Hydro-fluctuation Belt Research Articles

Response of plants and soils to inundation duration and construction of the plant‒soil association mode in the hydro‒fluctuation belt of the reservoir wetland

Hydro-Fluctuation Belt (HFB), a periodically exposed bank area formed by changes in water level fluctuations, is critical for damaging the reservoir wetland landscape and ecological balance. Thus, it is important to explore the mechanism of hydrological conditions on the plant-soil system of the HFB for protection of the reservoir wetland and landscape restoration. Here, we investigated the response of plant community characteristics and soil environment of the HFB of Tonghui River National Wetland Park (China), is a typical reservoir wetland, to the duration of inundation, as well as the correlation between the distribution of dominant plants and soil pH, nutrient contents, and enzyme activity by linear regression and canonical correlation analyses. The results show that as the duration of inundation decreases, the vegetation within the HFB is successional from annual or biennial herbs to perennial herbs and shrubs, with dominant plant species prominent and uneven distribution of species. Soil nutrient contents and enzyme activities of HFB decreased with increasing inundation duration. Dominant species of HFB plant community are related to soil environment, with water content, pH, urease, and available potassium being principle soil environmental factors affecting their distribution. When HFB was inundated for 0–30 days, soil pH was strongly acidic, with available potassium content above 150 mg kg−1 and higher urease activity, distributed with Arundo donax L., Polygonum perfoliatum L., Alternanthera philoxeroides (Mart.) Griseb., and Daucus carota L. communities. When inundated for 30–80 days, soil pH was acidic, with lower available potassium content (50–150 mg kg−1) and urease activity, distributed with Beckmannia syzigachne (Steud.) Fern.+ Polygonum lapathifolium L., Polygonum lapathifolium L., Medicago lupulina L. + Dysphania ambrosioides L. and Leptochloa panicea (Retz.) Ohwi communities. Using the constructed HFB plant-soil correlation model, changes in the wetland soil environment can be quickly judged by the succession of plant dominant species, which provides a simpler method for the monitoring of the soil environment in the reservoir wetland, and is of great significance for the scientific management and reasonable protection of the reservoir-type wetland ecosystem.

A photographic method to identify reservoir geohazards induced by rock mass deterioration of hydro-fluctuation belt

Potential geohazards triggered by the rock mass deterioration (RMD) of the hydro-fluctuation belt (HFB) in the Three Gorges Reservoir area (TGRA) severely threaten the lives and property of people, it is necessary and urgent to timely identify this kind of potential geohazard. Aiming at this issue, several typical evolution modes of potential RMD-induced geohazards were generalized, and an unmanned aerial vehicle (UAV) photographic method integrating the orthophotography, three-dimensional multi-angle oblique photography and high-precision digital elevation model (DEM) was proposed to early recognize the newly formed potential RMD-induced geohazards. By resolving the problem of poor precision in the orthophotographic images of high steep bank slopes, the proposed method improved the recognition reliability of potential reservoir geohazards in the HFBs. Taking the bank slopes from Zigui County to Badong County as the study area, 116 new potential RMD-induced geohazard sites were identified by the presented approach, including 64 and 52 sites on the left and right bank, respectively. Through field verifications, 17 and 19 sites on the left and right bank were found to be consistent with existing hazards, indicating the effectiveness of the proposed approach in avoiding the false and missing recognitions of potential RMD-induced reservoir geohazards at current levels of knowledge and technology. The study can provide a valuable reference for the early identification of RMD-induced geohazards in reservoir areas.

Network of Soil Fungi and the Microfauna Community under Diverse Anthropic Disturbances under Chrysopogon zizanioides Planting in the Reservoir

The reservoir coastal zone is the transitional zone between the terrestrial ecosystem and the aquatic ecosystem. Soil is an essential part of the terrestrial ecosystem and vital for life on Earth. To understand the composition and diversity of the soil eukaryotic microbial community under the background of artificial planting of Chrysopogon zizanioides in various habitats after reservoir construction, including the original habitat (OH), the hydro-fluctuation belt (HB), and the road slope (RS), and to analyze the interaction between the main groups of eukaryotic microorganisms, this study conducted 18S rDNA amplification high-throughput sequencing of the soil eukaryotic microbial community. The study found that the dominant phylum of eukaryotic microorganisms in the three habitats was consistent, but there were significant differences in the community and diversity of eukaryotic microorganisms in the three habitats. The differences in fungal communities between sample sites were greater than those of soil microfauna. Correlation analysis showed that nitrogen, phosphorus, and organic matter were significantly correlated with eukaryotic microbial diversity, with alkaline-hydrolyzed nitrogen and total phosphorus significantly correlated with fungal communities and pH and water content correlated with soil microfauna. Co-occurrence network analysis found that the interactions between fungi and the correlation between fungi and soil microfauna dominated the eukaryotic microbial community, and the interactions between eukaryotic microbes in different habitats were dominated by positive correlations. After the construction of the reservoir, the newly formed hydro-fluctuation belt reduced the types of interrelationships between fungi and microfauna compared to the original habitat. The road slope provided protection of the supporting project for the reservoir construction, although there was also planted vegetation. Eukaryotic microbes declined significantly due to the damage to and loss of the organic layer, and the decline in microfauna was the most significant, resulting in a simple structure of the soil food web, which affects the function and stability of the soil ecosystem.

Dissolution feature differences of carbonate rock within hydro-fluctuation belt located in the Three Gorges Reservoir Area

The stability of geological environment in the Three Gorges Reservoir Area (TGRA) has experienced severe challenges due to the 30 m hydro-fluctuation belt (HFB). The vertical dissolution features vary with the mechanism of water and rock interaction. Although dissolution features have been adequately explained by physical and mechanical parameters, the characterization of chemical changes in dissolution is vital but frequently neglected information. For this purpose, the hyperspectral characteristics and mineralogical composition variation of rock HFB in different areas of the Triassic Daye Formation are tested to elucidate the dissolution behaviors. Then, the deterioration degree of dissolution is quantified by a multi-objective data integration based on Random Forest Regression (RFR) model. The spatial distribution of dissolution and the seasonal deterioration characteristics are identified depending on the spectral response of carbonate. Specifically, the dissolution degree is proportional to elevation, and inverse to the bedding angle at 0–40° in the investigated stratum. Combined with the hydrological characteristics of study area, the corresponding regional phenomena can be distinguished as reservoir water dominated, rainfall dominated, and coupled action. Affected by reservoir water and acid rainfall, the HFB may deteriorate most severely from January to April. In addition, the contribution of RFR model integrated spectral and geometric data to the deterioration evaluation of the HFB is discussed, which can effectively enhance the identification of rock mass boundary in a single spectral data model. Thus, these results are conducive to the rapid evaluation of regional geomorphological characteristics and the monitoring of geological disasters in the TGRA.

Dynamic damage evolution of bank slopes with serrated structural planes considering the deteriorated rock mass and frequent reservoir-induced earthquakes

To investigate the dynamic damage evolution characteristics of bank slopes with serrated structural planes, the shaking table model test and the numerical simulation were utilized. The main findings indicate that under continuous seismic loads, the deformation of the bank slope increased, particularly around the hydro-fluctuation belt, accompanying by the pore water pressure rising. The soil pressure increased and then decreased showed dynamic variation characteristics. As the undulation angle of the serrated structural planes increased (30°, 45°, and 60°), the failure modes were climbing, climbing-gnawing, and gnawing respectively. The first-order natural frequency was used to calculate the damage degree (Dd) of the bank slope. During microseisms and small earthquakes, it was discovered that the evolution of Dd followed the “S” shape, which was fitted by a logic function. Additionally, the quadratic function was used to fit the Dd during moderately strong earthquakes. Through the numerical simulation, the variation characteristics of safety factors (Sf) for slopes with serrated structural planes and slopes with straight structural planes were compared. Under continuous seismic loads, the Sf of slopes with straight structural planes reduce stalely, whereas the Sf for slopes with serrated structural planes was greater than the former and the reduction rate was increasing.

Experimental Study on the Triaxial Compression Properties of Coarse-Grained Filling Soil under Drying–Wetting Cycles

To explore the mechanical properties of coarse-grained filling soil in the hydrofluctuation belt of the Baihetan reservoir, a fast drying–wetting cycle method for large-scale triaxial tests was developed and a series of large-scale triaxial compression tests of coarse-grained soil were conducted under drying–wetting cycles. The results show that the drying–wetting cycles and the confining pressure are both important factors affecting the mechanical properties of coarse-grained soil. The influences of the first and second cycles on the deviatoric stress–strain curve of the coarse-grained soil are the greatest, while the influences of the third to seventh cycles tend to be stable. The peak strain is not affected by the drying–wetting cycles but only increases with increasing confining pressure. The axial strain and volumetric strain at the volume expansion point decrease with increasing number of drying–wetting cycles but increase with increasing confining pressure. The secant modulus of the peak point decreases with increasing number of drying–wetting cycles, and the initial tangent modulus decreases slightly. The influence of the drying–wetting cycles on the cohesion of the coarse-grained soil is greater than that on the internal friction angle. The typical “bulging” phenomenon occurred after the specimens were destroyed. A damage constitutive equation was developed by introducing a damage variable into the hyperbolic model to reflect the influence of the number of drying–wetting cycles. The model parameters were obtained and the proposed model was verified by fitting the experimental results.

Border polje soil in Southwest China originated from non-karst areas: Evidence from geochemical fingerprint data

The purpose of this study was to provide scientific evidence to inform decisions on sediment mitigation strategies. A sediment fingerprinting approach was applied to identify soil sources for a border polje (BP) between karst (K) and non-karst (NK) areas in Southwest China. Three composite geochemical fingerprints, composed of basic, conservative, and high variability fingerprints, were used to quantify source contributions from two original groups (geology and land use), and three new classifications (two-, three-, and four-clusters) obtained using the k-means cluster analysis. The bi-plot, range test, tracer variation rate, and virtual mixture were used to test the reliability of each model configuration. The five classifications enabled the identification of > 85.7 % of the source samples. The two-cluster classification was consistent with the geology; the three-cluster divided the K into slope and depression, and the four-cluster further partitioned the NK into hydro-fluctuation belt of reservoirs (HFLRs) and highlands. The goodness of fit for these models was generally > 75 % and uncertainties were < 7.1 %. The HFLRs contributed > 90 % of soil parent material in the BP. The contribution of HL to the dry land near the NK in the BP was lower than that of HFLRs. Depressions contributed more than half to the dry land near the foothills of the limestone in the BP rim, followed by HFLRs. These findings highlight that the fluviatile sediments from NK areas significantly contribute to the BP. Hence, the identification of soil sources in the BP requires an evaluation from the perspective of hydrology, geology, and anthropogenic activities.

Endophytic Klebsiella aerogenes HGG15 stimulates mulberry growth in hydro-fluctuation belt and the potential mechanisms as revealed by microbiome and metabolomics.

Growth promotion and stress tolerance induced by endophytes have been observed in various plants, but their effects on mulberry regularly suffering flood in the hydro-fluctuation belt are less understood. In the present study, endophytic Klebsiella aerogenes HGG15 was screened out from 28 plant growth promotion (PGP) bacteria as having superior PGP traits in vitro and in planta as well as biosafety for silkworms. K. aerogenes HGG15 could actively colonize into roots of mulberry and subsequently transferred to stems and leaves. The 16S ribosomal RNA (V3–V4 variable regions) amplicon sequencing revealed that exogenous application of K. aerogenes HGG15 altered the bacterial community structures of mulberry roots and stems. Moreover, the genus of Klebsiella was particularly enriched in inoculated mulberry roots and was positively correlated with mulberry development and soil potassium content. Untargeted metabolic profiles uncovered 201 differentially abundant metabolites (DEMs) between inoculated and control mulberry, with lipids and organo-heterocyclic compounds being particularly abundant DEMs. In addition, a high abundance of abiotic stress response factors and promotion growth stimulators such as glycerolipid, sphingolipid, indole, pyridine, and coumarin were observed in inoculated mulberry. Collectively, the knowledge gained from this study sheds light on potential strategies to enhance mulberry growth in hydro-fluctuation belt, and microbiome and metabolite analyses provide new insights into the growth promotion mechanisms used by plant-associated bacteria.

Investigation on the dynamic cumulative damage mechanism and stability of bedding rock slope under the deterioration of rock mass in the hydro-fluctuation belt

Investigation on the dynamic cumulative damage mechanism and stability of bedding rock slope under the deterioration of rock mass in the hydro-fluctuation belt

Nutrient Inputs Alleviate Negative Effects of Early and Subsequent Flooding on Growth of Polygonum hydropiper With the Aid of Adventitious Roots.

Riparian plants are exposed to harmful stress induced by flooding, which is often accompanied by eutrophication in the Three Gorges Reservoir Region. The phenomenon is mainly caused by domestic sewage discharges, slow water flow, and agricultural fertilizer pollution. Simulating abiotic stress, such as flooding at the initial period, can act as a signal and induce positive responses of plants to subsequent severe stress. In addition, eutrophication supplies nutrients, provides a favorable environment in the early stages of plant, and facilitates good performance in later development. However, whether early flooding (with or without eutrophication) acts as positive cue or as stress on plants at different developmental stages remains unclear. To address this question, seeds of Polygonum hydropiper were collected from low and high elevations in the hydro-fluctuation belt of the Three Gorges Reservoir Region. Plants germinated from these seeds were subjected to shallower and shorter early flooding treatments with or without eutrophication. Subsequently, plants were subjected to deeper and longer flooding treatments with or without eutrophication. Early flooding and eutrophic flooding significantly induced generation of adventitious roots, suggesting morphological adaptation to flooding. Although early flooding and eutrophic flooding treatments did not increase plant biomass in subsequent treatments compared with control, stem length, length and width of the 1st fully expanded leaf, and biomass of plants in the early eutrophic treatment were higher than these of the early flooding treatment plants. These results suggest a negative lag-effect of early flooding, and also indicate that nutrient inputs can alleviate such effects. Similarly, subsequent eutrophic flooding also enhanced plant growth compared with subsequent flooding, showing significantly higher values of leaf traits and adventitious root number. Plants originated from low elevation had significantly higher functional leaf length and stem biomass compared with those from high elevation. These results suggest that nutrient inputs can alleviate negative effects of early and subsequent flooding on growth of P. hydropiper with the generation of adventitious roots.

Dynamic stability assessment of reservoir colluvial landslide using a hypoplastic clay constitutive model considering the effects of drying-wetting cycles on the hydro-fluctuation belt

The hydro-fluctuation belt of reservoir landslides undergoes repeated drying-wetting (D–W) cycles due to the annual fluctuation of water level in the Three Gorges Reservoir Area. Mechanical properties of the hydro-fluctuation belt subjected to D-W cycles should be considered for the evolution of landslide stability affected by seasonal rainfall and periodic reservoir water fluctuations. In addition, a reliable constitutive model essential for evaluating landslide stability should be employed to describe the mechanical property of soil. In this study, taking the Tangjiao landslide as an example, a series of drained triaxial and oedometer tests were conducted to study the effects of D-W cycles on the shearing and compression behaviors of the sliding mass soil. Then, the time-varying parameters of a hypoplastic clay constitutive model were calibrated based on the soil experiments under different D-W cycles. Eventually, the hydro-mechanical coupled simulation analyses were performed to study long-term deformations of the landslide front part influenced by actual rainfall and reservoir water fluctuations. Moreover, the evolution of landslide stability was analyzed using the vector-sum method based on stress fields with different time steps. The test results show that the D-W cycle significantly affects the mechanical property of soil. The hypoplastic model predicts well the shearing and compression behaviors of soil under different D-W cycles. The numerical results indicate that the soil weakening in the hydro-fluctuation belt increases the deformation magnitude of the toe slope and gradually decreases the landslide stability. This study provides some references for the dynamic stability assessment and long-term hydro-mechanical simulation of reservoir landslides.

Role of Rhizospheric Bacillus megaterium HGS7 in Maintaining Mulberry Growth Under Extremely Abiotic Stress in Hydro-Fluctuation Belt of Three Gorges Reservoir.

Plant growth-promoting rhizobacteria have been shown to play important roles in maintaining host fitness under periods of abiotic stress, and yet their effect on mulberry trees which regularly suffer drought after flooding in the hydro-fluctuation belt of the Three Gorges Reservoir Region in China remains largely uncharacterized. In the present study, 74 bacterial isolates were obtained from the rhizosphere soil of mulberry after drought stress, including 12 phosphate-solubilizing and 10 indole-3-acetic-acid-producing isolates. Bacillus megaterium HGS7 was selected for further study due to the abundance of traits that might benefit plants. Genomic analysis revealed that strain HGS7 possessed multiple genes that contributed to plant growth promotion, stress tolerance enhancement, and antimicrobial compound production. B. megaterium HGS7 consistently exhibited antagonistic activity against phytopathogens and strong tolerance to abiotic stress in vitro. Moreover, this strain stimulated mulberry seed germination and seedling growth. It may also induce the production of proline and antioxidant enzymes in mulberry trees to enhance drought tolerance and accelerate growth recovery after drought stress. The knowledge of the interactions between rhizobacteria HGS7 and its host plant might provide a potential strategy to enhance the drought tolerance of mulberry trees in a hydro-fluctuation belt.

Catchment-wide flooding significantly altered microplastics organization in the hydro-fluctuation belt of the reservoir

SummaryHydro-fluctuation belt (HFB) is the most sensitive area of a large reservoir. This research aimed to identify the impact of catastrophic flooding on the local microplastics organization in the HFB soil of the Three Gorges Reservoir, the largest reservoir in China. We found that the catchment-wide flooding efficiently alleviated the local microplastics abundance from 7,633 to 4,875 items/kg (from 44 to 18 mg/kg) but added to the pollution risk in the reservoir body. After flooding, the overall size distribution of local microplastics was minimally altered. Interestingly, the preferential retention of the small-sized polyethylene was found in HFB after flooding. Approximately 5.0×1014 items (∼2,360 tons) of microplastics were evacuated into the reservoir, equivalent to 15.8 wt% of the plastic flux of the Yangtze River into the ocean. We observed that HFB is a significant source of local microplastics in reservoir, and the long-term source–sink transformation mechanism in the HFB should be further investigated.

Effects of Drying-Flooding Alternation on Sediment–Water Nitrogen Fluxes in Hydro-fluctuation Belt of the Danjiangkou Reservoir

Effects of Drying-Flooding Alternation on Sediment–Water Nitrogen Fluxes in Hydro-fluctuation Belt of the Danjiangkou Reservoir

Effect of weakening of sliding zone soils in hydro-fluctuation belt on long-term reliability of reservoir landslides

The impoundment of the Three Gorges Reservoir in China inevitably caused the reservoir landslides to develop toward instability, which has attracted widespread attention. Taking the Huangtupo Riverside Slump 1# with the structural characteristics of double sliding zones as a case, this study focuses on the sliding zone soils in the hydro-fluctuation belt affected by the periodic fluctuations of reservoir water level. The wetting-drying cycles test is carried out to simulate the cyclic impact of the fluctuations on the sliding zone soils. Hence the weakening law of the strength parameters is illustrated and well characterized by an exponential function model. Considering the different number of wetting-drying cycles, the long-term reliability of the shallow and deep sliding surfaces is quantified via the imbalance thrust force method and reliability theory. The results indicate that the local failure probability of both sliding surfaces gradually rises as the number of wetting-drying cycles increases. In particular, the shallow sliding surface presents a greater local failure probability than that of the deep one since more slices are in the hydro-fluctuation belt. Besides, the sensitivity of the landslide response to the strength parameters is different, and the internal friction angle is much greater than the cohesion. The area of the hydro-fluctuation belt plays a significant role on the long-term reliability of the landslide, which should be closely monitored to guide the reservoir operation.

外源激素处理对三峡消落带落羽杉扦插生根的影响

为优选落羽杉大龄母树插穗的扦插繁殖技术，以期培育大量的落羽杉良种壮苗满足三峡消落带植被修复的需要，采用正交试验设计，探究不同外源激素、浓度以及处理时间对三峡消落带落羽杉大龄母树插穗扦插生根的影响，运用隶属函数法对各处理生根情况进行综合评价。结果表明：（1）落羽杉插穗皮部和愈伤组织处均有不定根伸出，两处不定根数量分别占不定根总数的63.9%和36.1%；（2）4种外源激素中，吲哚丁酸（IBA）+萘乙酸（NAA）（等质量比）和IBA处理的插穗生根效果最好，NAA处理次之，生根粉（ABT）处理效果最差；（3）5种浓度（50 mg/L、100 mg/L、150 mg/L、200 mg/L和250 mg/L）之间的处理效果无显著差异；（4）4种处理时间（2 h、4 h、6 h和8 h）中，4 h处理的插穗生根效果最佳；（5）26个处理组合中，（IBA+NAA）×150 mg/L×4 h处理组合和NAA×250 mg/L×4 h处理组合的平均隶属函数值最高，分别为0.83和0.82，清水对照的平均隶属函数值最低，为0.05。研究初步验证了皮部生根是落羽杉大龄母树插穗的主要生根方式，筛选出三峡消落带原位适生落羽杉大龄母树插穗扦插的两种较佳处理组合为（IBA+NAA）×150 mg/L×4 h和NAA×250 mg/L×4 h。;To optimize the cutting propagation technology of the Taxodium distichum for cultivating a large number of T. distichum seedlings to meet the needs of vegetation restoration in the fluctuating zone of the Three Gorges Reservoir, an orthogonal experiment design was used to explore the effects of different exogenous hormones, concentrations and treatment time on rooting of cuttings of elder T. distichum in the hydro-fluctuation belt of the Three Gorges Reservoir. Besides, the subordination function was used to comprehensively evaluate the rooting condition of the cuttings. Results showed that:(1) The number of adventitious roots protruding from the bark and the callus accounted for 63.9% and 36.1% of the total number of adventitious roots, respectively; (2) Among these 4 exogenous hormones, IBA+NAA (mass ratio 1:1) and IBA (Indolebutyric acid) had the best effectiveness, followed by NAA (Naphthalene acetic acid), and ABT rooting powder was the poorest; (3) There was no significant difference in facilitating rooting of the cuttings among the five concentrations (50 mg/L, 100 mg/L, 150 mg/L, 200 mg/L and 250 mg/L); (4) Among these 4 treatment times (2 h, 4 h, 6 h and 8 h), the treatment time of 4 h had the best effectiveness; (5) Among these 26 treatment combinations, (IBA+NAA)×150 mg/L×4 h and NAA×250 mg/L×4 h had the highest average subordinate function value of 0.83 and 0.82, respectively; and the control group had the lowest average subordinate function value of 0.05. In this study, it was preliminarily verified that bark rooting was the main way of rooting of the cuttings from elder T. distichum, and (IBA+NAA)×150 mg/L×4 h and NAA×250 mg/L×4 h were suitable treatments for cutting propagation of elder T. distichum in the hydro-fluctuation belt of the Three Gorges Reservoir.

A novel model for regional susceptibility mapping of rainfall-reservoir induced landslides in Jurassic slide-prone strata of western Hubei Province, Three Gorges Reservoir area

Jurassic facility-sliding strata have been identified as a fundamental factor affecting the occurrence of rainfall-reservoir induced landslides in western Hubei Province, China Three Gorges Reservoir area. Regional landslide susceptibility mapping is the most effective method for landslide prediction and mitigation. To solve the current problem of identifying the true landslides and non-landslides, a novel hybrid model based on the two steps self-organizing mapping-random forest (two steps SOM-RF) algorithm is proposed. The identified high and very high susceptibility zones are located within the hydro-fluctuation belt and regions with low altitude based on the datasets before 2014. Deviation and variance of other ten datasets are generated to evaluate the reliability of the maps for the problem of unbalanced sample sizes. Two typical landslides occurred in 2017 have been found in the very high susceptibility zone, which emphasized the validity of susceptibility mapping. To verify the effectiveness of selecting true landslides and non-landslides based on two steps SOM model, recorded landslides and non-landslides randomly chosen from landslide-free areas are put into the single RF model for comparison. The receiver operating characteristic curve and Accuracy index are applied to compare the performance of the landslide susceptibility maps created based on two steps SOM-RF and the single RF model. The results demonstrate that the consideration of true landslides and non-landslides is effective in producing a more accurate landslide susceptibility map with superior prediction skill and higher reliability.

Distribution and source of microplastics in China's second largest reservoir - Danjiangkou Reservoir

Fresh water microplastic pollution is of pressing concern globally, but its distribution and sources in reservoirs are poorly documented. Danjiangkou Reservoir is the second largest reservoir in China and is divided into the Han Reservoir and Dan Reservoir. In this work, microplastic abundances and morphological characteristics of the reservoir were investigated. The microplastic abundance of 15 main tributaries of the reservoir was also measured. The vertical distribution (in water column and sediment), horizontal distribution (in Han Reservoir and Dan Reservoir) and source of microplastics were analyzed. Microplastics accumulated in the middle layer of the reservoir, and the size and color of the microplastic particles changed from the surface to the bottom, which implies that surveys of surface water are not enough to determine the microplastic contamination for deep water reservoirs. In the surface water, the microplastic abundance in the Han Reservoir was lower than that in the Dan Reservoir (p < 0.05), but microplastic abundance did not differ significantly in the intermediate and bottom water. Tributaries were one of the main sources of microplastics for Han Reservoir but not for Dan Reservoir. Agricultural cultivation in the hydro-fluctuation belt might be an important source of microplastics in the Dan Reservoir, which should be given additional attention. The results of this study can provide valuable information for developing microplastic sampling strategies in deep water reservoirs. Further studies are recommended to investigate the process through which microplastics in the hydro-fluctuation belt enter the reservoir and the sinking behavior of microplastics in the reservoir.

The impact of the endophytic bacterial community on mulberry tree growth in the Three Gorges Reservoir ecosystem, China.

Plant-associated microbes influence plant performance and may also impact biotic and abiotic stress tolerance. The microbiome of mulberry trees planted for ecological restoration in the hydro-fluctuation belt of the Three Gorges Reservoir Region, China, exhibited distinct patterns of localization. The endosphere exhibited lower α-diversity relative to the rhizosphere, but was more closely related to host growth status, especially in stem tissues. Pantoea was the predominant bacterial genus inhabiting the stems of two well-growing plants, while sequences identified as Pseudomonas and Pantoea were abundant in poorly growing plants. The complexity of the endophytic community was more connected to growth status in well-growing plants than it was in poorly growing plants. Among 151 endophytes cultured from collected samples of mulberry, 64 exhibited plant growth-promoting (PGP) potential in vitro and the majority of beneficial taxa were harvested from well-growing plants. Collectively, the present study indicates that the recruitment of beneficial endophytes may contribute to mulberry fitness under abiotic stress, and it provides a foundation for the development of a new strategy in vegetation restoration.

Soil erosion calculation in the hydro-fluctuation belt by adding water erosivity factor in the USLE model

Soils in the hydro-fluctuation belts of the reservoirs are most highly influenced by the special hydro-conditions and reservoir operation, leading to unique soil erosion process and largely accelerate soil erosion intensity. The present study aimed to estimate soil erosion rate in the hydro-fluctuation belt of the Pubugou Reservoir, Southwest China, based on the framework of Universal Soil Loss Equation (USLE). An attempt has been made to modify the original USLE by including the reservoir water erosivity (W), a new factor into the model. Soil erosion rate from different land use types were quantitatively estimated, using the USLE and the modified USLE respectively. Field observation showed that soil erosion rate in dry farmland, bare land and grassland was 4700, 44600 and 5050 t/km2, respectively. The erosion rate assessed by the modified USLE was closely related to that recorded from the field monitoring data. The findings of this study clearly highlight the importance of inclusion of the W factor to the original USLE model while assessing soil erosion in the reservoir hydro-fluctuation belt.