Dongting Research Articles

Flood hydrograph coincidence analysis of the upper Yangtze River and Dongting Lake, China

In hydrological research, flood events can be analyzed by flood hydrograph coincidence. The duration of the flood hydrograph is a key variable to calculate the flood hydrograph coincidence risk probability and determining whether flood hydrograph coincidence occurs, while the actual duration of the flood hydrograph is neglected in most of existing related research. This paper creatively proposes a novel method to analyze the flood hydrograph coincidence risk probability by establishing a five-dimensional joint distribution of flood volumes, durations and interval time for two hydrologic stations. More specifically, taking the annual maximum flood of the upper Yangtze River and input from Dongting Lake as an example, the Pearson Type III and the mixed von Mises distributions were used to establish the marginal distribution of flood volumes, flood duration and interval time. Subsequently, the five-dimensional joint distribution based on vine copula was established to analyze the flood hydrograph coincidence risk probability. The results were verified by comparison with a historical flood sequence, which show that during 1951–2002, the hydrograph coincidence probabilities corresponding to its flood event coincidence volumes of 2.00 × 1011 m3, 4.00 × 1011 m3, and 6.00 × 1011 m3 are 0.213, 0.123, and 0.049, respectively. It has provided theoretical support for flood control safety and risk management in the middle and lower Yangtze River. This study also demonstrates the significant beneficial role of regulation by the Three Gorges Water Conservancy Project in mitigating flood risk of the Yangtze River. The hydrograph coincidence probability corresponding to its flood event coincidence volume of 2.00 × 1011 m3 has decreased by 0.141.

Quantitative assessment of hydrological alteration over multiple periods caused by human activities at the Jingjiang Three Outlets, China

Abstract The Jingjang Three Outlets (JTO) play a major role in the water-sediment transport from the Yangtze River to Dongting Lake. The hydrological regimes at the JTO (Songzi, Taiping, and Ouchi) had been changed due to the Jingjiang Cutoffs (JC), the Gezhou Dam (GD), and the Three Gorges Dam (TGD). Based on hydrological data from 1955 to 2019, the variation trend in annual streamflow was detected using three techniques, and the hydrological alteration was assessed with the Range of Variability Approach. Conclusions are as follows: (1) the inflection points consistent with human activities and the time series were divided into periods of P1 (1955–1971), P2 (1972–1985), P3 (1986–2002), and P4 (2003–2019); (2) human activities made a greater contribution to streamflow change than climate change; (3) the hydrological alteration degree caused by the JC, GD, and TGD projects were 56%, 47%, and 52% at the Songzi outlet; 57%, 41%, and 57% at the Taiping outlet; and 57%, 41%, and 57% at the Ouchi outlet; and (4) the ability of division from the Yangtze River to Dongting Lake is weakening and the hydrological regimes at the JTO are deteriorating due to the JC, GD, and TGD, resulting in negative impacts on the biotic composition, structure, and function of riparian ecosystems. This study provides useful insight for ecosystem protection under hydrological alteration.

A sediment record of terrestrial organic matter inputs to Dongting Lake and its environmental significance from 1855 to 2019

The extensive anthropogenic activities and their potential impacts on lakes during the Anthropocene could be recorded in the sediments. In this study, the composition of biomarkers (i.e., n-alkanes and n-fatty acids), total organic carbon (TOC), and particle size in 210Pb-dated sediment cores from West Dongting Lake were investigated to trace the historical trend of anthropogenic inputs and their environmental significance. The TOC content was in the range of 3.15–27.32 mg g−1. The n-alkanes and n-fatty acids were distributed from C11–C33 and C12:0–C34:0, respectively. The short- and long-chain biomarkers accounted for a significant proportion of the total. Aquatic plants and algae living in West Dongting Lake were the main source (short-chain) followed by leaf waxes derived from terrestrial C3 plants (long-chain), as demonstrated by their concentrations. The variations of the key indicators i.e., the carbon preference index (CPI), aquatic plant n-alkane proxy (Paq), vascular plant n-alkane proxy (Pwax), and the ratio of unit short- to long-chain n-alkanes (L/H) also indicated that the aliphatic hydrocarbon fractions were mainly composed of short- and long-chain biomarkers. The sedimentary biomarkers had a significant temporal heterogeneity, which was controlled by different factors and sedimentary processes. Fine particles (<16 µm) were the dominant particle size (66.91%–78.52%) in the sediment. Both values of the dry/wet climate proxy (Kd) and average particle size were consistent over time. The dominance of terrestrial C3 plant-derived long-chain molecules gradually changed, with algae-derived short-chain molecules then becoming dominant. The hot and drought climate conditions and enhanced agricultural inputs from 1855 to 2019 in the watershed resulted in a decrease of terrestrial C3 plants and rapid growth of algae in the lake water.

Changes of soil microbial biomass carbon, nitrogen, and enzyme activities in East Dongting Lake wetlands at different water levels

We analyzed soil quality based on soil microbial characteristics of three different vegetation types in the wetlands of East Dongting Lake, including Carex tristachya wetland (CTW), Phragmites australis wetland (PAW), and Salix babylonica wetland (SBW). The soil microbial biomass carbon (MBC), nitrogen (MBN) and enzyme activities were measured and the key influen-cing factors were analyzed during the normal, flood, and dry periods. The results showed that: 1) The amounts of MBC, MBN, and the activities of invertase and cellulase (except cellulase of dry season) in 0-10 cm were higher than those in 10-20 cm for all wetlands, while the catalase activity showed an opposite pattern. 2) The amounts of MBC and MBN and the values of MBC/TOC and MBN/TN for the 0-20 cm soil layer of each vegetation type wetland were the lowest in flood period. 3) Soil invertase activity for each vegetation type wetland in the 0-20 cm soil layer peaked in the dry period, while soil cellulase activity peaked in the normal period. The seasonal fluctuation of soil catalase activities in all wetlands were small, with activities being slightly higher in flood period than the other two periods. 4) Among different vegetation types, soil invertase activity of PAW was significantly higher than that of other vegetation types, and cellulase activity of which was the lowest in both normal and flood periods. There was no difference in these two enzymes activities among wetlands during the dry period. The highest soil catalase activity was found in CTW during normal period and in SBW during dry period, respectively, while its lowest value was in PAW during flood period. 5) Soil MBC, MBN and invertase activity were correlated positively with soil TOC, TN and TP, and negatively correlated with soil pH. The activities of soil cellulase and catalase were significantly negatively correlated with TOC, TN, TP and positively correlated with pH. It suggested that the seasonal fluctuation of water level affected soil C, N, P contents and pH values, with consequences on soil MBC, MBN and enzyme activities.

Changes of phosphorus delivery from Yangtze River to Dongting Lake under new water and sediment conditions

Impounding the Three Gorges Reservoir (TGR) has altered the water-sediment transportation regime in the Yangtze River (YR) downstream, with inevitable effects on phosphorus (P) transport behavior in river-connected lakes. In this study, we investigate the characteristics of water, suspended sediment (SS), and P transportation, adsorption, and bioavailability at the three inlets along YR diverted to Dongting Lake through field surveys, adsorption experiments, and historical data analysis. The results showed that P transportation was significantly correlated with sediment (p < 0.01) and fine sediment particles dominated the transportation of particulate phosphorus (PP) and bioavailable phosphorus (Bio-P). Before the TGR impoundment, the dissolved inorganic phosphorus (DIP) concentration (0.03 mg/L) at the three inlets maintained a low level despite high P input, which was mainly due to the P adsorption and removal effect by sediment with high concentration and fine-grained texture. In addition, we reveal two changes at the three inlets caused by the impoundment: (1) SS content and discharge were reduced by an order of magnitude and the particle size was coarsened by three times; (2) the PP flux and bioavailability significantly decreased, whereas the transportation proportion of DIP increased. Consequently, the P buffering and adjusting capacity by sediment in the pristine river ecosystem from dam upstream supplies and downstream resuspension were notably weakened. Currently, the SS content at the three inlets (0.07 g/L) is far below the lower critical threshold (0.20 g/L) obtained through experiments that can effectively remove phosphate. Additionally, the decline of water and sediment supply from YR to Dongting Lake increased water transparency and prolonged water retention time in lake. With continuous TGR regulation and construction of upstream cascade reservoirs, the risk of algal blooms in river-connected lakes is significantly exacerbated.

Spatial–Temporal Variations of Total Nitrogen and Phosphorus in Poyang, Dongting and Taihu Lakes from Landsat-8 Data

Poyang Lake, Dongting Lake, and Taihu Lake are the largest freshwater lakes in the middle and lower reaches of the Yangtze River, China. In recent years, the eutrophication level of lakes has increased with the development of the social economy and caused many environmental and social problems. The concentrations of total nitrogen (TN) and total phosphorus (TP) are the key indicators of the degree of eutrophication, but the traditional ground monitoring methods are not capable of capturing such parameters in whole lakes with high spatial-temporal resolution. In this paper, empirical models are established and evaluated between the TN and TP and remote sensing spectral factors in the three lakes using Landsat 8 Operational Land Imager (OLI) satellite data and in-situ data. The results show that the inversion accuracy is higher than 75%. The TN and TP concentrations in the three lakes are inversed based on the Google Earth Engine (GEE) platform from 2014 to 2020 and their spatial-temporal variations are analyzed. The results show that the concentrations of TN and TP in Poyang Lake were decreased by 5.99% and 7.13% over 7 years, respectively, and the TN in Dongting Lake was decreased by 5.25% while the TP remained stable. The temporal changes in TN and TP concentrations displayed seasonal variations. A low concentration was observed in summer and high concentrations were in spring and winter. The average concentrations of TN and TP in Taihu Lake were higher than that of the other two lakes. The TP concentration was increased by 17.3% over 7 years, while the TN concentration remained almost stable. The variation in TN in Taihu Lake was the same as the growth cycle of algae, with higher value in spring and winter and lower value in summer, while the concentration of TP was lower in spring and winter and higher in summer. The spatial distribution of TN and TP concentrations in the three major lakes was significantly affected by human activities, and the concentrations of TN and TP were higher in areas near cities and agricultural activities.

Integrating land use/land cover change with change in functional zones’ boundary of the East Dongting Lake National Nature Reserve, China

The boundaries of the East Dongting Lake National Nature Reserve's (EDLNNR) functional zones have been adjusted over time due to conditional changes. However, there is no systematic study being conducted on the EDLNNR's historical trend of land use/land cover (LULC). Therefore, it is crucial to understand the relationship between changes in functional zones' boundary and spatio-temporal changes in the LULC from pre-establishment to the present time for adequate protection. The objective of this study is to understand the spatio-temporal dynamics of LULC changes from 1979 to 2019 in the three functional zones of EDLNNR during the dry season. LULC transition matrix and landscape metrics at the landscape level were also used to investigate the land type dynamics and landscape fragmentation, respectively. An increase in the marsh area was observed in all three functional zones of EDLNNR. The built-up area was increased due to the conversion of agricultural land. The landscape metrics-based analysis showed that the EDLNNR was less fragmented in 2019 than the previous record in 2016, due to the adjustment action of the three functional zones' boundary of the EDLNNR in 2018. The excluded area of the EDLNNR was from its experimental zone, which includes densely populated areas and surrounding agricultural land and woodland. The spatio-temporal LULC change information can offer effective management and conservation of different functional zones of the EDLNNR. This study can also act as a case model for effective management of other protected areas worldwide.

Spatio-temporal evaluation of the urban agglomeration expansion in the middle reaches of the Yangtze River and its impact on ecological lands

In developing countries, urban agglomerations have become one of the most important carriers of urbanization. In China, one of the largest national urban agglomerations is the UAMRYR (urban agglomeration in the middle reaches of the Yangtze River), which has the fastest urban development in Central China and is home to critical ecological spaces. On this basis, this study analyzed the urban expansion and loss of ecological lands in UAMRYR by establishing a spatial database, grid system, rose maps, and scenario simulation. The highlights of results are as follows: the urban expansion of UAMRYR includes four stages of development: steady growth, accelerated development, peak, and deceleration. Polarized development has occurred in the region, with the Wuhan, Changsha-Zhuzhou-Xiangtan, and Nanchang metropolitan areas having high levels of urban expansion while the other cities have varying levels of urban growth. The loss of ecological land was found to have a highly similar curve and spatial distribution with the urban growth. In terms of ecological land types, the loss of agricultural land accounted for more than half of ecological lands lost overall. Losses in forests, grasslands, wetlands, and water areas varied for different areas, depending on particular conditions and specific environmental characteristics of the city. The three metropolitan areas experienced the highest increases in urban built-up areas; they also had the highest loss of ecological land, which can have critical consequences given their proximity to the Yangtze River, Poyang Lake, Dongting Lake, and other important environmental sensitive areas. The simulation results show that the UAMRYR is projected to maintain a rapid expansion rate from 2020 to 2030. If the urban expansion, particularly in the metropolitan areas, is not managed well and controlled, serious ecological damage could be inflicted on the Yangtze River Basin.

Microplastics retention by reeds in freshwater environment

Microplastic pollution has recently gained increasing attention. The accumulation of microplastics in plants has been confirmed in the marine environment. However, the extent of the microplastic retention in freshwater plants is still unknown. In this study, sediment and plant samples from six reed farms in the wetland of East Dongting Lake were collected and analyzed. The abundance of microplastics in the sediment of reed farms varied from 125.7 to 1219.5 items/kg dry weight (dw), with an average of 511.2 ± 295.0 items/kg. Moreover, different levels of microplastic abundance were found in reeds from 0 to 14 items/individual. The abundance of microplastics in sediment samples was moderate compared to that worldwide and higher than that in other regions of Dongting Lake. The microplastic pollution level was significantly higher in the reed vegetation belt than that in other sampling positions. On the basis of the distribution and characteristics of the collected microplastics, lake water and fishery are suggested as important sources of microplastics. Furthermore, the factors influencing microplastic retention in the reeds are discussed. This study, as the first direct evidence demonstrating that freshwater reeds tend to accumulate microplastics, constitutes valuable reference for future research.

Spatial variability and potential controls of soil organic matter in the Eastern Dongting Lake Plain in southern China

Spatial variability and potential controls of soil organic matter in the Eastern Dongting Lake Plain in southern China

Occurrence and ecotoxicological risk assessment of perfluoroalkyl substances in water of lakes along the middle reach of Yangtze River, China

Polyfluoroalkyl substances (PFASs) are widely distributed in aquatic environment, and the potential ecological risk of PFASs has become a new challenge in recent years. But there were few integrated studies about the distribution, source appointment and risk assessment of PFASs in water of lakes along the middle reach of Yangtze River, China. Hence, this study investigated the pollution characteristics, source apportionment, ecological risks assessment of eleven PFASs from the surface water in this region. The total concentrations of PFASs (∑PFASs) ranged from 12.43 to 77.44 ng L−1 in this region. The ∑PFASs in Hong and Poyang Lakes were higher than those in Dongting Lake and middle reach of Yangtze River (p < 0.05). The compositions of PFASs in the middle reach of Yangtze River and along three lakes were similar, being with a larger proportion of short-chain PFACs. The food packaging and metal plating sources were identified as the main sources by two models. The total risk quotients (∑RQs) showed the ecological risk for algae in the middle reach of Yangtze River, Dongting and Poyang Lakes were negligible, but the low risk in some sites of Hong Lake. The EDIs of ∑PFASs were much lower than the tolerable daily intake recommended by the European Food Safety Authority. The results of this study were significant for developing effective strategies (e.g. short-chain substitution and restriction) of controlling PFASs pollution in the middle reach of Yangtze River and along lakes.

Phenological mismatch caused by water regime change may explain the population variation of the vulnerable lesser white-fronted goose in east Dongting Lake, China

Phenological mismatches between migratory birds and food availability driven by global warming have been found to influence the fitness and population dynamics of several herbivorous goose species in Arctic breeding sites. However, the effect of phenological mismatches at wintering sites have been inadequately studied. We used long-term data to explore the consequences of water regime changes on phenological mismatch (i.e., days between arrival of geese and timing of the optimal Normalized Difference Vegetation Index [NDVIopt]) and detect the relative role of the mismatch as a driver of annual variations in abundance and distribution of the Lesser White-fronted Goose Anser erythropus (a vulnerable species on the IUCN Red List) in East Dongting Lake, which is the one of this species’ largest wintering sites worldwide. The NDVI of the Carex meadow (i.e., the dominant vegetation in East Dongting Lake wetland and also the major food resource for the geese) was used as the phenology metric. Results showed that the water recession pattern greatly influenced food conditions when geese arrived at the site. Early water recession led to significantly higher NDVI, whereas late water recession led to significantly lower NDVI than did the optimal water recession. However, the suitable habitat area was significantly larger under the optimal water recession pattern. Both early and late water level recessions caused greater mismatches and resulted in lower geese abundance and a more concentrated distribution. NDVI was positively correlated with aboveground biomass and negatively correlated with N% of Carex spp. High biomass and low N% related to high NDVI caused by early water recession may indicate unfavorable food conditions at the time that geese arrive and reduced sustainable food availability in mid-winter, while a low NDVI and limited habitat area caused by late water recession may indicate an insufficient food supply. In conclusion, non-optimal water recession led to a greater phenological mismatch and resulted in limited habitat quality (e.g., lower leaf N%) under early water recession but limited habitat quantity (e.g., smaller habitat area and lower aboveground biomass) under late water recession, and ultimately threatened the Lesser White-fronted Goose. Our results contributed to explaining the decline of the Lesser White-fronted Goose population in this wintering site.

Investigation of inner‐basin variation: Impact of large reservoirs on water regimes of downstream water bodies

AbstractLarge dams and reservoirs alter not only the natural flow regimes of streams and rivers but also their flooding cycles and flood magnitudes. Although the effect of dams and reservoirs has been reported for some vulnerable locations, the understanding of the inner‐basin variation with respect to the effects remains limited. In this study, we analyse the Three Gorges Dam (TGD) built on the Changjiang mainstream (Yangtze River) to investigate the dam effect variations in the system of interconnected water bodies located downstream. We investigated the effect of flow alterations along the downstream river network using discharge time series at different gauging stations. The river–lake interactions (referring to the interactions between the Changjiang mainstream and its tributary lakes i.e. the Dongting and Poyang lakes) and their roles in modifying the TGD effect intensity were also investigated in the large‐scale river–lake system. The results show that the water storage of the tributary lakes decreased after the activation of the TGD. Severe droughts occurred in the lakes, weakening their ability to recharge the Changjiang mainstream. As a consequence, the effect of the TGD on the Changjiang flow increase during the dry season diminished quickly downstream of the dam, whereas its impact on the flow decrease during the wet season gradually exacerbated along the mainstream, especially at sites located downstream of the lake outlets. Therefore, when assessing dam‐induced hydrological changes, special attention should be paid to the changes in the storage of tributary lakes and the associated effects in the mainstream. This is of high importance for managing the water resource trade‐offs between different water bodies in dam‐affected riverine systems.

Genomic polymorphisms at the crhr2 locus improve feed conversion efficiency through alleviation of hypothalamus-pituitary-interrenal axis activity in gibel carp (Carassius gibelio).

Improvement in fish feed conversion efficiency (FCE) is beneficial for sustaining global food fish supplies. Here, we show that a set of polymorphisms at locus of the corticotropin releasing hormone receptor 2 (crhr2), which is involved in hypothalamus-pituitary-interrenal (HPI) axis signaling, is associated with improved FCE in farmed allogynogenetic gibel carp strain CAS III compared with that in the wild gibel carp strain Dongting (DT). This set of polymorphisms downregulates the expression levels of crhr2 mRNA in the brain and pituitary tissues in gibel carp strain CAS III compared with those in strain DT. Furthermore, compromised HPI axis signaling is observed in gibel carp strain CAS III, such as decreased α-melanocyte stimulating hormone protein levels, plasma cortisol content, and stress responses. Moreover, enhanced activation of protein kinase B/mammalian target of rapamycin complex 1 signaling observed in the muscle tissue of strain CAS III in comparison to that in strain DT indicated elevated anabolic metabolism in strain CAS III. Thus, these studies demonstrate that the genetic markers associated with compromised HPI axis signaling, such as crhr2, are potentially useful for genetic selection toward improvement in farmed fish growth and FCE, which would reduce fishmeal consumption and thereby indirectly facilitate sustainable fisheries.

Comparative analysis of the impact of weather conditions and human activities on air quality in the Dongting and Poyang Lake Region during the COVID-19 pandemic

During the COVID-19 lockdown, only the most basic and necessary production activities were retained in China. Such strict measures have caused many inconveniences to the people and the economy, but also provided the research community with a rare opportunity to compare the effects of weather conditions and human activities on air quality in the region. Here, a comparative analysis of the impact of weather conditions and human activities on air quality in the Dongting and Poyang Lake Region (DPLR) is proposed during the COVID-19 pandemic based on a circulation-to-environment approach. T-mode objective circulation classification method was applied to explore the effects of weather conditions on the concentration of two typical pollutants (PM2.5 and ozone) affecting the DPLR. PM2.5 and ozone concentrations under the nine identified circulation patterns are discussed. Under the control of circulation type CT1, CT3 and CT6, the PM2.5 concentrations in this area are high, while under the control of CT2 and CT9, the ozone concentrations are high. By comparing the variation in PM2.5 and ozone concentrations in three important cities in the region (Wuhan, Changsha, and Nanchang) during the three stages (Before Controlling, During Controlling and After Controlling) of COVID-19 from January to April 2020 and the corresponding months of a reference period (2015–2019), it is found that after controlling the human activities, the PM2.5 concentration dropped by 37.45%, while the ozone concentration increased by 111.83%. Ozone concentration was mainly affected by the synoptic circulation pattern, while the PM2.5 concentration was more affected by human activities.

Form Finding and Aesthetic Design for Pylons of Cable-supported Bridges

Pylons of cable-supported bridges are especially important components. They are generally large in scale and bear the main loads of the bridge, involving requirements both in structural performance and aesthetics. In this paper, a new form finding method for the pylon is proposed, with the use of bi-directional evolutionary structural optimization (BESO) method and the application of aesthetic rules. The principle of BESO method and the process for the form finding of the pylon are discussed. Pylons of the Hangrui Dongting Lake Bridge and the 3rd Panama Canal Bridge are used as cases to illustrate the proposed method. These two bridges are a suspension and a cable-stayed bridge with a main span of 1480 m and 530 m, respectively. The Golden-section and the Rectangle-division methods, together with the morphologic feature from local culture, are used to achieve harmony between the bridge and the environment. It is shown that the requirements mentioned above can be more easily achieved with the proposed method as well as some aesthetic rules.

Evaluation and spatial-temporal evolution of water resources carrying capacity in Dongting Lake Basin

Abstract A three-dimensional rating index system for water resources system–water environment system–socioeconomic system is constructed based on data from Hunan Dongting Lake Eco-environment Monitoring Center, Hunan Provincial Water Resources Bulletin, and Hunan Statistical Yearbook. The water resources carrying capacity (WRCC) of Dongting Lake Basin from 2009 to 2018 is evaluated by the TOPSIS model combined with analytic hierarchy process (AHP) and entropy weight, and then the temporal evolution and spatial distribution characteristics of the WRCC of the Dongting Lake Basin are analyzed. The results show that: (1) The WRCC in the Dongting Lake Basin decreases from a good level to a reasonable level during the period. Among them, the WRCC of the Ouchi River, Hudu River, and Songzi River Basins decreases significantly. (2) There are obvious spatial differences in the WRCC of the Dongting Lake Basin in 2018, the WRCC order is Lishui River, West Dongting Lake, Zijiang River, South Dongting Lake, Yuanshui River, Xiangjiang River, East Dongting Lake, Songzi River, Hudu River, Ouchi River, with scores of 0.586, 0.526, 0.472, 0.448, 0.416, 0.397, 0.393, 0.313, 0.306, and 0.304, respectively. Finally, some policy recommendations for improving the WRCC of the Dongting Lake Basin are proposed.

Wetland restoration in the East Dongting Lake effectively increased waterbird diversity by improving habitat quality

Wetland restoration is an effective way to recover degraded wetlands worldwide. The Dongting Lake wetland, an important wintering habitat for waterbirds, has suffered considerable degradation due to climate change and human disturbance during the last two decades; however, wetland restoration projects have now been implemented to improve waterbird diversity in the Dongting Lake. Based on annual waterbird and habitat survey data (2012/2013–2019/2020), we aimed to compare the differences in habitat variables (e.g., sedge [Carex spp.] meadow area, mudflat area, water area, and the normalized difference vegetation index of the sedge [Carex spp.] meadow) between the restored and unrestored wetlands to confirm whether wetland restorations could improve habitat quality. We also evaluated whether wetland restoration could effectively improve waterbird diversity by comparing the differences in waterbird populations at the community, foraging guild, feeding habitat guild, and species levels in the restored and unrestored wetlands. The results indicated that the restored wetland could provide more diverse and suitable habitats than the unrestored ones, particularly in terms of a sufficient variety of water habitats of different depths for waterbirds. The restored wetland was able to support substantial and diverse waterbird populations during the winter season. Specifically, compared to the unrestored wetlands, the restored wetland generally had higher species richness, individual density, and Shannon–Wiener diversity index at the community level; higher densities or proportions of different foraging guilds (tuber feeders, herbivores, fish eaters, insectivores, and omnivores, except herbivores geese), and of different feeding habitat guilds (G [0–10 cm], G (20–50 cm), G (20–70 cm), and G (>70 cm) guilds); and higher densities or proportions of the target species (except the lesser white-fronted goose and bean goose) at the species level. The larger waterbird populations in the restored wetland might be closely related to suitable crucial habitats, as indicated by positive correlation between their abundance and suitable habitat areas. Creating diverse suitable habitats for waterbirds, according to their habitat requirements, should be the first consideration in future wetland restorations. These findings provide a basis for wetland restoration and protection of wintering waterbird diversity in the Dongting Lake as well as in the middle and lower reaches of the Yangtze River floodplain.

Research on Inversion Mechanism of Chlorophyll—A Concentration in Water Bodies Using a Convolutional Neural Network Model

For Case-II water bodies with relatively complex water qualities, it is challenging to establish a chlorophyll-a concentration (Chl-a concentration) inversion model with strong applicability and high accuracy. Convolutional Neural Network (CNN) shows excellent performance in image target recognition and natural language processing. However, there little research exists on the inversion of Chl-a concentration in water using convolutional neural networks. Taking China’s Dongting Lake as an example, 90 water samples and their spectra were collected in this study. Using eight combinations as independent variables and Chl-a concentration as the dependent variable, a CNN model was constructed to invert Chl-a concentration. The results showed that: (1) The CNN model of the original spectrum has a worse inversion effect than the CNN model of the preprocessed spectrum. The determination coefficient (RP2) of the predicted sample is increased from 0.79 to 0.88, and the root mean square error (RMSEP) of the predicted sample is reduced from 0.61 to 0.49, indicating that preprocessing can significantly improve the inversion effect of the model.; (2) among the combined models, the CNN model with Baseline1_SC (strong correlation factor of 500–750 nm baseline) has the best effect, with RP2 reaching 0.90 and RMSEP only 0.45. The average inversion effect of the eight CNN models is better. The average RP2 reaches 0.86 and the RMSEP is only 0.52, indicating the feasibility of applying CNN to Chl-a concentration inversion modeling; (3) the performance of the CNN model (Baseline1_SC (RP2 = 0.90, RMSEP = 0.45)) was far better than the traditional model of the same combination, i.e., the linear regression model (RP2 = 0.61, RMSEP = 0.72) and partial least squares regression model (Baseline1_SC (RP2 = 0.58. RMSEP = 0.95)), indicating the superiority of the convolutional neural network inversion modeling of water body Chl-a concentration.

Re-description of the loach species Leptobotia citrauratea (Teleostei, Botiidae), with the description of L. brachycephala from southern Zhejiang Province, China.

Leptobotia citrauratea (Nichols, 1925), a loach species, originally described from Dongting Lake, was recently rehabilitated, based on the examination of the holotype and non-topotypical specimens. Several field surveys conducted from 2016 to 2019 in Zhejiang, Jiangxi and Hunan Provinces, P.R. China, yielded many specimens of Leptobotia which were initially identified as L. citrauratea. Molecular and morphological analyses of these specimens demonstrated that two distinct species are involved. One was identified as L. citrauratea, represented by specimens from both the Poyang and Dongting Lake (type locality) systems in Jiangxi and Hunan Provinces, and the other species is described as L. brachycephala, represented by specimens from the Ou-Jiang and Qu-Jiang, two coastal rivers of Zhejiang Province, China. Leptobotia brachycephala resembles L. citrauratea and L. micra in having a row of orange dots or an orange stripe along the dorsal mid-line of the body, extending from the nape to the caudal-fin base – a unique character in Leptobotia. Leptobotia brachycephala differs from L. citrauratea and L. micra Bohlen & Šlechtová, 2017, in caudal-fin shape and pelvic-fin insertion and proportional measurements including caudal-fin length, head length, predorsal length and anal-fin length. Its species status was further corroborated by position in a molecular phylogenetic analysis, based on the mitochondrial cyt b gene and its minimum uncorrected p-distance (2.9%) from congeneric species.