Middle Yangtze River Floodplain Research Articles

Functional diversity dynamics of waterbird communities driven by water levels at Shengjin Lake, a small river-connected shallow lake in the middle and lower Yangtze River floodplain.

Gate-controlled activities in lakes can directly or indirectly influence the assembly of waterbird communities. Shengjin Lake, a Ramsar site, is a typical river-connected and gate-controlled shallow lake in the lower and middle Yangtze River floodplain in China, comprising three sub-lakes (upper, middle, and lower) based on topographical features. We surveyed wintering waterbirds at Shengjin Lake from October 2022 to March 2023. We divided the winter water level period into nine phases based on the characteristics of water level changes. By measuring functional diversity, we aimed to provide insights into the differences in waterbird communities among the three sub-lakes under different water level conditions. Multiple linear regression was used to analyze the relationship between habitat factors and functional diversity. We further explored the relationship between specific functional traits and habitat factors through a combination of the R-mode linked to the Q-mode and the trait-environment correlation matrix (fourth-corner analyses) to explain the mechanism underlying waterbird community assembly. When the water level fluctuated in the range of 10.43-10.74 m (Huanghai elevation), the three sub-lakes had significant habitat differences and high habitat heterogeneity, increasing functional richness and functional dispersion of the upper and lower lakes, both of which significantly differed from those of the middle lake. Habitat heterogeneity and mudflat habitats have positive effects on functional diversity. The difference in functional diversity was primarily determined based on the foraging traits and strata of waterbirds. Habitat filtering of particular traits is a major driving force underlying the assembly of waterbird communities. Overall, we suggest that the minimum water level in the wintering period at Shengjin Lake should be regulated between 10.43 and 10.74 m. These findings provide reasonable suggestions for water level regulation and a theoretical basis for conserving waterbird diversity at Shengjin Lake.

Decoupling of nitrogen, phosphorus and biogenic silica in floodplain sediments in response to land use change and hydrological alterations

Human activities are altering global biogeochemical cycles of nitrogen (N), phosphorus (P) and biogenic silica (BSi). In order to reveal nutrient dynamics in response to human disturbances, this study explores burial rates and ratios of N, P and BSi in 210Pb-dated sediment cores from eight lakes in the middle Yangtze River floodplain. Mean burial rates of N, P and BSi increased substantially from the early 20th century, except for a hiatus in the 1970s. Before the 1960s, the stable ratios of N:P, N:BSi and P:BSi indicated the nutrient supply from clastic sources, while arable land expansion enhanced nutrient burial in lakes. Although damming increased the retention of N, P and BSi in upstream reservoirs after the 1960s, anthropogenic N and P release to the lakes outpaced the retention by dams, as suggested by continuous increases in N and P burial rates. The concurrent increase in BSi burial rate suggested that nutrient enrichment promoted diatom production at the earlier stage, while rising N:BSi and P:BSi ratios and declining BSi burial rate from the 1990s indicated the Si depletion with further eutrophication. Spatial heterogeneities among the lakes were linked to site-specific factors such as hydrological connectivity and macrophyte growth. Synchronous increases in N, P and BSi burial rates before the 1960s mainly responded to deforestation and arable land expansion; thereafter, the decoupling of N, P and BSi likely resulted from intensive farming (e.g., fertilizer usage) and damming. Given new dam construction and land use change in river basins, the BSi depletion relative to N and P is likely occurring in riverine floodplains worldwide.

The Foraging Window for Greater White-Fronted Geese (Anser albifrons) Is Consistent with the Growth Stage of Carex

Food resources are key limiting factors for migratory waterbirds, and the foraging strategies adopted by herbivorous waterbirds are affected by food availability in wetland habitats. The greater white-fronted goose (Anser albifrons) is mainly dependent on Carex in the lower and middle Yangtze River floodplain. Exploring the relationship between the growth conditions of Carex and the foraging strategies adopted by wintering greater white-fronted geese has important ecological implications for habitat protection and management. In this study, scan sampling and focal animal sampling were used to record the foraging behaviors of greater white-fronted geese wintering at Shengjin Lake, and the plant height and water content of Carex were surveyed simultaneously. The relationship between plant characteristics and foraging behaviors was tested using a linear regression equation. The results showed that Carex had two growth periods at Shengjin Lake, and the pecking rate and foraging time budget of greater white-fronted geese were higher during these two periods. Plant characteristics were positively correlated with goose foraging behaviors. The strategic adjustment of the foraging behaviors adopted by wintering greater white-fronted geese was consistent with the growth stage of Carex, which is the optimal foraging window for greater white-fronted geese. During the foraging windows, geese changed their foraging strategies to obtain more energy in order to guarantee successful wintering and migration.

Paleolimnological records for tracking dam-induced changes in the composition and supply of sediment to middle Yangtze floodplain lakes

A global boom in dam construction has reduced sediment loading of large rivers, as well as their connected floodplains. In order to explore potential effects of hydrological regulation on floodplain ecosystems, this study presents concentrations of inorganic elements, organic matter content and grain size spectra in 210Pb-dated sediment cores of five lakes in the middle Yangtze River floodplain. These lakes had free hydrological connectivity with the Yangtze River before the operation of local sluice gates, and hence K-rich but Al-poor particulates from the upper Yangtze reaches can be transported into lakes during periods of high river discharge. After hydrological regulation, sedimentary K/Al ratios registered substantial decreases in the study lakes, probably due to the declining supply of fine-grained and K-enriched riverine particulates from the Yangtze River. In East Dongting Lake, a hydrologically open lake proximal to the Three Gorges Dam (TGD), the sharp decrease in K/Al ratio after 2003 mainly responded to declining sediment supply from the Yangtze River after the TGD operation. In addition, prolonged water retention time probably promoted aquatic production and greater deposition of organic matter, as indicated by recent increases in organic matter content in the upper strata of the dammed lakes. Taken together, sedimentary K/Al ratios provide essential information on effects of past hydrological changes on sediment supply and aquatic productivity over multi-decadal timescales in these floodplain lakes with scarce monitoring data. The impacts of dam construction during recent decades on sediment composition in middle Yangtze floodplain lakes might be widespread in other similar floodplains worldwide. Thus sedimentary records can be utilized to inform and direct floodplain management.

Is Intestinal Bacterial Diversity Enhanced by Trans-Species Spread in the Mixed-Species Flock of Hooded Crane (Grus monacha) and Bean Goose (Anser fabalis) Wintering in the Lower and Middle Yangtze River Floodplain?

Simple SummaryIntestinal microbes play an indispensable role in host physiology and their alteration can produce serious effects on vertebrates. In this study, we analyzed the characteristics of intestinal bacterial community of hooded crane and bean goose whose niches overlap at Shengjin Lake, China, and investigated how host internal factors and inter-species interactions affected the diversity and spread of intestinal bacteria of the two species over three wintering periods. We have found that direct or indirect contact with each other increased the diversity of host intestinal bacteria and caused bacteria to spread among species in the mixed-species flock. In addition, a total of 63 pathogens were identified, of which 38 (60.3%) were found in the gut of both species. These findings could help our understanding of the factors that influence gut bacteria in wild waterbirds, which are also major contributors to the spread of pathogens worldwide.Diversity of gut microbes is influenced by many aspects, including the host internal factors and even direct or indirect contact with other birds, which is particularly important for mixed-species wintering waterbird flocks. In this study, Illumina high-throughput sequencing was used to analyze the intestinal bacteria of the hooded crane and bean goose whose niches overlap at Shengjin Lake. We tested whether contact time enhances the trans-species spread of gut bacteria. Results indicate alpha-diversity and microbial composition displayed significant separation between the two hosts in every wintering period, although the number of bacteria types shared increased with increasing contact time. For the same species, with the lengthening of contact time, alpha-diversity and the number of operational taxonomic units (OTUs) in the host intestine augmented, and the common OTUs and structural similarity of microflora in the middle and late periods were more than in the early and middle periods. In addition, we found a very high proportion of shared pathogens. Our results indicate that, although intestinal microflora of different species were separated, direct or indirect contact in the mixed-species flock caused the spread of gut bacteria trans-species, indicating that more attention should be paid to intestinal pathogens in wild birds.

Temporal-spatial patterns of intestinal parasites of the Hooded Crane (Grus monacha) wintering in lakes of the middle and lower Yangtze River floodplain

Parasites have adverse effects on the life and survival of many migratory waterbirds, especially birds on the endangered species list. Hooded Cranes are large migratory colonial waterbirds wintering in wetlands, which are prone to parasite infection, thus monitoring the diversity of parasites is important for sound wetland management and protection of this species. From November 2012 to April 2013, we collected 821 fresh faecal samples from the three lakes (Poyang, Caizi and Shengjin Lake) in the lower and middle Yangtze River floodplain, and detected with saturated brine floating and centrifugal sedimentation methods. Parasite eggs were quantified with a modified McMaster’s counting method. In this study, 11 species of parasites were discovered, i.e., two coccidium (Eimeria gruis, E. reichenowi), five nematodes (Capillaria sp., Strongyloides sp., Ascaridia sp., Trichostrongylus sp., Ancylostomatidae), three trematodes (Echinostoma sp., Echinochasmus sp., Fasciolopsis sp.) and one cestode (Hymenolepis sp.). About 57.7% of the faecal samples showed parasitic infection. All species of parasites were found at the three sites except Hymenolepis which was not found at Poyang Lake. While most samples were affected by only one or two species of parasites, infection by Eimeria spp. was the most common (53.1%). From One-Way ANOVA analysis of the three lakes, parasite species richness index (p = 0.656), diversity index (p = 0.598) and evenness index (p = 0.612) showed no significant difference. According to the statistical analysis of our data, there were no significant difference in parasite species richness index (p = 0.678) and evenness index (p = 0.238) between wintering periods, but a strong difference in diversity index (p < 0.05). Our study suggests that in the wintering Hooded Crane populations, parasite diversity is more sensitive to changes in the overwintering periods than to locations. This also indicates that with the limitations of migration distance, the parasites may not form the differentiation in Hooded Crane populations of the three lakes.