Three Gorges Reservoir Region Research Articles

Nutritional status of the reservoir tributary backwater area and implications for nutrient control

Understanding the spatial and temporal distribution and driving factors of the nutritional status in the backwater area of typical tributaries in the Three Gorges Reservoir Region (TGRR) is important for the prevention and control measures. In this study, the Environmental Fluid Dynamics Code (EFDC) was used to extend in situ monitoring data, followed by the application of hydrogen and oxygen isotope data and scoring methods to predict the nutritional status in the backwater area of the Daning River. The results indicated that the nutritional status-sensitive period mainly ranged from May-October and was distributed at the end of the backwater area and tributary bay. The water temperature and intermediate density flow were identified as the key factors inducing deterioration in the nutritional status at the end of the backwater area and tributary bay, respectively. Nutrient reduction in the mainstream and tributary areas significantly affected the nutritional status in the backwater area. Notably, hydrodynamic adjustment under reservoir objectives is indispensable for improving the water environment in tributary bay after reaching the water quality standard. Our findings highlight the necessity of focusing on the upper reaches of the tributaries and reservoir for nutrient control and emphasize the importance of combining reservoir operation strategies to mitigate the deterioration in the nutritional status.

Ecological Security Pattern based on XGBoost-MCR model: A case study of the Three Gorges Reservoir Region

The ecological resistance surfaces (ERS) are a critical component in constructing the Ecological Security Pattern (ESP) and reflects the ecological security level of a region. However, research on optimizing the construction of the ERS is limited. This study focuses on selecting 11 ecological resistance factors from two categories: natural conditions and human activities. Using the XGBoost (eXtreme Gradient Boosting) - MCR (Minimum Cumulative Resistance) algorithm, a comprehensive framework to analyze the ESP in the Three Gorges Reservoir Region (TGRR) is constructed. The results reveal the following key findings: (1) The ecological source areas in the TGRR decrease from northeast to southwest, covering a total area of approximately 12,400 km2, accounting for 21.57% of the total area. (2) The ecological corridors amount to 45, exhibiting spatial distribution patterns that vary across different regions. In the northeast, ecological corridors demonstrate a branching and radial distribution pattern, while in the southwest, they primarily extend along the edges of the study area. Corridors in the central region extend from west to east. (3) The ecological security assessment based on the XGBoost algorithm demonstrates high reliability, as the predicted results align well with the actual conditions in the TGRR. (4) The comprehensive framework of the ESP, based on the XGBoost-MCR model, allows for automatic optimization of algorithm parameters using known environmental samples. The study contributes scientific references to ecological environmental protection in the TGRR, while also offering valuable insights for optimizing ERS construction, ESP development, and integrating machine learning techniques in ecological security research.

Understanding the role of atmospheric deposition on the environmental load of per- and polyfluoroalkyl substances: A case study in Three Gorges Reservoir, China

Sixty-nine total suspended particle (TSP) samples, paired with forty-eight surface soil samples, covering four seasons from January 2021 to November 2021, were collected from the Three Gorges Reservoir Region (TGRR). Twenty per- and poly-fluoroalkyl substances (PFASs) were analyzed to evaluate their contamination characteristics and understand the role of atmospheric deposition on the environmental loads in TGRR. The annual average concentrations of PFASs in TSP and soil were 37.2 ± 1.22 pg·m−3 and 0.798 ± 0.134 ng·g−1, respectively. For TSP, concentrations were highest in spring and lowest in summer. For soil, it was in autumn and winter, respectively. The seasonality was more influenced by anthropogenic activities than by meteorological conditions or physicochemical parameters of the soil. Positive matrix fractionation (PMF) indicated that, based on annual averages, PFOA-based products (40.2 %) were the major sources of PFASs in TSP, followed by PFOS-based products (25.2 %) and precursor degradation (34.6 %). The highest source contributor for PFASs in spring was precursor degradation (40.9 %), while in other three seasons, it was PFOA-based products (39.9 %, 40.9 % and 52.0 %, respectively). The mean atmospheric dry and wet deposition fluxes of PFASs were estimated at 4.38 ng·m−2·day−1 and 23.5 ng·m−2·day−1, respectively. The contribution of atmospheric deposition to the inventory mass of PFASs in the surface soil was 22.3 %. These findings fill a gap in knowledge regarding the processes and mechanisms of the occurrence, sources and atmospheric deposition of PFASs in the TGRR.

Modeling Escherichia coli concentrations for health risk analysis in the Three Gorges Reservoir Region, Chongqing, China

Escherichia coli (E. coli), a typical fecal coliform, can enter surface rivers through daily wastewater and septic effluents, as well as the use of fecal fertilizers. Pathogenic strains of E. coli pose a significant public health risk. Despite China’s rapid economic and social development, sanitation and watershed management still face challenges. In this study, we employ a combined model of the Soil and Water Assessment Tool and Quantitative Microbial Risk Assessment to predict pollution changes, considering social development and climate change. Our aim is to quantify the risks and assess pollution prevention strategies for E. coli in the Three Gorges Reservoir (TGR) region. The results indicated that under moderate development, the average E. coli concentrations and disease burdens were 367 ± 75 CFU/100 mL and 23.4 (95 % Confidence Interval (CI): 2.8–72.6) Disability-Adjusted Life Years (DALYs, per 1,000,000 population per year), respectively. Under rapid development, these values were 330 ± 58 CFU/100 mL and 21.2 (95 % CI: 2.6–65.1) DALYs, respectively. Implementing a point strategy, mainly increasing sewage collection rates, could reduce E. coli concentrations by approximately 30 % and disease burdens by 27–28 %. For a diffuse strategy, primarily extending composting duration, reductions of 9 % in E. coli concentrations and 7–8 % in disease burdens were observed. Combining both strategies resulted in a 40 % decrease in E. coli concentrations and 35–36 % reduction in disease burdens. This model, incorporating social development, climate change, and microbial risk, provides insights into predicting pollution changes and evaluating the effectiveness of prevention strategies for E. coli in the TGR region and similar watersheds.

Trade-offs between grain supply and soil conservation in the Grain for Green Program under changing climate: A case study in the Three Gorges Reservoir region

Understanding the trade-offs between ecological benefits and cost of grain supply caused by ecosystem restoration is essential for decision-making. Nevertheless, due to climate change, the benefits of ecosystem restoration and cost of grain supply change across various spatial locations, thereby complicating the trade-offs. Taking one of China's largest scale ecosystem restorations, the Grain for Green Program (GGP), as an example, this study used the Three Gorges Reservoir (TGR) region as the case study area and combined the crop environment resource synthesis (CERES)-Crop model, future land-use simulation (FLUS), and the revised universal soil loss equation (RUSLE) to simulate future grain supply and soil erosion during 2021–2050 under three climate change and socioeconomic development scenarios (SSP1-2.6, SSP2-4.5, SSP5-8.5) in the TGR region. The results showed that: (1) Until 2050, the implementation of GGP would bring a large soil conservation benefit by reducing soil erosion of 2.47–5.68 million tons, at the cost of 130,277–660,279 tons decrease in grain production in the TGR region. (2) Under SSP5-8.5 climate change scenario with the highest rainfall in the future, the GGP would maintain the greatest soil conservation benefits, resulting in a total amount of soil erosion decrease by 2.55 to 5.68 million tons. (3) Trade-offs between benefit of reducing soil erosion and cost of grain supply vary considerably across income. Specifically, GGP benefits are greater under low-income and higher-emission scenarios, with significant gains in soil erosion control and less impact on grain supply. In contrast, in high-income and low-emission scenarios, the GGP results in less soil erosion control and greater impact on grain supply.

Co-circulation of Hantavirus, Pathogenic Leptospira spp., and Bartonella spp. in Rodents in the Wanzhou Section of the Three Gorges Reservoir Region, 2021-2023.

Background: Rodent is a reservoir of various zoonotic pathogens. Wanzhou section of the Three Gorges reservoir region (TGRR) is a superior habitat for rodents, and the situation of rodent-borne zoonotic pathogens in this region has not been surveyed in recent years. Materials and Methods: Rodents were night trapped with mousecage or mousetrap in urban and surrounding towns' indoor or outdoor areas of the Wanzhou section of the TGRR, and nucleic acid was extracted from their lung or a mixture of liver, spleen, and kidney. Commercialized qPCR kits for pathogenic Leptospira spp., Rickettsia typhi, Anaplasma phagocytophilum, Bartonella spp., Orientia tsutsugamushi, and Francisella tularensis and qRT-PCR kits for hantavirus (HV), and severe fever with thrombocytopenia syndrome virus (SFTSV) were used for the detection of associated pathogens in collected rodents. Results: From 2021 to 2023, 604 rodents belonging to 10 species were collected. HV and pathogenic L. spp. were detected positive, with infection rates of 0.66% (4/604) and 1.32% (8/604), respectively. B. spp. were detected positive with an infection rate of 4.73% (19/402) in the rodents trapped in 2022 and 2023. Other five pathogens were all detected negative. Conclusion: This study showed that the Wanzhou section of the TGRR had HV, pathogenic L. spp., and B. spp. co-circulation in rodents. Hence, more attention should be paid to the prevention and control of associated rodent-borne diseases.

A comparative evaluation of clustering methods and data sampling techniques in the prediction of reservoir landslide deformation state

ABSTRACT Landslides exhibiting step-wise deformation characteristics are extensively dispersed throughout the Three Gorges Reservoir (TGR) region of China. Predicting the deformation state of landslides in TGR holds paramount significance in landslide early warning and risk management. Machine learning-based landslide deformation state prediction is a combination of clustering and imbalanced classification. This paper compares the efficacy of three prevalent clustering methods, namely K-means, Density-Based Spatial Clustering of Applications with Noise (DBSCAN), and Gaussian Mixture Model (GMM), in the clustering analysis process. Furthermore, the paper evaluates the performance of three widely-used data sampling technologies, namely Synthetic Minority Oversampling Technique (SMOTE), SMOTE-Edited Nearest Neighbors (SMOTE-ENN), and ADAptive SYNthetic Sampling (ADASYN), in the imbalanced classification process. The Baijiabao and Bazimen landslides in the TGR region, which exhibit step-wise deformation characteristics, are used as case studies. Results indicate that DBSCAN and GMM exhibit significant advantages in the clustering process. Meanwhile, the mixture models that integrate oversampling technologies and classification algorithms perform exceptionally well in imbalanced classification. The aforementioned algorithms are recommended for predicting the deformation states of step-wise landslides in the TGR region. The machine learning-based predictive models can serve as potent instruments in facilitating the implementation of early warning systems aimed at mitigating landslide risks.

Impacts of environmental and socioeconomic factors on gross ecosystem product of the Three Gorges reservoir area, China

AbstractEnvironmental and socioeconomic drivers would alter landscapes, bringing various effects with different directions and magnitudes. Demonstrating these driving effects is key to relieving the conflicts between territorial vegetation restoration and regional economic growth. However, the relationship between ecological protection and economic development due to landscape dynamics has not been systematically demonstrated as environment is difficult to quantify by the monetary value. In this article, we explored the changes in gross ecosystem product (GEP) in the Three Gorges (TG) reservoir area and constructed a conceptual framework to explicate its driving mechanism. Our results suggested that topographic, soil, and climatic factors positively impact on GEP through their important effects on vegetation structure, distribution, and succession. Additionally, reforestation policies promote the conversion of farmland and grassland to forestland in the TG reservoir region, which was the main contributor to enhancing GEP. Conversely, socioeconomic factors negatively impact GEP, of which effects were mainly manifested by changes in the proportion of ecological land. Therefore, it is essential to maintain a suitable land use proportion in this region to optimize GEP, and we proposed a landscape restoration program to enhance four ecosystem productions. This article provides a reference for land resource allocation for environmental protection and sustainable development in ecologically fragile areas.

Patterns and drivers of plant carbon, nitrogen, and phosphorus stoichiometry in a novel riparian ecosystem.

Carbon (C), nitrogen (N), and phosphorus (P) stoichiometry serve as valuable indices for plant nutrient utilization and biogeochemical cycling within ecosystems. However, the allocation of these nutrients among different plant organs and the underlying drivers in dynamic riparian ecosystems remain inadequately understood. In this study, we gathered plant samples from diverse life forms (annuals and perennials) and organs (leaves, stems, and roots) in the riparian zone of the Three Gorges Reservoir Region (TGRR) in China-a novel ecosystem subject to winter flooding. We used random forest analysis and structural equation modeling to find out how flooding, life forms, plant communities, and soil variables affect organs C, N, and P levels. Results showed that the mean concentrations of plant C, N, and P in the riparian zone of the TGRR were 386.65, 19.31, and 5.27 mg/g for leaves respectively, 404.02, 11.23, and 4.81 mg/g for stems respectively, and 388.22, 9.32, and 3.27 mg/g for roots respectively. The C:N, C:P and N:P ratios were 16.15, 191.7 and 5.56 for leaves respectively; 26.98, 273.72 and 4.6 for stems respectively; and 16.63, 223.06 and 4.77 for roots respectively. Riparian plants exhibited nitrogen limitation, with weak carbon sequestration, low nutrient utilization efficiency, and a high capacity for nutrient uptake. Plant C:N:P stoichiometry was significantly different across life forms and organs, with higher N and P concentrations in leaves than stems and roots, and higher in annuals than perennials. While flooding stress triggered distinct responses in the C, N, and P concentrations among annual and perennial plants, they maintained similar stoichiometric ratios along flooding gradients. Furthermore, our investigation identified soil properties and life forms as more influential factors than plant communities in shaping variations in C:N:P stoichiometry in organs. Flooding indirectly impacts plant C:N:P stoichiometry primarily through alterations in plant community composition and soil factors. This study underscores the potential for hydrologic changes to influence plant community composition and soil nutrient dynamics, and further alter plant ecological strategies and biogeochemical cycling in riparian ecosystems.

A regional-level spatiotemporal perspective of land use and land cover change impact on forest aboveground biomass in three gorges reservoir region, China

This study used multi-platform remote sensing datasets to assess the impacts of land use and land cover (LULC) change on forest biomass density across the Three Gorges Reservoir (TGR) region along the Yangtze River. This study maps land use and land cover (LULC) change and forest aboveground biomass estimation (AGB) using Sentinel-2A and GEDI-L4B data based on observations between 2019 and 2022. The data analysis results of monitoring revealed a strong association frequency between land-use change and forest land cover since the significant relationship with forest aboveground biomass density has also been explored. The total deforestation decreased significantly in 2022. The accuracy assessment results show a classification accuracy of between 90.4% and 94.1%, with a kappa coefficient of 82.4%–92.1%. For the TGR region forest, the minimum to maximum mean above-ground biomass values are from 15.81 to 373.66 Mgha-1, respectively. Moreover, the fitting performance of the statistical analysis of aboveground biomass density of forest mean for the forest was quite decent with training (R 2: 0.92, RMSE: 12.30 Mg/ha) and testing (R 2: 0.79, RMSE: 18.07 Mg/ha) datasets. The results highlight LULC change impacts, particularly forest land class over forest AGB stands, and the effectiveness of the GEDI-L4B product in regional biomass estimation in the TGR region.

Hysteresis effect and seasonal step-like creep deformation of the Jiuxianping landslide in the Three Gorges Reservoir region

Slow-moving landslides are common in the Three Gorges reservoir (TGR) region. It may evolve into massive landslide hazards due to reservoir level fluctuation and rainfall. The assessment of slow-moving reservoir landslides is critical for the prevention and control of geological hazards. A step-like deformation mechanism for slow-moving landslides is proposed. Here, we use various wavelet tools to process the time series of 16 years continuous monitoring surface displacement of the Jiuxianping landslide at TGR. Then, the methods are used to investigate the correlation and hysteresis between the trigger factors (rainfall and reservoir level fluctuation) and reservoir landslide creep displacement. Owing to the influence of reservoir level fluctuation and rainfall, the triggering factors of displacement in different regions differ and show prominent hysteresis characteristics. Furthermore, the contribution of GPS monitoring points and InSAR fusion technology to creep landslide assessment is discussed, which can effectively reduce the possibility false alarms in landslide prediction. These mechanisms can be used to explain why some sliding bodies can keep stable after very large and long-time deformation. Therefore, these results are crucial for effective and reasonable geological hazard prevention and control in the TGR region.

Organic Carbon Controls Mercury Distribution and Storage in the Surface Soils of the Water-Level-Fluctuation Zone in the Three Gorges Reservoir Region, China.

The particular condition of the water-level-fluctuation zone (WLFZ) in the Three Gorges Reservoir (TGR), the largest hydroelectric reservoir in China, raises great concerns about mercury (Hg) contamination and ecological risk. In addition, previous research found that soil organic carbon (SOC) plays an essential role in controlling Hg distribution and speciation. However, there is minimal information on the Hg storage distribution and their relationships with SOC in the WLFZ in TGR. This study investigated Hg distribution, storage, and their relationships with SOC in the surface soils in WLFZ. The results showed that the total Hg (THg) content in the surface soils ranged from 18.40 to 218.50 ng g-1, with an average value of 78.17 ± 41.92 ng g-1. About 89% of samples had THg content above the background value in Chongqing, showing specific enrichment of Hg in WLFZ due to contamination in the TGR. The surface soils have low SOC, with an average value of 8.10 ± 3.90 g kg-1. Moreover, THg content showed consistent distribution with the SOC in WLFZ, with a significantly positive correlation (R = 0.52, p < 0.01, n = 242). THg storage (201.82 ± 103.46 g ha-1) in the surface soils was also significantly positively correlated with the SOC storage (R = 0.47, p < 0.01, n = 242). The reduced SOC sequestration, due to the periodical alternative "flooding-draining" and frequent reclamation and utilization of WLFZ, decreased the Hg adsorption in soil. Those might result in the re-release of Hg into waters when WLFZ is flooded. Therefore, more attention should be directed towards Hg cycling and the consequent environmental risks in the TGR region.

The development characteristics and mechanisms of the Xigou debris flow in the Three Gorges Reservoir Region

Debris flow is a common geological hazard in mountainous areas of China, often causing secondary disasters and seriously threatening residents and infrastructure. This paper uses the Xigou debris flow in the Three Gorges Reservoir Region (TGRR) as an example case study, the development characteristics and initiation pattern of which were analyzed based on field investigation. The disaster dynamics software DAN-W was then used to simulate the entire initiation-movement-accumulation process of the debris flow and conduct the debris flow dynamics analysis. The paper also simulated and predicted the movements of landslides in the formation area of a debris flow after its initiation. The results show that the movement duration of the Xigou debris flow was approximately 40 s, the maximum velocity was 37.1 m/s, the maximum thickness of the accumulation was 18.7 m, and the farthest movement distance was 930 m, which are consistent with the field investigation. When the volumes of landslide transformed into a new source material of debris flow are 5 × 104, 10 × 104, 15 × 104, 20 × 104, and 26 × 104 m3, the movement distances of the debris flows are 250, 280, 300, 340, and 375 m, respectively. When the volume of the source material exceeds 20 × 104 m3, debris flow movement can seriously impact the residential houses at the entrance of the gully. This paper can provide a scientific basis for the prevention and mitigation of the Xigou debris flow.

Vertical niche differentiation of comammox Nitrospira in water-level fluctuation zone of the Three Gorges Reservoir, China

Comammox (CMX) Nitrospira bacteria (NB) can accomplish ammonia oxidation independently, and their niche differentiation holds promise for their ecological and survival functions. In this work, the vertical niche differentiation of CMX NB was investigated in the soils of 6 water-level fluctuation (WLF) zones (both natural and artificial) in the Three Gorges Reservoir (TGR) region. The results demonstrated that the level of clade A amoA was obviously reduced with increasing soil depth in the natural WLF zones and one of the artificial WLF zones. However, in the other two artificial WLF zones, the abundance of this gene was not dramatically reduced with depth. The level of clade B amoA did not markedly decrease with increasing soil depth in most WLF zones and remained stable in the three WLF zones. Total nitrogen (TN) had the most significant effect on the abundance of CMX NB. Clade A.1, clade A.2.1, clade A.2.2, clade A.3, and clade B of CMX NB co-occurred simultaneously in all WLF zones. The number of operational taxonomic units (OTUs) of clade A in the two types of WLF zones first increased and then decreased with increasing depth, whereas the number of OTUs of clade B continuously increased with depth in the artificial WLF zone. Total carbon (TC) and pH, as environmental factors, affected the community structure of CMX NB. This study confirmed the vertical differentiation of the abundance and diversity of CMX NB in the WLF zones of the TGR region, and the artificial restoration of the WLF zones affected the niche differentiation of CMX NB to a certain degree.

Soil erosion rates on sloping cropland fragment underlain by contrasting lithologies

This study examines the pattern of soil erosion rates in a cropland fragment underlain by limestone and purple sandstone (referred to as the CLP) in the Three Gorges Reservoir Region (TGRR) using the 137Cs and 210Pbex techniques. A total of 96 bulk cores and 18 sectioned cores were collected from the CLP. In addition, 4 bulk and 4 sectioned cores were extracted from each of two reference sites. Based on the 137Cs and 210Pbex inventories obtained from these cores, the soil erosion rates were assessed. The results indicate that the 137Cs and 210Pbex inventories both increase downslope, while the calculated soil erosion rates both decrease. This implies that the intensity of soil erosion decreases downslope, which is a combined response to the effect of gravity, the short slope length, and the gentle gradient of the cropland. The soil erosion rates derived from 137Cs were generally higher than those determined using 210Pbex. This shows that soil erosion was more intense from 1954 onward than during the period between 1920 and 1954, reflecting the impact of disturbance by cultivation, which has increased rapidly over the past 60 years. The soil erosion rate on the limestone area was similar to that in the purple sandstone area, but higher than that reported from karst regions experiencing rocky desertification. This suggests that, providing that there is no evidence of karst rocky desertification, the soil erosion intensity in cropland underlain by limestone is similar to that underlain by purple sandstone. This result provides a new insight into the pattern of soil erosion intensity on the cultivated hillslopes of karst and non-karst regions at the scale of the cropland fragment. It will also help to improve our understanding of surface processes in karst and non-karst areas subject to intense cultivation.

Effects of overconsolidation on the reactivated residual strength of remoulded deep-seated sliding zone soil in the Three Gorges Reservoir Region, China

Due to the landslide-prone geological conditions, many landslides have occurred in the Three Gorges Reservoir Region (TGRR), most of which are slow-moving ancient landslides characterized by preexisting shear surfaces. In this study, with the purpose of making full use of reactivated residual strength to prevent and treat the slow-moving landslides, such as designing anti-slide piles, the Huangtupo landslide as a typical reactivated ancient landslide in the TGRR was selected to study the overconsolidation (OCR) effect on the reactivated residual strength of deep-seated sliding zone soil by conducting a series of laboratory ring shear tests. It was found that after a short rest of one day, the reactivated residual strength increased with the increase of OCR under a given normal effective stress, but it was lost after a small shear displacement. The overconsolidation effect on reactivated residual strength at a lower stress was more prominent than that at a higher stress. Very coarse sand with a size of 1–2 mm inside the remoulded deep-seated sliding zone soil sample exerts direct control on the reactivated residual strength, and it significantly influences the overconsolidation effect on reactivated residual strength. The results could provide a reliable scientific basis for improving the stability analysis and reinforcement measures of the slow-moving landslides in the TGRR, as well as can be applied to similar slow-moving landslides in other areas.

Heavy metals in the water-level-fluctuation zone soil of the three Gorges Reservoir, China: Remobilization and catchment-wide transportation

• Selective HMs remobilization was observed in WLFZ soils. • Catchment-wide flood promotes the transport of HMs from the WLFZ soil into the TGR. • Erosion, runoff, and leaching released 36.61 Gg of HMs in soils in 2020. • Runoff-induced labile metals accounted for approximately 10% of fluxes in the TGR. • WLFZ soils act as a potential source of HMs in the TGR. Water-level-fluctuation zone (WLFZ) is a sensitive zone influencing the transformation between sink to source for heavy metals (HMs), which suffers from cyclic inundation and exposure during different hydrological regimes. To better understand the geochemical cycling of HMs in the WLFZ, we performed temporal analysis and transport quantification of HMs in the world’s largest freshwater WLFZ: Three Gorges Reservoir (TGR), China. From 2002 to 2020, HM contents in WLFZ soils fluctuated and gradually stabilized. In 2020, selective remobilization of HMs was observed, which were mainly influenced by four environmental factors: Fe and Mn oxides, soil pH, dissolved organic carbon, and soil mobility-resupply ability. Multiple models were developed to quantify the HM fluxes in 2019 and 2020 induced by soil erosion, runoff, and leaching. In 2020, HMs liberated in the TGR region catchment increased from 13.35 (2019) to 36.61 gigagram (Gg), including 6.90 Gg of non-residual fraction and 1.34 Gg of labile metals. Otherwise, metal fluxes of WLFZ soils into the TGR increased 1.96 times, which were attributed to integrated factors, including the increase of runoff, soil erosion, sediment load, and remobilization of HMs resulting from the catchment-wide flood in 2020. In particular, the runoff-induced labile metals only accounted for ∼ 10% of HM fluxes entering the TGR. We inferred that catchment-wide flood was an important control on HM transport in terrestrial and aquatic systems of the TGR region catchment. This study makes a novel contribution to the understanding of the transformation between sink to source of the WLFZ, and for targeted management of its ecological and environmental impact.

Land-Use Transformation and Landscape Ecological Risk Assessment in the Three Gorges Reservoir Region Based on the “Production–Living–Ecological Space” Perspective

Rapid urbanization and land-use change cause risk in regional ecological security. It is very significance to explore the evolutionary trend of land-use change and landscape ecological risk (LER) in an ecologically fragile area, especially in terms of maintaining sustainable development in a regional ecological environment. We selected the Three Gorges Reservoir Region (TGRR) as the study area based on land-use and land-cover data for 2000, 2010, and 2020. The land-use classification system used here was constructed using the perspective of the production–living–ecological space (PLES). The GIS spatial-analysis technique and FRAGSTATS 4 software were used. We used the method of the land-use transfer matrix, the landscape ecological risk assessment model, the ecological contribution rate of land-use transfer, and spatial autocorrelation analysis. We performed quantitative analysis of the spatio-temporal pattern of PLES and its LER in the TGRR over the past 20 years. The results show that: (1) The area of human living space (HLS) has expanded significantly—by 1469.37 km2 (+326.66%), while the area of agricultural production space (APS) has been compressed by both the urban/rural living space (URLS) and the forestland ecological space (FES), particularly during the last 10 years; (2) The overall LER results were medium, but LER is increasing; (3) The LER in the northern area of the Yangtze River is higher than in the south. The Wanzhou district and the downstream areas had a lower LER; and (4) The transformation from agricultural production space to forestland ecological space and urban/rural living space has had a higher contribution rate to the LER compared to other events. These results can be used as a reference for land planning, sustainable development, and ecological civilization construction in ecologically fragile areas.

Distinct effects of sediment regulation on phytoplankton community assembly in the tributaries and mainstream of the Three Gorges Reservoir

Sediment regulation (SR) maintains the water storage capacity of the Three Gorges Reservoir (TGR), but the influences of SR on riverine phytoplankton communities, especially in the upper reservoir, have not yet been investigated. In this study, the first description of the membership of the phytoplankton community was provided, together with hydrodynamic and environmental factors before, during, and after implementation of SR in the TGR region was investigated. A total of 84 taxa of phytoplankton from 6 phyla were recorded during the three stages of SR. There were no significant impacts of SR on phytoplankton assemblages in the mainstream. But in the tributaries, the replacement components of beta diversity increased from 0.39 to 0.63, and the biomass reduced from 1.36 to 0.49 mg/L. Bray-Curtis distances revealed that phytoplankton community in the mainstream and tributaries became more similar after SR (PERMANOVA, p = 0.592). Based on the investigated environmental variables, stochastic processes play a vital role in structuring the phytoplankton community in the TGR region, although SR decreased the relative importance of stochastic processes for phytoplankton assembly in the tributaries. This study indicates that SR plays a critical role in accelerating turnover rates within phytoplankton communities in tributaries, which has important implications for preventing phytoplankton bloom, and more significantly, for maintaining river–reservoir system sustainable development.

Photosynthetic acclimation of riparian plant Distylium chinense to heterogeneous habitats

Distylium chinense is an evergreen dominant shrub with strong adaptability under heterogeneous habitats, including natural riparian zone (NRZ), anti-seasonal water level fluctuation zone (ASWLFZ), and no water level fluctuation zone (NWLFZ) in the Three Gorges Reservoir Region (TGRR) in China. In order to understand the photosynthetic ecological adaptability and habitat adaptation strategies of D. chinense under heterogeneous habitats, its photosynthesis and chlorophyll fluorescence parameters were investigated. The results showed that photosynthetic characteristics were significantly different among heterogeneous habitats (p<0.05). The PSII potential activity and PSII maximum photochemical efficiency (Fv/Fm) of D. chinense in the ASWLFZ were the highest among heterogeneous habitats. Non-photochemical quenching coefficient (qN) in the NWLFZ was higher than that in the NRZ and ASWLFZ (p<0.05). Stepwise regression analysis showed that water use efficiency and stomatal conductance were correlated with specific leaf area (SLA), leaf area and leaf dry weight. Regression curve fitting and canonical correspondence analysis revealed that light intensity, soil water content, air humidity and temperature were the main factors affecting photosynthetic characteristics and leaf functional traits. Our results evidenced that D. chinense adapted to the high water content and low light intensity environments, especially in the valley waterfall habitats, by increasing stomatal conductance and net photosynthetic rate, reducing SLA and maintaining moderate qN and Fv/Fm with adopting a profligate water use pattern to improve photosynthetic productivity. Therefore, D. chinense has a wide photosynthetic acclimation to different environments, which provided baseline information for the conservation and ecological restoration in the newly formed hydro-fluctuation zone and other similar degenerative riparian ecosystem.