Abstract:Contents of 2020,Journal of Lake Sciences

Abstract:Chemical oxygen demand (COD) is a comprehensive index to measure the amount of organic matter and reflect pollution degree of organic matter in water. Meanwhile, COD is also an important assessment index of environmental quality standard for surface water (GB 3838-2002). However, due to time consuming, the use of toxic and harmful reagents in the determination process and the easiness to produce secondary pollution, the current potassium permanganate and potassium dichromate COD determination methods are not environmentally friendly and cannot reflect the current rapid and real-time technical requirements. Therefore, there is an urgent need to develop a simple, rapid and efficient, sensitive and reliable, environmentally friendly and pollution-free green alternative detection method of COD. Firstly, from the perspective of bibliometrics by comparing total publication number of COD subject in China and the developed countries in the world, this study analyzes the urgency of developing alternative methods of COD in China. Based on the dataset of 706 samples covering a large range of COD concentration from 65 lakes and reservoirs in China, the high-precision linear relationship models between chromophoric dissolved organic matter (CDOM) absorption coefficient at 350 nm and 254 nm and COD concentration are constructed. In addition, the threshold and standard of CDOM absorption coefficient used to assess the surface water environmental quality was determined. Our linear models can be widely used to accurately and quantitatively characterize organic matter concentration and assess pollution degree in different types (deep and shallow water, large, medium and small area) and different trophic states (oligotrophic, mesotrophic, and eutrophic) of lake and reservoir waters with certain universality. By comparing the advantages and disadvantages of CDOM absorption coefficient and traditional COD measurement methods of potassium permanganate and potassium dichromate, this study demonstrates the feasibility and application prospect using CDOM absorption coefficient to substitute COD concentration for characterizing organic matter quantity and assess the pollution degree in lakes and reservoirs.

Abstract:Aerobic anoxygenic photosynthesis bacteria (AAPB) are heterotrophic prokaryotes widely distributed in typical water habitats such as oceans, lakes, and rivers. They can use organic matter in the environment as nutrients to obtain energy for cell growth and metabolism absorb organic matter from environment to maintain cell growth and metabolism but also rely on its own unique chlorophyll to complete the photosynthesis without oxygen production, playing an important role in water material circulation and energy flow. In recent years, more and more AAPB species have been reported one after another. Based on molecular phylogenetic analysis of photosynthetic genes such as the M subgene (pufM) of the photosynthetic reaction center, most AAPB belong to Alpha-, Beta-, and Gamma-proteobacteria. Moreover, the abundance and diversity of AAPB show heterogeneity in spatial and temporal geographic pattern varying with habitats. This article reviews and summarizes the research progress on AAPB's habitats and growth characteristics, abundance and distribution, ecological functions, and environmental drivers. At present, there are few reports on AAPB in reservoir ecosystems. The author proposes to conduct research on AAPB diversity distribution, environmental driving factors and ecological functions in reservoir habitats to enrich the understanding of the ecological structure and metabolic functions of functional microbial populations in aquatic ecosystems.

Abstract:Eutrophication induced by human activities may has a critical impact on the carbon cycle of Lake Taihu. Assisted by the technique of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), we investigated the molecular characteristics of dissolved organic matter in Meiliang Bay of Lake Taihu over the algal blooming-disappearance cycle at 2017-2018 to better understand the influence of algae blooming to the dissolved organic matter pool. The results show that during the algal-blooming period, the massively increasing productivity from algae have changed the amount and the molecular characteristics of dissolved organic matter in water from Lake Taihu. Basically, the concentration of dissolved organic carbon as well as the proportion of the relatively labile components (CHO-compounds, aliphatic compounds, and low-molecular-mass compounds with higher H/C and O/C values) increased during the algal-blooming period. While in the algal-disappearance period, due to both the low input of algal biomass and the continuous degradative progress of dissolved organic matter in the water column, the concentration of dissolved organic carbon decreased. Synchronously, the proportion of the relatively refractory components (CHOS-compounds, CHONS-compounds, CRAM compounds, high-molecular-mass compounds, and low-molecular-mass compounds with lower H/C and O/C values) increased. The dynamics of the molecular characteristics of dissolved organic matter in Meiliang Bay of Lake Taihu indeed propose the critical impact of eutrophication on the regional carbon cycle, asking for further research.

Abstract:To get a better understanding of the impact of the major water environment factors on the eutrophication status of Lake Ulansuhai located in a cold and arid region, VAR model was introduced to identify the impact based on the water environment factors (such as salinity, pH and water depth) monitored in January and July between 2013 and 2018 at the typical representative sites in the lake. The contribution of the water environment factors to the eutrophication status was analyzed by the variance decomposition analysis method. The ranges of the water environment factors were suggested that would construct an appropriate eutrophication status in the lake. The results showed that the variance contribution of the water environmental factors to the eutrophication status of the lake was significant at the initial stage and then tended to be stable. The contribution rate by means of the comprehensive variance of salinity, pH, and water depth was up to 66.62%. This suggested that if the indexes of salinity, pH, and water depth in Lake Ulansuhai were controlled among the range of 0.06-2.68 g/L, 7.50-8.63, and 1.76-3.50 m respectively, the 94.4% of the lake open water area would not presented as eutrophication. In this case, the average of the salinity, pH, and water depth would be 1.55 g/L, 8.15, and 2.33 m, respectively. This indicated that the lake eutrophication status could be controlled to some extend through artificially regulating the lake water environment factors.

Abstract:With the rapid development of urbanization, heavy metal pollution resulting from runoff increase and vary greatly in different land use. However, there is still a lack of research on the risk assessment of heavy metal carried by the runoff. In Suzhou urban area, four land use types including commercial area, residential area, historical and cultural protection area, and cultural and educational area were selected to monitor the content of Cu, Zn and Pb in rainfall runoff. Further, the ecological risk of these three heavy metals was evaluated by risk quotient (RQ), which was on the basis of predicted no-effect concentration (PNEC) obtained by species sensitivity distribution (SSD) curve. Based on the event mean concentration (EMC) of six effective rainfall events, compared with the Environmental Quality Standard for Surface Water (GB 3838-2002), statistical results show that Zn and Cu in the rainfall runoff meet grade Ⅱ water quality standard, while Pb is inferior to grade V water quality standard, which are mainly affected by the traffic activities and roofing materials in different land use types. Correspondingly, commercial area is polluted by all these three heavy metals worst, the other areas are polluted in different degrees by different heavy metals, resulting in a large difference in toxicity to aquatic organisms. Generally, the ecological risks by heavy metals in rainfall runoff are in high-risk degree, and in the order of Pb > Cu > Zn. Therefore, the current environmental quality standard for surface water in China does not fully consider the ecological impact and underestimates the ecological risks of heavy metals.

Abstract:In order to study the distribution characteristics, sources and ecological risks of polycyclic aromatic hydrocarbons (PAHs) in the sediments of lakes along the middle reaches of the Yangtze River, surface sediments were collected from 12 lakes in the region in July 2018. The contents of 16 PAHs were determined by gas chromatography-mass spectrometry (GC-MS). The results indicated that 16 kinds of priority PAHs were all detected in these lake sediments. The contents of total PAHs were between 572.7-1766.2 ng/g(dw)(with the mean value of 976.5±285.0 ng/g(dw)). The highest content of PAHs in the sediments of Wuhan Lake East was 1634.8±111.4 ng/g (dw). Compared with lake sediments in other domestic and oversea areas, the PAHs content in the middle reaches of the Yangtze River was higher than that of Lake Fuxian, Lake Qinghai and Lake Bosten in remote areas of China, but lower than that of Lake Chaohu and Lake Taihu in the lower reaches of the Yangtze River and the economically and industrially developed areas in the United States. According to the results of single PAH clustering analysis, 12 lakes can be divided into three types. Type 1 was mainly occupied by low ring of 64.04%±7.02%. Type 2 was mainly equivalent occupied by low ring and middle ring, which accounting for 50.76%±5.17% and 49.24%±5.17%, respectively. Type 3 was homogeneous occupied by different rings, which accounting for 35.35%±3.56%, 26.17%±0.45%, and 38.48%±3.84% from low ring to high ring. According to the distribution characteristics of PAHs in this area and the results of isomer ratio method and principal component analysis, the main source of PAHs in type 1 lake sediments is the mixed source of biomass combustion and petroleum, such as coal and wood. The main sources of PAHs in lake sediments of type 2 and type 3 are low-temperature combustion of biomass such as coal and wood, exhaust emissions from motor vehicles burning gasoline and diesel, and high-temperature combustion of fossil fuels such as industrial coking. The significant correlation between PAHs and total organic carbon (TOC) in the sediments indicates that, the content of TOC in the sediments is the key factor affecting the distribution of PAHs in the lake sediments in the middle reaches of the Yangtze River. The risk assessment results of the risk quotient method, that the RQ_NCs of PAHs in lake sediments in the middle reaches of the Yangtze River are all less than 800, and the RQ_MPCs are greater than 1, indicating that the PAHs in the lake sediments along the middle reaches of the Yangtze River presents a moderate risk level.

Abstract:With the implementation of source controlling and pollution intercepting in Taihu Basin, sediment has become a non-negligible pollution source in Lake Taihu. To simulate endogenous release dynamically, a diagenesis model based on EFDC model was established taking ammonia nitrogen and nitrate nitrogen as the water quality targets. The Latin hypercube sampling (LHS) was adopted to permute 200 combinations of 18 diagenesis model parameters, and the statistical method of probability distribution was applied to analyze uncertainty, similarly for standard rank stepwise regression method to identify sensitive parameters. The results showed that the nitrogen concentration was characterized by the spatial features that the uncertainty was greater in Meiliang Bay and the northwest lake area, and the temporal features that the uncertainty was largest in summer and then was in spring and winter. The uncertainty increased with the rise of the background concentration of water quality. The sensitive parameters for ammonia nitrogen were diffusion coefficient in porewater and reaction velocity for nitrification whose contribution rates to the uncertainty of ammonia nitrogen were 41.68% and 37.82% respectively. The sensitive parameters for nitrate nitrogen were diffusion coefficient in porewater and reaction velocity for denitrification in the aerobic layer, the contribution rates to the uncertainty of nitrate nitrogen were 29.15% and 42.34% respectively. The predominantly sensitive parameters were mainly related to nitrification, denitrification and diffusion process at sediment-water interface. With the growth of algae from dormancy to aggregation, the uncertainty of simulation results increased, and dominantly sensitive parameters turned from biochemical parameters to hydrodynamic parameters. The research discerned the key physicochemical processes and pivotal parameters in endogenous release in Lake Taihu, which can be references for further researches on the endogenous release of other nutrient such as carbon and silicon, and for the laboratory simulation qualitatively of endogenous release in large shallow lakes.

Abstract:The effects of eutrophication on the energy flow and material flow for lake ecosystems need to be studied. Most of previous studies showed the impacts of eutrophication on the structure and function of lake food web, while the influences of eutrophication on the nitrogen and carbon sources for consumer communities were limited. In view of this, the largest shallow eutrophic lake in North China Plain—Lake Baiyangdian was selected as the study area. According to the physical-chemical parameters in water and sediment, the Lake Baiyangdian was subdivided into three habitats(Habitat 1 strongly influenced by wastewater discharge(Sites Ⅰ and Ⅱ), Habitat 2 influenced by aquaculture and densely populated villages(Sites Ⅴ, Ⅶ and Ⅷ), and Habitat 3 influenced the least by human disturbances (Sites Ⅲ, Ⅳ and Ⅵ)). In April and August 2018, the samples for pelagic organisms, benthic organisms and fish were collected, respectively. Carbon and nitrogen stable isotope techniques were used to quantitatively calculate the contribution percentage of benthic and pelagic organism for the carbon and nitrogen sources of consumer communities. The results showed that: 1) according to the seasonal variation of water and sediment parameters, except pH, the values of chemical oxygen demand (COD), Ammonia nitrogen in sediments (NH₃-Ns), total nitrogen (TN), and total phosphorus in sediment (TPs) in April were higher than that in August, while the other parameters were existed higher values in August; in terms of spatial distribution, temperature (T), water depth (WD), dissolved oxygen (DO), total carbon in sediments (TCs) were showed the highest values in Habitat 3, while the other parameters were showed the highest values in Habitat 1; 2) According to the spatial distribution of δ¹³C and δ¹⁵N, for the same populations, the degree of enrichment were appeared significantly different at three habitats; while for the seasonal variation, the values of δ¹³C for the consumer communities showed significant difference, while the values of δ¹⁵N without significant difference; furthermore, the δ¹³C and δ¹⁵N of the consumer communities were existed the negatively correlated; 3) According to the spatial distribution of consumer trophic level (TL), the TL was appeared significantly different at three habitats; for the same consumer community, the highest values were appeared in Habitat 1, while the lowest values were appeared in Habitat 3; in terms of the temporal variation, the TL was not existed the significantly difference; 4) For the pelagic organisms, the contribution percentage for the carbon and nitrogen sources of consumer communities were appeared higher values in April, and the highest values were existed in Habitat 1; while for the benthic organisms, the contribution percentage for the carbon and nitrogen sources of consumer communities were appeared higher values in August, and the highest values were existed in Habitat 3; 5) Through correlation analysis, the results showed that the δ¹³C of consumer communities were appeared the negatively correlated with TP, TCs, TN in sediment (TNs), total organic carbon in sediment (TOCs), TPs; while the δ¹⁵N were existed the positive correlation with TP, TCs, TNs, TOCs, TPs. Therefore, the eutrophication can influence the carbon and nitrogen sources for consumer communities, and change the energy flow and material flow for the lake ecosystem.

Abstract:A large amount of organic algal-detritus after cyanobacterial bloom settled on the surface of the sediment, which has an effect on the mineralization characteristic of sedimentary organic matter, and then the biogeochemical cycle of carbon, nitrogen, and phosphorus. In this study, the central area of Yuqiao Reservoir was selected as the sediment sampling point. By the addition treatments of different densities of algal-detritus (×1 and×20 treatments) and blank controls, the effects of algal-detritus accumulation on the mineralization and their environmental effects were studied to provide some theoretical basis for drinking water environmental restoration and scientific management under the influence of cyanobacteria bloom. The results showed that the addition of algal-detritus lowered the pH value of overlying water and changed the activity of biological enzymes in the sediments. The higher the density of algal-detritus, the lower the pH value of the overlying water and the greater the fluctuation were. The×1 treatment had higher invertase activity, meanwhile the×20 treatment had higher protease activity and alkaline phosphatase activity. Secondly, the addition of algal-detritus had a significant effect on sedimentary mineralization pathways and release rates of mineralization products. The higher the density of algal-detritus, the greater the mineralization rate of sedimentary organic matter was. Moreover, the×1 treatment mainly enhanced aerobic mineralization with the increasing release of CO₂; the×20 treatment mainly enhanced anaerobic methanogens mineralization with the increasing release of CH₄. Thirdly, the diffusion and release fluxes of nitrogen and phosphorus were significantly different in algal-detritus addition treatments with different densities. Sediment adsorption was dominated in the×1 treatment, in which the average release rates of NH₄⁺ and PO₄^3- in overlying water differed slightly from the blank controls. In the×20 treatment, the flux of NH₄⁺ showed the tendency of sediment adsorption in the initial ten days and transferred to releasing potential in the remained time, while the releasing flux of PO₄^3- to overlying water was existed during the whole incubation period. The average release rates of NH₄⁺ and PO₄^3- in the×20 treatment (0.223 mg/(L·d) and 0.075 mg/(L·d), respectively) were significantly higher than those of the other treatments. In general, the accumulation of high density of algal-detritus promotes the mineralization of organic carbon, nitrogen, and phosphorus, releasing a large amount of CO₂, CH₄, and nutrients to the overlying water, which decreases water quality and contributes to the growth and reproduction of cyanobacteria.

Abstract:Carbonate mineral weathering coupled with aquatic photosynthesis on the continents is an important part of the global carbon cycle. The biological carbon pump is a key mechanism for stabilizing carbonate weathering-related carbon sinks. Little research has been done on the changes and control factors of biological carbon pump effects and their effects on hydrochemistry after the damming of river. In this study, two dammed karst rivers (Pingzhai Reservoir and Lake Hongfeng) were systematically sampled to study the changes and control factors of biological carbon pump effect and their effects on the variations of hydrochemistry. The results show that the hydrochemistry of the rivers have no obvious changes, while the hydrochemistry of the two reservoirs show significant seasonal variations. The temperature and pH of the two reservoirs are both higher in summer and lower in winter, while electrical conductivity (EC), HCO₃^- concentration and pCO₂ show lower in summer and higher in winter. The biological carbon pump effect which is indicated by the chlorophyll-a (Chl.a) concentration and dissolved oxygen saturation is stronger in summer and weaker in winter. Dissolved inorganic carbon is consumed by aquatic phototrophs to form organic matter and release oxygen, which are the main factors that cause the increase of pH and dissolved oxygen (DO) in summer, and the decrease of electric conductivity (EC), HCO₃^- concentration, and pCO₂ in winter. In the space, the Chl.a and DO concentrations of the reservoirs are larger than that in the rivers, and EC, HCO₃^- concentration and pCO₂ are lower than that in the rivers. This indicates the biological carbon pump effect of the reservoir is significantly increased due to river impoundment after the rivers were dammed. Correlation analysis of Chl.a with carbon, nitrogen, phosphorus concentrations and stoichiometry revealed that the biological carbon pump effect of the Pingzhai Reservoir and Lake Hongfeng is affected by carbon fertilization effect. The carbon fertilization effect of biological carbon pump detected here may indicate that aquatic photosynthesis in karst damped rivers may be controlled not only by N and/or P but also by C. This research may have implications for control of eutrophication in karst lakes with high alkaline.

Abstract:Fate of colloids in urban lakes is of great significance for understanding the migration and transformation of contaminants in the lake water environment. Microbial degradation and self-assembly are the main ways for the degradation of colloids in lake water. However, until now, few studies were focused on the degradation of size-dependent fluorescent properties of colloids under these two processes. In this study, water samples from the largest lake in Nanchang City (i.e. Lake Yaohu, namely L sample) and one of its tributaries (namely R sample) were collected. Combined cross-flow ultrafiltration and three-dimensional excitation-emission matrix fluorescence spectroscopy, this study investigated the degradation of fluorescent properties in different sizes of colloids in water (i.e. the original sample, <1 μm, <0.45 μm and <1 kDa sample) from L and R sample with and without microorganisms. Based on the parallel factor analysis, three humic-like fluorescence components (C1-C3) and one protein-like fluorescence component (C4) were identified. In the initial water sample, both L and R samples show higher fluorescence intensity for the humic-like fluorescence components, and most of which are concentrated in the small-size (1 kDa-0.45 μm) of colloids. The reduction of fluorescence substance in L and R samples was dominated by microbial degradation and self-assembly with self-assembly contributing nearly 50%. Compared to the soluble phase (<1 kDa), the effect of microbial degradation on the reduction of fluorescence components was higher in the medium- (<1 μm) and large- (the initial sample) size of water. Overall, protein-like substances, preferentially decomposed by microorganisms, are transferred from the large size of colloids to the small size of colloids; while humic-like substances, degraded dominantly by hydrolysis, are transferred with the opposite way from the small size of colloids to the large size of colloids.

Abstract:To investigate greenhouse gas flux on the water-air interface in autumn, the large enclosures were built up in the near-shore zone of the northwestern Lake Chaohu, China. The YL-1000 large-scale bionic cyanobacteria removal equipment was used to salvage cyanobacteria in situ. The characteristics of CH₄ and CO₂ fluxes and their influencing factors in the salvaging and control zone were observed by static chamber method equipped with a portable greenhouse gas analyzer. The results showed that the concentration of chlorophyll-a and suspended solids (SS) (29.6±2.5 μg/L and 12.5±1.2 mg/L, respectively) in the salvaging zone significantly decreased with the reduction rate of 72% and 85%, respectively, compared with those in the control. The removal of particulate matter like total nitrogen, total phosphorus, SS and COD_Mn after salvaging was effective. The microbially-derived humic-like (C1) and autochthonous protein-like (C3) components in the DOM significantly decreased during the salvaging process. The C1 and C3 fluorescence intensity (0.18±0.02 RU and 0.06±0.01 RU, respectively) in the salvaging zone were significantly lower than those of control (0.26±0.05 RU and 0.12±0.03 RU, respectively), which suggested that salvaging can effectively control the release of algal-derived dissolved organic matter. The average flux of CH₄ in the control (17.473±1.514 nmol/(m²·s)) was twice than that of the salvaging zone (7.004±4.163 nmol/(m²·s)). In the salvaging zone, CH₄ flux was significantly positively correlated with Chl.a, C1 and C3 components, which suggested that algal-derived organic matter could promote CH₄ flux. The CO₂ flux showed a significant upward trend in the salvaging zone and remained constant in the control. The CO₂ flux (-0.200±0.069 μmol/(m²·s)) in the salvaging zone was significantly higher than that in the control (-0.344±0.017 μmol/(m²·s)). The CO₂ flux was significantly negatively correlated with Chl.a and temperature in salvaging zone. The total greenhouse gas emission reduction for CH₄ and CO₂ is 0.275±0.076 mol/(m²·d) (carbon dioxide equivalent). The results reveal that the continuous cyanobacterial salvaging process in Lake Chaohu reduces the flux of greenhouse gas on the water-air interface, and can slow down the vicious cycles between cyanobacterial blooms and lake eutrophication and climate warming.

Abstract:In this paper, based on the remote sensing image data, the hydrological data from 1987 to 2016, and the high-resolution topographic data, we extracted the wetland vegetation information of the Lake Dongting and constructed the multi-cycle water level fluctuation measurement. On this basis, stepwise regression method and polynomial fitting were used to estimate the key hydrological variables and to quantify the effects of hydrological process on the two typical wetland vegetation. The main conclusions as follows: 1) From 1987 to 2016, the area of the whole vegetation had a significant increasing trend in the whole wetland, especially the Populus euramevicana community. And in East Lake Dongting, the Phragmites australis community occupied the space of Carex brevicuspis community, which promoted the whole beach to the center of the lake. 2) Water level fluctuation in flood season was the determinant towards the distribution of Carex brevicuspis and Phragmites australis. There was a non-linear response of water regime to the area of Carex brevicuspis. When the average water level was about 29 m during flood season, it will be most suitable for the growth of Carex brevicuspis. For the Phragmites australis community, low flow in flood season was more favorable for its growth and development. Water level fluctuation during rising and retreating season were the secondary important regime factor influencing the distribution of wetland vegetation in East Lake Dongting. Lower water level in the two season can facilitate the distribution of Phragmites australis.

Abstract:Submerged plants are important components in lake ecosystems, their production and distribution pattern are affected by environmental factors, especially the hydrologic regime. Lake Dongting is an important large lake in the Yangtze River Basin with free hydrologic connection to the main stream. In recent years, due to influences of human disturbances and climate change, environmental factors such as hydrologic regime and water quality of Lake Dongting have been changed dramatically, resulting in the decline of submerged plants, which calls urgent science-based rehabilitation. Thus, there is a need to have further study on submerged plants at Lake Dongting. In this study, West Lake Dongting was selected as the research area. Submerged plant communities and 12 environmental indicators were investigated in 98 sampling plots at 11 sites in West Lake Dongting during summer in 2018 and 2019. Independent t-test and redundancy analysis were used to evaluate the relationship between the submerged plants and environmental factors, and to explore the effects of hydrologic regime change on submerged plants between years. Results showed that: 1) Submerged plants in West Lake Dongting were mainly distributed at semi-isolated sub-lakes or free flooding lake bays where with shallower water depth, better water quality and more stable water body, whilst there is less distribution at sites in major flowing channels and with high water fluctuation. Water depth, transparency, total phosphorus in bottom sediment and water pH showed significant differences between sites with and without appearance of submerged plants in West Lake Dongting; 2) Biomass of submerged plants was significantly correlated with pH, water depth and total phosphorus in water; 3) At free flooding lake bay, biomass of submerged plants was higher in 2018 than it in 2019. It is supposed to be the result of water level raising processes during May to August 2019 when was key growing stage of submerged plants. A continuously high-water level adversely impacted plant growth. Maintaining natural hydrologic regime, habitat heterogeneity with free flow in the lake, and healthy water quality were proposed to be the key factors to rehabilitate submerged plants in the West Lake Dongting. Sites at free flooding lake bay or semi-isolated sub-lakes those with water depth less than 3 meters, appropriate water nutrients, low water flow rate and less waves were recommended to be rehabilitated in priority.

Abstract:Water availability is a key factor that sustains plant growth and determines vegetation distribution pattern. Plant water uptake pattern is regarded as a foundation to reveal the interaction mechanism between hydrological changes and vegetation succession. As the largest freshwater lake in China, the hydrological regime of Lake Poyang has been encountering a dramatic change in terms of water level variations, which generated a large influence on the water recharge of the wetland ecosystem. In this study, the replenishment sources of soil water in the Artemisia capillaris community, a typical mesophyte vegetation in the Lake Poyang wetland, were explored by using the stable isotopes (δ¹⁸O and δD). The stable isotopes composition of rainfall, lake water, groundwater, soil water and the plant water were analyzed. The main water uptake depth and the proportions of water uptake by A. capillaris were further investigated, using a direct inference method and the IsoSource mixing model. The results showed that the lake water and soil water isotopes were enriched, while the groundwater isotopes were rarely fractionated, relative to local precipitation isotopes. The wetland groundwater is likely to be recharged by the long-term rainfall and the lake water. During the rainy season (April-June), soil water in the A. capillaris community was mainly recharged by the local rainfall. During the summer months (July-August), the deep soil water was most likely to be supplied by lateral lake water and the groundwater. Accordingly, the soil water moved upward from deep to shallow soil layers under strong evaporation. In the growing season, A. capillaris mainly absorbed soil water at 0-80 cm depths and showed plasticity in switching water sources from different soil layers. When the soil water content was high (April-May), A. capillaris mainly used water from shallow soil layers (0-40 cm), accounting for 49%-68% of the total water uptake. When the shallow soil becomes dry (June-August), A. capillaris mainly absorbed deep soil water from deep soil layers (40-80 cm). The proportions of soil water uptake at 40-80 cm were up to 74%-95%. However, the main water source of A. capillaris again switched to the soil water at top soil layer (0-15 cm) during the mature stage (September-October), and the proportions of water uptake were in the range of 41%-70%. Overall, these findings reveal that lake water is an important replenishment source of the soil water in mesophyte vegetation community in the Lake Poyang wetland. A. capillaris could adjust water uptake depth according to the soil water availability, suggesting a strong drought tolerance. This study is helpful to provide scientific reference for the ecosystem evolution and wetland protection in the Lake Poyang-floodplains.

Abstract:Cylindrospermopsis raciborskii and Staurastrum spp. are the common dominant species in (sub) tropical reservoirs. To understand the effect of iron on seasonal dynamics and growth C. raciborskii and Staurastrum spp., we investigated and analyzed the driving effect of iron on the biomass and the relative biomass of them, in a typical tropical reservoir. And we performed batch culture experiments with C. raciborskii N8 and Staurastrum sp. FACHB-1449 under three iron concentrations (0.029 mg/L, 0.29 mg/L, 0.689 mg/L) with two kinds of phosphorus source respectively, and we compared the difference of the specific growth rate, alkaline phosphatase activity and siderophore between the two species. The results showed that, C. raciborskii and Staurastrum spp. are the dominant genera in phytoplankton community, the highest proportion of the both was 82% in phytoplankton biomass; the different of the response to environmental conditions mainly reflected in the changes of biomass with iron concentration between the two genera, such as the significant linear regression was detected between C. raciborskii biomass and dissolved iron concentration, but not in Staurastrum spp. biomass. In culture experiments, the maximal specific growth rate of C. raciborskii N8 was 0.098 d^-1±0.01 d^-1 at iron concentration of 0.689 mg/L with inorganic phosphorus and it significantly decreased with the decrease of iron concentration in both phosphorus source condition, concurrently, siderophore was detected in all of the treatments with C. raciborskii N8; comparatively, the specific growth rate of Staurastrum sp. FACHB-1449 was no significant difference among the six treatments, which was 0.079 d^-1±0.001 d^-1 in all of the treatments, and no siderophore was detected in all of the treatments, which mean the phosphorus source and iron concentration did not significantly effect on the specific growth rate. In addition, the alkaline phosphatase activities was significantly higher in the treatments with C. raciborskii N8 than in the treatments with Staurastrum sp. FACHB-1449 under organic phosphorus source, and the alkaline phosphatase activities in the treatments with C. raciborskii N8 significantly decreased with the decrease of iron concentration, but not in the treatments with Staurastrum sp. FACHB-1449. It was concluded that the supply of dissolved iron was critical to the seasonal dynamics of biomass and dominance of C. raciborskii, the growth of C. raciborskii is more vulnerable than Staurastrum spp. to iron concentration decrease, and the limiting effect of iron on C. raciborskii will be enhanced under inorganic phosphorus deficiency condition.

Abstract:Lake Wushan is a highly eutrophic, shallow lake connected to the Yangtze River, and a national wetland park. In order to study phytoplankton structural characteristics in the lake stocked densely with silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis), we conducted a field survey on the phytoplankton community and lake trophic status from September 2017 to August 2018. Trophic status indices (TLI) showed the water quality was between mesotrophic and heavy eutrophic state. A total of 100 phytoplankton species (genera) belonging seven phyla were identified; twenty-three dominant species including nine species of Cyanophyta, eight species of Chlorophyta and both three species of Bacillariophyta and of Cryptophyta were observed. The dominant groups were Cyanophyta in summer and autumn, Chlorophyta and Cryptophyta in winter and spring. The phytoplankton size distribution had a trend biased toward miniaturization. Microcystis sp., Merismopedia tenuissima, Chlorella chlorophylla, Chlorella sp., and Cyclotella sp. were the predominant species in our 2017-2018 annual survey. The peak biomass appeared in June, reaching 34.77 mg/L, and the peak abundance appeared in July, reaching 341.46×10⁶ cells/L. Both of redundancy analyses and linear correlation analyses showed that total phosphorus, temperature and pH were positively correlated with phytoplankton abundance and biomass, and total phosphorus and temperature were also positively correlated with the biomass and abundance of Cyanophyta and the dominant genus. Our results showed that the abundance and biomass of phytoplankton were high, indicating high risks of cyanobacterial water blooms in summer months. Nitrogen was at least as important as phosphorus in limiting phytoplankton production in Wuhan lakes.

Abstract:Mussels play an important role in the enrichment and transformation of elements in wetland ecosystems. In this study, Arconaia lanceolata, Hyriopsis cumingii, Cristaria plicata, and Unio douglasiae were used to analyze the content of five trace elements (Cu, Zn, As, Cd, Pb) in different tissues (visceral mass, mantle containing gills, foot ). The results showed that all five elements were detected in four species of mussels. The average content of each element in the tissues of the four species of mussels was visceral mass > mantle > foot, except for the average content of Zn in the tissues of U. douglasiae was shown as mantle > visceral mass > foot. The average content of each trace element in the four species of mussels was Zn>Cu>As>Pb>Cd; The average contents of Cu and Pb in the four species of mussels were expressed as A. lanceolata > C. plicata > U. douglasiae > H. cumingii. The content of Pb in the tissues of A. lanceolata was 2.62-6.99 times of the other three mussels. The average content of Zn is expressed as U. douglasiae > A. lanceolata > H. cumingii > C. plicata, As is expressed as U. douglasiae > H. cumingii > C. plicata > A. lanceolata, Cd appears as A. lanceolata > U. douglasiae > H. cumingii > C. plicata, the content of Cd in U. douglasiae and A. lanceolata is 2.75-6.08 times of H. cumingii and C. plicata. The difference in the content of trace elements between different species is greater than the spatial difference in the content of trace elements of a certain kind. Mussels in the estuary of Lake Chaohu, where the trace element is polluted heavily, have a higher content of trace elements and the contents of trace elements in tissues in estuaries with less pollution are also relatively low, indicating that mussels can be used as indicator organisms for monitoring of trace element pollution in Lake Chaohu. The contents of Pb and Cd in the four mussels did not exceed the limit of the national food safety standards, but the safety risks caused by As accumulation in H. cumingii and U. douglasiae were not excluded, and large quantities of food were not recommended.

Abstract:For exploring the macroinvertebrate community characteristics of the Weihe River mainstream and its typical tributaries originating from the northern Qinling Mountains, investigation of water environment and macroinvertebrates was conducted in 40 sampling sites in October 2017 and May 2018. Furthermore, Margalef richness and biological index (BI) biological indices were used to assess the water quality of studied rivers. Altogether 210 macroinvertebrates species were identified, belonging to 187 genera, 75 families, 8 classes and 5 phyla. Aquatic insects were the dominant group, accounting for 89.0% of the total species number, and the Baetis sp. was the dominant species in all studied rivers. The tributary Shitou River, had the highest values of total density(616.3 ind./m²), and the highest total biomass(5.265 g/m²). Whereas the total density (125.6 ind./m²) and total biomass (0.289 g/m²) of macroinvertebrates were both lowest in the Weihe River mainstream. The Shannon-Wiener diversity index(H')and Margalef richness index(R)of five typical tributaries were characterized by good water quality and significantly higher than those of the Weihe River mainstream, whereas the Pielou evenness index(J)showed insignificant difference between mainstream and tributaries. Pearson correlation analysis and the multiple linear regression analysis showed that “Silt plus clay” type substrate, conductivity, pH and nitrate nitrogen were the primary environment factors effecting the macroinvertebrate community characteristics in studied rivers. According to the water quality evaluation results of the richness index and the BI method, 73.3% and 80.0% of the mainstream sites were identified as moderately to heavily polluted, but 80.0% and 68.0% of tributary sites were identified as non-polluted to slightly polluted. This study can provide basic data supports for ecological management and protection in the Weihe River Basin.

Abstract:To explore the C, N, and P ecological stoichiometric characteristics of leaves and fine roots of Taxodium distichum (L.) Rich in the water-level fluctuation zone of the Three Gorges Reservoir (TGR) region. The C, N, and P content and their ratio in leaves and fine roots of T. distichum in Zhong County under three submergence treatments—Deep Submergence (DS), Moderate Submergence (MS), and Shallow Submergence (SS) were measured and analyzed in July 2018. The results showed that: (1) The C content in leaves of T. distichum showed a trend of SS>DS>MS group, and SS group was significantly higher than that in MS group; there was no difference in C content of fine roots under three submergence treatments. (2) The N and P content in fine roots showed a synergistic growth trend of DS < MS < SS group; the N and P content in leaves showed a cooperative decrease trend of DS>MS>SS group, and the N and P contents of the leaves was about 3 times and 2 times of that in fine roots, respectively. (3) The C/N and C/P ratios of the leaves were significant or extremely significantly lower than those of fine roots in submergence treatment group; the N/P ratio was higher than that of fine roots, and its ratio was relatively constant. Moreover, the N/P ratio between leaves and fine roots showed a trend of SS > DS > MS group. (4) Correlation analysis showed that there was a significant negative correlation between leaf P content and fine root N content, and the leaf N/P ratio was significantly positively correlated with fine root N/P ratio. This work demonstrates that the leaves and fine roots of T. distichum have integrity in the process of growth and metabolism, the nutrients and photosynthetic products are distributed between the above- and below ground parts to maintain the dynamic balance of nutrients, so that the T. distichum has homeostasis and thus adapt well to and respond to changes in the water-level fluctuation zone of the TGR region.

Abstract:Submerged macrophytes play an important role in stabilizing the water environments, thus restoration of submerged macrophytes has been the key to the restoration of shallow eutrophic lakes. Meanwhile, mussel stocking has been conducted as a parallel measure for submerged macrophytes restoration, because the filter-feeding mussels can improve and maintain a higher water clarity which it will enhance the growth of macrophytes. However, mussels, acting as an important spawning substrate for bitterling, may also facilitate the population development of bitterling fish (the common name for cyprinid fishes from the subfamily Acheilognathinae). The effects of bitterling fish on aquatic ecosystems are not clear. In the present study, we conducted an outdoor mesocosm experiment to study the effects of bitterling fish on water quality, the growth of submerged macrophytes and the attached periphyton, and the relationship between mussel and macrophytes. Three treatments were set with 4 replicates for each group, they are control (without mussel and bitterlings), mussels (with Sinanodonta woodiana), and mussel-bitterlings treatment (with both A. woodiana and Acheilognathus macropterus), meanwhile all the mesocosms were planted with equal density and biomass of Vallisneria denseserrulata. The results showed that the presence of bitterlings significantly increased the concentrations of total phosphorus, total dissolved phosphorus, suspended solids (TSS, OSS and ISS) and Chl.a of phytoplankton, but not for total nitrogen and total dissolved nitrogen. At the end of the experiment, the growth rate (both RGR and total individual), root-shoot biomass ratio, and maximum leaf length of macrophytes did not differ significantly between the mussel and control mesocosms, while the mean individual biomass of macrophytes in the mussel group was significantly higher than that of the controls which may be related to the higher biomass of periphyton on the surface of macrophytes leaves, though not significant compared with the controls. However, the presence of bitterlings did not significantly affect the mussel-macrophytes relationships. In comparison with the mussel's treatment, although bitterlings did not affect the RGR and total individuals of macrophytes, the maximum length of leaves was higher in the mussel-bitterling mesocosms than mesocosms with mussels, while the root-shoot biomass ratio was lower. These changes may be caused by the much higher concentrations of nutrients, suspended solids, Chl.a of phytoplankton and biomass of periphyton on the surface of leaves induced by the bitterlings which may boosted the growth of macrophytes leaves. Our results have important implications for lake management and restoration: bitterling is a small omnivorous fish which is widely distributed in lakes in the middle and lower reaches of Yangtze River. Moreover, they are highly correlated with submerged macrophytes and recovered quickly after lake restoration, so the monitoring and management of the small omnivorous fish, like bitterling in our study, should be strengthened when restoring and managing of shallow lakes.

Abstract:Sediment resuspension in shallow lakes promotes the nutrients release, which leads to the internal pollution, degrading the water quality and lake ecology. This research aims to study the impact of rigid vegetation on wave-driven sediment resuspension through wave flume experiments. It could provide a theoretical reference for environmental management and ecological restoration of shallow lakes and coastal wetlands. Vegetation canopies were constructed by rigid cylinders considering three diameters and 12 vegetation densities. The near-bed instantaneous velocity was measured within vegetation canopies and under different wave conditions by a Nortek Vectrino at sampling rate of 200 Hz. Suspended sediment concentrations were measured using an optical backscatter with frequency of 20 Hz. The vegetation-generated turbulence was positively linear with the root mean square of wave velocity. This vegetated turbulence increased with an increasing ratio (A_w/S) of wave excursion (A_w) to stem spacing (S) when A_w/S>1, and was similar with bare bed case when A_w/S<1. The concentration of sediment resuspension increased with growing solid volume fraction. The critical state of resuspension was initiated when the suspended sediment concentration exceeded the background level. Higher solid volume fraction generated higher turbulence, which promoted a small critical wave velocity. A vegetation-generated turbulence model for sediment resuspension was proposed and validated using the measured turbulence in the model canopy. Therefore, we confirmed that the magnitude of stem-generated turbulence is a function of solid volume fraction. This model proved the key role of turbulent kinetic energy to control the initial sediment resuspension. Based on this, a threshold model of critical velocity for sediment resuspension was proposed and validated. It could predict the critical near-bed wave velocity for sediment resuspension within rigid vegetation canopy or sheath with diameters of 0.32 cm to 1.2 cm. The applicable particle size was limited to 85-280 μm.

Abstract:Since the mid-1980s, the braided channel reach of the Lower Yellow River has formed some abnormal river bends. Analysis of the evolution processes and characteristics of abnormal river bends are of great significance for the regulation of the braided reach. Based on the remote sensing imagery and the cross-sectional topography, this study describes the evolution processes of abnormal river bends and variation of morphological characteristic parameters. The result shows that the abnormal river bends in braided channel reach of the Lower Yellow River have the characteristics of short evolution duration, high distortion level and prone to natural cutoff and the bends in different location have different evolution characteristics. The first bend in the upper braided reach evolves slowly and the cut-off period is long. The second bend in the middle braided reach evolves rapidly and highly distorted. The third bend in the lower braided reach evolves rapidly and is prone to generate natural cutoff. Variation of river bend morphology reflects the evolution process of three abnormal river bends, which are corresponding to the bend formation and cutoff processes. The formation of the abnormal river bend is a process in which the curvature radius and river bend spacing decreases, and the bend curvature radius, angle of water flow and bend amplitude increase. The maximum curvature radius of the three bends in the braided reach are 1.20, 2.10 and 1.61, respectively, reflecting the distortion degree of different bends. After cut-off, the curvature radius, angle of water flow, bend amplitude and river bend spacing are about 605%, 59%, 27%, and 133% of the extreme value during the evolution of the “Ω” shape river bend. For “M” shape river bend, angle of water flow, bend amplitude and river bend spacing after cutting are about 37%, 83%, and 152% of their extreme values. The cross-sectional profile at the Yiluo River outlet reflected that the beach on the concave bank of the river bend continuously collapsed at a rate of about 94 m/a during the formation period of abnormal river banks. The cut-off has a great influence on the cross-sectional profile. After cut-off, the beaches on both bank collapsed, and the river channel widen at a rate of 148 m/a. The erosion at the riverbed developed from the deep point to its two sides.

Abstract:The spatial-temporal distribution characteristics, composition and its change rule of different seasons of total suspended solids (TSS) in Lake Gehu, were analyzed by annual investigation in 2018-2019. The key impacting factors of TSS and relationship between it and nitrogen, phosphorus were discussed. The results showed that the annual variation of TSS concentration ranged from 11.80 to 105.87 mg/L, and the average concentration was 41.87±18.09 mg/L. The temporal and spatial differences of TSS in Lake Gehu were significant. The spatial distribution trend of the lake area south of the highway (B area) was larger than that of the lake area north of the highway (A area), and the coastal area was higher than the central area. As a whole, the seasonal change was manifested as summer > autumn > spring > winter, and summer was significantly higher than other seasons. The proportions of inorganic suspended solids (ISS) and organic suspended solids (OSS) in TSS of the whole lake body were significantly different, with the value of 75.5% and 24.5%, respectively. Both area A and area B was dominated by ISS. Linear fitting showed that TSS had extremely significant positive correlation with particulate nitrogen, total phosphorus and particulate phosphorus. The correlation between TSS and chlorophyll-a was also significant. Based on the above analyses, algal blooms and sediment resuspension were important factors affecting the concentration of suspended solids in water.

Abstract:Based on the features of diurnal variation of ice surface albedo in the Lake Ulansuhai, the relationship between solar elevation angle and geographic coordinates and Julian days, together with normalized time, to express the diurnal variations of the ice albedo. Linear combinations of four probability density distribution functions with exponential forms, including Laplace, Gauss, Gumbel, and Cauchy equations, were used to simulate the diurnal variations in observed ice albedo from sunrise to sunset with solar elevation angle more than 5°. The results reveals that the Laplace combined statistical model is the best fit to the observations. It can not only clearly show the double-peak distribution in the diurnal variation in ice surface albedo when the elevation angle is greater than 5°, but also express the U-type distribution between the two peaks as the elevation angle is more than 15°. This model has advantages of simple form in expression and clear physical meaning. The length parameter is close to half day, and the peak location is associated with the time of sunrise, and the asymmetry of the two peaks can be also shown. It provides a solid foundation for the parameterization schemes on the diurnal variations in lake ice surface albedo in different regions.

Abstract:Time sequence of the SZK1507 core derived from AMS¹⁴C dating, and the content of the total nitrogen (TN), total organic carbon (TOC) and the C/N values as well as the mean grain size, magnetisability are utilized to reconstruct the environmental changes in the Hangbu River Valley of the Lake Chaohu Basin, East China during the Holocene. The comprehensive analyses of multiple alternative proxies indicated that the evolutionary process of Lake Chaohu Basin in the Holocene could be divided into four periods. The climate was moist in Period Ⅰ ( from 10050 cal. a B.P. to 9700 cal. a B.P.) and Period Ⅲ (from 9250 cal. a B.P. to 5300 cal. a B.P.), and lake level of Lake Chaohu was high inferred from the low values of TN, TOC, C/N, mean grain size and magnetisability. Period Ⅱ (from 9700 cal. a B.P. to 9250 cal. a B.P.) and Period Ⅳ (from 5300 cal. a B.P. to the present) were dry, and the Lake Chaohu had low lake level, suggested by the high values of mean grain size and magnetisability, TN, TOC, C/N. Some global-scale abrupt climatic change events (e.g., 9.3 ka B.P., 8.2 ka B.P., and 4.2 ka B.P. events) were also recorded in this sediment core. Comparing the lacustrine records of SZK1507 core to other observations of climate variability, such as the northern hemisphere summer solar insolation, the sunspot numbers etc during the Holocene, we discovered that the abrupt climatic change events occurring in the Lake Chaohu Basin were affected by the variation of summer solar insolation in the northern hemisphere, the solar activities, the volcanic activities, and the complex feedback mechanism among them principally.

Abstract:The 2008 M_w 7.9 Wenchuan earthquake triggered more than 56000 landslides and induced huge clastic sediment along the Longmen Shan orogen, which had impacted earth surface processes within the catchment. However, little is known about the changes in riverine sedimentary compositions and depositional processes associated with the earthquake. Characterized by high sedimentation rate (averaging 74 cm/a), the continuous sediment in the Zipingpu Reservoir, the lower reaches of the Minjiang River provides valuable records of sediment transfer and compositions before and after the earthquake. In this paper, the strontium isotopic ratio (⁸⁷Sr/⁸⁶Sr) and elemental concentrations of reservoir sediments were measured. The results showed that there are significant differences in both ⁸⁷Sr/⁸⁶Sr ratios and elemental compositions before and after the earthquake. Both ⁸⁷Sr/⁸⁶Sr and Rb/Sr ratios decreased after the earthquake, with a positive correlation with CIA, implying increased contribution of fresh debris to the river sediments by the earthquake-triggered landslides, in particular during 2010 and 2011 when there had intense monsoonal rainfall. The difference of sedimentary compositions before and after the earthquake provides a basis of potential tracers for reconstructing hydroclimatic and tectonic events and their environmental impacts using sedimentary records.