Impoundment Of Three Gorges Reservoir Research Articles

The reservoirs gradually changed the distribution, source, and flux of particulate organic carbon within the Changjiang River catchment

The increasing number of dams and reservoirs affects the delivery of fluvial particulate organic carbon (POC) to the sea due to their trapping effect. Here, we study the POC characteristics of the Changjiang River over three periods to explore the impact of reservoirs on POC sources and flux. We found that the Three Gorges Reservoir (TGR) significantly raised the proportion of riverine primary productivity (RPP)-derived POC downstream, while cascade reservoirs improved the RPP upstream. Since the beginning of TGR impoundment, POC flux into the sea has decreased, whereas the proportion of RPP-derived POC into the sea has gradually increased. Our results demonstrate that the TGR and cascade reservoirs changed organic carbon sources and improved the labile composition in the Changjiang River, which may adversely impact carbon storage. These findings could be applicable to other rivers affected by dams worldwide.

Application of 210Pbex in elucidating contemporary sedimentary dynamics in the water-level fluctuation zone of the Three Gorges Reservoir, China

Excess 210Pb (210Pbex) has been widely applied as a proxy indicator for establishing the chronology of sediments in lakes where the sedimentation processes comply with the assumptions for using 210Pbex dating models. However, little is known regarding the applicability of 210Pbex to elucidate contemporary seasonal sedimentary dynamics in reservoir water-level fluctuation zones (WLFZs). In the present study, sedimentary core and bulk sediments were collected from the WLFZ of the Three Gorges Reservoir (TGR) in China, and the physical and chemical properties were determined. Results for 210Pbex activity, total organic carbon, and total nitrogen of bulk sediments indicate pronounced elevation-dependent spatial variation (p < 0.05), but 137Cs activity and particle composition show no systematic trends, allowing 210Pbex activity to be used to differentiate seasonal stratigraphy. For the sedimentary core, therefore, sediment layers with lower 210Pbex activity were inferred to represent sedimentation during wet seasons, when the 210Pbex concentration was diluted by a higher suspended sediment load, whereas sediment layers characterised by higher 210Pbex activity were ascribed to sedimentation during dry seasons, when the tranquil water favoured 210Pbex fallout to be absorbed by suspended sediments and then deposited in the WLFZ. Hereupon, temporal variation is observed in annual sedimentary thickness, with relatively low sedimentation rates during the initial stage (2006–2008) of the TGR impoundment, followed by relatively high sedimentation rates from 2009 to 2013. Over the period from 2014 to 2017, sedimentation rates were low because the suspended sediment was intercepted by upstream cascade reservoirs. Subsequently, sedimentation rates were higher during 2018–2019 as a consequence of an increase in extreme rainfall events. The findings herein highlight that 210Pbex-based seasonal stratification discrimination is effective approach to establish high-resolution sedimentary chronosequences and that net sedimentation rates in WLFZ are controlled by inflow suspended load of the TGR.

Sediment deposition of Three Gorges Reservoir and its impact on the reservoir area in recent 20 years

泥沙问题是三峡工程建设与运行中的关键技术问题之一,只有妥善处理好泥沙问题,才能保证三峡工程长期有效使用,维持水库功能的全面发挥。本文首先结合实测水文、河道地形观测资料,对三峡水库运行近20年来的泥沙淤积特性及水库排沙比进行了较为全面的分析研究,并与已有研究成果进行了对比;其次,围绕防洪、航运以及坝前段的泥沙淤积等方面,进一步分析了水库淤积产生的影响。结果表明:三峡水库蓄水以来,在不考虑区间来沙的情况下,三峡水库共淤积泥沙20.484亿t,近似年均淤积1.102亿t,水库排沙比为23.6%,水库年均淤积量为原论证预测值的33%。其中,库区干流段累计淤积泥沙17.835亿m³(变动回水区冲刷0.694亿m³;常年回水区淤积18.529亿m³),淤积在水库防洪库容内的泥沙为1.648亿m³(干、支流分别淤积1.517亿m³和0.131亿m³),占水库防洪库容的0.74%,“十一五”攻关阶段研究得出的多年平均淤积量及排沙比较实测值均偏大,变动回水区冲淤则出现反向的情况,主要原因是研究采用的入库沙量偏大以及近期河道采砂和水库优化调度等影响。水库淤积对防洪库容和地下电厂的影响尚小,对库区部分水道航道条件产生了一定的影响,应加以关注。;Sediment problem is one key technical issue in the construction and operation of the Three Gorges Project. Only by properly handling the sediment problem can we ensure the long-term effective use of the Three Gorges Project and maintain a full play of the reservoir function. In this paper, the characteristics of sediment deposition and the sediment discharge ratio of the Three Gorges Reservoir (TGR) in the past 20 years have been comprehensively analyzed and studied based on the observed hydrological and river topographic data, and compared with the existing research results; Secondly, the influence of reservoir sedimentation is further analyzed in terms of flood control, navigation and sediment deposition in front of the dam. The results show that since the TGR impoundment, the total sediment deposition of the TGR is 2.0484 billion tons, approximately 110.2 million tons per year, the sediment discharge ratio of the reservoir is 23.6%, and the average annual sediment deposition of the reservoir is 33% of the original demonstration prediction value without considering the sediment from the interval. Among them, the accumulated sediment deposition in the main stream section of the reservoir area is 1.7835 billion m³ (69.4 million m³ scoured by the fluctuating backwater area; 1.8529 billion m³ silted by the perennial backwater area), and the sediment deposition in the reservoir flood control storage capacity is 164.8 million m³ (151.7 million m³ silted by the main stream and 13.1 million m³ silted by the tributary respectively), accounting for 0.74% of the reservoir flood control storage capacity. The average annual sediment deposition and sediment discharge measured during the 11th Five Year Plan period are relatively large, the scouring and silting in the fluctuating backwater area are reversed, mainly due to the influence of the large amount of sediment entering the reservoir, the recent sand mining in the river channel and the optimal operation of the reservoir. The influence of reservoir siltation on flood control storage capacity and underground power plant is still small, and it has a certain impact on some waterway conditions in the reservoir area, which should be paid attention to.

Analysis of the evolution pattern and causes of downstream gigantic hydraulic projects

Abstract The Jingjiang reach, located in the middle Yangtze River, downstream of the Three Gorges Reservoir (TGR), is a typical curved reach. After TGR impoundment, the evolution behaviors of the Jingjiang reach changed, mainly because one or more original factors, including geological conditions, existing projects, bending radius, upper reaches' regimes, and incoming water and sediment changed. In this paper, these influencing factors were investigated by using the measured data and the mathematical models that were proposed by the authors in a previous paper, and consequently, the evolution laws of the curved reach were analyzed. The results showed that the existing river nodes reduced the influence of the upstream river regime on the evolution of curve reaches and also slowed the speed of convex bank scouring and concave bank depositing. Constructed projects could reduce sediment transport intensity from the concave bank to the convex bank. The decrease in incoming sediment after TGR impoundment was beneficial to convex bank scouring. The increase in median water period duration was favorable for convex bank scouring and concave bank depositing. Both convex bank and concave bank were scoured when the incoming sediment concentration decreased sharply. The sediment concentration of suspended load would stabilize near the saturation point, and the riverbed would be scoured when there is sediment concentration under the saturation point, while the riverbed would be deposited when the sediment concentration reaches the saturation point.

Potential hydrological regime requirements for spawning success of the Chinese sturgeon Acipenser sinensis in its present spawning ground of the Yangtze River

AbstractReservoir impoundment often alters the hydrological regimes of the river and consequently leads to the extinction of some sensitive species. This study analysed the spawning response of a critically endangered (CR) species, Chinese sturgeon Acipenser sinensis, under the changing hydrological regimes caused by the Three Gorges Reservoir (TGR). Based on our statistic analysis, we inferred that the long duration (&gt;100 days) and large magnitude (&gt;1.8 * 106 m3/s) of high flow pulse in the flood season and low accumulated water temperature in October (&lt;660°C) and November (&lt;540°C) were key hydrological regimes to induce the spawning success of Chinese sturgeon. Such hydrological regimes could not be satisfied after the third phase of the TGR impoundment in 2005, which decreased the suitability of the flow (HSIF) and temperature (HSIT) regimes for the spawning of Chinese sturgeon. However, a significant complementary relationship between high HSIF and low HSIT was found in all years of successful spawning after 2005, but it did not occur in the nonspawning years of 2013, 2015 and 2017, which could be the reason for spawning failure in these years. In the years 2018 and 2019, although the complementary relationship existed, the spawning failure in these 2 years was probably due to few parent fish. Therefore, we suggest that future conservation measures should focus on both optimizing operations of the TGR to ensure suitable hydrological conditions and restocking with adult fish to ensure successful spawning.

Long-term impacts of reservoir operation on the spatiotemporal variation in nitrogen forms in the post-Three Gorges Dam period (2004-2016).

Nitrogen (N) is an essential nutrient limiting life, and its biochemical cycling and distribution in rivers have been markedly affected by river engineering construction and operation. Here, we comprehensively analyzed the spatiotemporal variations and driving environmental factors of N distributions based on the long-term observations (from 2004 to 2016) of seven stations in the Three Gorges Reservoir (TGR). In the study period, several water quality indexes of the river reach improved, whereas N pollution was severe and tended to be aggravated after the TGR impoundment. The anti-seasonal reservoir operation strongly affected the variations in N forms. The total nitrogen (TN) concentration in the mainstream of the Yangtze River continuously increased, although it was still lower than that in the incoming tributaries (Wu and Jialing rivers). Further analysis showed that this increase occurred probably because of external inputs, including the upstream (76%), non-point (22%), and point source pollution inputs (2%). Additionally, different N forms showed significant seasonal variations; among them, the TN and nitrate nitrogen concentrations were the lowest in the impoundment season (October-February), and the ammonia nitrogen concentrations were the highest in the sluicing season (March-May). Redundancy analysis revealed that the water level and distance to the Three Gorges Dam were significant contributors to N forms distribution. Our findings could provide a basis for managing and predicting the water quality in the Yangtze River.

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

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

Impact of Three Gorges Reservoir Water Impoundment on Vegetation–Climate Response Relationship

In recent years, the impact of global climate change and human activities on vegetation has become increasingly prominent. Understanding vegetation change and its response to climate variables and human activities are key tasks in predicting future environmental changes, climate changes and ecosystem evolution. This paper aims to explore the impact of Three Gorges Reservoir (TGR) water impoundment on the vegetation–climate response relationship in the Three Gorges Reservoir Region (TGRR) and its surrounding region. Firstly, based on the SPOT/VEGETATION NDVI and ERA5 reanalysis datasets, the correlation between climatic factors (temperature and precipitation) and NDVI was analyzed by using partial correlation coefficient method. Secondly, nonlinear fitting method was used to fit the mapping relationship between NDVI and climatic factors. Then, the residual analysis was conducted to evaluate the impact of TGR impoundment on vegetation–climate response relationship. Finally, sensitivity index (SI), sensitivity variation index (SVI) and difference index (DI) were defined to quantify the variation of vegetation–climate response relationship before and after water impoundment. The results show that water impoundment might have some impacts on the response of vegetation–climate, which gradually reduced with increasing distance from the channel; comparing with the residual analysis method, the SI and DI index methods are more intuitive, and combining these two methods may provide new ideas for the study of the impact of human activities on vegetation.

Land Use Pattern and Vegetation Cover Dynamics in the Three Gorges Reservoir (TGR) Intervening Basin

The Three Gorges Reservoir (TGR) intervening basin is one of the most important, ecologically fragile and sensitive areas in the upper reaches of the Yangtze River. Since the completion and operation of the TGR, the change of the ecological environment in this region—with vegetation as an indicator—has been a consistent focus of attention. Based on the six phases of land use data and normalized difference vegetation index (NDVI), temperature and precipitation data from 1998 to 2017, the change and trend of land use and vegetation cover in the TGR intervening basin were analyzed quantitatively by using a transition matrix, linear regression and partial correlation analysis. The area of unchanged land use type is 56,565 km2, accounting for 97.27% of the total area of the basin. The vegetation coverage with NDVI as the indicator showed a significant upward trend, with a growth rate of 7.5%/10a. The impact of temperature on vegetation was greater than that of precipitation on vegetation. The non-linear fitting curve of NDVI to temperature and precipitation rose with the time course of TGR impoundment, although the mechanism remains to be studied further. In general, climate change, ecological restoration measures, urbanization and reservoir impoundment did not significantly change the spatial distribution pattern of land use and the climate driving mechanism of vegetation growth in the TGR intervening basin.

Impact of the three gorges reservoir operation on the hydrological situation of Poyang Lake

The operation of Three Gorges Reservoir (TGR) has changed the hydrological situation of Yangtze River and its connected lakes. Based on the hydrodynamic model, the influence of TGR operation from 2009 to 2014 on the Poyang Lake has been evaluated. It is found that TGR impoundment reduced the discharge of the Yangtze River and the water level of Poyang Lake, brought the decreasing of the backflow phenomenon. Especially in October, the discharge and water level of Hukou station (HKS) decreased by 9.6% and 1.09 m respectively, and this effect could be up to the Kangshan area. Meanwhile, TGR operation has also increased the water level of HKS by 0.1~0.56 m from December to May, which only affected the vicinity of Duchang. In addition, TGR operation also increased the maximum water level of HKS from April to June by 0.1~0.34 m, and that from July to August decreased by 0.22~0.4 m which is beneficial to reducing the flood control risk of Poyang Lake. But TGR impoundment changed the water exchange process between Yangtze River and Poyang Lake, and advanced the dry season, which had a certain impact on the water supply and ecological environment of the lake area.

Study on the Flow-sediment Conditions and River-bed Erosion and Deposition of Chongqing Reach after the Impoundment of Three Gorges Reservoir

Chongqing city is the important node of golden waterway of Yangtze River. As the promotion of the Yangtze River economic belt strategy and normal operation of Three Gorges Reservoir (TGR), more and more attention has been paid to the sediment problem of Chongqing reach. After the experimental storage of 175m in the TGR, Chongqing reach is located in the fluctuating backwater area, with export boundary conditions and river-bed erosion and deposition changed. In recent years, with the water storage of cascade reservoirs in the lower reaches of Jinsha River, the condition of water inflow and sediment in this section has changed and the river-bed is adjusted accordingly. According to prototype observation data from 2003 to 2017, the flow-sediment conditions and river-bed erosion and deposition of Chongqing reach after the impoundment of TGR at different stages were comarred and analyzed. Results showed that during the initial storage period of TGR, from June 2003 to May 2008, sediment erosion and sediment was mainly related to water and sediment of upstream, with whole reach in a state of erosion and intensity was about 140.8 million m3 every year. After the impoundment of TGR, from September 2008 to October 2012, the condition of incoming water and sediment in Chongqing reach maintained original change trend and sediment erosion was mainly related to impoundment of TGR, with whole reach in a state of erosion, but intensity was small. From October 2012 to December 2017, sand from upstream of Chongqing reach reduced greatly, so river bed was drastically adjusted and scour intensity increased significantly, was about 312.2 million m3 every year. It concluded that decrease of upstream sediment is one of the important reasons for increased scour intensity in Chongqing reach.

Influence of the three Gorges Reservoir on the shrinkage of China's two largest freshwater lakes

Abstract The impoundment of the Three Gorges Reservoir (TGR), the largest hydropower project in the world, has altered the sediment deposition and erosion regime of downstream-linked rivers and lakes. The extent to which the TGR impoundment has changed the surface areas of the two largest freshwater lakes in China, Lake Dongting and Lake Poyang, remains largely unknown. Here, we compared the surface areas of the two lakes pre and post the TGR impoundment as well as with a modelled non-TGR scenario. We found that the mean surface areas of Lake Dongting and Lake Poyang during the post-TGR period (2003–2016) were significantly smaller than in the pre-TGR period (1956–2002) and in the modelled non-TGR scenario (2003–2016). The impoundment of TGR has led to a shift from a sediment deposition regime to an erosion-dominated regime of the downstream-linked rivers and the two lakes. The impoundment of TGR further changed the seasonal variabilities in discharge and water level in the downstream-linked rivers and the two lakes, especially in the flood season. Our results suggest that TGR resulted in a 5.1%, 16.2%, and 12.2% decrease of the surface area of Lake Dongting in June 2003–September 2006, October 2006–September 2008, and October 2008–December 2016, respectively, and a corresponding decrease of 12.4%, 19.6%, and 15.8% for Lake Poyang. These changes cannot be attributed to variations in rainfall as no significant differences were found in the annual or monthly mean rainfall in the watersheds upstream of Luoshan and Jiujiang + Hukou between the pre-TGR and the post-TGR period. Our results call for the development of a strong holistic management plan for cascading reservoirs, including TGR, to minimize the damage of downstream lake ecosystems.

A Review of Studies on the Biogeochemical Behaviors of Mercury in the Three Gorges Reservoir, China.

The Three Gorges Reservoir (TGR) is a relatively large reservoir, and its water level management actions produce a widespread water level fluctuation zone (WLFZ), which has characteristics of both terrestrial and aquatic ecosystems. Here, an integrated overview of current knowledge on Hg behaviors in the TGR, especially the WLFZ, as well as exposure risk to local residents was presented. Hg levels in the TGR were comparable with other natural aquatic systems. WLFZ in the TGR was confirmed to be an environment favorable for Hg methylation by enhancing microbial activity, promoting sulfur cycling and increasing the level of low-molecular-weight organic matters. However, elevated fish Hg concentrations did not follow the impoundment of TGR, indicating no obvious reservoir effect, while it is still noteworthy that frequently consuming fish is likely to be a methylmercury (MeHg) exposure pathway for specific populations e.g. fishermen around the TGR.

Multivariate analysis performed to identify the temporal responses of fish assemblages to abiotic changes downstream of the Gezhouba Dam on the Yangtze River

AbstractImpoundment of the Three Gorges Reservoir (TGR) and overharvesting are anthropogenic factors that have had a dramatic effect on Yangtze fish. This study used the multivariate analysis to quantify the relationship between abiotic alterations (seven variables from the TGR impoundment and fishing activities) and fish response, revealing the processes through which abiotic changes affect fish assemblages over a 14‐year period (1999–2012). Fish assemblages temporally clustered into three groups that were strongly associated with the TGR impoundment. Eleven species that accounted for 98.44% of dissimilarities contributed to these three clustered groups. Variation in fish assemblages primarily resulted from a decline in three lotic species without spawning grounds downstream, fluctuations in four lotic species with spawning grounds downstream, and increases in three eurytopic species. Abiotic changes resulted from the TGR impoundment (TGR water levels, sediment, and water temperature), together with fish activities (fishing intensity), significantly affected the temporal patterns of the fish assemblages. Results suggest that the decline in lotic species can be attributed to the blocking and declines in the downstream movement of lotic species caused by increased water levels in the TGR. Increases in eurytopic species and declines in other species were caused by habitat fragmentation via a decline in sediment discharge and changes in water temperature. Fishing activities affected fish assemblages throughout the entire period of observation, particularly during the initial impoundment period from 2003 to 2005. These findings highlight the degree to which those anthropogenic factors affected the fish assemblages in temporal processing.

Nutrient Distribution Characteristics of the Sediment-water System in the Xiangxi River During the Impoundment of TGR

This study characterizes the nutrient distribution of the sediment-water system in the Xiangxi River (XXR) during the impoundment of the Three Gorges Reservoir (TGR). In 2016, the research group obtained samples in the Xiangxi River, analyzed the distribution of nitrogen, phosphorus, and O.M. (organic matter) in the sediment-water system, explored the characteristics of "source-sink" between the interstitial water and overlying water, and carried out a cluster analysis for the sampling sites. The results showed that ρ(TN) in the sediments was higher than in the estuary, and the ρ(TN) was close to that in the middle and downstream samples of the river. The ρ(TP) in the upstream sample was the highest of all sites, ρ(O.M.) presented low distribution characteristics in the downstream, and the maximum value of ρ(O.M.) exceeded the critical point (1.5%) within a depth of 10 cm, and there was a certain risk of release. For the distribution in the overlying water, ρ(DTN) and ρ(DTP) were the largest in the estuary, ρ(DTN) decreased from the estuary to the upstream, and ρ(DTP) did not change along the river. During the study, DTN, NH4+-N, and DTP in all sites (except CJ point) were released as nutrients to the overlaying water as the "source," but some points for NO3--N and PO43--P presented as "sources," and some of them presented as "sinks." The "source-sink" process of nitrogen was stronger than that of phosphorus. This was due to the difference between the oxidation environment at the bottom of the XXR and the stream flow backward depth of the Xiangxi bay during impoundment. Based on the results of a cluster analysis, the characteristics of CJ, 1, and 2 indicated similar sediment-water systems, while the characteristics of 3 and 4 were similar.

Spatiotemporal Variations of Extreme Precipitation under a Changing Climate in the Three Gorges Reservoir Area (TGRA)

The Three Gorges Dam (TGD) is one of the largest hydroelectric projects in the world. Monitoring the spatiotemporal distribution of extreme precipitation offers valuable information for adaptation and mitigation strategies and reservoir management schemes. This study examined variations in extreme precipitation over the Three Gorges Reservoir area (TGRA) in China to investigate the potential role of climate warming and Three Gorges Reservoir (TGR). The trends in extreme precipitation over the TGRA were investigated using the iterative-based Mann–Kendall (MK) test and Sen’s slope estimator, based on weather station daily data series and TRMM (Tropical Rainfall Measuring Mission) data series. The mean and density distribution of extreme precipitation indices between pre-dam and post-dam, pre-1985 and post-1985, and near and distant reservoir area were assessed by the Mann–Whitney test and the Kolmogorov–Smirnov test. The ratio of extreme precipitation to non-extreme precipitation became larger. The precipitation was characterized by increases in heavy precipitation as well as decreases in light and moderate rain. Comparing extreme precipitation indices between pre-1985 (cooling) and post-1985 (warming) indicated extreme precipitation has changed to become heavier. Under climate warming, the precipitation amount corresponding to more than the 95th percentile increased at the rate of 6.48%/°C. Results from comparing extreme precipitation for the pre- and post-dam, near reservoir area (NRA) and away from the reservoir area (ARA) imply an insignificant role of the TGR on rainfall extremes over the TGRA. Moreover, the impoundment of TGR did not exert detectable impacts on the surface relative humidity (RH) and water vapor pressure (WP).

Potential causes of habitat degradation and spawning time delay of the Chinese sturgeon (Acipenser sinensis)

In fish conservation, it is important to simulate fish habitat suitability and determine the potential impact on habitat quality and species behavior. This study analyzed the impact of several hydraulic projects on fish habitat quality and spawning time by numerical modeling. The case study involved the only Chinese sturgeon spawning site in the Yangtze River, China. Four habitat assessment indexes reflected both habitat quality and spatial characteristics, including fragmentation and connectivity. Previous studies did not simulate the water temperature impact on the fish habitat; spawning time delay was attributed to water temperature increases and discharge decreases. The results of the present study showed that the water temperature increase from the Three Gorges Reservoir (TGR) impoundment primarily caused the habitat degradation and spawning time delay. The effect of the water temperature increase on the degradation of average habitat suitability was eight times that of a decrease in discharge. A 25-day delay in the water temperature trend line was significantly correlated with a 26-day delay in the first spawning date. A decrease in discharge after TGR impoundment did not cause the spawning date delay. The Dike Project mainly impacted spawning site connectivity. Controlling the water temperature of the released water discharge is the most important means of conserving the wild Chinese sturgeon. This research can benefit other regions considering hydraulic projects by identifying potential factors impacting fish habitat quality and overall ecosystem health.

Coarse and fine sediment transportation patterns and causes downstream of the Three Gorges Dam

Reservoir construction within a basin affects the process of water and sediment transport downstream of the dam. The Three Gorges Reservoir (TGR) affects the sediment transport downstream of the dam. The impoundment of the TGR reduced total downstream sediment. The sediment group d≤0.125 mm (fine particle) increased along the path, but the average was still below what existed before the reservoir impoundment. The sediments group d>0.125 mm (coarse particle) was recharged in the Yichang to Jianli reach, but showed a deposition trend downstream of Jianli. The coarse sediment in the Yichang to Jianli section in 2003 to 2007 was above the value before the TGR impoundment. However, the increase of both coarse and fine sediments in 2008 to 2014 was less than that in 2003 to 2007. The sediment retained in the dam is the major reason for the sediment reduction downstream. However, the retention in different river reaches is affected by riverbed coarsening, discharge, flow process, and conditions of lake functioning and recharging from the tributaries. The main conclusions derived from our study are as follows: 1) The riverbed in the Yichang to Shashi section was relatively coarse, thereby limiting the supply of fine and coarse sediments. The fine sediment supply was mainly controlled by TGR discharge, whereas the coarse sediment supply was controlled by the duration of high flow and its magnitude. 2) The supply of both coarse and fine sediments in the Shashi to Jianli section was controlled by the amount of total discharge. The sediment supply from the riverbed was higher in flood years than that in the dry years. The coarse sediment tended to deposit, and the deposition in the dry years was larger than that in the flood years. 3) The feeding of the fine sediment in the Luoshan to Hankou section was mainly from the riverbed. The supply in 2008 to 2014 was more than that in 2003 to 2007. Around 2010, the coarse sediments transited from depositing to scouring that was probably caused by the increased duration of high flow days. 4) Fine sediments appeared to be deposited in large amounts in the Hankou to Jiujiang section. The coarse sediment was fed by the riverbed scouring, and much more coarse sediments were recharged from the riverbed in the flood years than in the dry years. 5) In the Jiujiang to Datong section, the ratio of fine sediments from the Poyang Lake and that from the riverbed was 1: 2.82. The sediment from the riverbed scouring contributed more to the coarse sediment transportation. The contribution was mainly affected by the input by magnitude and duration of high flows.

Heavy metal pollution in sediments of the largest reservoir (Three Gorges Reservoir) in China: a review.

The Three Gorges Dam in China is the world's largest dam. Upon its completion in 2003, the Three Gorges Reservoir (TGR) became the largest reservoir in China and plays an important role in economic development and national drinking water safety. However, as a sink and source of heavy metals, there is a lack of continuous and comparative data on heavy metal pollution in sediments. This study reviewed all available literatures published on heavy metals in TGR sediments and further provided a comprehensive assessment of the pollution tendency of these heavy metals. The results showed that heavy metal concentrations in TGR sediments varied spatially and temporally. Temporal variations indicated that Hg in tributaries, as well as As, Cd, Cr, Cu, Ni, Pb, and Zn in the mainstream, exhibited a higher probability to exceed background values after the impoundment of TGR. Pollution assessments by contamination factor, geoaccumulation index, and potential ecological risk were similar. High Cd and Hg concentrations in both the mainstream and tributaries are a cause for much concern. However, sediment quality guidelines produced different results, as most previous studies adopted different sampling and measurement strategies. The data inconsistencies and lack of continuity regarding the reservoir confirm the need for a continuous monitoring network and the development of quality criteria relevant to the sediments of the TGR in the future.

Impact of upstream river inputs and reservoir operation on phosphorus fractions in water-particulate phases in the Three Gorges Reservoir

The impoundment of the Three Gorges Reservoir (TGR) has changed water-sand transport regime, with inevitable effects on phosphorus transport behavior in the TGR. In this study, we measured phosphorus fractions in water and suspended particles transported from upstream rivers of the TGR (the Yangtze River, the Jialing River and the Wu River) to reservoir inner region over the full operation schedule of the TGR. The aim was to determine how phosphorus fractions in water and particulate phases varied in response to natural hydrological processes and reservoir operations. The results showed that total phosphorus concentration (TP) in water in the TGR inner region was 0.17±0.05mg/L, which was lower than that in the Yangtze River (0.21±0.04mg/L) and the Wu River (0.23±0.03mg/L), but higher than that in the Jialing River (0.12±0.07mg/L). In the TGR inner region, there was no clear trend of total dissolved phosphorus (TDP), but total particulate phosphorus (TPP) showed a decreasing trend from tail area to head area because of particle deposition along the TGR mainstream. In addition, the concentrations of TPP in water and particulate phosphorus in a unit mass of suspended particles (PP) in the TGR inner region were higher in October 2014 and January 2015 (the impounding period and high water level period) than that in July 2015 (the low water level period). The temporal variations of PP and TPP concentrations in the TGR may be linked to the change of particle size distribution of suspended particles in the TGR. The particle size tended to be finer due to large-size particle deposition under stable hydrodynamic conditions in the process of TGR impoundment, resulting in high adsorption capacities of phosphorus in suspended particles. The results implied that phosphorus temporal variations in the TGR could exert different impacts on water quality in the TGR tributaries.