Lake Caizi Research Articles

Monitoring water clarity of lakes in the Middle-Lower Yangtze Plain using Landsat observations (1984–2023)

Using the improved Quasi-Analytical Algorithm (QAA) and Landsat data, we documented the long-term changes in water clarity of the 17 largest lakes in the Middle-Lower Yangtze Plain from 1984 to 2023. A comprehensive dataset with over 4600 water clarity maps, reconstructed from 2511 Landsat series images, was compiled. The water clarity changes of these 17 lakes have a clear seasonal variation pattern, with the highest in summer and the lowest in winter. Over the past 40 years, water clarity of 59 % lakes shows a downward trend, with Junshan Lake showing the highest decrease rate of −0.0231 m/yr. 41 % lakes water clarity are showing an upward trend. From 1984 to 1990, the highest average ZSD (Secchi disk depth) values were recorded in Changhu Lake, Junshan Lake, Honghu Lake, Futou Lake, and Gehu Lake. These lakes, however, experienced the most significant declines compared to period from 2021 to 2023. Chaohu Lake, Taihu Lake, Caizi Lake, and Nanyi Lake, which had the lowest average ZSD during 1984–1990, showed the most substantial increases. Analyzing the monthly distribution of water level and ZSD data reveals that water clarity exhibits different seasonal variations in relation to water levels. The comprehensive dataset and analysis provide a crucial scientific basis for informed water resource management and policy-making in the region.

Deteriorating wintertime habitat conditions for waterfowls in Caizi Lake, China: Drivers and adaptive measures

China has made enormous strides to achieve high-quality development and biodiversity conservation, and the establishment of nature-protected areas is one of the essential initiatives. Caizi Lake involves a natural reserve and two national wetland parks, accommodating winter migratory waterfowl over the middle and lower Yangtze River basin in China. However, the water transfer from the Yangtze River to the Huai River (YR-HR water transfer) has modified the winter hydrological conditions of Caizi Lake, negatively affecting wintertime waterfowl habitats. Hence, conserving wintertime waterfowl habitats necessitates knowledge of the dynamical mechanisms behind the impacts of YR-HR water transfer on wintertime waterfowl habitats and adaptive measures. Here we developed a machine learning model, the normalized difference vegetation index, and on-spot observatory datasets such as the spatial distribution of waterfowl species and underwater topography of Caizi Lake. We found that the rising winter water level of Caizi Lake encroaches on winter waterfowl habitat with extremely high suitability. Meanwhile, rising water levels reduced waterfowl food sources. Thus, rising water levels due to YR-HR water transfer deteriorated waterfowl living conditions over Caizi Lake. Therefore, we proposed adaptive measures to alleviate these negative effects, such as water level regulation, artificial feeding of waterfowls, restoration and reconstruction of contiguous mudflats, grass flats. This study highlights human interferences with waterfowl habitats, necessitating biodiversity conservation at regional scales.

Differences in Waterbird Communities between Years Indicate the Positive Effects of Pen Culture Removal in Caizi Lake, a Typical Yangtze-Connected Lake

Considering the negative effects of wetland degradation, various measures have been implemented to restore wetland habitats for aquatic organisms, and their effectiveness levels must be assessed. To reduce the effects of aquaculture on aquatic communities, pen culture facilities, which are widely distributed in Yangtze-connected lakes, were removed in 2018. We surveyed and compared waterbird communities in Caizi Lake during the four months before (2017–2018) and after net pen removal (2021–2022) to evaluate their effect on the diversity and species composition of wintering waterbirds. After net pen removal, the richness and number of individual waterbird species increased, whereas the Shannon–Wiener diversity index did not change because the increase in the bird number throughout the year was mostly associated with a few species. The response of individual numbers of different guilds to the removal of net pens differed. The number of deep-water fish eaters, seed eaters, and tuber feeders increased, whereas that of invertebrate eaters decreased. The species composition also changed, particularly in the northeastern and southwestern parts of the lake. Differences in waterbird communities between the winters of 2017–2018 and 2021–2022 indicated that net pen removal had a positive impact on waterbird communities.

Source apportionment of heavy metals and their effects on the species diversity of plant communities in the Caizi Lake wetland, China.

This study investigated the effects of heavy metals on the species diversity of the Xinjian Dyke Wetland, an ecosystem where reclaimed farmlands are being transformed back into wetlands through the introduction of indigenous plants. The sources of soil heavy metals were analyzed, and correlation analyses were conducted to assess the relationships between heavy metal content and biodiversity indices. The results indicated that (1) the mean contents of Hg, Cd, Cu, Zn, As, Cr, and Pb were higher than the control values, with the content of Hg, Cd, Cu, and Zn exceeding the national standard; (2) the soil heavy metals mainly came from pesticides, chemical fertilizer, transportation, sewage irrigation, and the soil matrix; and (3) Hg and As were not significantly correlated with the diversity indices, but there was a highly positive correlation for Cu, Cr, and Pb, and a significant negative correlation for Zn and Cd. Collectively, our findings indicated that heavy metals have different effects on the plant species diversity inXinjian Dyke reconstruction area. The ecological restoration of wetlands from reclaimed farmlands should reasonably increase tolerant species and maximize the ecological niche differentiation of the species. Moreover, functionally redundant species should not be planted.

Intestinal Microbiota of Anser fabalis Wintering in Two Lakes in the Middle and Lower Yangtze River Floodplain.

The intestinal microbiota of migratory birds participate in the life activities of the host and are affected by external environmental factors. The difference in habitat environment provides diversity in external environmental selection pressure for the same overwintering waterfowl, which may be reflected in their intestinal microbiota. Caizi lake and Shengjin Lake in the Middle and Lower Yangtze River Floodplain are the main habitats for migratory waterfowl in winter, especially the Anser fabalis (A. fabalis). It is important to explore the changes in intestinal microbiota composition and function of A. fabalis in the early overwintering period to clarify the effect of habitat size and protection status on intestinal microbiota. In this study, the composition and structural characteristics of the intestinal microbiota of A. fabalis in Shengjin Lake (SL) and Caizi Lake (CL) were preliminarily explored in order to obtain data for the migratory birds. In both SL and CL groups, 16S rRNA amplicon sequencing analysis showed that Firmicutes was the dominant bacterial phylum, but the relative abundance showed significant differences. Lactobacillus was the most abundant genus in both SL and CL groups. At the species level, the abundance of L. aviaries was the highest, with a relative abundance in both SL and CL groups of more than 34%. When comparing the average relative abundance of the 15 most abundant genera, it was found that Subdoligranulum, Exiguobacterium, and Terrisporobacter had higher abundances in the intestinal microbiota of CL A. fabalis, while Streptococcus and Rothia had higher abundances in the intestinal microbiota of SL A. fabalis. There was only a positive correlation between Bacteroidota and Proteobacteria in the intestinal microbiota flora of SL A. fabalis, and the species were closely related. At the same time, there were positive and negative correlations between Firmicutes and Actinomycetes. However, CL is mainly associated with a positive correlation between Firmicutes and Actinomycetes, and there are also a small number of connections between Firmicutes. PICRUSt1 prediction analysis revealed that the Clusters of Orthologous Groups (COG) functions of SL and CL involve energy production and transformation, amino acid transport and metabolism, carbohydrate transport and metabolism, and transcription. Understanding the changes in intestinal microbiota in Aves during the overwintering period is of great importance to explore the adaptation mechanism of migratory Aves to the overwintering environment. This work provides basic data for an A. fabalis intestinal microbiota study.

Metagenomic analysis of gut microbiota and antibiotic-resistant genes in Anser erythropus wintering at Shengjin and Caizi Lakes in China.

Migratory birds are the primary source and reservoir of antibiotic-resistant genes (ARGs) related to their gut microbes. In this study, we performed metagenomics analysis to study the gut microbial communities and ARGs of Anser erythropus wintering at Shengjin (SJ) and Caizi (CZ) Lakes. The results showed that bacteria, fungi, viruses, and archaea were the dominant gut microbes. Principal component analysis (PCA) indicated that the microbiota compositions significantly differed between the two populations. Diet may be the most crucial driver of the gut microbial communities for A. erythropus. This species fed exclusively on Poaceae spp. at Shengjin Lake and primarily on Carex spp. at Caizi Lake. Tetracycline, macrolide, fluoroquinolone, phenicol, and peptide antibiotics were the dominant resistant types. ARGs had a significantly higher abundance of operational taxonomic units (OTUs) in the Shengjin Lake samples than in Caizi Lake samples. PCA indicated that most Shengjin Lake samples significantly differed in gut microbiota composition from those obtained at Caizi Lake. This difference in gut microbiota composition between the two lakes' samples is attributed to more extensive aquaculture operations and poultry farms surrounding Shengjin Lake than Caizi Lake. ARGs-microbes associations indicated that 24 bacterial species, commonly used as indicators of antibiotic resistance in surveillance efforts, were abundant in wintering A. erythropus. The results revealed the composition and structural characteristics of the gut microbiota and ARGs of A. erythropus, pointing to their high sensitivities to diet habits at both lakes. This study also provides primary data for risk prevention and control of potential harmful pathogens that could endanger public health and therefore are of major significance to epidemiological and public health.

Gut Fungal Communities of Anser erythropus Wintering at Shengjin Lake and Caizi Lake in China

Gut Fungal Communities of Anser erythropus Wintering at Shengjin Lake and Caizi Lake in China

Spatio-Temporal Distribution Patterns and Determinant Factors of Wintering Hooded Cranes (Grus monacha) Population

Hooded Cranes (Grus monacha) rely on wetlands for the majority of their life cycle and respond to the environmental conditions during the wintering period. Future conservation planning should be driven by an understanding of how cranes respond to environmental factors at degraded wetland sites and the changes in their spatio-temporal distribution. In recent years, the spatial and temporal distribution of waterbirds and determinant factors have become a research focus. However, research on the specific factors influencing the relative abundance of Hooded Cranes from multiple perspectives in the different habitat patches at Shengjin and Caizi Lakes is lacking. Therefore, from 2021 to 2022, we investigated the quantity and distribution of Hooded Cranes in the upper part of Shengjin and Baitu Lake part of Caizi Lakes. We considered multiple habitat variables, including patch size, food biomass, food availability, and human disturbance, and analyzed the dynamic changes in the distribution of the population in different wintering periods. We used model selection and averaging to select the best model and identify key variables. During different wintering periods, the spatio-temporal distribution of the crane population differed in the upper part of Shengjin Lake, but the crane was mainly distributed in the northern part of the Baitu Lake part of Caizi Lake. The model that included food biomass and patch size was the best for predicting the relative abundance of Hooded Cranes. Cranes foraged in areas with large patches and abundant food resources. Therefore, we suggest reserving patch integrity and availability in the current habitats and protecting and restoring the main food resources to provide high-quality habitat patches and plentiful food resources for wintering populations of Hooded Cranes.

The impacts of water level fluctuations from paddy fields and aquaculture ponds on wetland habitats for wintering waterbirds: Implications for wetland management

The distribution and composition of wetland habitats for wintering waterbirds are heavily influenced by water level fluctuations. Through polder construction and aquaculture activities, paddy fields and aquaculture ponds have decreased the lateral connectivity of water level fluctuations in the lake. However, the impacts of water level fluctuations on habitat suitability, which can be seen using high-resolution images analysis, often cannot separate disturbances caused by the paddy fields and aquaculture ponds, and it is difficult to capture the actual impact of water level fluctuations on wetland habitats. Based on remote sensing image data and hydrological data, we selected Caizi Lake as a study site and comparatively analyzed the changes in wintering waterbird habitats in a water level sequence under the two scenarios. Our work showed that paddy fields and aquaculture ponds should be considered as potential options for creating more suitable habitats for migratory waterbirds if combined with reasonable and effective management of the water level within the paddy fields and aquaculture ponds. The present study results could facilitate the management and sustainable utilization of Caizi Lake wetlands and provide support for creating small habitats by managing the water levels of paddy fields and aquaculture ponds.

Bacterial community composition and indicators of water quality in Caizi Lake, a typical Yangtze-connected freshwater lake.

Caizi Lake is an important lake connected to the Yangtze River in Anhui Province and a crucial connection for the Yangtze-to-Huaihe Water Diversion Project. There were marked differences in trophic status of the six sampling sites based on the physicochemical characterization. The Bacterial Eutrophic Index (BEI), used to quantify water quality, was well related to Carlson's trophic state index (TSI) (Spearman's ρ = 0.829, P<0.05). Mean TSI and BEI were 54 and 0.58, respectively, indicating that Caizi Lake was slightly eutrophic. Actinobacteriota were the predominant bacterial phylum in the water and Acidobacteriota in sediments. The diversity and composition of the bacterial community was markedly different between sites for water but not sediment samples. Unlike other Yangtze-connected freshwater lakes, the distance-based redundancy analysis revealed that dissolved oxygen affected the composition of the planktonic bacterial community (P<0.001), while total phosphorus was the major factor in the sediments (P<0.05). The water quality of Caizi Lake has significantly improved since a few years ago. These results contribute to the long-term monitoring of the ecological quality of the water environment along the Yangtze River to the Huaihe River.

Organising a juvenile ratio monitoring programme for 10 key waterbird species in the Yangtze River floodplain: analysis and proposals

BackgroundIn the face of continued degradation and loss of wetlands in the Yangtze River floodplain (YRF), there is an urgent need to monitor the abundance and distribution of wintering waterbirds. To understand fully observed annual changes, we need to monitor demographic rates to understand factors affecting global population size. Annual reproduction success contributes to dynamic changes in population size and age structure, so an assessment of the juvenile ratio (i.e. first winter birds as a proportion of total number aged) of overwintering waterbirds can be an important indicator of the reproductive success in the preceding breeding season.MethodsDuring 2016–2019, we sampled juvenile ratios among 10 key waterbird species from the wetlands in the YRF. Based on these data, we here attempt to establish a simple, efficient, focused and reliable juvenile ratio monitoring scheme, to assess consistently and accurately relative annual breeding success and its contribution to the age structure among these waterbird species.ResultsWe compared juvenile ratio data collected throughout the winter and found that the optimal time for undertaking these samples was in the early stages of arrival for migratory waterbirds reaching their wintering area (early to mid-December). We recommend counting consistently at key points (i.e. those where > 1% biogeographical flyway population were counted) at sites of major flyway importance (Poyang Lake, East Dongting Lake, Shengjin Lake, Caizi Lake, Longgan Lake and Chen Lake). Based on this, the error rate of the programme (155 planned points, the count of 10 waterbird species is 826–8955) is less than 5%.ConclusionsWe established a juvenile ratio monitoring programme for 10 key waterbird species in the wetlands of the YRF, and discuss the feasibility and necessity of implementing such a future programme, and how to use these data in our monitoring and understanding of the population dynamics of these waterbird populations.

Intestinal Microbes of Hooded Cranes (Grus monacha) Wintering in Three Lakes of the Middle and Lower Yangtze River Floodplain.

Simple SummaryIntestinal microbes are critical to host health, and are affected by environmental factors. In this study, we investigated the intestinal microbes of Hooded Cranes wintering at three lakes with different environmental characteristics in the middle and lower Yangtze River floodplain in China, aiming to provide insights into the effects of habitat size and protection status of birds on their intestinal microbes. We found that the Hooded Cranes at the smaller lake had higher intestinal bacterial and fungal diversity than those at the larger lake. In addition, more diverse and abundant pathogens were found in the gut of Hooded Cranes that lived in the relatively poorly protected habitat than those that lived in well-protected habitat. This study contributes a new perspective for understanding the intestinal microbes of wintering migratory waterbirds at different habitats, and will help to understand the survival status of the vulnerable waterbirds at different habitats for their better conservation.Intestinal microbes participate in life activities of the host, and are affected by external environmental factors. Different habitat sizes and protection status provide different external environmental selection pressures for the same wintering waterbirds, which may be reflected in their intestinal microbes. Hooded Cranes are vulnerable migratory waterbirds with similar numbers wintering at three different lakes in the middle and lower Yangtze River floodplain, Poyang, Caizi, and Shengjin Lakes. Here, we analyzed the characteristics of intestinal bacterial and fungal communities of Hooded Cranes wintering at the three lakes to clarify the effect of habitat size and protection status on intestinal microbes, using high-throughput sequencing technology. Our results showed that community composition and diversity of intestinal microbes were significantly different among lakes with different habitat size and protection status. The Hooded Cranes at Shengjin Lake (small) had higher intestinal microbial alpha-diversity (for both bacteria and fungi) than those at Poyang Lake (large), which might be induced by social behavior of more waterbirds per unit area. The Hooded Cranes at Caizi Lake (relatively poorly protected habitat) had more diverse and abundant intestinal potential pathogens than Shengjin Lake (well-protected habitat). Our results indicated that the environmental pressure of a habitat might affect intestinal microorganisms and more attention might be needed for the vulnerable waterbirds at the habitat of poor protection status.

Influence of river-lake isolation on the water level variations of Caizi Lake, lower reach of the Yangtze River

In order to explore the water level variations of Caizi Lake under river-lake isolation, the monthly water level of the Chefuling station in Caizi Lake from 1989 to 2018 and the daily water level, rainfall and flow of local hydrological stations in 2018 were analyzed by using the Mann-Kendall trend test and wavelet analysis. Results showed that the difference of the average water level of Caizi Lake between the flood and dry seasons was 3.34 m, with a multi-year average water level of 10.42 m above sea level. The first and second main periods of the water level of Caizi Lake were 128 and 18 months, respectively, with 4 and 29 “up-down” cycles, respectively. From 2018, the next 3–4 years were likely to be the low water level period. The water level of Caizi Lake was significantly correlated with that of the Anqing hydrological station of the Yangtze River (r=0.824, P<0.01). In addition, the current hydrological staging of Caizi Lake was about 30 days behind than before the sluice was built. Under the dual influences of the river-lake isolation and the Yangtze-to-Huaihe Water Diversion Project (YHWD), the hydrological regime change of Caizi Lake and its eco-environmental effect needed long-term monitoring and research.

Effects of Human Activities on the Diversity of Waterbirds Wintering in a Shallow Lake of the Middle and Lower Yangtze River Floodplain, China

Human activity is the major factor driving the wetland degradation in shallow lakes. Human exploitation of lake wetlands alters the habitats of wintering waterbirds, and, in turn, waterbird diversity in the shallow lakes. In the present study, we surveyed species composition, abundance, and habitat characteristics of waterbirds in three types of wetland habitats (natural lakeside wetlands, paddy fields, and aquaculture ponds) at Caizi Lake, a shallow lake in the middle and lower Yangtze River during the wintering period, and investigated the effects of habitat change driven by human activity on the diversity of wintering waterbirds. There were significant differences in species composition and abundance among the three wetland habitats (natural lakeside wetlands, aquaculture ponds, and artificial paddy fields); however, there were no significant differences among the habitats with respect to the number of waterbirds. The numbers of overwintering waterbird species and waterbird individuals in aquaculture ponds and lakeside wetlands were significantly higher than the numbers in the paddy fields, indicating that wintering waterbirds prefer natural lake wetlands and aquaculture ponds. Principal component analysis of the three wetland habitat types revealed that factors influencing waterbird diversity include wetland area, vegetation cover, water level, and degree of human interference. Therefore, minimizing human interference and ensuring suitable habitats at specific periods could facilitate the maintenance of waterbird diversity.

Flexible Foraging Response of Wintering Hooded Cranes (Grus monacha) to Food Availability in the Lakes of the Yangtze River Floodplain, China.

Simple SummaryWith increasing human activity, bird habitats are being degraded and lost. In order to survive, birds have to adapt to the deteriorating environment. In this study, we surveyed the availability of food resources to Hooded Cranes in a degraded wetland. We found that cranes adopted flexible foraging strategies in response to the abundance and availability of different food resources in mosaic wetland landscapes at different periods during winter. The results also showed that the deeper the food was buried, the more time the cranes spent, and foraging frequency and foraging success rate were based on food abundance. It provided an evidence basis for the protection and management of waterbirds, especially Hooded Cranes.Wetlands are disappearing or degrading at an unprecedented rate due to the increase in human encroachment and disturbance, eventually leading to habitat loss for waterbirds, which is the primary cause of the decline in the Hooded Crane (Grus monacha) population. The Hooded Cranes have to constantly adjust their foraging strategies to survive to cope with this situation. In order to study how cranes respond to food resources in mosaic habitat, we surveyed a total of 420 food quadrats and 736 behavioral samples from three habitats during three wintering periods in Shengjin Lake and Caizi Lake. We measured temporal and between-habitat differences in foraging time budget, foraging frequency, and foraging success rate. Akaike’s information criterion was selected between the models of food abundance and availability. The results indicated that the wintering cranes spent the majority of their time (66.55%) foraging and shifted their foraging behaviors based upon food abundance and availability in different habitats. Our analyses also indicated that cranes were willing to forage more food with poor sediment penetrability in sub-optimal habitats. Foraging time budget was based on the food depth, and the foraging frequency and foraging success rate were based on food abundance. Cranes adopted flexible foraging strategies in response to the alternative food resources in mosaic wetland habitats, as it could mitigate the negative impacts of habitat loss and facilitate survival.

Variations in gut bacterial communities between lesser white‐fronted geese wintering at Caizi and Shengjin lakes in China

The avian gut microbiota plays an important role in shaping the health of its host. However, knowledge of gut bacteria in birds lags behind that of other animals. In this study, we investigated the gut bacterial communities of lesser white‐fronted geese (Anser erythropus) wintering at Shengjin Lake and Caizi Lake, China, using high‐throughput sequencing (Illumina MiSeq). Altogether, 1,053,624 high‐quality sequences and 4,405 operational taxonomic units (OTUs) were acquired from 30 fecal samples (15 per lake). The OTUs represented eight phyla and 17 classes from the Caizi Lake samples and seven phyla and 16 classes from the Shengjin Lake samples. Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes were the dominant phyla. The spatial distance and the Chao1, Simpson, and Shannon indices showed that the alpha diversity differed significantly between the samples from both lakes. The phylogenetic tree and heatmap analyses showed that all the Caizi Lake samples were clustered together and all the Shengjin Lake samples were clustered together. These findings suggest that diet may be an important driver of gut microbial community structure in the birds from each lake, and the obvious differentiation in their gut microbial structures may indicate that the bacteria are highly sensitive to food sources at both lakes.

Impacts of habitat filtering on taxonomic and functional composition of fish communities in Lake Caizi, lower reaches of the Yangtze River

于2018年6-8月在长江下游菜子湖流域沿岸带、敞水区、湖口和河道4种典型微生境分别设置样点进行鱼类调查，探讨生境过滤对鱼类物种和功能组成的影响.共采集鱼类5目31属43种，其中沿岸带湖泊定居性、山溪河流性及江湖洄游性鱼类物种数均较低，河道山溪河流性鱼类物种数较高.通过对各微生境间物种组成的差异分析，显示出4种微生境条件下的鱼类群落均有显著差异，且沿岸带、敞水区和河道的代表种分别为、鳙、草鱼、鲢，华鳈、光唇蛇鮈、蛇鮈.通过单因素多元方差分析解析不同生境过滤条件下鱼类物种和功能多样性的差异，发现在物种多样性层面，沿岸带的Richness指数和Shannon-Wiener指数显著低于其他微生境；在功能多样性层面，不仅发现沿岸带显著较低的RaoQ指数，同时发现河道的FDiv指数显著高于其他微生境类型.;To assess the impacts of habitat filtering on taxonomical and functional compositions of fish communities, we conducted a fish survey in four typical microhabitats(i.e., littoral zone, open water, lake inlets and river channel) of the Lake Caizi, lower reaches of the Yangtze River Basin, in June-August, 2018. Forty-three fish species belonging to 5 orders and 31 genera were caught in total. More riverine species lived in the river channel microhabitat, while less of lacustrine biota, river-lake migratory and riverine species lived in the littoral zone microhabitat. Further analysis revealed that there exist significant differences in fish community compositions among the four microhabitats. Meanwhile, the dominant species of river channels were Sarcocheilichthys sinensis, Saurogobio gymnocheilus and Saurogobio dabryi, while Aristichthys nobilis, Ctenopharyngodon idellus, Hypophthalmichthys molitrix were dominant in the open water of the lake. In addition, Hemiculter leucisculus were found dominated in the littoral zone. By using one-way PERMANOVA analysis, we found both richness index and Shannon-Wiener index in littoral zone were significantly lower. In contrast, indices of functional diversity were stronger predictors for the impacts of habitat filtering on floodplain fishes, which showed that the RaoQ index in littoral zone was significantly lower while the FDiv index in river channel was significantly higher than those in the other three microhabitats.

Predicting hydrological impacts of the Yangtze-to-Huaihe Water Diversion Project on habitat availability for wintering waterbirds at Caizi Lake

Quantifying the relationship between hydrological regime and habitat availability is the first step to predict potential impacts of water engineering projects on waterbirds, particularly in periodically flooded wetlands. The proposed Yangtze-to-Huaihe Water Diversion Project (YHWD) cuts through Caizi Lake, which is of international importance for wintering waterbirds. In order to explore the potential impacts of the project on habitat availability for the wintering waterbirds, we first built linear models to fit relationships between land cover patterns and water level dynamics in the lake, and then used generalized linear mixed models to test effects of habitat variables (water area, grassland area and mudflat area) on bird abundances of different functional groups. The avian habitat use differed among guilds, and was correlated with the land cover pattern, which was strongly dependent on seasonal water level fluctuations. Following water recession in autumn, the exposure of riparian habitats was more prominent in the eastern part of the lake, where the channel of the proposed YHWD project is located. This part of the lake is also where we located most of the important bird areas. Compared to the current situation, 54.3% of the grassland and 60.5% of the mudflats are predicted to be lost during winter due to the projected water level rise, resulting in reduced habitat availability for grass foragers, invertebrate eaters and tuber feeders. In order to mitigate potential impacts of the YHWD project, we suggest habitat compensations by construction of artificial habitats, and maintenance of water level regime at the whole lake by restoring similarity in water level fluctuations between Xizi Lake and Caizi Lake.

The impacts of water level fluctuations between wet and dry seasons on taxonomic and functional diversity of fish communities in the ecotone floodplain of Lake Caizi

水位的洪枯变化通过江湖连通影响泛滥平原湖泊鱼类的组成和分布，因而江湖过渡带是反映泛滥平原生态系统鱼类交流和多样性变动的关键区域.尽管如此，针对江湖过渡带鱼类群落随水位洪枯变化的研究十分匮乏.本研究以菜子湖江湖过渡带为例，分别在洪水和枯水期选取包括静水和流水生境的样点对鱼类群落进行系统的调查采样，探讨水位洪枯变化对菜子湖江湖过渡带鱼类物种和功能多样性的影响.共采集到鱼类6目12科37属52种，其中，洪水期和枯水期物种数差异显著，分别采集到鱼类50和42种，而静水生境和流水生境物种数差异不明显，分别采集到鱼类47和48种.与洪水期相比，枯水期山溪河流性鱼类的物种数、重量、尾数和优势度百分比分别减少了7.3%、6.3%、14.4%和12.0%；与静水生境相比，流水生境山溪河流性鱼类的物种数、重量、尾数和优势度百分比分别增加了5.3%、14.6%、18.0%和22.3%.SIMPER分析结果显示，麦穗鱼（Pseudorasbora parva）、蛇鮈（Saurogobio dabryi）、（Hemiculter leucisculus）、鲤（Cyprinus carpio）、鲫（Carassius auratus）、短颌鲚（Coilia brachygnathus）、似鳊（Pseudobrama simoni）、翘嘴鲌（Culter ilishaeformis）、达氏鲌（Culter dabryi）、光唇蛇鮈（Saurogobio gymnocheilus）和无须鱊（Acheilognathus gracilis）是引起水位洪枯变化以及不同生境类型鱼类群落结构差异的主要物种.优势度分析结果表明枯水期和静水生境的优势种鱼类相似，重要值较高的优势种鱼类为鲤、鲫、和似鳊；而洪水期和流水生境的优势种鱼类同样相似，重要值较高的优势种鱼类为麦穗鱼、蛇鮈、光唇蛇鮈和短颌鲚.通过双因素方差分析解析了水位洪枯变化和不同生境类型对鱼类物种和功能多样性的影响.发现洪枯水位变化仅对物种多样性指数中的物种数（Richness）产生显著差异，而对功能多样性的3个指数（功能丰富度指数（FRic）、功能离散指数（FDiv）和功能分散指数（FDis））均有显著影响.洪水期鱼类的Richness、FRic、FDiv和FDis指数均显著高于枯水期.同时，静水生境条件下的FRic指数要显著高于流水生境.本研究发现，与传统的物种多样性相比，基于功能性状的功能多样性对水位的洪枯变动更为敏感，河流周期性洪泛是泛滥平原生态系统中鱼类功能补充的重要方式.;Water level fluctuations between wet and dry seasons, assisting by lateral connectivity, play a fundamental role in underpinning the composition and distribution of fish fauna in floodplain lakes. The ecotone floodplains between the floodplain rivers and lakes are generally considered as the key areas where witness the exchange of fish species and the variations of biodiversity. However, the study of changes in taxonomic and functional diversity of fish communities in the ecotone floodplain in response to water level fluctuations is limited. Here we address this issue by measuring temporal (dry and wet seasons) and spatial (lotic and lentic habitat patches) changes in taxonomic and functional diversity of fish communities in the ecotone floodplain between the Yangtze River and Lake Caizi. A total of 52 species belonging to 37 genera, 12 families and 6 orders were collected in our study. Among them, there were significant differences in species number between wet and dry seasons, with 50 species and 42 species collected respectively. On the other hand, there was no significant difference in the number of species between lentic and lotic habitat patches, with 47 species and 48 species collected respectively. In comparison with wet season, the species richness, weight, abundance and importance value percentage of riverine species decreased by 7.3%, 6.3%, 14.4% and 12.0% in dry season. In comparison with lentic habitat patches, the species richness, weight, abundance and importance value percentage of riverine species increased by 5.3%, 14.6%, 18.0% and 22.3%. The fish fauna differences between seasons (dry and wet) and habitat patches (lentic and lotic) were determined by the abundance of Pseudorasbora parva, Saurogobio dabryi, Hemiculter leucisculus, Cyprinus carpio, Carassius auratus, Coilia brachygnathus, Pseudobrama simony, Culter ilishaeformis, Culter dabryi, Saurogobio gymnocheilus and Acheilognathus gracilis. Important value analysis showed that the dominant species of fish in lentic habitat patches and dry season were similar, and the dominant species of fish in lotic habitat patches and wet season were similar as well. The dominant species in wet season and lotic habitat patches were P. parva, S. dabryi, S. gymnocheilus and C. brachygnathus, while the dominant species in dry season and lentic habitat patches were C. carpio, C. auratus, H. leucisculus and P. simoni. Two-way ANOVA analysis indicated that one taxonomic diversity indices (Richness) and three functional diversity indices (FRic, FDiv and FDis) significantly differed between wet and dry seasons. Taxonomic richness, functional richness, functional divergence and functional dispersion were significantly higher in wet season than in dry season. Meanwhile, the functional richness was significantly higher in lentic than in lotic habitat patches. Functional diversity exhibited higher sensitivity than the traditional taxonomic diversity, since three functional diversity indices showed significant variations between wet and dry seasons. Meanwhile, our study highlight important functional recruitments of fish assemblages triggered by seasonal flood pulses.

Water level characteristics of Lake Caizi, lower reaches of the Yangtze River during wintering period based on long-term hydrological alteration

湖泊生态水位过程对维持湖泊生态系统结构、过程和功能的完整性具有重要意义，也是当今湖泊科学领域面临的重要科学问题.基于菜子湖湖区水位站（车富岭水位站）1956-2018年日水位资料，采用pettitt突变检验法分析水位的突变性特征.结合年保证率法得到菜子湖车富岭水位站低水位值，并在此基础上分析了低水位发生时间及历时、候鸟越冬期水位变化速率及其生态水位的区间阈值.主要结论有：菜子湖车富岭水位站1956-2018年年均水位无显著突变.菜子湖车富岭水位站低水位发生时间均值为年内的344 d，年际标准差为27 d，低水位的年均历时为69 d，标准差为49 d，有6年（1978、1997、2015-2018年）未发生低水位事件.菜子湖候鸟越冬期水位变化速率的均值为-0.009 m/d，年均值为-0.034~0.009 m/d，日均值为-0.051~0.016 m/d.菜子湖低水位发生时间的区间阈值为332~351 d，历时的区间阈值为33~98 d，变化速率的区间阈值为-0.070~0.020 m/d.加强菜子湖候鸟越冬期湿地生境保护适应性调度试验研究及生态环境监测，为菜子湖输水水位优化控制和菜子湖湿地生态保护提供科学依据.;The ecological water level process of lakes is of great significance for maintaining the integrity of the lake ecosystem structures, processes and functions, and is also an important scientific issue of lake science field nowadays. Based on the daily water level data, pettitt test was used to analyze the abrupt change characteristics of water level of Lake Caizi at Chefuling Station from 1956-2018. The low water level of Lake Caizi at Chefuling Station was obtained using the annual guaranteed frequency method. The starting time and duration of low water level, the water level change rate during the overwintering period of migratory birds and the interval threshold of ecological water level were analyzed accordingly. The main conclusions are as follows:there is no significant abrupt change point in the average annual water level of Lake Caizi at Chefuling Station from 1956 to 2018. The average occurrence time of low water level of Lake Caizi at Chefuling Stations is day 344, with the inter-annual standard deviation 27 days. The average duration time of annual low water level is 69 days with the standard deviation 49 days. Among the calculated 63 years, there are 6 years (1978, 1997, 2015-2018) without low water level event. The average rate of water level change during the overwintering period of migratory birds is -0.009 m/d, the annual average rate is -0.034-0.009 m/d, and the daily average rate is -0.051-0.016 m/d. The interval threshold of the occurrence of low water level of Lake Caizi is 332-351 d, the interval threshold of the duration time is 33-98 d, and the interval threshold of water level change rate is -0.070-0.020 m/d. Strengthening experimental study on habitat adaptation and ecological environment monitoring during the overwintering period of migratory birds to provide scientific basis for water level regulation and wetland protection of the Lake Caizi.