Water Level Fluctuation Zone Research Articles

Rhizosphere microbial community structure in the water-level-fluctuation zone under distinct waterlogging stresses

Rhizosphere microbial communities are believed to be vital in the adaption of dominant plants to strong waterlogging stress in the water-level-fluctuation zone (WLFZ). However, limited knowledge is available on their patterns in the WLFZ under distinct waterlogging stresses. Here, rhizosphere and non-rhizosphere bacterial and fungal communities derived from two typical dominant plants (Rumex acetosa L. and Oxybasis glauca) in the WLFZ of Three Gorges Reservoir, China were analysed through high-throughput sequencing. A total of 63 phyla, 173 classes, 259 orders, 287 families and 518 genera of bacteria, as well as 15 phyla, 50 classes, 124 orders, 265 families and 652 genera of fungi were detected in soils with different waterlogging stress intensities. The most dominant bacterial and fungal phyla in each sample are Proteobacteria and Ascomycota, respectively. Bacteria and fungi in soil may increase their microbial ɑ diversity under the intensity of waterlogging stress to cope with this stress. LEfSe analysis showed that the impact of waterlogging stress on fungal community structure in soil is more prominent than that on bacteria. Key fungal biomarkers can be found in each soil sample, but in many samples, key bacterial biomarkers cannot be found. The metabolic pathways related to aerobic respiration type I and de novo biosynthesis of adenosine ribonucleotides dominate in the microbial community. Redundancy analysis revealed that the structure of rhizosphere microbial communities in different plants is significantly influenced by environmental factors. This study provides a theoretical basis for understanding the relationship between plants and their second genome (rhizosphere microorganisms) in extreme habitats, such as the WLFZ of large reservoirs.

Rare bacterial taxa drive the ecosystem multifunctionality in lake water-level-fluctuating zone during seasonal water level fluctuations

Complex microbial community plays a crucial role in driving soil ecosystem multifunctionality. Water-level-fluctuating zone (WLFZ) of lakes serves as vital transitional areas between land and water, exhibiting crucial ecological functions. However, the relationship between soil moisture-sensitive bacterial communities and ecosystem multifunctionality remains poorly understood. In this study, we conducted a two-year seasonal field survey in the WLFZ of one large flooding lake. By using amplicon sequencing, we explored the changing characteristics of soil bacterial communities during water level fluctuations and their driving role in ecosystem multifunctionality. A simultaneous decrease in soil bacterial diversity and ecosystem multifunctionality was observed as the soil transitioned from drought to flooding states. Soil bacterial diversity was positively correlated with ecosystem multifunctionality, and rare bacterial sub-communities showed a higher correlation with multifunctionality than the overall bacterial community. Random forest regression analysis demonstrated that rare bacterial sub-communities were the optimal predictor variable for ecosystem multifunctionality in the WLFZ. Additionally, Actinobacteriota and Methylomirabilota held significance in predicting multifunctionality under drought and flooding states, respectively. This study highlighted the predominant role of soil rare bacterial sub-communities in driving ecosystem functionality in the WLFZ.

Seasonal wet–dry transition and denitrifying communities contributed to nitrous oxide emissions in the water-level fluctuating zone of the largest freshwater lake in China

The water-level fluctuating zone (WLFZ) is the alternating dry/wet zone in freshwater lakes, and plays a crucial role in nitrogen (N) biogeochemical cycling and nitrous oxide (N2O) emissions. However, N2O emission fluxes, the underlying microbial mechanisms, and their feedbacks to global warming in the extensive WLFZ of the freshwater lakes with dramatic water-level variations remain unclear. Here, we sampled through both wet and dry seasons and compared the N removal rates, N2O emission fluxes, composition and co-occurrence network properties of the denitrifying microbial communities of the WLFZ, continuously flooded, and non-flooded zones covered with the dominant plant (Carex. cinerascens) in Poyang Lake, the largest freshwater lake of China. We observed higher potential denitrification (1.129–5.657 nmol N g-1h−1) and anammox (0.047–0.756 nmol N g-1h−1) rates in the WLFZ for both wet and dry seasons than those in the other two zones. A large seasonal N2O sink-source transition (−2.297 and 0.297 μg m-2h−1 for wet and dry season, respectively) was observed in WLFZ. Moreover, the composition of nirK and nirS communities significantly varied in WLFZ between the wet and dry seasons. Especially, several keystone taxa (e.g., Mesorhizobium and Rhodanobacter) were enriched in the WLFZ and were responsible for denitrification and N2O emissions under drought stress in the dry season. Variations in denitrification rates and N2O fluxes were driven by pH, C and N substrates, as well as the co-occurrence network properties, including natural connectivity and small-world coefficients of the nirK and nirS communities. Our results suggested that WLFZ in freshwater lakes under future climate change scenarios would be a substantial N2O source and aggravate climate, which would result in the positive feedback.

Differential insights into the distribution characteristics of archaeal communities and their response to typical pollutants in the sediments and soils of deep-water reservoir

This study focused on the Fengshuba deep-water reservoir in South China, and systematically explored the distribution characteristics of archaeal communities in the sediment and soil in water level fluctuation zones and their response mechanisms to typical pollutants. The results show that Euryarchaeota and Bathyarchaeota are the dominant phyla in sediment archaeal communities, while Thaumarchaeota dominates in soil. The absolute abundance of archaea in the sediments was lower than that in the soils, but the diversity and richness of archaeal communities were higher than those in the soils. Seasonal changes affected the composition of sediment archaeal communities, and the archaeal compositions in the two habitats also showed significant differences. The neutral community model indicates that the assembly of archaeal communities in sediments is mainly governed by stochastic processes, while deterministic processes dominate in soils. The responses of archaeal communities to pollutants in the two habitats were significantly different. Among them, the carbon-nitrogen ratio and tetracycline concentration are the key factors driving seasonal changes in the archaeal communities in the sediment. Structural equation modeling further showed that the archaeal community in the sediment was positively correlated with organochlorine pesticides and antibiotics, while the archaeal community in the soil showed an opposite trend. This study provides new insights into the complexity of interactions between archaeal communities and typical contaminants in reservoir systems.

Effects of wet-dry alternation on organic phosphorus dynamics and sediment characteristics in the intertidal zone of Nansi Lake

The study of the fractions and distribution characteristics of organic phosphorus in the sediment of the water level fluctuating zone of Nansi Lake is conducive to revealing the transformation of phosphorus in the lake, and has important scientific significance for controlling the eutrophication of Nansi Lake. Based on the sediment of the water level fluctuation zone of Nansi Lake. The improved Hedley continuous grading extraction, ultraviolet-visible spectroscopy and three-dimensional fluorescence spectroscope were used to characterize the structural characteristics and stability of organic molecules in the sediment, and to reflect the differences in the structure and stability of organophosphate in the water level fluctuating zone. Principal component analysis (PCA), Redundancy analysis (RDA) and correlation heat map analysis were used to analyze the correlation between phosphorus and physicochemical index. The results showed that the alternation between wet-dry conditions was more favorable for the release of phosphorus from sediment, compared to continuous inundation conditions. Moreover, the higher the frequency of wet-dry alternations, the greater the release of phosphorus in different forms from the sediment. Wet-dry alternation resulted in a reduction of substituent on the aromatic rings of sediment DOM (dissolved organic matter), and the continuous drying would increase the molecular weight and humidification degree of DOM in the sediment. Correlation analysis showed that NaOH-Po content in sediment was significantly negatively correlated with TP, IP, OP and various organophosphorus forms, indicating a close transformation relationship between phosphorus forms in sediment. The results can provide a scientific basis for controlling the release of endogenous phosphorus and the risk of eutrophication in Nansi Lake.

Assessment of the Divergent Influence of Natural and Non-Seasonal Hydrological Fluctuations on Functional Traits and Niche Characteristics of Plant Guilds along the Xiangxi River, China

The reservoir water level fluctuation zones (RWLFZs) and the natural riparian zones (NRZs) are two riparian ecosystems with dramatically opposite hydrological rhythms that notably influence the plant guilds. However, little is known about the discrepancies of the functional traits and niche characteristics of plant guilds in the RWLFZs and NRZs under different flooding rhythms. The aims of this study were to assess the divergent influence of natural and non-seasonal hydrological fluctuations on functional traits and niche characteristics of plant guilds. The results showed that 78 vascular plant species were identified in the riparian zones of the Xiangxi River basin. The dominant species were annuals in the two riparian ecosystems and their percentage increased temporally from 65.79% in the NRZs to 67.34% in the RWLFZs. Compared with the NRZs, the specific leaf area, vegetation coverage and the aboveground biomass in the RWLFZs significantly increased by 74%, 27% and 19.6%, respectively, while the water-use efficiency of the RWLFZ decreased by 59.6% and there was no significant difference in the net photosynthetic rate between them, which showed that annuals in the RWLFZs adopted the R adaptation strategy of being fast-growing with a short lifespan and quickly acquiring and investing resources by altering leaf morphology, including expanding the leaf area. The Simpson dominance index of RWLFZs was significantly higher than that of NRZ. Thus, counter-seasonally hydrological alterations had significant effects on functional traits of dominant species in the RWFLZs. Moreover, the highly adaptable and widely distributed species with larger niche breadths and high important values usually had a higher niche overlap value in the RWLFZs than in the NRZs, which showed that the competition in the plant communities after experiencing anti-seasonal flooding was much more intraspecific than interspecific and would facilitate the expansion of species niches. Our findings imply that the species with large niche breadths and high important values should be prioritized in ecological restoration efforts in the newly formed hydro-fluctuation zones of the TGR.

Influence of anti-seasonal inundation on geochemical processes of arsenic speciation in the water-level-fluctuation zone soil of the Three Gorges Reservoir, China

Since the completion of Three Gorges Dam, the water-level-fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR) experiences the periodic anti-seasonal inundation. However, knowledge for mechanisms of mobilization and transformation of arsenic (As) in WLFZ soils of the TGR remains scarce. To address this gap, a combination of field observation and simulated flooding experiments attempts to illustrate the As mobilization, the transformation between As(V) and As(III), and the factors driving these processes. The study revealed that anti-seasonal inundation (with a temperature at 13 ℃) mitigated As release from submerged soils. Interestingly, the total As and ratio of As(III) (the more toxic form of As) concentrations in porewater at 13 ℃ was lower, and the prevalence of As(III) occurred later than those at 32 °C (imitate the seasonal inundation condition). The results indicated that the As reduction and the corresponding toxic risks in submerged soils were alleviated under anti-seasonal inundation. The study proposes the reduction of As-bearing manganese (Mn) mineral assemblages and competitive adsorption of dissolved organic carbon (DOC) as primary mechanisms for As mobilization. Furthermore, microorganism-mediated detoxification/reduction processes involving DOC, nitrogen, and Mn (oxyhydr)oxides were identified as central pathways for As(III) enrichment under anti-seasonal inundation. This study enhances understandings of the biogeochemical processes and fate of As in WLFZ soils influenced by artificial regulation of the reservoir.

Optimization and Assessment of Carbon Sink in the Water Level Fluctuation Zone in the Three Gorges Reservoir Area Adapted to Water Level Changes

Optimization and Assessment of Carbon Sink in the Water Level Fluctuation Zone in the Three Gorges Reservoir Area Adapted to Water Level Changes

Functional Segregation of Resource Utilization Strategies between Invasive and Native Plants and Invasion Mechanisms in the Water Level Fluctuation Zone: A Case Study of Pengxi River in Three Gorges Reservoir, China

The ecosystem of the water level fluctuation (WLF) zone of the Three Gorges Reservoir (TGR) is highly vulnerable and sensitive due to its unique cyclical flooding and drought conditions. The ecological impact of biological invasion in this area is particularly severe, making it crucial to study the differences in resource utilization strategies between invasive plants (IPs) and native plants (NPs) using functional traits to explore the mechanisms of invasion. We selected the WLF zone of Pengxi River in the TGR area and conducted a multi-scale study along the elevation gradient. The results reveal that at the regional scale, IPs have a larger height and specific leaf area, smaller leaf tissue density, and specific root length compared to NPs, showing a preference for enhancing aboveground resource acquisition over leaf defense capabilities. They allocate more tissue construction resources to their roots to withstand environmental pressures, which may be the key to their successful intrusion, highlighting the role of niche differentiation. On the community scale, the H and SLA of IPs and NPs are positively correlated with elevation, while the LTD of IPs shows a negative correlation. At elevations of 175 m and below, IP and NP exhibit functional convergence, while above 175 m, functional divergence was observed. This indicates that although the different resource utilization strategies are crucial for successful IP invasion, the environmental filtering from periodic floods and drought pressures play a significant role in community assembly in the WLF zone, allowing IP to integrate into habitats with similar functional characteristics already inhabited by NP and establish their own communities.

Magnetic properties of sediments within the water-level fluctuation zone of the Three Gorges Reservoir and their response to provenance and hydrodynamic conditions

Magnetic properties of sediments within the water-level fluctuation zone of the Three Gorges Reservoir and their response to provenance and hydrodynamic conditions

UAV-based modelling of vegetation recovery under extreme habitat stresses in the water level fluctuation zone of the Three Gorges Reservoir, China

Impoundment of the Three Gorges Reservoir on the upper Yangtze River has remarkably altered hydrological regime within the dammed reaches, triggering structural and functional changes of the riparian ecosystem. Up to date, how vegetation recovers in response to compound habitat stresses in the water level fluctuation zone remains inexplicitly understood. In this study, plant above-ground biomass (AGB) in a selected water level fluctuation zone was quantified to depict its spatial and temporal pattern using unmanned aerial vehicle (UAV)-derived multispectral images and screened empirical models. The contributions of multiple habitat stressors in governing vegetation recovery dynamics along the environmental gradient were further explored. Screened random forest models indicated relatively higher accuracy in AGB estimation, with R2 being 0.68, 0.79 and 0.62 during the sprouting, growth, and mature periods, respectively. AGB displayed a significant linear increasing trend along the elevational gradient during the sprouting and early growth period, while it showed an inverted U-shaped pattern during late growth and mature period. Flooding duration, magnitude and timing were found to exert greater negative effects on plant sprouting and biomass accumulation and acted as decisive factors in governing the elevation-dependent pattern of AGB. Localized spatial variations in AGB were modulated by other stressors such as sediment burial, soil erosion, soil moisture and nutrient content. Occurrence of episodic summer floods and vegetation distribution were responsible for an inverted U-shaped pattern of AGB during the late growth and mature period. Generally, AGB reached its peak in August, thereafter an obvious decline by an unprecedent dry-hot climatic event. The water level fluctuations with cumulative flooding effects exerted substantial control on AGB temporal dynamics, while climatic condition played a secondary role. Herein, further restorative efforts need to be directed to screening suitable species, maintaining favorable soil condition, and improving vegetation pattern to balance the many trade-offs.

Study on the Application of Water Resource Management Based on GF-7 Stereo Mapping Satellite

Abstract. GF-7 satellite was successfully launched on 3 Nov 2019. The two-line stereo camera can effectively obtain 20 km-width panchromatic stereo images with resolution better than 0.8m and 3.2m-resolution multispectral images. Through the composite mapping mode of stereo camera and laser altimeter, the satellite realizes 1:10,000-scale stereo mapping. This article selected the Qiafuqihai Reservoir and its upstream of the Yili River Basin as the study area. Hydrological landforms and vegetation coverage were monitored and three-dimensional dynamic simulation software was developed to verify the potential application of GF-7 stereo mapping satellite data in supporting drainage basin water resource allocation and management in future scenarios. 3 meters DSM derived from GF-7 surveying and mapping satellite finely portrayed the characteristics of hydroponic landforms of small watersheds. The upstream of Qiafuqihai was divided into eleven small watersheds. The water density was 8.5 times more than which was produced from STRM 90m. The elevation of the water-level fluctuation zone of the Qiafuqihai Reservoir ranged from 970 to 998 meters with the water area changed from 28.3 to 57.6 square kilometres. The terrain in the northwest and northeast was flat, with the main vegetation types being natural grasslands (64.9%) and arid lands (5.03%). The three-dimensional dynamic visualization software was developed and demonstrated hydrology information, vegetation coverage information and dynamic changes in the landform of the basin in three-dimensional environment. GF-7, the stereo surveying and mapping satellite, could be perfectly able to support the application of water resources deployment and management in the future.

Elevation-related variations of soil disintegration and its driving forces in the water level fluctuation zone of the Three Gorges Reservoir, China

Soil disintegration is a key process of the early stages of soil erosion. The water level fluctuation zone (WLFZ) in reservoirs undergoes seasonal changes involving periodic alternations in inundation and exposure that can affect soil disintegration. In this study, we conducted experiments on pre-wetted undisturbed soil samples obtained from different elevations ranging from 155 to 180 m a.s.l. and different soil depths (0–10 and 10–20 cm) in the WLFZ of the Three Gorges Reservoir (TGR), upper Yangtze River, China. We investigated how soil disintegration varies depending on elevation within the WLFZ and used principal component analysis (PCA) and stepwise regression to identify the dominant variables affecting soil disintegration. Results show the following: (1) The disintegration ratio, which is a measure of the amount of soil disintegration that occurs during experiments, varied in the range of 0.45 %–4.79 % over 60 min, with 79 %–100 % of the disintegration occurring within the first 30 min. The disintegration ratio increases with decreasing elevation in the WLFZ. Soil samples from a depth of 0–10 cm disintegrated 0.43 % less on average than those from a depth of 10–20 cm. The relationship between disintegration rate and elevation can be expressed using an exponential function with R2 > 0.80. (2) The main variables loading onto the first three principal components (explain 91.4 % of the variation in all variables) identified by PCA were those involving soil aggregates, the plant root system, and soil particle-size, respectively. (3) Stepwise regression identified >0.25 mm water-stable aggregate content (Ws0.25) and root mean diameter (Droot) as the strongest predictors of soil disintegration and yielded a linear regression equation with R2 = 0.88. Ws0.25 and Droot were the most influential variables on the elevation-dependent occurrence/degree of disintegration. Such information is essential for understanding the occurrence and prevention of bank erosion in reservoir areas.

Arsenic mobilization across the sediment-water interface of the Three Gorges Reservoir as a function of water depth using DGT and HR-Peepers, a preliminary study

The artificial regulation of the Three Gorges Reservoir (TGR) creates large water level fluctuation zones (WLFZ) that may change the behavior of metals and metalloid in sediment, particularly redox sensitive elements. Mobilization of As, Fe and Mn across the sediment-water interface (SWI) in the TGR as a function of different water depth (periodically and permanently submerged sediments, respectively) was in situ determined by diffusive gradients in thin films (DGT) and high-resolution dialysis technique (HR-Peeper), respectively. The results showed that the mobilization of As was significantly affected by Fe/Mn especially Mn, across the SWI. Duo to the oxic-anoxic transitional state in near bottom water, the reduced Fe and Mn in sediment pore water could be oxidized and precipitated again, leading to the co-precipitation of As with Fe/Mn oxides (hydroxides). Consequently, concentrations of As, Fe and Mn in labile phases and pore water were generally low across the SWI, then they sharply increased at a few centimeters below the SWI. Considering different water depth, various trends were found in labile phase, whereas concentrations of As, Fe and Mn in pore water in permanently submerged sediments were significantly higher than those in periodically submerged sediments. The dry-re-wetting alternation processes in the WLFZ may play vital roles in the resupply capacity of sediments as it was found that periodically submerged sediments with longer re-wetting time had higher Fe/Mn resupply capacity than those with shorter re-wetting times and permanently submerged sediments.

Evaluating the influence of Cynodon dactylon on the wave force and wave erosion in the water-level fluctuation zone of the Three Gorges Reservoir Area

Wave erosion is the main erosion type in the water-level fluctuation zone (WLFZ) of the Three Gorges Reservoir Area (TGRA). Despite vegetation can effectively mitigate wave erosion in the WLFZ, its influence on the wave force and wave erosion remains unclear. Therefore, the wave experiments were conducted under 3 Cynodon dactylon coverage rates (0, 30% and 60%) and 9 wave conditions (3 wave heights of 4, 6 and 8 cm combined with 3 wave periods of 1, 2 and 3 s) to analyse the wave force (expressed as the wave pressure on the slope surface and the pore water pressure in the slope) and wave erosion rate, and the factors influencing wave erosion were identified. The results indicated that the wave pressure, pore water pressure and wave erosion rate increased by 19.14%–104.75%, 16.84%–65.04% and 23.33%–91.64%, respectively, as wave height increases. The wave pressure decreased by 1.50%–31.23% followed by an increase by 22.05% to 87.10% with the increase of wave period, whereas the pore water pressure and wave erosion rate decreased by 28.33%–53.59% and 20.46%–63.59%, respectively. However, these quantities decreased by 2.10%–50.84%, 17.06%–40.23% and 17.28%–82.18%, respectively, with the increase of Cynodon dactylon coverage rate. It was also discovered that the pore water pressure and Cynodon dactylon coverage rate attained the highest positive and negative correlation coefficients with the wave erosion rate, respectively. In addition, pore water pressure accumulation is the most critical influence factor on wave erosion, and Cynodon dactylon could effectively reduce the pore water pressure via its roots, thus improving the slope wave erosion resistance. This study could be useful to understand the mechanism of plants on controlling wave erosion and could provide a scientific reference for wave erosion control and the ecological construction in the WLFZ.

Elucidation of the dominant factors influencing N2O emission in water-level fluctuation zones in a karst canyon reservoir, southwest China

The water-level fluctuations zones (WLFZs) are crucial transitional interfaces within river-reservoir systems, serving as hotspots for N2O emission. However, the comprehension of response patterns and mechanisms governing N2O emission under hydrological fluctuation remains limited, especially in karstic canyon reservoirs, which introduces significant uncertainty to N2O flux assessments. Soil samples were collected from the WLFZs of the Hongjiadu (HJD) Reservoir along the water flow direction from transition zone (T1 and T2) to lacustrine zone (T3, T4 and T5) at three elevations for each site. These soil columns were used to conduct simulation experiments under various water-filled pore space gradients (WFPSs) to investigate the potential N2O flux pattern and elucidate the underlying mechanism. Our results showed that nutrient distribution and N2O flux pattern differed significantly between two zones, with the highest N2O fluxes in the transition zone sites and lacustrine zone sites were found at 75 % and 95 % WFPS, respectively. Soil nutrient loss in lower elevation areas is influenced by prolonged impoundment durations. The higher N2O fluxes in the lacustrine zone can be attributed to increased nutrient levels resulting from anthropogenic activities. Furthermore, correlation analysis revealed that soil bulk density significantly impacted N2O fluxes across all sites, while NO3−and SOC facilitated N2O emissions in T1-T2 and T4-T5, respectively. It was evident that N2O production primarily contributed to nitrification in the transition zone and was constrained by the mineralization process, whereas denitrification dominated in the lacustrine zone. Notably, the annual N2O efflux from WLFZs accounted for 27 % of that from the water-air interface in HJD Reservoir, indicating a considerably lower contribution than anticipated. Nevertheless, this study highlights the significance of WLFZs as a vital potential source of N2O emission, particularly under the influence of anthropogenic activities and high WFPS gradient.

Effects of Water-Level Fluctuation on Soil Aggregates and Aggregate-Associated Organic Carbon in the Water-Level Fluctuation Zone of the Three Gorges Reservoir, China

Water-level fluctuation (WLF) can destroy soil aggregates and induce soil organic carbon (SOC) loss, potentially triggering impacts on the concentration of atmospheric carbon dioxide. However, responses of soil aggregate content and aggregate-associated organic carbon to WLF have not been well studied, especially in the water-level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR). Therefore, samples from different elevations (145 m, 155 m and 165 m) in the WLFZ of the TGR were collected for experiments. The wet sieving method was used to divide soil into silt and clay (<0.053 mm), micro-aggregate (0.053–0.25 mm) and macro-aggregate (>0.25 mm). The K2Cr2O7-H2SO4 oxidation method was used to measure total SOC content in different soil aggregates. A modified Walkley and Black method was used to measure labile carbon in different soil aggregates. Results showed that macro-aggregate content substantially decreased, while micro-aggregate content remained stable and silt and clay fraction accumulated with a decrease in water-level elevations. Moreover, total SOC content and labile carbon in macro-aggregate were obviously higher than those in the micro-aggregate and the silt and clay fraction. Macro-aggregate contributed the most to SOC sequestration, while micro-aggregate contributed the least, and the contribution of macro-aggregate increased with a decrease in water-level elevations. We concluded that the macro-aggregate was the most active participant in the SOC sequestration process, and preferentially increasing the macro-aggregate content of the lowest water-level elevation was conducive to an improvement in soil carbon sequestration potential and would mitigate climate change.

The evaluation of wetland reconstruction with nature-based solutions for eco-economic sustainable development

Nature-based solutions (NBS) are effective approaches for solving ecological and economic problems related to wetland reconstruction, while emergy and exergy are well suited for evaluating reconstructed eco-economic systems. In this paper, we executed a wetland reconstruction project involving a mulberry-fir woodland and dike-pond complex (MFWDPC) with NBS in the water-level fluctuation zone of the Three Gorges Reservoir (TGR), China. We evaluated the coupling mode of this eco-economic system by using emergy and exergy theories. After wetland reconstruction, the emergy density that entered the MFWDPC was 1.48E + 18 sej yr−1 hm−2, in which the naturally renewable flow accounted for 96.31 % of the emergy inflows, and the emergy sustainability index (ESI) for the eco-economic system was 708.88. The exergy and specific exergy were 2.41E + 14 j yr−1 and 2.08E + 08 j yr−1 kg−1, respectively, and the emergy/exergy ratio was 1.55E + 03 for the MFWDPC. In addition, mulberry trees with strong flooding tolerance provided good economic benefits due to the use of these plants in reconstructed eco-economic systems. Our study of NBS for wetland reconstruction helps in understanding the synergistic symbiosis between ecosystems and economic systems, thereby promoting the reconstruction of degraded wetlands in China and other regions.

Phreatic Line Calculation of Reservoir Landslide under Complex Hydraulic Conditions—A Case Study

A seepage field, influenced by rainfall and reservoir water level fluctuation, is closely associated with the stability of the reservoir landslide. Understanding the phreatic line variation inside the landslide is of significant importance for the analysis and evaluation of slope stability. Currently, most of the boundaries of phreatic line analytical models and the hydrological conditions are simplified, resulting in discrepancies between the outcomes derived from these models and the actual situation. Given this, the newly proposed analytical model is refined by addressing the following two issues. Firstly, the consideration of variable-speed reservoir level fluctuations is incorporated, and secondly, the reservoir bank within the water-level fluctuation zone is treated as non-vertical. Under the combined effect of reservoir water level fluctuation and rainfall, the Boussinesq Differential Equation of unsteady seepage is established and applied to the Majiagou landslide in Three Gorges reservoir area. The results of the analytical solution are basically consistent with the measured groundwater level results, which has demonstrated the accuracy of the proposed model. Consequently, the proposed model can quickly and accurately calculate the groundwater level of landslides, which provides an effective means for the prediction and early warning of reservoir landslides.

The interaction between N, P in the overlying water of the reservoir Water-level fluctuation zone and submerged decomposition of Cynodon dactylon

During the process of inundation in the Water-level fluctuation zone(WLFZ), the N and P content in the overlying water will vary due to the release of soil nutrients, directly impacting the decomposition process of plants. However, current research on the effects of such water changes on plant decomposition is insufficient, hindering an accurate assessment of its impact on water environments. This study simulated changes in water quality during inundation and designed 8 types of water with different initial nutrient levels. Taking the typical WLFZ plant, Cynodon dactylon, as the subject, the decomposition and dynamic changes of N and P in these water bodies were studied. The results showed that inundation significantly increased the N and P content in the water, and the initial forms of N and P significantly affected the release of plant decomposition during inundation. Moreover, the release of PN and PP from the soil stimulated the activity of aquatic microorganisms, enhancing the self-purification capacity of the water body, and leading to a decrease in N and P content in the water body after 60 days of inundation. This study reveals the impact of N and P released from WLFZ soil on plant decomposition and the concentrations of N and P in the overlying water. providing critical insights into WLFZ ecosystem management.