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Allochthonous organic matter plays an important role in nutrient cycling and energy mobilization in freshwater ecosystems. However, the subsidies of this carbon source in floodplain ecosystems have not yet well understood. We used a Bayesian mixing model and stable isotopes (δC and δN) of primary food resources and dominant molluscs species, to estimate the relative importance of allochthonous carbon sources for consumers in a representative sub-lake of Poyang Lake during a prolonged dry season. Our study inferred that terrestrial-derived carbon from Carex spp. could be the primary contributor to snails and mussels in Dahuchi Lake. The mean percentage of allochthonous food resources accounted for 35%-50% of the C incorporated by these consumers. Seston was another important energy sources for benthic consumers. However, during the winter and low water-level period, benthic algae and submerged vegetation contributed less carbon to benthic consumers. Our data highlighted the importance of terrestrial organic carbon to benthic consumers in the wetlands of Poyang Lake during the prolonged dry period. Further, our results provided a perspective that linkages between terrestrial and aquatic ecosystems might be facilitated by wintering geese via their droppings. [ABSTRACT FROM AUTHOR]

Concentrations and tissue distribution of organochlorine pesticides (OCPs) in different tissues of freshwater fish, silver carp ( Hypophthalmichthys molitrix) and bighead carp ( Aristichthys nobilis), collected from Poyang Lake, China's largest shallow lake, and were studied. OCPs were detected with the observed concentrations ranging from 280.67 to 1,006.58 ng/g wet weight (ww) for bighead carp and from 67.28 to 930.06 ng/g ww for silver carp. Composition analysis demonstrated OCPs in both fish were from the same polluted environment, and then, the species-specific bioaccumulation might be mainly due to the different fish age as well as the different feeding habits elucidating from the stable carbon (δC) and nitrogen (δN) isotope analysis. Tissue distribution indicated that dietary intake was the major exposure route of OCPs for both fish and higher accumulation potency of OCPs by the hepatobiliary-related tissues (such as liver, kidney, bile, and heart). The higher metabolic activities of these tissues elucidating from the higher values of δN might be the potential-determined factor responsible for the tissue-specific accumulation. [ABSTRACT FROM AUTHOR]

Poyang Lake is the largest freshwater lake in China and is of global importance for the conservation of migratory waterbirds of the East Asian - Australasian Flyway. Recent dam construction on the Yangtze River and its tributaries for agriculture and hydroelectric power has affected the hydrological regimes in downstream lakes. The Three Gorges Dam changed the hydrological regime of downstream lakes by reducing wet season flooding and expanding water storage in the dry season., Despite the critical role of Poyang Lake in regional and global biodiversity conservation and the potential adverse ecological impacts of the Three Gorges Dam on downstream lakes, there have been few studies of the hydrological requirements of wintering waterbirds in the middle Yangtze floodplains., We assembled a predictor matrix including three hydrological variables (annual inflow, maximum water level in high water season or Max WL and minimum water level in low water season or Min WL) and two climatic variables (annual rainfall and biological cumulative temperature or Bio T). Using the predictor matrix and annual waterbird census, we built group-specific generalised additive models ( GAM) to investigate how waterbird population variations were related to climatic and hydrological factors in the Poyang Lake National Natural Reserve. We then used the modelled predictor-response curves to identify the optimal lake water levels for each waterbird group., The community-level model selected group and the group-varying-coefficient term of Bio T, Inflow and Max WL as explanatory variables. At group level, tuber eaters and sedge foragers responded positively to Bio T and Min WL. Seed eaters, invertebrate eaters and fish eaters responded positively to Inflow and negatively to Max WL and Min WL. Based on the modelled predictor-response curves, we propose the following optimal water level ranges for Poyang Lake wintering waterbird conservation: a) maximum high water season level should be less than 17.4 m; and b) minimum low water level should be between 8.2 m and 8.8 m. [ABSTRACT FROM AUTHOR]

Seasonal variation in nitrogen isotope ratios (δ15N) of four baseline candidates belong-ing to the planktonic and benthic food webs of Lake Poyang, China, was investigated. These baseline candidates were particulate organic matter (POM), sediment organic matter (SOM), a filterer mussel (Corbicula flumine), and a grazer snail (Bellamya aer-uginosa). δ15N values of POM and SOM varied significantly among the sampling seasons, while no significant seasonal variation was observed among the δ15SN values of the mussels and snails sampled in different seasons. POM δ15N was correlated with lake water PO4-P, while SOM δ15N was correlated with NO3-N. Mussel <515N and lake water TN, NO3-N, and PO4-P were significantly correlated as were snail δ15N and TN, TP, and NO3-N. SOM and snails were better bioindicators of the water column nutri-ent concentration of Lake Poyang. The significant correlations between mussel δ15N and POM, as well as between snail δ15N and SOM, indicated the potential use of these baselines in trophic evaluations in planktonic and benthic food webs in this water-level fluctuating lake. [ABSTRACT FROM AUTHOR]

We compared the stable isotope ratios of δ13C and δ15N of four basal food sources and eight fish species collected in spring and summer from the largest freshwater lake in China, Lake Poyang. The aim was to study the temporal variations in the fishes' energy sources. The δ13C and δ15N ratios of all eight species of fish were higher in summer. Employing the IsoSource mixing model, we identified that the terrestrial plant Carex spp. was the most important primary producer supporting fish biomass in spring when the water level was low; meanwhile, the submerged macrophyte Potamogeton malaianus made consistent contributions to fish. However, in summer, when the water level was high, the submerged macrophyte Ceratophyllum demersum was the most important primary production source for fish. Our study indicated that feeding links in floodplain lakes are complex and modified by hydrologic seasonality. [ABSTRACT FROM AUTHOR]