declined by 80% and 65% respectively (Syroechkivskiy 2006). Swan Geese, breeding in northeast China, southeast Russia and eastern Mongolia, have suffered repeated years of poor reproduction across large parts of the breeding range in recent years due to drought and human disturbance (O. Goroshko, N. Tseveenmyadag, and L. Su, personal communications).

Collectively these species depend heavily on Poyang Lake in winter for survival. Alternate habitats within the lower Yangtze River floodplain are declining or stable in their condition. No evidence suggests that the condition of other wetland ecosystems within the Yangtze floodplain is improving. Loss of Poyang Lake as important habitat for these other waterbird species may be as critical as it is with Siberian Cranes.

D. Experience from other lake basins in the Yangtze River basin

Predicting what might happen at Poyang Lake if a dam were constructed at its outlet is difficult, considering existing data for Poyang Lake. In lieu of data for Poyang we examined other aquatic systems in the region to describe how they responded to similar hydrological changes. Other lakes in the middle/lower reaches of the Yangtze have not responded well to hydrological isolation from the Yangtze. Generally, damming lakes and rivers erects barriers to the


movement of flora and fauna and reduces the seasonal variability in water level fluctuations within these aquatic systems (Baxter 1977). Within the Yangtze basin many aquatic systems have seen a marked increase in the number and magnitude of hydrological alterations since the 1950’s (Chen et al. 2001, Chen et al. 2004, Fang et al. 2006).

Over the last three decades, intensive hydrological engineering projects seeking to control flooding and provide irrigation to neighboring agricultural land isolated all but two of the lakes in the region: Dongting and Poyang (Chen et al. 2004). Isolation from the Yangtze and the reduction of fluctuation in water levels for other lakes have contributed to the extensive reclamation and conversion of wetlands and shallow lakes to agricultural use (Chen et al. 2001). In the middle reaches of the Yangtze River, between the cities of Yichang (Hu Bei Province) and Houkou (Jiang Xi Province), all but two of thirty-three lakes surveyed had a significant decrease in their surface area since the 1950’s (Fang et al. 2006). Impacts of these activities have included significant declines in water quality and clarity, dramatic alterations of nutrient cycling, and a decline of biodiversity across the region. While it is difficult to put an economic value on these impacts, the national government recently pledged fourteen billion dollars to address the degradation of Tai Hu, located in the Yangtze River delta near Shanghai (AFP 2007).

Since the 1980’s a significant reduction in the seasonal fluctuations of the surface elevation of Tai Hu, combined with a dramatic increase of anthropogenic inputs of phosphorus, have contributed to blooms of toxic Microcystis algae (Chen and Wang 1999). While the increased nutrient loading of Tai Hu since the 1990’s appears to be the proximate cause of the algae blooms (Ye et al. 2007), experimental water transfers into the lake from the Yangtze, mimicking natural hydrological fluctuation within the system, temporarily reduced algae and nutrient concentrations and had a short-term positive impact on the water quality of the lake (Hu et al. 2008). The financial costs of these blooms are substantial. Microcystis in Tai Hu eliminated the lake as a source of drinking water and directly impacted the thirty-six million people who live in the lake basin (Qin et al. 2007). Short-term solutions such as trucking in bottled water exceeded five billion dollars in 2007 for portions of one city, Wuxi, alone (Li 2008). Other solutions, such as the purchase of water filters, can cost households nearly three hundred dollars each and are not available for low-income households (Qian 2008). Recently, these blooms occur seasonally in Tai Hu, but examples from other lakes in the Yangtze basin indicate that a shift within the lake to one permanently dominated by algae could occur.

Lake Biandantang (Hu Bei Province) provides a relevant example of how the transition from an ecosystem dominated by submerged aquatic vegetation can change to one dominated by algae as a result of altering the way nutrients cycle through lakes of the Yangtze. This lake is part of the larger Baoan Lake complex where Kai et al. (2003) found nearly 93% of the lake bottom to be populated with submerged aquatic vegetation. Shortly after this study, however, Xing et al. (2006) described a shift within the Biandantang portion of the lake from a plant community dominated by submerged aquatics to a community dominated by algae. In doing so the wetland


was altered from a carbon sink, predominately composed of vegetation, to a carbon source. This dramatic change was primarily due to reducing water level fluctuations in the system and a corresponding shift in the aquaculture practices within the lake. Other studies of lakes have focused on the increased availability of phosphorus and nitrogen throughout the water column as a result of the rapid turnover of the shorter-lived algae (Sand-Jensen and Borum 1991). This shift from vegetation to algae fundamentally alters the manner in which nutrients flow through the system and often makes it very difficult to restore an aquatic system after the shift of primary producers has occurred (Scheffer et al. 1993). It also has important consequences for primary consumers, and all the organisms that depend on those primary consumers, within the system (Carpenter et al. 1985).

The damming of Poyang Lake, and the potential to reduce the natural variation of water levels within the system, may mimic these trends observed in other lakes within the Yangtze basin and around the world. Declines in biodiversity in both flora and fauna occurred throughout the middle reaches of the Yangtze River, with much of this decline linked to increased human activities (Fang et al. 2006). This trend reflects observations made in other regions of the world where dynamic aquatic systems have suffered declines in biodiversity and ecosystem function after damming (Kingsford 2000). The impacts of enforcing stability within dynamic aquatic systems appears to have a particularly negative effect with regard to feeding guilds of waterbirds dependent on the range of habitats these systems produce (Kingsford et al. 2004). While it may not be possible to fully predict the effects of altering the fluctuation of water levels within Poyang Lake through impoundment, damming around the world appears to follow general trends in the alteration of physical characteristics of the system which negatively affect flora and fauna adapted to un-impounded flow regimes (Bunn and Athington 2002). It is highly likely that the flora and fauna, as well as the overall ecosystem function at Poyang, will follow similar patterns. If true, this decline will have deleterious effects that extend beyond wildlife and affect all users of the Poyang system, particularly local human communities that depend on the lake for a variety of goods and services.

E. Significance of different water management strategies if a dam is constructed

Our analysis has looked at the impacts of three different minimum water levels, reflecting three different ways that water could be managed if the outlet dam is constructed. Yet it is probable that any dam, if constructed, would enable managers to maintain water at any of these minimum depths during the course of any one winter, or at different elevations during the same winter.

Management of any dam will be responsive to many needs and economic considerations. A dam constructed at Poyang will need to respond to a range of weather extremes and also impacts on hydrology from other water management activities in the basin such as Three-Gorges Dam or dams on the tributaries. It is unlikely that the dam, once built, would always maintain minimum water levels of 12 m even if highly desirable for safeguarding wintering waterbirds. While the


12 m minimum water level carries the least risk for wintering waterbirds, it nevertheless could pose significant threat for those species most dependent on Poyang Lake, including Siberian Cranes and Oriental White Storks, during extreme years. But since the 12 m scenario may be dependent on a dam that could alternatively maintain 14 m or 16 m depths, the much greater risks to waterbirds from these higher water levels must be considered in comparing impacts of construction of the dam with the no dam option.

Information gaps

Because of the ecological importance of Poyang Lake, acquiring additional data and developing the following analytical tools will greatly benefit any decisions made on major development projects such as the proposed outlet dam. Current gaps that this report has identified are:

A. A DEM, at an acceptable vertical and horizontal resolution for the entire Poyang Lake, should be made available so that an impact assessment can be made for the entire basin rather than a subset of that basin.

B. It is critical to understand habitat use of various foraging guilds in other parts of the lake basin. Doing so would make it possible to assess the importance of the main lake, including the inland delta at Nanjishan Nature Reserve, relative to the sub-lakes along the periphery that have been more intensively studied.

C. Of all the six foraging guilds identified in this report, data for tuber-feeding species is best (though still inadequate). Data for some of the non-tuber foraging guilds, especially grazers, piscivores and insectivores would be critical to acquire. Especially important would be studies on foraging depths and foods of the highly specialized Oriental White Stork, an endangered species with 90% of its population wintering at Poyang Lake.

D. We understand little about how plant communities might change at Poyang Lake in response to changing water levels, especially the sedge community.

E. A hydrological model that incorporates seiches and isolation of water bodies at different water levels would be essential for informing the next stage of model creation. These two steps would greatly help future impact assessments of proposed development projects.

F. There is a great need for economic and ecological cost/benefit analyses to better weigh and understand options that are being considered.

G. More work is required to identify management needs at Poyang Lake as a whole under a no dam scenario.

H. The interaction between waterbird habitat and human use of these same lands is poorly understood and will comprise a critical component of any successful future management strategy.


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Figure 1. Poyang Lake at high water (left) and low water (right) with study area and Nanjishan Nature Reserve, an adjacent protected area, overlaid

图1. 在鄱阳湖高低水位时研究区（图中示左）和南矶山自然保护区（图中示右）及周边保护区域。


Figure 2. Detailed study area. The red boundary is the study area included within the Digital Elevation Map while the base map is a LANDSAT image taken on December 10, 1999 and represents the average low water elevation (11.98 m Wu Song) in Poyang Lake. Da Hu Chi, Si Xia Hu, Mei Xi Hu, and Sha Hu are the long-term study lakes within Poyang Lake Nature Reserve.

图2. 研究区详图。红线范围内的研究区在数字高程图内，湖区内其他部分的全图基于1999年12月10日的陆地卫星，代表鄱阳湖平均低水位（11.98m 吴淞）。大湖池、寺下湖、梅西湖和沙湖是鄱阳湖自然保护区长期研究湖。


Figure 3. LANDSAT image (taken December 10, 1999) of study area with ground-truthed sedge areas outlined in yellow. Green areas may or may not include sedges but these areas have not been ground-truthed.

图3.研究区LANDSAT卫星图（1999年12月10日），内黄线圈画处为经过实地调查的莎草分布带

。图中绿色区域为可能的莎草分布区，但未经实地调查核实。


Elev

atio

n W

uson

g (m

)

13.0 14.0 15.0 16.0

Grass Sedge Vallisneria or Potamogeton Submerged Aquatic or Mud

Vegetation Zones of Da Hu Chi

Figure 4. An illustration of different vegetation zones at Da Hu Chi in relation to elevation (Wu Song) moving from high (left) to low (right). In Da Hu Chi the average elevation of the sedge zone was 15.34 m (Wu Song) and of the mud zone was 14.4 m (Wu Song). The zones, as measured at Da Hu Chi, were defined as (Wu Song): Grass Zone >16.0 m, Sedge Zone = 16.0-14.6 m, Submerged Aquatic or Mud zone = 14.6-14.3 m, and Vallisneria or Potamogeton Zone = 14.3-13.9 m.

图4. 大湖池不同植物群落沿地势水位（吴淞高程,以下涉及水位均为吴淞高程）由高（左）到低（右）水平分布带示意图。莎草群落带在大

湖池的平均海拔为15.34 m（吴淞），泥滩带为14.4 m。在大湖池调查的其他分布带的高程为：草滩带>16.0 m，莎草带16.0-14.6 m, 沉水或泥滩带14.6-14.3 m, 苦草或眼子菜 14.3-13.9 m。


Figure 5. The number of tubers sampled during fall, 2004 at Da Hu Chi in relation to the basin elevation (Wu Song) where the tubers were sampled. Lower elevation means deeper water during inundation periods so the more deeply flooded zones are on the left and more shallowly flooded zones are on the right.

图5. 2004年秋季大湖池在莎草分布带块茎数量样方调查结果。在丰水期低海拔意味着深水，图中所

示由左向右水位逐渐变浅。


Figure 6. Coverage of water at 11.98 m (Wu Song) in the study area. Yellow lines define the current sedge zone and blue denotes standing water. DEM data is super-imposed on a LANDSAT image created December 10, 1999.

图6. 在海拔11.98 m (吴淞)水位时研究区水淹情况。黄线内区域为目前的莎草带，蓝色代表水域。DEM 数据叠加在1999年12月10日LANDSAT卫星影像上。








Figure 9. Water elevation in Da Hu Chi (brown), the Xiu River (blue) and the Gan River (red) for two years (May 1, 2005 to April 30, 2006; May 1, 2006 to April 30, 2007). Da Hu Chi is completely dry at approximately 14.52 m (Wu Song). If the connection between Da Hu Chi the Xiu River were not obstructed the lake would drain rapidly each year. In both years (as in most years), however, Da Hu Chi is managed so that it never dries completely. Where the brown line lies above the red and blue lines, Da Hu Chi is hydrologically isolated from Poyang Lake.

图9. 大湖池（淡棕色）、修河（蓝色）、赣江（红色）二年水位，2005年5月1日至2007年4月30日。大湖池在约

14.52 m (吴淞) 时全部干枯。假如大湖池和修河相连处无控水设施，大湖池每年都会很快的干枯。然而，在这二年间（与

大多年份一样），由于管理措施的实施大湖池从未完全干枯。在淡褐色线高于蓝色和红色时是大湖池与鄱

阳湖分离期。


Figure 10. The relationship between Tundra Swan use days and Vallisneria tubers is indicated by the year when they were observed. Swans are measured in use days: one observed swan during one day equals 1 use day, two observed swans during one day equals two use days. The relationship between swans and tuber numbers is direct: when numbers of tubers were high, many swans utilized Da Hu Chi during winters beginning in 1999 through winters beginning in 2004. The year 2004 is an anomalous year in these data and the higher number of swans in Da Hu Chi during this year may be a result of greater access to food resources due to unusually high water conditions. R2, without 2004, explained 94% of the variation in the relationship between tuber density and swan-use days.

图10. 用年份数表达在观察年小天鹅对栖息地利用日数与苦草的块茎关系。天鹅的利用日：1天观察到1只天鹅等于一个利用日，1天观察到2只天鹅等于2个利用日。天鹅与块茎的关系是直接的相关：在

大湖池在1999-2000和2004-2005冬季，当块茎数量高，天鹅利用量也相应高。 2004年的数据是一个反常的年份。那年的数量过高可能是由于反常高水位条件所致。去掉2004年数据，R2可以解释94%的在块茎的密度与天鹅利用日之间的关系


Figure 11. Waterbird census locations located outside of Poyang Lake where tundra swans (yellow) and Siberian cranes (red) were counted (Lei et al. 2008a). The study area at Poyang Lake for this report is outlined in red.

图11越冬水鸟调查地点，其中在鄱阳湖以外记录到的小天鹅（黄色）和白鹤（红色）的地点。本报告所涉及的研究区为红线内。


8. Appendices Foraging depths within the study area, as determined by the DEM, at minimum water elevations of 12 m, 14 m, and 16 m (Wu Song). Foraging depths are given in units of 0-10 cm, 0-20 cm, 0-30 cm, 0-50 cm, and 0-100 cm for each water elevation. These elevations are overlaid on a LANDSAT image taken on December 10, 1999.

8 附录。用DEM确定在最低水位12m, 14m, 16m时研究区内的觅食深度。在每个水位觅食深度划分为：0-10 cm. 0-20 cm, 0-30 cm, 0-50 cm, 和 0-100 cm。这些图层叠加在LANDSET 1999年12月10日卫星图片上。


A. Foraging depths (light blue) with 12 m (Wu Song) minimum elevations. Dark blue is water that is deeper than indicated foraging depth. 在最低水位12 m (吴淞) 条件下的相应深度的觅食去（浅蓝）。深蓝处水深与觅食区。

0-30 cm 0-50 cm

0-100 cm


B. Foraging depths (light blue) with 14 m (Wu Song) minimum elevations. Dark blue is water that is deeper than indicated foraging depth. 在最低水位14 m (吴淞) 条件下的相应深度的觅食去（浅蓝）。深蓝处水深与觅食区。

0-30 cm

0-10 cm 0-20 cm

0-50 cm

0-100 cm


C. Foraging depths (light blue) with 16 m (Wu Song) minimum elevations. Dark blue is water that is deeper than indicated foraging depth. 在最低水位16 m (吴淞) 条件下的相应深度的觅食去（浅蓝）。深蓝处水深与觅食区。

0-30 cm

0-10 cm 0-20 cm

0-50 cm

0-100 cm

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