Abstract:Mass flux is an important basis for maintaining the relationship between lakes and rivers, while the key of mass flux is water flux. Aiming to a goal of constructing a clear water that are conducive to both the Yangtze River and Poyang Lake, the Poyang Lake Hydraulic Project (PLHP) in planning will be operated according to a proposed water level regulating scheme in the view of ecology, in which is controlling over the lake level in the dry season instead of the wet season. By using two-dimensional hydrodynamic model, this paper conducts a quantitative analysis concerning the potential impacts of the water level regulating scheme of PLHP under three typical hydro-years (wet, normal and dry years) on stream flow of the Yangtze River. According to the simulation results, during a PLHP water level regulating period, the difference, the discharge from the lake to the Yangtze River is very small, only varied from -0.2% to -0.7% compared with two modeling scenarios (with or without the PLHP). The discharge under those two scenarios is basically maintained in a balanced state, though the seasonal distribution time from the lake to the Yangtze River is changed. During the dry season, the project has minor impact on the flow of the Yangtze River, or even increases the amount of water discharges. The dry year has a maximum effect of the increased discharge, followed by normal year and the third by wet year. The increased discharge in different hydro-years varies from 2.1% to 17.0%. In normal year and dry year, the lake level before the beginning of the PLHP regulation is much lower than the highest regulated water level of 9 m, so that the existing PLHP regulation scheme, which proposes to regulate the water level to 14-15 m on September 15, has obvious defects and need a further optimization.

Abstract:The published study suggested that cyanobacteria bloom was a phenomenon of excessive reproduction and aggregation with certain nutrient levels, climate and hydrological conditions and was the result of the comprehensive effect of meteorological and water environmental factors such as total nitrogen, total phosphorus, pH values. It was also found that annual outbreak of cyanobacteria bloom in Lake Dianchi indicated that, under the current condition of water quality, the main factor was the meteorological factor. In order to further explore the regularity between meteorological factors and occurrence of cyanobacterial bloom, the relationship between frequency of cyanobacteria bloom and meteorological factors were studied, by using the remote sensing data of cyanobacteria bloom and the monthly meteorological data from the stations nearby Lake Dianchi from 2010 to 2011. The results showed that the cyanobacterial bloom frequency had significant correlation with the average temperature, minimum temperature, average wind speed, cumulative sunshine hours and precipitation, which had a significant negative correlation with sunshine hours and wind speed, respectively. Among the factors, the wind speed had the highest correlation coefficient. It showed that the weaker wind speed was the most closely related to the occurrence of cyanobacteria bloom in Lake Dianchi. And this further verified that the stability of the water body had a more important effect on the occurrence of cyanobacteria bloom, under certain conditions of sufficient nutrients for requires of cyanobacteria bloom. These results can be used as a scientific prediction to forecast the occurrence of cyanobacteria bloom, and to take appropriate measures to reduce the impact of the cyanobacteria bloom.

Abstract:The relationship between water surface reflectance and total depth integrated algae biomass can be very complex as different kinds of algal vertical distributions can occur. For this reason, effectively identifying the algae vertical profiles is fundamental to estimate algal biomass. Gaussian profiles are the most typical algae vertical profiles which occur in most environmental conditions (including external and internal system). In this research, a back propagation (BP) neural network was established to estimate Gaussian distribution parameters of the vertical structure h and σ by wave bands R_rs(469), R_rs(555), R_rs(645) and chlorophyll-a concentration band C_Chl.a(0). The BP neural network was trained by using 3000 simulated datasets (radiative transfer simulation based on in-situ measured data by HydroLight), and verified by another 200 groups of simulated data and measured data. The correlation coefficient between estimated and measured h and σ were 0.97 and 0.95, while the relative errors were 13.20% and 12.36%, respectively. The relative error of h and σ was mostly less than 30%. This indicated that it is a good effectiveness of BP neural networks to estimate the vertical distribution parameters and able to explore the three dimensional algal distribution in Lake Chaohu, thereby providing a significant theoretical basis for remote sensing estimation of algal biomass.

Abstract:Samples of sediment and cyanobacteria were collected at a cyanobacteria gathering area of western-half area of Lake Chaohu. The distribution patterns of seven heavy metals (Cd, Cr, Cu, Zn, Pb, Ni and Mn) were studied, and the fractions of Cd and Mn were analyzed using the European Communities Bereau of Reference (BCR) sequential extraction procedure. In addition, laboratorial experiments were carried out to simulate the variations in the heavy metal contents during the cyanobacteria humification, and the effect of cyanobacteria humification on the adsorption and desorption of heavy metals were discussed. The results showed that the heavy metal contents of surface sediments exceed the background values, presenting different values of each sampling site. The closer near the Nanfei River, the higher pollution degree was. Potential Mobile Index analysis showed that, compared to Mn, Cd was more likely to cause the secondary pollution in the western-half area of Lake Chaohu. Correlations analysis indicated that both two heavy metals (Cd and Mn) showed a significant positive correlation between metal speciation and total metal value. Lake Chaohu was considered as a typical algae lake, and the sources and distributions of two heavy metals (Cd and Mn) were related to the algae boom. Combined with the study of adsorption and release by cyanobacteria humification, the present study speculates that the cyanobacteria humification could influence the migration and release of Cd and Mn in Lake Chaohu.

Abstract:In this study, samples were collected from overlying water and surface sediment in Shanmei Reservoir and Huinü Reservoir in Quanzhou City, Fujian Province. The efficiency of nitrogen load reduction by thin-layer capping with biozeolite in the source water reservoirs was investigated through a series of laboratory-scale static simulating experiments. The effect of dissolve oxygen concentration in overlying water on reducing nitrogen load was discussed and the mechanism to reduce nitrogen load by thin-layer capping with biozeolite was also explored. The results showed that the reduction efficiency of total nitrogen in overlying water ranged from 58.89% to 65.75% by thin-layer capping with biozeolite at a dose rate of 1 kg/m²(the thickness of 1 mm), and the reduction efficiencies of total nitrogen, ammonium nitrogen and organic nitrogen in sediments were in the range of 10.39%-13.08%, 32.35%-44.56% and 8.41%-11.04%, respectively. To overlying water of the main form of nitrate, the lower the dissolve oxygen concentration of overlying water, the better the efficiency of biological denitrogenation by high efficient bacteria. Therefore, thin-layer capping with biozeolite is efficient and feasible to reduce nitrogen load in the source water reservoirs. However, it is urgent to understand the mechanisms of nitrogen transportation and transformation in remediation process of sediment using thin-layer capping with biozeolite.

Abstract:The main objective of this study is to identify the feasibility of improving the nitrogen removal efficiency in low C/N wetlands by arranging aquatic macrophyte species with different phonological characteristics. We conducted a pilot experiment, adding warm-season species of Hydrilla verticillata to cold-season species of Oenanthe javanica at a floating-bed constructed wetland system (FCW), in order to quantify the effects of the decomposition of the warm-season macrophyte residue on the nitrogen removal efficiency under the condition of low temperature during autumn and winter seasons. The results showed that the adding of H. verticillata significantly increased the C/N ratios in the organic carbon shortage systems of FCW, and thus improved total nitrogen and nitrate nitrogen removal efficiency due to stimulating denitrification activities. During the four cycle periods of the phenophase-combined FCW, compared with the control group, the removal efficiency of total nitrogen in each period was increased by 23.03%, 10.90%, 18.55% and 22.93% respectively, and the removal efficiency of nitrate nitrogen was increased by 38.28%, 20.74%, 17.87% and 17.06%, respectively. Therefore we conclude that it is feasible to improve the nitrogen removal efficiency by re-arrangement of warm and cool season plants in the low C/N wetlands.

Abstract:Wetland soil is a significant pool of nitrogen (N) and phosphorus (P) sequestration in the wetland ecosystem in which the aquatic higher plants plays an important role. Field sampling and indoor analysis were conducted by two communities of the common reed (Phragmites australis) & the common reed + cattail (Typha latifolia) from Qinhu Lake wetland to enhance our understanding of the immobilization of N & P in the soil. Organs biomass of common reed & cattail, contents of total nitrogen (TN) & total phosphorus (TP) and their impacts on soil TN & TP contents were analyzed. Results showed that (1) consumption effect of Qinhu Lake wetland on soluble TN and TP was observed, especially a bigger effect on TN. (2) Common reed could enhance the efficiency of N enrichment in wetland soil (below 30 cm soil layer) and the effect is much higher than that in common reed + cattail community. Order of the TN and TP storage from high to low in the organs of common reed was root>stem>leaf>spike, while the order in cattail was root>spike>stem>leaf. (3) TN and TP contents in the stem and leaf of the common reed and cattail in the summer were higher than other seasons significantly, while TN content of common reed stems in the summer was 70%-84% higher and TP content was 81%-92% higher than other seasons. (4) The common reed would consume soil P when cattail would offset P because of the different mechanism response to P limitation. Therefore, the configuration mode of common reed + cattail could improve the efficiency of N and P sequestration of the wetland soil.

Abstract:Nitrogen is a dominant nutrient influencing and controlling eutrophication, and different nitrogen forms can make diverse contributions to water quality. The contents of different nitrogen forms in suspended sediments and surface sediment of East Tiaoxi River were determined by sequential extraction procedure. In addition,their distribution characteristics and influence factors were discussed. The results showed that the nitrogen pollution in East Tiaoxi River were serious with an average concentration of 4.48 mg/L, and the water quality in the middle reach of East Tiaoxi River was better than that in the upper and lower reaches. The amounts of four nitrogen forms in suspended sediments were significantly higher than those in surface sediment, in addition, the percentage of iron-manganese oxides bound nitrogen (IMOF-N) with the mean concentration of 1506.94 mg/kg were higher than that of other three nitrogen forms in suspended sediment. The percentage of organic matter-sulfide bound nitrogen (OSF-N) with the mean of 625.31 mg/kg was highest in surface sediment. IMOF-N and OSF-N contents were significantly affected by cation exchange capacity and particle size in both suspended sediments and surface sediments, and they were also significantly correlated with total nitrogen(TN),indicating that IMOF-N and OSF-N were the main fractions of TN. The correlation results showed that the water quality had significant influence on IMOF-N and OSF-N,and the influence of water on suspended sediments was stronger than that on surface sediments. Furthermore, suspended particulates were beneficial to produce nitrate nitrogen in water. In contrast, sediments were available for generating ammonia nitrogen in water, and to some extent, suspended sediments has inhibitory effect on algae.

Abstract:Phytoplankton, water quality and water level in Hengshan Reservoir of Taihu Basin were studied with the meteorological indexes, in order to analyze the influence of hydrological process on diatom proliferation in the reservoir. The results reveal that the annual diatom biomass shows the significant fluctuations. The diatom proliferation in September is considerably high with the biomass of 14.27 mg/L. Genera of the dominant diatom are Synedra, Cyclotella, Achnanthes and Melosira, among which Synedra shows the highest abundance of dominance. Correlation of phytoplankton biomass with nutrients is weak and with the total nitrogen is even negative. Cyclotella biomass is positive related with soluble phosphorus. The water exchange rate in Hengshan Reservoir shows the strong controlling effect on algae biomass, diatom proliferation and nutrient level. Both total nitrogen and soluble phosphorus show the negative correlation with water exchange rate. The simulation analysis indicates that diatom biomass in Hengshan Reservoir is affected by the joint effects of hydrology and water quality. With the purpose of preventing and controlling diatom bloom in reservoirs, the management should pay an emphasis on both nutrient reduction and water residence time regulation.

Abstract:Epiphytic bacteria associated with colonial Microcystis may play an important role in the development of cyanobacterial bloom. However, information on characterization of Microcystis-associated bacteria is limited. In this study, eighteen Microcystis-associated bacteria which belonged to six bacterial groups: Alpha proteobacterium, Beta proteobacterium, Gamma proteobacterium, Actinobacteria, Cytophagia and Flavobacteriia, were isolated from four Microcystis species (M. wesenbergii, M. flos-aquae, M. firma and M. aeruginosa). Analysis by BIOLOG plate indicated that except for two isolates of Alpha proteobacterium and one isolate of Actinobacteria, the other isolates were capable of utilizing more than 10 carbon sources. Among 18 bacterial isolates, 12 isolates showed chemotaxis, 12 isolates displayed hydrophobicity, and 14 isolates exhibited autoaggregation ability. Except for Flavobacteriia, other five groups contained hydrophobic bacterial isolates. All six groups contained bacterial isolates with chemotaxis and autoaggregation ability. Most of bacterial isolates associated with each Microcystis species were capable of utilizing more than 10 carbon sources, and exhibited hydrophobicity. For each Microcystis species, there was at least one group of bacterial isolates exhibiting coaggregation ability. Except for M. flos-aquae, most of bacterial isolates associated with each of other three Microcystis species showed chemotaxis. The results indicated that active metabolic potential, chemotaxis, hydrophobicity, and the abilities of autoaggregation and coaggregation might help the bacteria colonize the Microcystis colonies.

Abstract:Zhelin Reservoir is a large canyon-reservoir in the midstream of the Yangtze River, and the storage capacity is 79.2×10⁸ m³ and length is 115 km. Through measurements on a moving vessel and at fixed-point sites in the Zhelin Reservoir in April, 2015, the distribution of phytoplankton, chlorophyll-a (Chl.a) concentration and main environment variables (including dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), dissolved silicon (DSi), water temperature, turbidity, dissolved oxygen (DO)) were analyzed. The redundancy relationship of phytoplankton taxa and environmental variables was analyzed using the software CANOCO 4.5. The results showed that, 1) the reservoir water was categorized as a middle-status in nutrients. There were 34 main phytoplankton species in the surface (the cell density of which exceeding 1000 cells/L), and the average biomass of reservoir was 0.41 mg/L. The dominant algae (dominance be equal or greater than 0.02) were the diatoms and cyanobacteria. DIN, DIP, DSi and water temperature can impact on the structure of algae, and the four factors were explained for more than 60% variation of the algal structure. 2) The reservoir had a significant phenomenon of subsurface chlorophyll maximum (SCM). The depth of SCM appears at the water depth from 3 to 8 m, and the thickness is about 2-7 m. The Chl.a in the SCM layer is 25.2%-74.1% among the total in the vertical. The algae in the SCM layer absorbed the nutrients, resulting in decreased concentrations of DIN, DIP and DSi and the increased DO concentration. 3) The reservoir had significant biological and biochemical filtering effect for the DSi. About 11% to 12% DSi were absorbed by organisms in the middle and upper area of in the reservoir, and accumulating about 21% DSi was absorbed by algae from upstream to downstream. 4) Nitrogen and phosphorus emissions by human activities have a serious impact on the ecology and water quality of the reservoir and the adjacent county region. The concentrations of Chl.a and DIP in the region is about 2.9 times and 3 times higher than that in the natural region of the reservoir, respectively.

Abstract:Phytoplankton is a key primary producer in inland water ecosystem because its community structure can indicate the water quality. To understand the phytoplankton community structure and the water quality state in Huaihe River Basin, 217 sites were set and the phytoplankton samples were collected in the basin in May 2013. The 244 taxa of phytoplankton (species and variety species) belonging to 104 genera 8 phyla were identified, of which the most abundant phyla is Chlorophyta, followed by Bacillariophyta. The average phytoplankton biomass was 3.93 mg/L, ranging from 0.04 to 83.62 mg/L, while Dinophyta, Bacillariophyta and Cryptophyta were major groups upon the biomass. The richness and biomass of phytoplankton was low in the small streams and the pathway to the sea, but high in the middle of the river. The main dominant species were Cryptomonas erosa, Chroomonas acuta, Cyclotella meneghiniana and Ceratium hirundinella, whose relative biomass were higher than 5%. The phytoplankton diversity index was low and most sites were in a medium-heavy pollution state.

Abstract:In 2012, the zooplankton community structure in Harbin section of Songhua River was surveyed, and chemical index evaluation methods were used to assess the condition of water quality. A total of 40 species of zooplankton were found, including 9 species of protozoa, 27 species of Rotifera, 2 species of Cladocera, and 2 species of Copepoda. There are 34 species which could be treated as polluted indicators, in which 10 species are in light level, 6 species are in o-β in middle level, 9 species are in β middle level, 4 species are in β-α middle level, and 5 species are in α middle level. The annual average richness is 1042.0 ind./L, and the biomass is 0.078 mg/L. The common species are Brachionus quadridentatus, Keratella cochlearis and Polyarthra trigla, which are all mesosaprobity pollution indicators. The pollution degree of all kinds at the sample sites is consistent with the seasonal variation and the annual variation, where the water quality of the upstream is better than that of the downstream. The ordination of seasonal pollution degree from strong to weak levels is summer>autumn>spring. Overall evaluation results showed that, Harbin section of the Songhua River has been polluted in middle eutrophication level and in moderately polluted state. This study reflects that the current status of water quality objectively provides the important scientific basis for the Songhua River water quality and ecological assessment, water environment monitoring and water resources management.

Abstract:Vallisneria natans is one of the most common submerged macrophytes in lakes of China. In present, the growth strategies of V. natans population in the water ecological restoration project remain unclear. In this paper, the responses of V. natans morphological traits such as leaf, stolon and tuber and population parameters such as plant number, stolon number and biomass to water depth were discussed on basis of one year effects after the implementation of water ecological restoration project. The growth strategies of V. natans were also analyzed. The results showed that the plant number per area and stolon number per area significantly decreased with the increasing of water depth, whereas the above-ground biomass increased significantly. The leaf length, leaf width, leaf thickness, leaf area, stolon length, stolon diameter and tuber diameter also increased significantly with the water depth increasing. Among them, the leaf length and leaf area varied dramatically because they were sensitive to water depth, whereas leaf width, leaf thickness, stolon length and diameter, and tuber diameter varied lightly and were insensitive to water depth. A trade-off between parent shoot growth and daughter shoot output was found under stress of less light. V. natans guarantees the resource utilization efficiency of parent shoots by increasing investments to leaf. On the other hand, V. natans improves the growth of daughter shoots by decreasing the parent shoot density, and thus the plant realizes the spatial niche expansion and population regeneration. In water ecological restoration project, considering the regeneration ability of V. natans population and construction maneuverability, water depth at appropriate 0.5 m to 1.0 m is suggested.

Abstract:To explore the seasonal variations of bacterioplankton community structure in Xuanwu Lake and identify the main factors affecting bacterioplankton community composition, the bacterial 16S rRNA terminal restriction fragment length polymorphism technology and multivariate statistical methods were applied. The results show that the Invsimpson, Shannon-Wiener and Pielou indexes were the highest in summer, and the lowest in spring. Nonmetric multidimensional scaling analysis showed that bacterioplankton community structure exhibited a seasonal pattern. Mantel test, canonical correlation analysis and variation partitioning analysis show that the most significant environmental factor on the bacterioplankton community structure was temperature, and followed factor was pH. The influence of nutrient concentration was not significant. Overall, this study will be helpful for better understanding of the bacterioplankton community composition in eutrophic lakes.

Abstract:The gastrointestinal microbiome plays a significant role in maintaining the stability of gastrointestinal environment of animals, and at the same time the composition of gastrointestinal microbial communities is also influenced by external environment such as diets. Studies on the gut microbiota structure can better understand the ecological conditions of animals. In this study, a total of 9 faeces samples were collected noninvasively from overwintering Hooded Cranes (Grus monacha) at Lake Shengjin, Anhui Province. Through high-throughput sequencing of V3-V4 regions of 16S rRNA of microbiome, there are 337447 reads and 708 Operational Taxonomic Units (OTUs). The OTU abundance reached the highest in the early wintering period, clustering 586 OTUs with average 323 OTUs. A total of 20 bacterial phyla and 201 genera were identified in the early wintering period, representing 175 genera from 15 bacterial phyla in the mid-wintering period. A total of 18 bacterial phyla with 182 genera were identified in the late wintering period. The results showed that the microbial diversity index such as Shannon-Wiener index and Simpson index had no significant differences in fecal samples of different wintering periods at Lake Shengjin. However, microbial composition had certain differences among three periods. At the microbial phylum level, the phyla Firmicutes (14.2%), Cyanobacteria (34.5%), Bacteroidetes (28.2%) were predominated in the early wintering period, and the phyla Firmicutes (40.4%), Actinobacteria (44.2%) and Proteobacteria (10%) were predominated in the mid-wintering period, while the phyla Firmicutes (43.2%) and Proteobacteria (31%) were predominated in the late wintering period. At the genus level, compared with the other two wintering periods, the amount of Clostridium was higher in the late wintering period and the amount of Prevotella decreased distinctly from the early to the middle-late wintering periods, while the amount of Clostridium increased distinctly from the early to the middle-late wintering periods. The variation of composition of gastrointestinal microbial may be explained by changes of diets of the Hooded Cranes in the wintering period. The study shed some light on overwintering ecology of Hooded Cranes.

Abstract:Freshwater mussels are one of the most endangered animal groups in the world. Testing the relationship between the traits and the risk of extinction of freshwater mussels would greatly facilitate the conservation and management of freshwater mussels. Mussels have unique life history. Since the glochidia of most mussels are obligate ectoparasites living on the fins or gill filament of host-fishes, the dispersal between different local populations of mussels depends on the host movement. In this study, we calculated local colonization and extinction rates for 39 mussel species sampled from 12 sites in the Lake Poyang basins, and used general linear models of Akaike information criterion and Schwarz Bayesian Criterion to determine the relative importance of each biological trait in local colonization and extinction rates. The result indicated that population structure and breeding time were the best predictors of local colonization. Distribution density, reproductivity, locomotivity and conservation status were the best predictors of local extinction rates. Local colonization and extinction rates of freshwater mussels were closely correlated with species biological traits and the biological traits can be used to predict local colonization and extinction patterns. Overall, it indicated that those local populations were becoming increasingly isolation and suffering an extinction crisis when the local extinction rates exceeded local colonization rate. This study provides a theoretical and practical foundation to the maintenance of mussel populations and biodiversity conservation.

Abstract:Ottelia acuminata is listed in Yunnan Province Protected Plants (Class III) as a rare and endangered plant species. Ottelia acuminata community used to be a dominant community type in Yunnan's plateau lakes, but it is only found in a limited number of lakes nowadays with its observable changing characteristics. In the present study, species composition and distribution patterns of the community in Lake Jianhu were studied, with plot method and dispersal coefficient method in order to understand the development trend of the population, the relationship between its distribution pattern and environmental factors, and to provide some scientific basis for the protection of Ottelia acuminata and plateau lakes. The results showed that the community was composed of 18 species belonging to 12 families and 14 genera, with submerged type, free-floating type, floating-leaved type and hygrophyte as four major life forms. The distribution pattern of Ottelia acuminata and Potamogeton malaianus was clumpy, while other species were randomly distributed. The aggregation intensity of Ottelia acuminata was the highest among all species, which was close to the maximum clump distribution. Ex-situ conservation, basin maintenance and habitat management are some promising approaches to effectively slow down lake swamping process and conserve Ottelia acuminata community.

Abstract:With the LGR-floating chamber method, a 24-hour continuous monitoring was carried out in the initial impoundment period of Three Gorges Reservoir, in order to understand the greenhouse gases fluxes (carbon dioxide and methane) across the water-air interface of Caotang River which is the primary tributary of the reservoir. The results indicated that the fluxes of carbon dioxide and methane across the water-air interface appeared an obvious characteristic of diurnal variation. The fluxes of carbon dioxide ranged from -81.642 to 180.991 mg/(m²·h), and the average fluxes of carbon dioxide were 17.346 mg/(m²·h). As a result, the overall carbon dioxide showed “absorb by day and emit at night”. Methane was emitted all day with the average fluxes of methane 0.064 mg/(m²·h) showed “strong at day and weak at night”. The fluxes of carbon dioxide and methane had a positive correlation with wind speed while a negative correlation was observed with water temperature of surface layer, dissolve oxygen and chlorophyll-a. It could be explain the most important factors that influence emissions at water-air interface were phytoplankton photosynthesis and bacterial metabolism process in the surface water. The changes in greenhouse gases emissions at water-air interface were also relevant to special environment (density current and thermal stratification) due to the interaction between main current and tributaries. The hydrodynamic factors were the key factors that affect carbon cycle and the greenhouse gases fluxes across the water-air interface in backwaters of tributaries, which would be worth researching.

Abstract:Model estimation is one of the main method in greenhouse gas flux monitoring of water-air interface, which has made many achievements. However, many environmental factors will be uncertain influence on the final result in the process of monitoring. In Pengxi River of Three Gorges Reservoir, the water-gas interface greenhouse gas flux (CO₂, for example) was estimated with the model estimation, and the local sensitivity analysis fixed Morris screening method was carried out for all the parameters in model estimation on greenhouse gas diffusion flux. The research shows that the model estimation is used to calculate greenhouse gas flux on water-air interface in Pengxi River, Three Gorges Reservoir has high feasibility and reliability; wind velocity, water temperature and pH value will affect the monitoring results. And the stronger the wind speed, the higher the water temperature, the smaller the pH value, the greater the CO₂ diffusion flux; The pH value is a highly sensitive parameter, while wind speed and water temperature are sensitive parameters. In the monitoring process in Pengxi River of Three Gorges Reservoir, the instrument should be corrected in order to ensure the accuracy of pH value before sampling.

Abstract:The climate pattern has shifted from the warm-dry to warm-wet conditions in the arid northwestern China since 1980s. Changes in ice melting and precipitation in alpine areas caused by this climatic change can alter wetland hydrological processes, which in turn have an effect on biological habitats and ecosystem functions. Together with local instrumental data, this study investigates the effect of climate change on chironomid succession over the past 60 years using the redundancy analysis (RDA) based on sedimentary chironomid assemblages and sedimentary proxies including ²¹⁰Pb dating, total organic carbon (TOC) contents and particle size, from a sediment core derived from a dish-like depression in the Bayinbuluk alpine wetland. Chironomus plumosus-type was the dominance of chironomid species before 1990s, and replaced by phytophilous including Dicrotendips nervosus-type and Paratanytarsus penicillatus-type after that years. RDA results showed that TOC contents and particle size were the most important variables influencing the chironomid succession. The two factors can explain 31 percent of chironomid variations. Climatic through altering the water balance which affects aquatic vegetation, water turbidity and soil erosion, can affect chironomid succession indirectly.

Abstract:We measured several indexes including the stable organic carbon isotope (δ¹³C_org), the total nitrogen content, the total organic carbon content and the ratio of carbon and nitrogen content of bulk sediments in Lake Fuxian to exploring the sources of organic matters in sediments and the paleoenvironmental significance of δ¹³C_org during the last 5 ka. The results showed the organic matter inputs from both the terrestrial C₃ plants and the aquatic organisms as the main source to the lake sediments have greatly changed during the period of 5000-2300 cal a BP, and changed to the only aquatic input (submerged plants, phytoplankton and algae) since 2000 cal a BP. δ¹³C_org values of bulk sediments in Lake Fuxian were mainly affected by different organic matter inputs. Rapid changes of the δ¹³C_org values during the stage of 2300-2000 cal a BP may indicate that the paleoenvironment of Lake Fuxian basin has experienced a rapid climate event.

Abstract:Jiren Co is a small oligotrophic lake in West Sichuan plateau, located above the present tree-line and influenced by modern glacier meltwater input. Based on ²¹⁰Pb/¹³⁷Cs dating and multi-proxies (i.e., cladoceran, diatom and geochemical) from Jiren Co sediment core and using principal component analysis and redundancy analysis, this study analyzed the history of cladoceran assemblage change during the past 200 years, and reconstructed the environmental change of Jiren Co. Although cladoceran remains in Jiren Co was dominated by littoral species with significant changes over time, the core assemblages can divided into three distinct zones. After 1850 AD, the increase in abundance of Alonella nana, Chydorus sphaericus and Pleuroxus sp. and the decrease in Alona rustica and Alona guttata all indicate rising temperature and pH. After 1900 AD, cladoceran flux increased earlier than the change in abundance, which indicates the beginning of lake nutrition increases. This inconformity reflects the influence of climate warming and atmospheric nitrogen deposition, respectively. Multi-index analysis suggests that, over the past 150 years, climate warming and atmospheric deposition in the directly and indirectly effects (ice melt, vegetation and soil development) have affected the physical processes on the water temperature rise and prolonged ice-free period, nutrition processes on nitrogen and phosphorus increased, acid-base equilibrium processes on the increased alkalin. It changed the growing season and promoted the growth of algae, and finally affected on the assemblage and production of cladoceran. The synchronization change of cladoceran assemblage, algae and geochemistry proxies indicates a response of alpine lake to multi-environmental forcing under the background of continuous climate warming.

Abstract:Water samples were obtained in the Three Gorges Reservoir (TGR) and Fuling to Jiangyin reaches of the Yangtze (Changjiang) River from April 2006 to March 2007 after the TGR filling, in order to explore the reservoir influence on silica transport in the Yangtze River. The results reveal that the TGR would affect the silica delivery from the Yangtze River. In April and September-October, the dissolved silicate (DSi) concentration decreases along the reservoir due to the retention by the man-made lake, and increases in downstream reaches of the TGD due to the contributions from tributaries in the middle Yangtze River. The TGR trapped approximately 3%-6% DSi in 2006. The huge reservoir tends to remove DSi from the water column during the period between April and December; while it would add DSi from January to March. Biogenic silica (BSi) accounted for 2%-5% of total reactive silica in the Yangtze River. The diatom production plays a minor role in controlling BSi level in the Yangtze River. The retention of DSi loading in downstream reaches of the TGD was observed after impoundment, which would be concerned in the future.

Abstract:Lake Dongting is the second largest freshwater lake in China, directly connected to the Yangtze River. It has significance of practical effects on flood control, drought prevention and wetland conservation. This study addresses spatial-temporal variation in water surface area of Lake Dongting and its relationship with water level at Chenglingji of the Yangtze River. Water surface area were extracted from multi-temporal images of the Terra/MODIS (moderate-resolution imaging spectroradiometer) for the years 2000-2012. In combination of water level data of Chenglingji, a loop-like relationship was explored between the lake water surface area and the water level. Our results show that the lake area decreased from 2000 to 2012, with a strong seasonal variation in terms of rising (April-June), flooding (July-September), retreating (October-December) and drying (January-March) periods. The inundated area displays a seasonal change of spatial pattern with expansion from lake center to its maximum bounds during February-August and contraction from its maximum bounds to lake center during September-January. The lake water surface has a good correlation with the water level at Chenglingji and the correlation coefficient varies in seasons with the minimum value for drying period, the maximum for flooding period, and relatively high values for rising and retreating periods. The variation is probably related to the difference in controlling factors in different time periods. The Yangtze River has a relatively large impact on the loop-like relationship in drying season and flooding season, especially for the east Lake Dongting, which is the case even for high-and low-water years. Our findings offer an insight into the complexity of river-lake relationship and provide an important basis for flooding prevention in Lake Dongting and the mid-and lower-reaches of Yangtze River.

Abstract:Based on Digital Elevation Model(DEM) in 27 small watersheds of Dabie-South Auhui mountain area, the topographic information was extracted and the average peak time lag was calculated. By establishing the mathematical model of multiple linear regression and path analysis, the influence of the factors on the flood response of the river basin is discussed. The results show the following: At the level of the valley system, shape factor and roundness, valley relative elevation, channel branching frequency and the forest coverage rate affect the basin average peak time lag mainly. And basin relative elevation is the most fundamental explanatory variables; Different geomorphic factors interaction is complex. The multiple linear regression model of average peak time lag has 73.4% explanatory. Further more,the path analysis model respectively describes influence of each variable to the average peak time lag from direct effect and indirect effect. The results can provide important reference to analysis the flood response process of South Anhui mountain area. It is significant for flood control and disaster mitigation.