Three Gorges Reservoir Region Research Articles

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.

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.

The 2014 Zigui Earthquake Sequence near the Three Gorges Dam in China

AbstractSeismicity in the Three Gorges Reservoir (TGR) region increased noticeably as the water level of the reservoir rises, since the Three Gorges Dam (TGD) was built in 2003. Here, we determined moment tensors of six earthquakes in the 2014 Zigui earthquake sequence (ZGS) in the TGR region using local and regional broadband seismic waveform data. We also determined the focal depth of the mainshock using its teleseismic waveform data and then relocated the epicenter using its travel times at local stations. High-precision locations of 64 events in the sequence were obtained by combining the double-difference relative location result and the mainshock’s absolute location. The event locations and moment tensor solutions indicate that the ZGS occurred between depth 5 and 9 km on a previously unknown fault striking southwest and dipping ∼80° to the northwest. The event depth distribution and coulomb stress change estimation suggest that the ZGS were not induced directly by the reservoir water but triggered by the stress change from the annual reservoir water level variation. We estimated that the newly found fault has the potential for a magnitude 5.7 earthquake for which ground motion has a 16% probability to exceed the designed maximum intensity level at the TGD, though it would take more than 100 yr to accumulate the needed amount of slip.

Does agro-ecological efficiency contribute to poverty alleviation? An empirical study based on panel data regression.

Worldwide degradation of the ecological environment could be the cause of poverty. The poverty-stricken areas may face the dilemma of a "vicious circle of poverty." The complex ecological conditions have intertwined with poverty alleviation, which makes the demand for ecological poverty alleviation particularly prominent in these areas. However, the research on the relationship between agro-ecological efficiency and poverty are limited. It is far from clear what is the impact of the agro-ecological efficiency on poverty. To explore the impact of agro-ecological efficiency on poverty reduction, we adopt the panel data model based on cross-correlation and regression coefficient, using the data from 25 counties/districts in the Three Gorges Reservoir Region (TGRR) from 2006 to 2017. The results show that (1) there is significant heterogeneity in agro-ecological efficiency in the TGRR, and the agro-ecological efficiency in the middle area is significantly lower than that of the head and tail areas of the TGRR; (2) the improvement of regional agro-ecological efficiency could accelerate the alleviation of poverty; and (3) the widening of urban-rural income disparity is not conducive to poverty alleviation and eradication. This study would provide basis for further policy recommendations aimed at improving agro-ecological efficiency and alleviating poverty.

A County-Scale Spillover Ecological Value Compensation Standard of Ecological Barrier Area in China: Based on an Extended Emergy Analysis

Ecological compensation (EC) is an important way to solve the imbalance of cross-regional economic development and realize regional coordinated development. How to quantify the standard of EC has become a hot research topic. Firstly, this paper selected the Three Gorges Reservoir Region (TGRR) as the study area, and constructed a cross-regional spillover ecological value measurement model based on the extended emergy analysis. From the perspective of the “ecology–economy–society” complex ecosystem, this paper used emergy to reflect the social, economic, and ecological function and service value of the TGRR, and estimated the ecosystem emergy supply and consumption in the TGRR. Then, comparing the watershed ecosystem emergy supply and consumption, we can judge the status of the ecological surplus and deficit of the TGRR, and transfer the spillover ecological emergy to spillover ecological value (SEV) by using the emergy currency ratio (ECR). Finally, combined with different actual payment level coefficient, we can obtain a relatively objective and robust compensation standard. The results show that the SEV of the TGRR in 2016 is 2.70 × 1011 USD, which indicates that the TGRR is in the state of ecological surplus. The TGRR should get EC about 2.85 × 1011 USD according to the ECR. Based on the research results, it is suggested to expand the transfer payment to the TGRR. At the same time, it is suggested to formulate different ecological compensation standard (ECS) according to regional differences, which has important practical significance to establish the allocation standard of EC, and provides a typical case basis for other large reservoir areas or typical reservoir areas.

Variation of Hourly Extreme Precipitation in the Three Gorges Reservoir Region, China, from the Observation Record

Extreme hourly precipitation is amongst the most prominent driving factors of flash floods and geological disasters. Based on the hourly precipitation data of 35 stations in the Three Gorges Reservoir Region (TGRR) from 1998 to 2020, we analyzed the spatiotemporal variation characteristics of hourly extreme precipitation indexes. The selected indicators included the frequency, intensity, period, annual maximum, trend of hourly heavy precipitation (20–50 mm/h) and hourly extreme heavy precipitation (≥50 mm/h) in the TGRR. Closely related climatic factors such as the Western Pacific Subtropical High Intensity (WPSHI) were also discussed. The results showed that in 2010–2020, the cumulative frequency of heavy precipitation magnitude between 25 and 40 mm/h slightly increased, while the corresponding frequency for magnitudes ≥50 mm/h decreased. In summer, the frequency of both heavy and extreme heavy precipitation increased in June and decreased in August, indicating a shift of extreme events to an earlier time in the flood season. The cumulative frequency of heavy precipitation in July had a period of about 7a, and that of extreme heavy precipitation had a period of 3a. The annual average intensity of heavy precipitation and extreme heavy precipitation in the TGRR was 28.9 mm/h and 61.4 mm/h per station, respectively, and both fluctuated and insignificantly decreased from 1998 to 2020. The annual maximum hourly precipitation center in the TGRR moved downstream from west to northeast. The frequency of heavy precipitation was relatively small along the main stream of the river valley. Both the frequency and total amount of heavy precipitation in southeast of the TGRR were significantly higher than those in other regions. Heavy precipitation in the majority of stations with high elevation (higher than 500 m) showed a decreasing trend. The cumulative frequency of precipitation with an intensity of 20–50 mm/h was closely correlated with the Western Hemisphere Warm Pool (WHWP) Index in February and the WPSHI Index in January, and especially, the abnormal large annual frequency (top 20%) showed strong correlation with the two indexes, implying highly predictable factors for extreme events. The frequency of precipitation intensity above 50 mm/h was correlated with the Western Pacific Warm Pool (WPWP) Area Index in January and the WPWP Intensity Index in November of last year. The research results provide a strong and refined factual basis for the assessment and prediction of extreme precipitation, and for disaster prevention and mitigation, in the TGRR.

Biosafety assessment of Acinetobacter strains isolated from the Three Gorges Reservoir region in nematode Caenorhabditis elegans

Acinetobacter has been frequently detected in backwater areas of the Three Gorges Reservoir (TGR) region. We here employed Caenorhabditis elegans to perform biosafety assessment of Acinetobacter strains isolated from backwater area in the TGR region. Among 21 isolates and 5 reference strains of Acinetobacter, exposure to Acinetobacter strains of AC1, AC15, AC18, AC21, A. baumannii ATCC 19606T, A. junii NH88-14, and A. lwoffii DSM 2403T resulted in significant decrease in locomotion behavior and reduction in lifespan of Caenorhabditis elegans. In nematodes, exposure to Acinetobacter strains of AC1, AC15, AC18, AC21, A. baumannii, A. junii and A. lwoffii also resulted in significant reactive oxygen species (ROS) production. Moreover, exposure to Acinetobacter isolates of AC1, AC15, AC18, and AC21 led to significant increase in expressions of both SOD-3::GFP and some antimicrobial genes (lys-1, spp-12, lys-7, dod-6, spp-1, dod-22, lys-8, and/or F55G11.4) in nematodes. The Acinetobacter isolates of AC1, AC15, AC18, and AC21 had different morphological, biochemical, phylogenetical, and virulence gene properties. Our results suggested that exposure risk of some Acinetobacter strains isolated from the TGR region exists for environmental organisms and human health. In addition, C. elegans is useful to assess biosafety of Acinetobacter isolates from the environment.

Responses of Ecological Stoichiometric Characteristics of Carbon, Nitrogen, and Phosphorus to Periodic Submergence in Mega-Reservoir: Growth of Taxodium distichum and Taxodium ascendens.

Ecological stoichiometric studies can be useful for managing the deteriorated riparian zones of mega-reservoirs in which nutrients significantly impact the balanced vegetation cover. The present study aims to explore the effects of periodic submergence on the stoichiometric ecological characteristics of carbon (C), nitrogen (N), and phosphorus (P), as well as the growth conditions of two leading conifer species (Taxodium distichum and Taxodium ascendens) in the hydro-fluctuation zone of the Three Gorges Reservoir (TGR) region, China. The stoichiometrical contents of C, N, and P in fine roots, leaves, and branches, and the growth conditions of T. distichum and T. ascendens were measured in July 2019. The results showed that periodic submergence affected the stoichiometric characteristics and growth conditions of these two woody species, and the impact was restrained, but both grew well. The effects of inundation on the C, N, and P ecological stoichiometric characteristics differed in different parts of trees. In general, the C contents showed the following pattern: leaves > branches > fine roots. The N and P content showed the following pattern: leaves > fine roots > branches, while the C/N and C/P ratios showed an opposite trend to that of N and P. The N and P content in all parts of T. distichum (with means of 17.18 and 1.70 g/kg for leaves, 4.80 and 0.57 g/kg for branches, and 6.88 and 1.10 g/kg for fine roots, respectively) and T. ascendens (with means of 14.56 and 1.87 g/kg for leaves, 5.03 and 0.63 g/kg for branches, and 8.17 and 1.66 g/kg for fine roots, respectively) were higher than the national average level (with means of 14.14 and 1.11 g/kg for leaves, 3.04 and 0.31 g/kg for branches, and 4.85 and 0.47 g/kg for fine roots, respectively). Except for N and P contents in the leaves of T. distichum, there was a significant correlation between N and P elements in other parts (p < 0.05). Nevertheless, the N/P ratio (10.15, 8.52, 6.44, and 7.93, 8.12, 5.20 in leaves, branches, and fine roots of T. distichum and T. ascendens, respectively) was lower than the critical ratio of 14. The growth conditions of T. distichum and T. ascendens were significantly negatively correlated with their leaf C contents and significantly positively correlated with their fine root N and P contents. This study showed that T. distichum and T. ascendens could maintain their normal growth needs by properly allocating nutrients between different organs to adapt to the long periodic submergence in the hydro-fluctuation zone of the TGR region.