Abstract:Extinction of species is a natural process, yet human prosperity has eroded the habitats of millions of species, as a result, many species have disappeared (e.g., white-flag dolphin, Chinese paddlefish) or is going into extinction (e.g., Chinese sturgeon), but without coming of new species. Although the IUCN has established the quantitative standard of endangered species, it is more symbolic rather than practical, as it is impossible for all species to predict their future fates only through the same population dynamic model. On the endangered causes of species, there have many theoretical concepts based on the dynamics of population density (such as minimum viable population, effective population size, population bottleneck, founder effect, Allee effect, extinction vortex), which generally have poor operability, and thus is of little significance to the practical guidance of conservation biology. In this paper, a conceptual model of regime shift of species status is proposed. Species status depends on its composite survival fitness f_(s) and extinction risk (R) to external environments, which are affected by integrities of living space and ecological processes, food availability, and resistance to fatal artificial or nature disasters. f_(s) is determined by the product of the fitness of several determinant survival factors (s₁, s₂, s₃……):f_(s)=f_(s1) f_(s2) f_(s3)……, and f_(s) takes values of 0-1, with 1 being the maximum fitness (ideal status) but with 0 being complete absence of fitness. Therefore, zeroing of any determinant survival factor f_(s) would indicate species extinction (buckets effect). Index of species status [H_{(f, R)}] is determined by f_(s) and R. f_(s) can be used to assess and predict the extinction risk of species (e.g., it can be divided into 3-4 risk levels), the dynamics or processes before the critical point can be used as an early warning signal of speceis extinction, and the tipping point of species rescuing can be regarded as the lowest target of protective intervention. Of course, here is just a conceptual model, and each f_(s) still needs to be detemined and tested by data from real species.

Abstract:We collected the 35 literatures about water-demand for eco-environment of Lake Baiyangdian and systematically reviewed the methodologies and the corresponding calculation results. We identified the existing problem, and proposed research directions in the future according to the planning of the Xiong'an New Area. The statistical results shows that the lowest, suitable and highest water levels of Lake Baiyangdian are 7.45±0.66 m, 8.61±0.52 m and 9.46±0.51 m, respectively. Among the above three grades, water levels are highest in August and September, while lowest in May. In addition, extra water with the range of (1.35-6.20)×10⁸ m³ should be supplied to the Lake Baiyangdian annually to maintain the ecosystem status. However, the existing research on environmental water in Lake Baiyangdian is insufficient to support the construction of the New Area, such as significant differences in water-demand for eco-environment from various methods, the mechanism deficiency and rough time scales (year and month) in the ecological water demand calculation, without consideration the spatial heterogeneity in the lake and the connection of the lake and upstream rivers. Therefore, we proposed three research expectations, including the gridding and fine calculation, water quantity and quality simulation by restoring stages, as well as the recovering of the lake hydrodynamic process.

Abstract:Persistent organic pollutants (POPs) are widespread and persistent in the environment, and most of them are teratogenic, carcinogenic, and mutagenic. China is one of the countries with a high density of lakes in the world. Lakes play an important role in many aspects such as water supply, fisheries, and maintenance of ecosystem diversity. In addition, lakes are important sinks of POPs. The POPs in lake water can absorb and be utilized by aquatic organisms, which poses great risk to ecosystems and human health. Therefore, the distribution of POPs in lake water has an important impact on the surrounding ecosystem and human health. We collected 80 articles on the topic of POPs in Chinese lake water published from 2003 to February 2019. We collected and analyzed the published data of polycyclic aromatic hydrocarbons (PAHs), hexachlorocyclohexanes (HCHs), dichlorodiphenyltrichloroethane (DDX), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), polychlorinated diphenyl ethers (PCDEs), perfluorinated compounds (PFCs), and phthalate esters (PAEs). The POPs in Chinese lake water have been investigated in 49 lakes, involving 19 provinces, municipalities and autonomous regions in China, mainly located in the eastern region (n=32), and Yunnan-Guizhou Plateau (n=14). There were fewer studies in the Qinghai-Xinjiang Lake District (n=3), and other areas. Among them, PAHs, HCHs and DDX were the most studied POPs. Their average concentrations of ΣPAHs, ΣHCHs, and ΣDDX in Chinese lake water were 360.0±433.8 ng/L (n=26), 12.8±23.5 ng/L (n=30), and 12.8±24.6 ng/L (n=24). The concentrations of POPs in water of eastern lakes were higher than those in lakes in other areas. Although the relative proportions of ΣPAHs, ΣHCHs and ΣDDX to the concentration of total pollutants did not change significantly before and after the year of 2010, their concentrations decreased, suggesting that the compliance with the Stockholm Convention on persistent organic pollutants (POPs) and the mitigation of PAHs were effective in China. The depth of water (overlying water and interstitial water), sampling location (the inlet and outlet of lakes and within the lakes) were important factors for concentrations of POPs in Chinese lake water. The concentrations of POPs in Chinese lake water were correlated with human activities such as agricultural farming, domestic sewage, industrial sewage, and docks, and the type of POPs and geographical location of the studied area. Based on the research data collected from a large number of published literatures, this review revealed the distribution characteristics of POPs in Chinese lake water, and provided a scientific basis for the control and mitigation of POPs in Chinese lakes.

Abstract:In 2016, a heavy flood occurred and resulted the second highest water level of Lake Taihu in the history. The volume of water into Lake Taihu was 5.79×10⁹ m³ more than the average of previous years. Since then, the phosphorus index of Lake Taihu changed from a slow decline since 2010, to the so-called "phosphorus rebound". In order to study the relationship between phosphorus rebound and the great flood of 2016, this study analyzed the water volume, water quality, phosphorus flux, phosphorus storage in water and phosphorus migration in Lake Taihu. The change of phosphorus before and after the great flood was also carried out. The results showed that the large amount of phosphorus in the river channel during the flood period is the main cause of phosphorus rebound. Due to the impact of flooding, the net flux of phosphate into the lake in 2016 was 579.2 t more than the previous years' average, reaching 1683.0 t. Among them, the two floods contributed a great share, accounting for about 50% of the annual level (the floods from June to July and October brought 580.5 and 268.2 t of phosphorus, respectively). Another reason for the rebound of phosphorus is that there is a high phosphorus retention rate in Lake Taihu, and it is difficult for phosphorus to be discharged through the lake channel after entering the lake. From the fate of phosphorus after entering the lake, the water block with high-phosphorus concentration in the flood process, although there is a migration from the northwestern to the east and the south in Lake Taihu, the phosphorus concentration in the water body is significantly reduced (i.e., the retention phenomenon), resulting in high phosphorus concentration. The water block failed to reach the lake discharge area (Taipu Port, Wangyu River, etc.). Only a small part (205.3 t) of the net phosphorus flux in the whole year directly caused a rise of the phosphorus concentration in the water body, while the rest was retained in the sediment, which was significantly higher than the previous years. Phosphorus retained in Lake Taihu in 2016 is likely to destroy the phosphorus balance of the mud-overlying water at the end of the year, which has an indirect impact on subsequent changes in water quality.

Abstract:This study investigated the occurrence and distribution of perfluorinated compounds (PFCs) in surface water of Lake Qiandao. Surface water samples, collected from 13 sites in the lake were analyzed for 16 PFCs during wet and dry seasons in 2017. All samples were prepared by solid-phase extraction and analyzed using the ultra performance liquid chromatography interfaced to tandem mass spectrometry (UPLC-MS/MS). The results showed that 5 medium- and short-chain PFCs including C₄ perfluorinated sulfonate (PFSA) and C₄-C₆ and C₈ perfluorinated carboxylic acids (PFCAs) were detected in the surface water. The total concentrations of PFCs ranged from 1.70 to 6.21 ng/L, while perfluorooctanoic acid (PFOA) dominated, with ranges of 0.52-3.61 ng/L, and perfluorooctane sulfonate (PFOS) was not detected in all samples. Compared with other similar water bodies at home and abroad, the concentrations of PFOA and PFOS in Lake Qiandao were at low pollution levels. The ΣPFCs concentrations in surface water of most sites were higher in dry season than those in wet season, implying that it was from the point-source, and the spatial distribution varied more significantly among sampling sites in the dry season. The mass concentration of PFCs at the sampling sites located in upstream of the Xin'an River, the mainstream of the lake, such as Jiankou and Weiping were relatively high.

Abstract:Sedimentary carbon pool, as an important part of lake ecosystems, plays an important role in carbon cycle. However, there is little information on the impact of the cyanobacteria decomposition on the stability of sedimentary carbon pool. In this study, a simulated water-cyanobacteria-sediment system was established to investigate the effects of algal-derived organic carbon during the decline of cyanobacteria on easily oxidized organic carbon (EOC), recalcitrant organic carbon (ROC), microbial biomass carbon (MBC), light fraction organic carbon (LFOC) and heavy fraction organic carbon (HFOC) of sedimentary carbon pool. The results showed that, in the early stage of incubation (1-9 Days), ROC declined slowly, EOC and LFOC declined rapidly, in contrast, MBC increased. After incubation of 10-45 Days, the sediment TOC and ROC content increased. At the end of experiment (46-63 Days), organic carbon contents such as HFOC and ROC only slightly changed. With the outbreak of periodic cyanobacterial blooms, decomposition and accumulation of organic carbon in lake sediments will have a significant impact on the organic carbon composition and stability of the sediment carbon pool.

Abstract:Pollution of microplastics and heavy metals in aquatic eco-environment is attracting more and more attention. In the present study, in order to explore the bioaccumulation characteristics of microplastics and heavy metals in organisms, we selected eight dominant freshwater fish species in the Lake Poyang and Raohe River as the research materials. The concentrations of heavy metals (i.e. Cu, Cd, Pb, Zn and Cr) and microplastics in the fishes were measured and analyzed. The results indicated that the abundance of microplastics in water environment ranged from 10 to 64 items/L, with an average of 38.56 items/L. The abundance of microplastics in the digestive tract of the eight fish species ranged from 1.21 to 9.11 items/g, with an average of 5.40 items/g, while the abundance of microplastics in gills of fish varied between 0.61 and 5.00 items/g, with a mean of 2.87 items/g. There were four types of microplastics in fishes including debris, fibers, films and pellets. The polymer components were mainly polyethylene (PE), low-density polyethylene (LDPE), polypropylene (PP) and polystyrene (PS) that were mainly transparent and colorful. The particle size of microplastics ranged from 0.01 to 9.50 mm, and 79.07% of the microplastics had particle size>0.5 mm. The abundance characteristics (i.e. types, particle size, color and polymer composition) of microplastics in fishes were similar as those in water environment. The averaged bioaccumulation coefficient of microplastics in fishes was 178.29. The bioaccumulation ability of microplastics in fishes was ordered as follows:Channa argus, Pelteobagrus fulvidraco > Hemicculter leuciclus, Ctenopharyngodon idellus, Silurus asotus > Cyprinus carpio, Coilia ectenes, Carassius auratus. The contents of heavy metals including Cu, Cd, Pb, Zn and Cr in the muscle tissues of fishes were 4.27 mg/kg, 0.13 mg/kg, 0.28 mg/kg, 11.73 mg/kg and 0.53 mg/kg, respectively, which meet the requirements of pollution-free aquatic products and are lower than the health standards for human consumption. The enrichment ability of the fishes to the five heavy metals was ordered as follows:Zn > Cu > Cd > Pb > Cr. Different fish species showed different ability on the accumulation of a specific type of heavy metals, which is closely related to their feeding habits. The five heavy metals were detected on the surface of various microplastics by using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) methods, suggesting that microplastics may be the attachment carrier of heavy metal pollutants. Correlation analyses showed that the concentration of microplastics in fishes were significantly correlated with that of Cu, Cd and Pb, probably because that the presence of microplastics enhances the cumulative effects of Cu, Cd and Pb, and lead to the compound pollution effects.

Abstract:After supplying water to Tianjin City by the South-to-North Water Diversion Project (SNWD) in 2014, the water source has changed from a solely source of Luanhe to two sources. The new water diversion structure changed the amount of water into the Yuqiao Reservoir, which affected the total phosphorus (TP) retention of the reservoir. It is generally agreed that the TP loadings decrease with the decreasing of the inflow water of the reservoir. The longer hydraulic retention time (τ), the more favorable to TP retention, and thus the TP concentration of the reservoir decreases. However, we found that the TP loadings increased with the decreased inflow water when water supplied by SNWD, and the reservoir TP concentration also increased. What is the TP retention mechanism causing such a result? Based on the observed inflow water (W_IN) and the TP loadings (TPL_IN) from 2001 to 2018, the reservoir TP concentration and TP retention (R_P) were estimated by the Vollenweider model. Consequently, we estimated the ecological flows by controlling the amount of R_P at the level before the SNWD. The results showed that TPL_IN was non-monotonous respond to W_IN. There was a significantly positive relationship between τ and R_P during water diversion period. Interestingly, this positive correlation decreased with the increasing of τ. However, the R_P is negatively related to τ due to lower TPL_IN when considering both non-water diversion and water diversion period. Undergoing the new situation of two water sources in Tianjin City, it's feasible for maintaining oligotrophic or mesotrophic state of Yuqiao Reservoir. To control phosphorus retention, we suggest that the ecological flow into the reservoir is more than 500 million m³ every year, and the ecological outflow of the reservoir can be about 80% of the inflow.

Abstract:The bacterioplankton community is highly responsive to river changes and may affect the biogeochemical processes of river habitats. Consequently, understanding the temporal and spatial characteristics of bacterioplankton communities and revealing their ecological functions in river ecosystems have important scientific significance. In June and December 2016, the research team investigated the temporal and spatial characteristics of the bacterioplankton community structure in the downstream of Pearl River, and analyzed the sample components using 16S rRNA high-throughput sequencing technology. The dominant bacterial community included Proteobacteria, Actinobacteria, Bacteroidetes, Firmicutes, Verrucomicrobia and Cyanobacteria. The relative abundance of Proteobacteria was the highest, and its main components included Betaproteobacteria, Alphaproteobacteria and Gammaproteobacteria. The diversity index of Shannon-Wiener and Chao 1 in the wet season was higher than in the dry season, and the difference between Bacilli and Flavobacteriia was significant. The downstream of Pearl River can be divided into the Xijiang River, the middle of Pearl River Delta and the surrounding areas of Guangzhou. RDA analysis showed that water temperature(WT), dissolved oxygen(DO), phosphate(PO₄^3--P), silicate(SiO₄^2--Si), total phosphorus(TP) and transparency(SD)were the most significant environmental factors driving the change in bacterial community, and may have affected the increment metabolism of bacteria. Water temperature and transparency are important factors affecting seasonal differences. The differences between wet and dry seasons; DO; chemical oxygen demand(COD); and nutrients(PO₄^3--P, SiO₄^2--Si, TP)were important factors affecting spatial differences; these distinguished the mainstream of the Xijiang River, the middle of Pearl River Delta and the surrounding areas of Guangzhou. PICRUSt functional predictive analysis showed that Transporters, ABC transporters, DNA repair and recombination proteins were the main functions expressed by the bacterioplankton community in the downstream of Pearl River. The ABC transporters and Transporters were significantly higher in the wet season than in the dry season. The research results can provide a scientific reference for the ecological environment protection in the downstream of Pearl River.

Abstract:To study the effects of soil fauna on the rates of litter decomposition and soil nutrients return, litters of Carex cinerascens, Triarrhena lutarioriparia, and Phragmites australis were collected from Lake Poyang Wetland in November 2017. An in situ simulation experiments with three types of litters were carried out by the litter bag method. Decomposing bags with mesh sizes of 4.5 mm (large) and 0.1 mm (small) were used to assess the contribution of soil fauna in this study. The results showed that:the decomposition rate of litters was different among plants, with a significant higher decomposition rate of C. cinerascens than those of T. lutarioriparia and P. australis. There was a negative correlation between litter decomposition rate and litter carbon accumulation/nitrogen accumulation index (NAI_TOC/NAI_TN), and the remaining dry mass of litters; while a positive correlation with litter total phosphorus content; the total nitrogen content was different among litters, which has a degressive sequence as C. cinerascens, T. lutarioriparia, P. australis; the decomposition rate showed the same sequence among litters-the higher nitrogen litter, higher decomposition rate. The participation of soil fauna promoted the decomposition rate and the release of nutrient elements from litters and then regulated the return process of C, N, P elements to soil nutrient bank. This study will provide scientific data for the study on nutrient cycling of wetland ecosystem.

Abstract:The micro-environment formed by submerged plant photosynthesis is conducive to the formation of CaCO₃-P from co-precipitation of calcium and phosphorus in water, thereby permanently removing phosphorus from water and avoiding secondary pollution after plant decomposition. However, CaCO₃-P co-precipitation has obvious specific differences. Two submerged species, Potamogeton crispus L. and Ceratophyllum demersum L., were chosen to study the calcium addition (0,100 mg/L) on phosphorus removal and enrichment capacity of the plants under different phosphorus concentration (0, 0.2, 2 mg/L). The phosphorus fraction of plant ashes and the change of HCl-P were analyzed in order to help to select the submerged plants for ecological restoration projects. The results revealed that:(1) Both P. crispus L. and C. demersum L. could effectively reduce the concentration of total phosphorus (TP) and soluble reactive phosphorus (SRP). The calcium addition increased the decrease amplitude and P. crispus L. showed higher decrease amplitude than C. demersum L.; (2) For P. crispus L., the plant phosphorus content (dry weight) was the highest under the condition of high phosphorus and low calcium (2-0), while ash TP was under the condition of high phosphorus and high calcium (2-100). For C. demersum L., the plant phosphorus content (dry weight) was the highest under the condition of high phosphorus and high calcium (2-100), while ash TP was under the condition of medium phosphorus and low calcium (0.2-0);(3)When the phosphorus concentration was 2 mg/L, for P. crispus L. the calcium addition increased the content of HCl-P and H₂O-P, while decreased NaOH-P, resulting in the increase of the plant ash TP. For C. demersum L., the calcium addition increased the content of NaOH-P, while decreased HCl-P and H₂O-P contents, resulting in the decrease of the plant ash TP. This suggests that P. crispus L. enhanced phosphorus enrichment by increasing the content of adsorptive phosphorus and calcium phosphorus, while the C. demersum L. only significantly increased the content of organic phosphorus in the ash. Obviously, P. crispus L. has a competitive advantage than C. demersum L. because of stronger ability to form co-precipitation of CaCO₃-P under eutrophical water.

Abstract:The operation of the Three Gorges Dam has changed the flow and sediment conditions in the lower reaches of the reservoir, and it affected the ecological balance of the Lake Dongting and resulted in corresponding ecological problems. T-test was adopted for testing the consistency of the annual average water level based on the daily water level data of 1953-2018 at Chenglingji Station which is taken as the water level of the East Lake Dongting. The results show that the year of 2004 is an abrupt change point, indicating that the operation of Three Gorges Dam has resulted in the dramatic variation of water level at Chenglingji Station. Drawing on the IHA (Indicators of Hydrological Alteration) and RVA (Range of Variability Approach), an index system for calculating suitable ecological water level was presented in consideration of the range of monthly mean water level, the fluctuation range of annual water level, frequency and duration of high and low water level, and rate and frequency of water level condition changes. This index system can represent the requirements of the original ecological system intuitively and comprehensively. Using this index system, the suitable ecological water level of East Lake Dongting before the operation of the Three Gorges Dam was calculated for the following variables:1) the range of monthly mean water level (from January to December):17.07-18.34 m, 17.15-18.89 m, 17.65-22.23 m, 20.25-22.15 m, 22.85-24.90 m, 24.31-26.44 m, 26.88-29.16 m, 25.79-28.32 m, 25.12-27.56 m, 23.59-25.88 m, 20.65-22.81 m, 18.58-19.88 m, respectively; 2) annual acminimum water level:16.21-17.86 m, occurring from day 16 to day 51 (annual accumulative day); 3) annual maximum water level:28.54-31.48 m, occurring from day 187 to day 211 (annual accumulated day); 4) the high water level lasts 32.62-81.32 days at one time, the low water level lasts 52.13-107.65 days at one time, water level rises 21.9-26.45 times, the rate of water rising is 0.17-0.21 m/d, water level falls 23.17-27.6 times, the rate of water falling is 0.12-0.14 m/d. The results indicate that the monthly mean water level in January and February is 0.83 m and 0.27 m lower than the demand for suitable ecological water level, the monthly average water level in October is 0.83 m higher than the demand, the annual minimum water level is 0.39 m higher than the demand, occurring 6 days earlier than demand. The research results can provide a basis for the joint operation of Three Gorges and upstream cascade reservoirs.

Abstract:Lake Gaoyou, Nansi, and Dongping are key connecting points on the east line of the South-to-North Water Diversion Project and play vital roles in the safety of water transfer. In this study, three-dimensional fluorescence spectroscopy coupled with parallel factor analysis (EEMs-PARAFAC) was used to analyze the optical characteristics of CDOM and the relationships between fluorescence components and water quality parameters in the three lakes in different hydrological seasons, and to unravel the sources and optical composition characteristics of CDOM. Three fluorescent components were obtained using parallel factor analysis (PARAFAC), including a terrestrial humic-like C1, a tryptophan-like C2 and a tyrosine-like C3. Upstream inflowing discharge have notable effects on the source and optical composition of CDOM in Lake Gaoyou with fluorescence intensity (F_max) of C1 in the flood season is significantly higher than in the dry season (t-test, P<0.01), and C1 is positively correlated with a(254) (R²=0.85, P<0.01), indicating that terrestrial humic-like substances contributed primarily to the DOM pool in the lake. The contribution rate of C1 can reach 50%[F_maxC1/(F_maxC1 + F_maxC2 + F_maxC3)×100%]. Lake Gaoyou is greatly affected by the inflow water. Lake Dongping and Lake Nansi share similar source and optical composition of CDOM. The F_max mean of C2 and C3 in Lake Dongping and Lake Nansi were significantly lower in the flood season than in the dry season (t-test, P<0.01), indicating the two lakes have a higher autochthonous CDOM contribution during the dry season. Humic-like C1 in Lake Gaoyou can be used to trace the dynamics of dissolved organic carbon concentration, and the accumulation of humic-like substances may increase the concentration of total phosphorus, totoal nitrogen, and chlorophyll-a in the lake. However, the correlations between C1 and the main water quality parameters including humic-like C1 were poor in Lake Dongping and Lake Nansi, showing different CDOM optical characteristics from that of Lake Gaoyou.

Abstract:Reactive oxygen species (ROS) participate in photochemical reactions and redox reactions in natural water systems, and are important factors affecting the migration, transformation, environmental destination and ecological effects of organic pollutants in water. However, ROS production process in the degradation of grass-source soluble organic matter (DOM) is not clear at present. In this paper, an indoor simulation experiment was conducted to establish a method for the determination of the cumulative values of three ROS (³CDOM^*, ¹O₂ and·OH) in the laboratory, and then the production process of ROS in the DOM photodegradation process in the residual leaching solution of Carex tristachya was analyzed. Results showed that the cumulative content of ROS increased with the degradation of DOM. Among the three free radical contents, ³CDOM^* has the highest production content, and·OH production content was two orders of magnitude lower than the other two ROS. CDOM content was significantly positively correlated with the cumulative concentration of ³CDOM^*, ¹O₂ and·OH, especially with the highest significance level of ³CDOM^* and ¹O₂, followed by·OH, consistent with the ROS production mechanism of CDOM. The accumulation value of ROS concentration has a different linear correlation with the water quality index, which is negatively correlated with nitrate nitrogen, but positively correlated with nitrite nitrogen(NO₂^--N), and the effects of NO₂^--N on ROS concentration are extremely significant. Meanwhile, the attenuation of the peak fluorescence intensity of protein-like proteins is negatively correlated with the cumulative content of ROS, indicating that the degradation of small protein molecules is an important part of the ROS production in the process of DOM photodegradation. In conclusion, the research on ROS production process in the photodegradation process of grass-source DOM has increased the understanding of ROS production process, migration, transformation, home and mechanism of aquatic plants in the lake ecosystem.

Abstract:This study investigated the phytoplankton community structure and their relationship with habitats in Lake Nanhai of Baotou city, based on the data from November 2018 and January and March 2019 respectively. It found that the phytoplankton community comprised of Chlorophyta-Bacillariophyta-Cyanophyta in the freezing-thawing period. The niche traits of the dominant species in the freezing-thawing period were determined by using the improved Levins Niche Breadth Index and Petraitis Index. Results showed that there were seasonal changes in the niche breadth of the species under different habitats. Similarly, the niche overlap also changed with the seasons, with highest values during the icing period and lowest during the ice-melting period. Scenedesmus quadricauda was the most dominant species in the process of freezing and thawing. It's dominance degree, density, niche breadth and niche overlap are superior to other dominant phytoplankton species, and it can make full use of environmental resources, and be more competitive. Grey correlation analysis between dominant species and environmental factors showed that pH was the main factor affecting the density of dominant species of phytoplankton.

Abstract:In this work, six typical aquatic macrophytes, Potamogeton malaianus, Vallisneria natans, Phragmites australis, Acorus calamus, Nymphoides peltatum and Trapa incisa, were selected to investigate their root secretion characteristics of low molecular weight organic acids (LMWOAs) under the stresses of temperature, phosphorus (P) deficiency and high level of ammonia-nitrogen (NH₄⁺-N). Generally, the compositions and amounts of LMWOAs significantly varied among six species, with formic acid, lactic acid and oxalic acid as the dominate LMWOAs. Temperature didn't change the LMWOAs compositions but had significant effect on LMWOAs amounts. Higher temperature (30℃) was demonstrated to promote LMWOAs secretions for N. peltatum but evidently inhabit that of V. natans and A. calamus. The highest LMWOAs secretion of P. malaianus, P. australis and T. incisa was at 25℃. P deficiency and high level of NH₄⁺-N could significantly affect the compositions and amounts of LMWOAs. Under P-deficiency stress, the LMWOAs amounts secreted by V. spiralis, A. calamus and N. peltatum were increased by 68.68%, 55.30% and 257.82% respectively, and the acetic acid and malic acid were significantly secreted. In contrast, the LMWOAs amounts secreted by P. malaianus, P. australis and T. incisa were significantly reduced by 38.72%, 13.79% and 58.99% respectively, and the lactic acid, formic and succinic acid were completely inhibited. It indicated that V. natans, A. calamus and N. peltatum were more adaptive to low P sediment. Except for V. spiralis, high level of NH₄⁺-N significantly reduced the amounts of LMWOAs, especially lactic acid, malic acid and tartaric acid for all the investigated species. In conclusion, significant differences among LMWOAs secreted by macrophytes are closely associated with their tolerances to environmental stress, which will provide important scientific supports for aquatic ecosystem restoration.

Abstract:Submerged plants are an important component of aquatic ecosystems and play a significant role in the matter cycling and energy flowing of aquatic ecosystems. The coverage and biomass of submerged plants are key parameters for evaluating the stability of shallow water systems such as lakes. Owing to the echo detector has the feature of high efficiency and no damage monitoring, it has been used in submerged plant coverage monitoring. Its accuracy algorithm has also received more and more attention. Hangzhou West Lake, a shallow lake that submerged plants restored successfully, was chosen in this study. The BioSonics portable echo detector-MX was used to collect submerged plant echo samples. It combined with the artificial sample setting simultaneously, the submerged plant samples corresponding to the echo detection spot location are collected to verify the accuracy of the echo detection results. By establishing regression model, the relationship between the percentage of submerged plant volume (PVI) and the corresponding average fresh weight respectively obtained by echo detection and artificial sample was analyzed, the results show that the two parameters have good correlation. Interpolation analysis was carried out on the coverage data of submerged plants through the same season of different lakes and different seasons of the same lake in the unacquired area by using three interpolation methods called Ordinary Kriging, Inverse distance weighted interpolation and Radial Basis Function (RBF). The interpolation results are cross-validated to ensure the accuracy of the method. The accuracy of three methods are Inverse distance weighted interpolation > Radial Basis Function > Ordinary Kriging. The results will provide the technical support for monitoring submerged plant using the echo detection and interpolation analysis methods combined in large-scale shallow water bodies.

Abstract:This study takes the main lakes in Lake Ebinur Watershed as the research object, and samples along the Bortala River and Jing River in May (wet season) and August (dry season). The PARAFAC analysis method and the three-dimensional fluorescence region integration method is used to study the three-dimensional fluorescence characteristics of water and its seasonal variation with water quality. The results show that:1)In both dry and wet seasons, river DOM contains C1 (240, 425 nm) and C4 (265, 260 nm) kind of humus, C2 (225, 290 nm) uranium-like organic matter compounds. It found that fulvic acid is lower, while the aromatic protein, soluble microbial and humic acid were highest in dry season than wet season in Bortala River. The concentration of the aromatic protein and soluble microbial in dry season was higher than in wet season, and the fulvic acid and humic acid in dry season was lower than in the wet season in Jing River, based on fluorescence regional integral (FRI) analysis and the regional standards related to water quality and fluorescence. This indicates that the degree of decomposition in water is relatively high; 2)In this study, some conventional fluorescence indexes were selected to describe the fluorescence index characteristics of water in wet and dry season. It found that the three indexes (FI, BIX, HIX) of the water quality of Jing River and Bortala River in dry and wet seasons showed slight changes, comparing to larger changes in the Bortala River. In general, the change of water quality of Jing River and Bortala River in dry and wet seasons is mainly influenced by microbial activities and human activities; 3) In terms of the correlation coefficients of water quality parameters and fluorescence indexes in different seasons, the results showed that the relationship between BIX and COD concentration was best and a significant positive correlation in dry season(R=0.688, P<0.01). Secondly, there is a significant negative correlation between BIX and ammonium nitrogen concentration in wet season (R=-0.493, P<0.05). The study provides theoretical support and reference basis for the improvement of the governance of Lake Ebinur Watershed, which further proved that exogenous characteristics and the differences in different periods of DOM sources in the water.

Abstract:Understanding animal migration route and activity rhythm are of great significance to protection of migratory birds. From February to March 2019, 20 Bean geese (Anser fabalis) in Lake Poyang were tracked with satellite collars. We analyzed their migration routes and activity rhythm during their migration period based on the data collected from these GPS collars. The results showed that Bean goose started migration most early in 12, March, and some started in 25, April. The Bean geese were tracked for 60.5±15.6 days (n=19), with migration distance 1349.5±1004.9 km (n=18) and stop site number 6±3 (n=18). The spring migration routes of Bean goose formed two lines:the east line and the middle line. The east line passed through Anhui, Jiangsu, Shandong, Liaoning, Jilin, and Heilongjiang Provinces, and arrived at Russia. The middle line passed through Hubei, Anhui, Henan, Hebei, Inner Mongolia Provinces, and arrived at Mongolia. Bean goose didn't stay for a long time in stopover sites between 30°-40°N latitude, but stopped for a significant longer time (12.7±7.2 days) between 40°-50°N latitude. Northeast China Plain and the eastern Inner Mongolia plateau are important stopover sites for them. Bean goose is a diurnal animal; its activity level in day is significantly higher than that at night. In the pre-migration period, the activity peaks at 8:00-9:00 and 18:00-19:00, while the activity peaks occurred in 7:00-8:00 and 18:00-19:00 during migration. There was significant variation of average migration distance in different environment temperatures (n=8827,df=9,P=0.000), and its maximum migration distance (4.9±14.4 km/h) occurred in 0-5℃.

Abstract:Coilia nasus is one of the most important economic fishery species in the lower reach of the Yangtze River. It has two ecological types, one is anadromous and the other is freshwater resident. This study investigated the early resource of Coilia nasus in the lower reaches of the Yangtze River in Hukou, Anqing and Jingjiang during the peak breeding season from May to August 2016. The abundance, temporal and spatial distribution patterns of larval and juvenile C. nasus in the lower reaches of the Yangtze River and their variation and relationship with major environmental factors were analyzed. Results showed that the mean density of larvae and juveniles C. nasus in the Jingjiang section was highest during the investigation period. There was a short peak period between late June and early July in the surveyed river section, which may be related to the C. nasus spawning type. The occurrence of larval and juvenile C. nasus in Hukou section was earlier than in Anqing and Jingjiang section, which may result from resident C. nasus spawning in Hukou section. It is inferred that the special environment phenomenon of the back-flow of the Yangtze River stimulates the C. nasus gonad development, which resulted in more spawning populations in the Hukou section in August. The density difference of larval and juvenile C. nasus in the three sampling sites may be due to the difference between coastal topography and water dynamics. The water flow of larval and juvenile C. nasus at the highest density was lower in all river segments, and the water temperature was 25.87, 25.27 and 21.67℃, respectively. The hydrodynamic environment of the three sites meet the requirement for C. nasus spawning. Results in this study preliminarily reflect the spatial-temporal characteristics of larval and juvenile C. nasus in the lower reaches of the Yangtze River and provide information for C. nasus resource conservation.

Abstract:The Yangtze River basin is one of the most important habitat for the long supermaxilla (LS) and short supermaxilla (SS) phenotype estuarine tapertail anchovy Coilia nasus in China. Apart from the ecotype of anadromous migratory (AM) C. nasus (with LS), there are two different ecotypes of freshwater resident (FR) type C. brachygnathus (with SS) and landlocked (LL) type C. nasus taihuensis (with LS), which are traditionally believed to be discriminated in accordance with the length of supermaxilla. However, this subjective experience still needs to be confirmed by the field survey data. Therefore, in the present study the ecotypes assumed by supermaxilla approach of 566 different morphotypic C. nasus from different section in the Yangtze River and affiliated lakes in the middle and lower reaches of the Yangtze River Basin were discriminated by the otolith microchemical maps for AM and FR C. nasus obtained in our previous studies at first. Then, the length of supermaxilla, head and total body of the corresponding fish were comparatively studied. The results showed there were no significant differences between LS and SS types during their early development stage. However, the length of supermaxilla of the former would be longer than that of head when developed to the juvenile stage although that of the latter was still shorter than the length of head. Actually, the LS phenotype anchovies included two ecotypes of AM and FR individuals. The corresponding length ratios of their supermaxilla to head (S/H) were 1.170 ±0.075 and 1.165±0.064, respectively. Both of them had no significant difference from those of LL C. nasus taihuensis (1.178±0.087) also with long supermaxilla. Likewise, the SS phenotype anchovies could consist of both AM and FR ecotype individuals. However, the S/H ratios of AM and FR types were 0.922 and 0.918±0.062, respectively, which were significantly shorter than those of the aforementioned three LS phenotype anchovies. Thus, it might be better to classify C. nasus resources in the Yangtze River, Lake Taihu, Lake Poyang and Lake Dongting from traditional 3 ecotypes to 5 ecomorphotypes (i.e., AM and FR LS C. nasus, AM and FR SS C. nasus, and LL LS C. nasus taihuensis).

Abstract:It is an effective way to use the conceptual model of water and sediment to calculate the water-sediment process in loess region to analyze the current soil erosion and water-sediment reduction problems. There are errors in the rainfall data due to the temporal homogenization, missing measurements and mismeasurements, which influence the accuracy of the important input variable and dynamic factor of the model-rainfall, and then affect the accuracy of flow and sediment process simulation. Therefore, this study combines the rainfall dynamic system response curve method with the conceptual model of water and sediment to improve the accuracy of water and sediment process simulation. This method takes the water simulation part of the model as a response system to update the important input variable-mean area rainfall. Then the runoff, sediment yield and concentration is recalculated using the updated rainfall series to improve the accuracy of flow and sediment process simulation. After validating the feasibility of this method by the ideal case, an actual case is occurred in Caoping Basin in loess region. The results show that the method can both significantly improve the accuracy of the water and sediment simulation, and the average increases are 17.56% and 15.86% respectively.

Abstract:Based on the analysis of the evaluating indicators used in the study of probabilistic flood forecasting, a system of assessment criteria in probabilistic flood forecasting is established named as the "accuracy-reliability" joint assessment criteria system. In this system, the "accuracy" estimation refers to assess the precision of preferred prediction using the indicators like Nash-Sutcliffe efficiency, relative errors and so on. While the "reliability" assessment means to evaluate the reasonability of predicted interval using the indicators like containing ratio, deviation index and so on. Meanwhile, a new "reliability" assessment indicator named the containing ratio coefficient is proposed to assess the comprehensive reasonability of multiple predicted intervals. The accuracy-reliability joint assessment criteria system is tested in Wangjiaba subbasin in Huaihe River. The results suggested that this system gives a synthetic evaluation of the probabilistic flood forecasting.

Abstract:The rapid urbanization of Taihu Basin has changed the river morphology and affected their structure and connectivity. In order to reveal the change of stream structure, connectivity and the impact from urbanization, Zhangjiagang region, which has developed rapidly in recent years, was selected for research. Based on the related theories of landscape ecology and map theory, the water surface rate, river network density, river frequency and other indicators of the whole region and administrative regions were studied using the data of 2002 and 2015. Results show that:(1) The structural indexes of river network showed decreasing trends. The attenuation rates of water surface rate, river network density and river frequency were 15.7%, 12.6% and 33.3%, respectively. The river network was getting simpler, while the area and length development of main stream were synchronous. The change of river system in different districts varied spatially. The attenuation of water surface rate and river frequency in the south of Zhangjiagang were more severe than that in the north. The density and complexity of river network changed obviously in the northeast region. (2) The connectivity of river network in whole region was slightly improved with significant difference among regions. The connecting capacity of the river network in the northwest area along Yangtze River has been strengthened, while the unimpeded degree in the southeast area was weakened. The river systems cut off by polders, sluices and pumping stations need more rational scheduling schemes to enhance and maintain the connectivity of water. (3) The correlation between water surface rate, river network density, population and GDP were relatively high, and the spatial difference between the structural parameters of river system and its change rate in various regions was closely related to the population and economic development. (4) The number of river chains and nodes in river network were greatly affected by urbanization. The change of line point rate and actual connectivity were weakly correlated with urbanization indicators. This study can provide a foundation for the optimization of river network system structure, flood control, drainage construction, and help to develop management according to local conditions based on the characteristics of each area in Zhangjiagang.

Abstract:Sediment concentrations in the downstream would be unsaturated in a serious long-term after the operation of the Three Gorges Project, since sediment concentration recovery causes long distance erosion in middle reach of the Yangtze River. Based on the field data collected after the operation of the Three Gorges Project, the sediment transport patterns in middle reach of the Yangtze River was analyzed, and the influence of sediment recovery along the river bed with different particle size groups on river bed erosion was explored. Result showed that:the recovery of sand content of d ≤ 0.031 mm was mainly affected by the replenishment of riverbeds and the inflow of rivers and lakes in the early stage of water storage. With the decrease of the amount of sand with d ≤ 0.031 mm, the average annual sediment transport amount of that group at each station was much smaller than that before the water storage. Recovery was still mainly affected by riverbed recharge and inflow of rivers and lakes, which was one of the main causes of long-distance erosion in the downstream channel of the dam. In the early stage of water storage, the recovery of sand volume of 0.031 mm0.125 mm sand recovery was mainly affected by riverbed recharge, in the initial stage of water storage, the sand content of this particle size group was faster in the Yichang-Jianli section, and it reached the level before the water storage in Jianli Station. In the Yichang-Jianli section, the rate was still relatively fast as time passes, peaking at Jianli Station. The value was smaller than the level before the water storage. This was the main reason that the downstream river channel erosion was concentrated in the Yichang-Jianli River section.

Abstract:The unique geographical location of Lake Qinghai not only plays a role as a natural regulator for the climate around the lake, but also has abundant resources on the shoreline. Accurate and timely grasp of the shoreline dynamic changes of Lake Qinghai is of great significance to protect the ecological environment along the lake. Based on Landsat MSS/TM/OLI remote sensing images from 1973 to 2018 and water level data from 1961 to 2017, this paper studied the changes of shoreline and its impact on bird habitats. At the same time, the main factors affecting shoreline changes were discussed in combination with area, water level and meteorological data. The main conclusions are as follows:(1) In the past 45 years, the areas with the greatest changes in the shoreline of Lake Qinghai have been the Lake Shadao on the east coast, the Bird Island on the west coast, the Tiebuka Bay and the entrance to the Shaliu River on the north coast. Especially since 2004, the shoreline in the Bird Island had the largest retreat distance (5.52 km) and bird habitat expansion was about 97.94 km², which provided a better habitat for birds. (2) The length of the Lake Qinghai shoreline gradually extended at a rate of 0.88 km/a from 1973 to 2018. Before 1997, the length of the shoreline showed a relatively steady upward trend. Then, it showed a fluctuating downward trend from 1997 to 2004. After 2004, it showed a sharp increase in volatility, and the shoreline tortuosity also showed the same trend. (3) The overall shoreline length and tortuosity were not significantly affected by water level and area, but they responded differently to the dynamic changes of Lake Qinghai under different water levels. Especially when the water level was less than 3193.3 m or the area was less than 4249.3 km², the tortuosity of the shoreline showed the same trend with the change of water level and area. While the water level was higher than 3193.3 m, the tortuosity of the shoreline had been increasing, and the greater the rate of water level rise, the greater the annual variation of tortuosity. (4) The water level decline and land desertification of Lake Qinghai from 1973 to 2004 were the direct causes of lakeshore changes. Human activities and grassland degradation accelerated the change of lake shoreline. After 2004, as the water level of Lake Qinghai rebounded and the area expanded, the coastline gradually receded, especially during 2017-2018.

Abstract:Tracking regime shifts and procession of transforming ecosystem is an essential and efficient approach for lake management. In this study, a sediment core labeled XJ2018 (31°23'48.8″N, 119°43'33.8″E) was extracted and analyzed for reconstructing the past transitional processes of Lake Xijiu based on the biological (chironomid subfossils) and geological parameters (total nitrogen and total phosphorus). The changes of chironomid subfossil assemblage structure and the results of STARS based on PCA scores of chironomid assemblages both indicated Lake Xijiu had undergone a distinct stable-state transition in the past 40 years. The RSI index combined F-test revealed that an ecological shift took place in 1990s. Before 1990, there are high aquatic vegetable coverage and the chironomid was characterized by the macrophyte-related taxa (Cricotopus trifasciatus and Dicrotendipes spp.), thus the ecosystem in this stage can be regarded as plants dominated clear state. In 1990-2000, a remarkable ecology shift was detected due to the enclosed fish-farming and rapid agriculture developments, the macrophyte-related taxa have been gradually reduced while the euryphagic taxa (Tanypus chinensis and Microchironomus tabarui) has increased and gradually occupied a dominant position. The water status had been changed into the phytoplankton dominated turbid-water. During 2000-2010, the lake ecosystem deteriorated further and the macrophyte-related taxa were almost disappeared. After 2010, The reappearance of some macrophyte-related taxa and the decline of the euryphagic taxa indicate that with the implementation of the ecological restorations and managements, the environment of Lake Xijiu has improved slightly, but the phytoplankton dominated turbid-water was still sustained.

Abstract:《湖泊科学》编辑部：
在文献中经常可以见到氨氮、氨态氮、铵氮、铵态氮等术语.在中国知网CNKI检索《湖泊科学》已发表论文，发现这些术语的使用频率依次如下：氨氮（293篇）、铵态氮（189篇）、铵氮（30篇）和氨态氮（25篇），有些论文在使用相关术语上存在不规范甚至错误的现象.
水体中总氨（total ammonia）包括非离子氨（unionized ammonia，NH₃，也称游离氨，free ammonia）和阳离子形态的铵（ammonium，NH₄⁺，也称铵盐）等存在形态，NH₃对水生生物有毒性，而NH₄⁺被认为是没有毒性的或者显著低毒的.随pH值和水温的变化，两种形态会发生相互转化，pH值和水温越高，非离子氨形态比例越高，在夏季pH为8.5～9.0的水体，NH₃可占20%~50%.但是对于大多数的分析测定方法，不论是分光光度法、蒸馏-中和滴定法、气相分子吸收光谱法，还是离子色谱法，两者很难分离并分别测定.因此，在现行的《地表水环境质量标准》（GB 3838-2002）、《海水水质标准》（GB 3097-1997）和《地下水质量标准》（GBT 14848-2017）和《生活饮用水卫生标准》（GB 5749-2006）等国家标准中规定的水质指标——氨氮（NH₃-N），实际上包括上述两种形态（NH₃+NH₄⁺，以N计），严格来说是广义上的总氨氮（Total Ammonia Nitrogen，TAN），而在现行的《渔业水质标准》（GB 11607-1989）正是将测定的“总氨”（NH₃+NH₄⁺）浓度用于其监测项目“非离子氨”（NH₃）浓度的推导.
“铵氮”（NH₄⁺-N）过去曾经在1987年版的《水质铵的测定》系列国家标准分析方法中使用，后来在2009年修订后发布版中，将测定指标“铵”和“铵氮”统称为“氨氮”（NH₃-N），即为现行国家环保标准中的规范表述.因此，参照现行的国家环境保护标准《水质氨氮的测定》系列分析方法（2009年：水杨酸分光光度法、纳氏试剂分光光度法、蒸馏-中和滴定法；2013年：连续流动注射-水杨酸分光光度法），或者《水和废水监测分析方法》（第四版，2002年）测定的氨氮（即指总氨，包括NH₃和NH₄⁺两种形态），在论文中应该用氨氮（NH₃-N）规范表达，而不应该用氨态氮（NH₃-N）、铵氮或铵态氮（NH₄⁺-N或NH₄-N）等表达.
当然，在定性描述氮元素存在形态时，可以用非离子氨态氮（NH₃-N）、铵态氮（NH₄⁺-N）表达；随着新技术发展，如果这两种形态可以单独测定出来，则也可以采用类似说法分别描述两种形态氮的浓度.
综上所述，建议广大的科研人员、业务化技术人员在开展河流、湖泊、水库及海洋等地表水、沉积物间隙水、土壤孔隙水和地下水，以及污水等水质分析时，需参考国家环境保护标准《水质氨氮的测定》系列分析方法，规范使用氨氮（NH₃-N）等术语，相应的英文术语（ammonia nitrogen）也要规范使用并广泛宣传.