Microplastics in sediment of the Three Gorges Reservoir:abundance and characteristics under different environmental conditions

Freshwater microplastic pollution is an urgent issue of global concern,and research on the distribution in reservoirs is lacking.We investigated the microplastic pollution levels in wet sediments collected from the Three Gorges Reservoir,the largest reservoir of China.Results show that microplastics were ubiquitous in the sediments of the Three Gorges Reservoir,and their abundance ranged from 59 to 276 pp/kg(plastic particles per kg,dry weight).Economic development and total population were important factors affecting the spatial heterogeneity of microplastic abundance,and the contribution of large cities along the reservoir to microplastic pollution should be paid with more attention.Fibrous microplastics were the most abundant type of microplastic particles in reservoir sediments,whereas polystyrene,polypropylene,and polyamide were the main types of polymers.The apparent spatial heterogeneity in morphology and color of microplastics is attributed to different anthropogenic or landbased pollution sources.Moreover,the accumulation of microplastics near the inlet of tributaries reflects the role of potential contributors of tributaries.More importantly,multiple bisphenols(BPs)and heavy metals detected at the microplastic surfaces indicate that microplastics can act as carriers of these pollutants in the environment in the same way as sediments did,which may alter the environmental fate and toxicity of these pollutants.Therefore,we conclude that the Three Gorges Reservoir had been contaminated with microplastics,which posed a stress risk for organisms who ingest them along with their associated pollutants(BPs,heavy metals).

Long-Term Performance and Microstructural Characterization of Dam Concrete in the Three Gorges Project

This study investigates the long-term performance of laboratory dam concrete in different curing environments over ten years and the microstructure of 17-year-old laboratory concrete and actual concrete cores drilled from the Three Gorges Dam.The mechanical properties of the laboratory dam concrete,whether cured in natural or standard environments,continued to improve over time.Furthermore,the laboratory dam concrete exhibited good resistance to diffusion and a refined microstructure after 17 years.However,curing and long-term exposure to the local natural environment reduced the frost resistance.Microstructural analyses of the laboratory concrete samples demonstrated that moderate-heat cement and fine fly ash(FA)particles were almost fully hydrated to form compact micro structures consisting of large quantities of homogeneous calcium(alumino)silicate hydrate(C-(A)-S-H)gels and a few crystals.No obvious interfacial transition zones were observed in the microstructure owing to the longterm pozzolanic reaction.This dense and homogenous microstructure was the crucial reason for the excellent long-term performance of the dam concrete.A high FA volume also played a significant role in the microstructural densification and performance growth of dam concrete at a later age.The concrete drilled from the dam surface exhibited a loose microstructure with higher microporosity,indicating that concrete directly exposed to the actual service environment suffered degradation caused by water and wind attacks.In this study,both macro-performance and microstructural analyses revealed that the application of moderate-heat cement and FA resulted in a dense and homogenous microstructure,which ensured the excellent long-term performance of concrete from the Three Gorges Dam after 17 years.Long-term exposure to an actual service environment may lead to microstructural degradation of the concrete surface.Therefore,the retained long-term dam concrete samples need to be further researched to better understand its microstructural evolution and development of its properties.

Environmental heterogeneity and productivity drive the assemblage of benthic diatom:a case study of the Three Gorges Reservoir

Dam construction has a critical effect on river ecosystems in the world,resulting in a rapid decline in biodiversity and ecosystem health.However,the effect of dam construction on the assemblage pattern of benthic diatoms remains unclear.The benthic diatoms assemblages in the tributary backwater area of the Three Gorges Reservoir(TGR)were investigated under low water level(LWL)and high water level(HWL)conditions.Results show that Discostella stelligera,Nitzschia palea,and Craticula subminuscula were dominant species in LWL,while Achnanthidium minutissimum and Nitzschia dissipata were dominant in HWL.Furthermore,environmental variables,productivity parameters,diversity indices,and community similarity were found significantly different between LWL and HWL periods.The Mantel test indicated that both environmental and spatial factors had significant effects on diatom communities in backwater area,while productivity was also a key driving force in LWL.The variation partitioning analysis(VPA)further demonstrated that environment factors could explain the largest variance of diatom assemblages in HWL(9%)and LWL(11%),followed by spatial factors.The relative importance of productivity to diatom community was significantly enhanced in LWL,but only a slight effect was found in HWL.These results indicate that the diatom assemblages were shaped by both environmental filtering and spatial factors.The relative importance of spatial factors depended on the degree of productivity.Therefore,the homogenization of diatom communities due to environmental disturbance,e.g.eutrophication and dam building,is the underlying mechanism in assembling the benthic diatoms.

Climate,Ecosystem and Migration:The Three Gorges Dam Study

The Three Gorges Dam,known as one of the biggest project items throughout the history,is a milestone for the development of China.Since it was completed in 2006,the dam has been persistently supplying ample electricity to the southern and eastern part of China.Despite its impressive output and benefits notwithstanding,we have to objectively pay our attention to the long-term impact that the Three Gorges Dam leaves to the place where we live,especially the influence on the climate,the ecosystem and the migration pattern of the reservoir area.

Review of the Relocation of General Zhang Fei’s Temple in View of the Three Gorges Dam Project

As a national cultural property,General Zhang Fei’s Temple is the largest ancient architectural complex in the Three Gorges of the Yangtze River.It was built in the Han Dynasty and has a long history of nearly 2,000 years.In 1994,the Chinese government launched the Three Gorges Dam project at the Yangtze River and implemented the largest relocation project for the General Zhang Fei Temple to prevent it from being submerged.The temple was relocated 32 kilometers upstream along with the local people of Yunyang County,and the historic environment was rebuilt on the opposite side of the migrant city of New Yunyang County.The temple was restored successfully and the tradition of offering sacrifices to General Zhang Fei continued in the local community.The relocation project lasted for 8 years and became the largest cultural heritage conservation project of the People’s Republic of China at the end of the 20th century.This paper comprehensively summarizes and reviews the project goals,implementation process,and project highlights of this relocation,so as to provide an important case reference for heritage conservation projects in the future.

Building the Three Gorges Project for the Chinese Nation—An Interview with General Manager Lu Youmei, China Yangtze River Three Gorges Project Development Corporation

The Yangtze River has nurtured the fertile land on both its banks and hundreds of millions of Chinese people. but its raging waters have also wreaked havoc on the people living in its reaches. Since the founding of New China, large-scale surveys, planning, scientific research and feasibility studies have been carried out in an effort to harness the

Plankton community composition in the Three Gorges Reservoir Region revealed by PCR-DGGE and its relationships with environmental factors

To explore the relationships between community composition and the environment in a reservoir ecosystem, plankton communities from the Three Gorges Reservoir Region were studied by PCR-denaturing gradient gel electrophoresis fingerprinting. Bacterial and eukaryotic operational taxonomic units （OTUs）, generated by DGGE analysis of the PCR-amplified 16S and 18S rRNA genes, were used as surrogates for the dominant ＂biodiversity units＂. OTU composition among the sites was heterogeneous; 46.7% of the total bacterial OTUs （45） and 64.1% of the eukaryotic OTUs （39） were identified in less than half of the sampling sites. Unweighted pair group method with arithmetic averages （UPGMA） clustering of the OTUs suggested that the plankton communities in the Xiangxi Rive sites were not always significantly different from those from the Yangtze River sites, despite clear differences in their environmental characterizations. Canonical correspondence analysis （CCA） was applied to further investigate the relationships between OTU composition and the environmental factors. The first two CCA ordination axes suggested that the bacterial community composition was primarily correlated with the variables of NO3^--N, dissolved oxygen （DO）, and SiO3^2--Si, whereas, the eukaryotic community was mainly correlated with the concentrations of DO, PO4^3--P, and SiO3^2--Si.

Impact of the Three Gorges Dam on reproduction of four major Chinese carps species in the middle reaches of the Changjiang River

Silver carp(Hypophthalmichthys molitrix),bighead carp(Aristichthys nobilis),grass carp(Ctenopharyngodon idella),and black carp(Mylopharyngodon piceus) are the four major Chinese carps and are commercially important aquaculture species in China.Reproduction of these carp has declined since the construction of the Three Gorges Dam(TGD) due to an altered water flow and thermal regime in the Changjiang(Yangtze) River.However,details of the changes in reproduction of the four species are not well understood.To assess the impact of the TGD on reproduction of the four carp,we investigated their eggs and larvae at Yidu City,which is 80 km below the TGD,during 2005-2012.We examined differences in larval abundance of the four species in the Jianli section(350 km downstream of the TGD) before(1997-2002)and after(2003-2012) construction of the TGD.Based on these observations,the first spawning date of the four species was delayed a mean of about 25 days after the dam was constructed.Mean egg abundance in the Yidu section of the river was 249 million and mean larval abundance was 464 million,which were significant decreases since the 1980 s.Moreover,larval abundance in the Jianli section after the dam was constructed was significantly lower than that before construction(ANCOVA,P<0.05).The observed larval abundance accounted for only 24.66%of the predicted value in 2003 when the dam was first inundated.The present spawning grounds between the TGD and Yidu section of the river are very similar to those described in the 1980 s,and some spawning grounds exist upstream of the TGD.Large free-flowing stretches upstream of the TGD and the creation of artificially flooded downstream reaches are needed to stimulate spawning and effectively conserve these four major Chinese carps species.

Reductions in non-point source pollution through different management practices for an agricultural watershed in the Three Gorges Reservoir Area

Non-point source water pollution generated by agricultural production is considered a major environmental issue in the Three Gorges Reservoir Area （TGRA） of China. The Annualised Agricultural Non-Point Source Pollution （AnnAGNPS） model was selected to assess the impact of the application of various management treats, including seven crops, five fertilizer levels and three-group management practice scenarios, on water quality from Heigou River Watershed in TGRA. The scenario subsets include conservation tillage practice （CTP）, conservation reserve program （CRP） and conversion of cropland into forestland program （CCFP）. Results indicated that tea can not be replaced by other crops because comparatively tea resulted in a higher sediment yield. CTP with no-tillage was more effective to reduce sediment yield, but could increased nutrient loss. CRP reduced sediment yield significantly, but slightly benefited on nutrient loss. CCFP reduced not only sediment yield but also the nutrient loss significantly. The conversion of cropland with a slope greater than 10° into forestland was found to be the best scenario as the sediment yield export is less than 5 tons/ha and nutrient loss is within the permissible limit.

Potential impacts of Three Gorges Dam in China on the ecosystem of East China Sea

The Changjiang River in China was dammed in 2003. The possible changes in matters fluxes from the river downstream after the completion of Three Gorges Dam and their potential impacts on the ecosystem of the East China Sea are discussed . The estuarine and coastal waters in the East China Sea were heavily fertilized by the inflow of nutrient-rich freshwater from the Changjiang River, which has led to severe eutrophication and frequent harmful algal blooms ,thus worsening the ecosystem health in this area. Analy- sis showed that the nutrient loadings are very likely to be reduced in the lower Changjiang River due to the construction of Three Gorges Dam. Especially for the total phosphorus, the discharges to the East China Sea will be reduced by one-third, which would relieve the severe eutrophication in this area. However, the expected decrease in the riverine silicate discharge would lead the ratio of silicon to nitrogen to be much less than 1 in the estuarine and coastal waters and thus may cause an elevation of flagellate growth. The changes in the annual water discharges and their seasonal distributions below the dam will be minor. Reduction of suspended particulate matter loading, due to the sedimentation behind the dam, will reduce the nutrient loadings of the particulate form especially for phosphorus, and decrease the turbidity of estuarine and coastal waters. On the other hand, this may enhance the erosion of the delta and the coasts as well as modifythe benthic ecosystem.

Effect of nitrogen and phosphorus on the water quality in the Three Gorges Reservoir Area during and after its construction

A survey concerning the concentration of the nutrients in the Three Gorges Reservoir Area was carried out. This paper presents the parameters(NO 3 - N, NO 2 - N, Kjeldahl N, non ionic ammonia, P PO 4 and TP) determined at 16 sampling sites from 1997 to 1999 The dominant soluble nitrogen form was NO 3 - N followed by Kjeldahl N, NO 2 - N and non ionic ammonia. Mean values of NO 3 - N, NO 2 - N, Kjeldahl N and non ionic ammonia ranged from 0 50 to 2 37 mg/L, 0 022 to 0 084 mg/L, 0 33 to 0 99 mg/L and 0 007 to 0 092 mg/L respectively. Mean values of P PO 4 at most sampling sites were higher than 0 1 mg/L for subject to eutrophication. The major factors influencing the concentrations of N and P might be agricultural runoff, municipal and industrial effluents. In addition, 6 kinds of soil were sampled at the area where would inundated after the dam completed. Two approaches were adopted to simulate the N and P release from the inundated soils. The results showed that the soils would release nitrogen and phosphorus to the overlying water when the soils were inundated. The characteristics of soil affected the equilibrium concentrations of N and P between the soil and the overlying water.

Mapping landslide susceptibility at the Three Gorges Reservoir, China, using gradient boosting decision tree,random forest and information value models

This work was to generate landslide susceptibility maps for the Three Gorges Reservoir(TGR) area, China by using different machine learning models. Three advanced machine learning methods, namely, gradient boosting decision tree(GBDT), random forest(RF) and information value(InV) models, were used, and the performances were assessed and compared. In total, 202 landslides were mapped by using a series of field surveys, aerial photographs, and reviews of historical and bibliographical data. Nine causative factors were then considered in landslide susceptibility map generation by using the GBDT, RF and InV models. All of the maps of the causative factors were resampled to a resolution of 28.5 m. Of the 486289 pixels in the area,28526 pixels were landslide pixels, and 457763 pixels were non-landslide pixels. Finally, landslide susceptibility maps were generated by using the three machine learning models, and their performances were assessed through receiver operating characteristic(ROC) curves, the sensitivity, specificity,overall accuracy(OA), and kappa coefficient(KAPPA). The results showed that the GBDT, RF and In V models in overall produced reasonable accurate landslide susceptibility maps. Among these three methods, the GBDT method outperforms the other two machine learning methods, which can provide strong technical support for producing landslide susceptibility maps in TGR.

Impact of the Three Gorges Dam on the spawning stock and natural reproduction of Chinese sturgeon in the Changjiang River,China

Chinese sturgeon(Acipenser sinensis) is the flagship species of the Changjiang River.The migration route of this species is blocked by the first dam,the Gezhou Dam,and its reproduction is affected by the Three Gorges Dam(TGD),one of the largest dams in the world.We studied the impact of the impoundment of the Three Gorges Reservoir(TGR) since 2003 on the spawning stock and the natural reproduction of the Chinese sturgeon by using our monitoring data from 1997 to 2013.Results indicate that TGR impoundment has delayed the first spawning dates of the fish from middle-late October to late November,decreased the amount of spawning activities from twice to only once each year,and significantly reduced egg production.In particular,the fish did not demonstrate any spawning activities in 2013.Therefore,TGR impoundment significantly affects the natural reproduction of the fish downstream of the TGD.The spawning stock size of the fish is also predicted to further decrease in the future,which will lead to a risk of population extinction.Ecological regulations must be imposed on decreasing the water temperature to 20℃before mid-October and increasing water discharge downstream of the TGD in October to induce spawning of the Chinese sturgeon.

Fossil Association from the Lower Cambrian Yanjiahe Formation in the Yangtze Gorges Area,Hubei,South China

Apart from previously reported Small Shelly Fossils （SSFs）, a macroscopic fossil assemblage, comprising abundant algae, cone-shaped tubular fossil forms, and probable impressions of a megascopic metazoan, comes from the Lower Cambrian Yanjiahe Formation in the Yangtze Gorges area of western Hubei Province, south China. The visible fossils are preserved in thinlaminated siltstone or muddy siltstone intercalated between 8-15 ram-thick carbonate deposits, probably representing sedimentary settings of a constrained local depression in the shallow water carbonate platform during the Early Cambrian Meishucunian Stage. The macroscopic fossil association provides significant fossil evidence about the evolution of life from the late Precambrian to the ＇Cambrian explosion＇ interval.

Possibilities and challenges of expanding dimensions of waterway downstream of Three Gorges Dam

The waterway in the middle and lower reaches of the Yangtze River has long been known as the Golden Waterway and has served as an important link in the construction of the Yangtze River Economic Belt.Therefore,expanding its dimensions is a significant goal,particularly given the long-range cumulative erosion occurring downstream of the Three Gorges Dam (TGD),which has been concentrated in the dry river channel.With the regulation of the volume from upstream reservoirs and the TGD,the minimum discharge and water level of the river downstream are increasing,and creating favorable conditions for the increase of the depth of the waterway.The discharge compensation effect during the dry season offsets the decline in the water level of the river channel caused by the down-cutting of part of the riverbed,but the minimum navigable water level of the segment near the dam still shows a declining trend.In recent years,several waterway remediation projects have been implemented in the downstream reaches of the TGD and although the waterway depth and width have been increased,the channel dimensions are still insufficient in the Yichang-Anqing reach (with a total length of 1026 km),as compared to the upstream reservoir area and the deep water channel in the downstream tidal reaches.A comprehensive analysis of the water depth and the number and length of shoals in the waterway indicates that its dimensions can be increased to 4.5 m ×200 m and 6.0 m×200 m in the Yichang-Wuhan and Wuhan-Anqing reaches,respectively.This is also feasible given the remediation technologies currently available,but remediation projects need to be coordinated with those for flood prevention and ecological protection.

Flood management of Dongting Lake after operation of Three Gorges Dam

Full operation of the Three Gorges Dam(TGD) reduces flood risk of the middle and lower parts of the Yangtze River Basin. However,Dongting Lake, which is located in the Yangtze River Basin, is still at high risk for potentially severe flooding in the future. The effects of the TGD on flood processes were investigated using a hydrodynamic model. The 1998 and 2010 flood events before and after the operation of the TGD, respectively, were analyzed. The numerical results show that the operation of the TGD changes flood processes, including the timing and magnitude of flood peaks in Dongting Lake. The TGD can effectively reduce the flood level in Dongting Lake, which is mainly caused by the flood water from the upper reach of the Yangtze River. This is not the case, however, for floods mainly induced by flood water from four main rivers in the catchment. In view of this, a comprehensive strategy for flood management in Dongting Lake is required. Non-engineering measures, such as warning systems and combined operation of the TGD and other reservoirs in the catchment, as well as traditional engineering measures, should be further improved. Meanwhile, a sustainable philosophy for flood control, including natural flood management and lake restoration, is recommended to reduce the flood risk.

Acanthomorph Biostratigraphic Succession of the Ediacaran Doushantuo Formation in the East Yangtze Gorges,South China

Large acanthomorphic acritarchs have been found in chert of the Ediacaran Doushantuo Formation at several localities in South China, including the East Yangtze Gorges of Hubei Province,Weng＇an area of Guizhou Province, and elsewhere. However, their potential for biostratigraphic subdivision and correlation of Ediacaran successions is limited by facies control, taphonomic biases,and taxonomic problems. In the Yangtze Gorges, the Doushantuo Formation is generally subdivided into four lithologic members. However, in the Weng＇an area, the Doushantuo Formation comprises just a lower and upper part separated by a mid-Doushantuo erosional surface. In the Yangtze Gorges at the Zhangcunping section, the Doushantuo succession is similar to that at Weng＇an. So far, the correlation between the Yangtze Gorges and Weng＇an area, and elsewhere has been an issue of debate. To resolvethe debate, we selected eight sections in the Yangtze Gorges area and systemically sampled chert nodules of the Doushantuo Formation, focusing in particular on the upper Doushantuo Formation. Our data confirm two different assemblages appearing separately in the second and third members, which are separated by a negative δ13C excursion （EN2）. The lower assemblage is characterized by Tianzhushania and a diverse suite of large acanthomorphic acritarchs. The upper assemblage is distinguished from the lower assemblage, by （1） absence of Tianzhushania; （2） occurrence of abundant,100-150 μm, smooth-walled spherical microfossils; （3） occurrence of highly diverse acanthomorphic acritarchs including species extending from the second member and new forms in this member; （4）occurrence of unnamed new forms of protist; and （5） occurrence of the tubular microfossil Sinocyclocylicus guizhouensis. Since the Tianzhushania-dominated assemblage is not present in Australia, it seems that only the upper acanthomorph assemblage is present and thus the lower Doushantuo acanthomorph assemblage is missing in Australia.

Fractal characterization of sediment particle-size distribution in the water-level fluctuation zone of the Three Gorges Reservoir, China

The combined effect of periodic water impoundment and seasonal natural flood events has created a 30 m high water-level fluctuation zone(WLFZ) around the Three Gorges Reservoir(TGR), China, forming a unique eco-landscape. Siltation, eutrophication, enrichment of heavy metals, and methane emissions in the WLFZ have been widely associated with sediment and soil particles generated from the upstream catchment or upland slopes. However, little attention has been paid to the complexity of sediment particle-size distributions in the WLFZ. In the present study, core samples(from a 345 cm thick sediment core from the base of the WLFZ), slope transect surface samples(across/up a WLFZ slope), and along-river/longitudinal surface samples(from the reservoir reaches) were collected. Laser granulometry and a volume-based fractal model were used to reveal the characteristics of sediment particle-size distributions. Results indicate that the alternation of coarse and fine particles in the sedimentary core profile is represented as a fluctuation of low and high values of fractal dimension(D), ranging from 2.59 to 2.77. On the WLFZ slope transect, surface sediment particles coarsen with increasing elevation, sand content increases from 3.3% to 78.5%, and D decreases from 2.76 to 2.53. Longitudinally, surface sediments demonstrate a downstream-fining trend, and D increases gradually downstream. D is significantly positively correlated with the fine particle content. We conclude that D is a useful measure for evaluating sediment particle-size distribution.

Prediction of chlorophyll a concentration using HJ-1 satellite imagery for Xiangxi Bay in Three Gorges Reservoir

Since the impoundment of the Three Gorges Reservoir in 2003, algal blooms have frequently been observed in it. The chlorophyll a concentration is an important parameter for evaluating algal blooms. In this study, the chlorophyll a concentration in Xiangxi Bay, in the Three Gorges Reservoir, was predicted using HJ-1 satellite imagery. Several models were established based on a correlation analysis between in situ measurements of the chlorophyll a concentration and the values obtained from satellite images of the study area from January 2010 to December 2011. Chlorophyll a concentrations in Xiangxi Bay were predicted based on the established models. The results show that the maximum correlation is between the reflectance of the band combination of B4/（B2＋B3） and in situ measurements of chlorophyll a concentration. The root mean square errors of the predicted values using the linear and quadratic models are 18.49 mg/m3 and 18.52 mg/m3, respectively, and the average relative errors are 37.79% and 36.79%, respectively. The results provide a reference for water bloom prediction in typical tributaries of the Three Gorges Reservoir and contribute to large-scale remote sensing monitoring and water quality management.

Changes in cultivated land patterns and driving forces in the Three Gorges Reservoir area, China, from 1992 to 2015

Changes of cultivated land patterns caused by major water conservation projects are rarely reported. We selected the Three Gorges Reservoir area in China to study the change in area and landscape pattern of the cultivated land in the head,central, and tail areas of the reservoir that took place between 1992 and 2015;we then studied the spatial distribution of the cultivated land in the three parts of the reservoir;finally, we studied the driving forces behind the changes in the cultivated land. The results derived are as follows.(1) During the construction of the Three Gorges Project(TGP, 1992–2015), the area of cultivated land around the reservoir decreased by30.23 million ha. This reduction occurred in phases:the most severe change in cultivated land occurred during the later stage of the project(2002–2010);only 0.62 million ha of cultivated land did not change between 1992 and 2015.(2) Spatial pattern analysis showed that the cultivated land in the three parts of the reservoir changed from a northern distribution to a southern distribution;thus, the area of cultivated land in the north decreased over the time period. The area of cultivated land in the head and tail areas decreased by varying degrees, while it increased in the central area over the 23 years, indicating that the change in cultivated land showed regional differences.(3) The TGP, the policy of reverting farmland to forest,and urbanization were the main driving factors for the change of cultivated land, but there were differences in their impacts at different stages.(4) According to the patch dynamics of the land cover change, the degree of change gradually intensified during the early and later stages of the project and then stabilized during the operational period. Our research provides scientific support for the protection of cultivated land resources and food security in the reservoir area and for the coordination of social and economic development, which is of great significance to sustainable development in the reservoir area.