Dam inundation duration as a dominant constraint on riparian vegetation recovery.

The identification of limiting factors is essential for the ecological restoration of riparian ecosystems degraded by the damming of rivers, but remains unclear. Here, we quantitatively assessed the relative importance of environmental factors and revealed the main limiting factors for riparian vegetation restoration and their influencing mechanisms, using riparian plant and environmental data of seven large reservoirs in southwest China. We found that inundation duration had a significantly greater effect on riparian vegetation distribution, cover and diversity than environmental factors such as inundation depth, rainfall, humidity, temperature, sunshine hours, aspect, slope, surface relief, soil pH, available nitrogen (AN), available phosphorus (AP), and available potassium (AK); vegetation cover, species richness, complexity and dominance were highly significantly negatively correlated with inundation duration (p < 0.01); inundation for 5 months is close to the tolerance limit of most plants and poses a significant limiting effect on the vegetation restoration in the reservoir riparian. Therefore, the inundation duration should be highlighted in riparian vegetation restoration. Meanwhile, incorporating the riparian inundation into the river ecological scheduling objectives to shorten the inundation duration and thus radically alleviate the limitation is a new opportunity for vegetation restoration in the reservoir riparian.

Effects of habitat factors on the plant diversity on naturally-restored wind farm slopes.

This study investigated naturally-restored plant communities on wind farm slopes and analyzed the effects of various habitat factors on the plant diversity. The findings provide a technical support for the ecological restoration of mountainous slopes.Twenty-one slopes on five wind farms were selected and the characteristics of the habitat, including slope position, slope aspect, slope gradient, altitude, years since restoration, and plant communities, were recorded. The species richness of the plant communities and the vegetation diversity indexes of these wind farms were measured and calculated, including the Shannon-Wiener diversity index (H'), Pielou's species evenness index (J), and Margalef's richness index (R). The key factors influencing plant diversity were identified using a stepwise regression analysis. A total of 36 families, 54 genera, and 57 species of plants were identified in this study with the Gramineae, Compositae, Rosaceae, Liliaceae, and Juglandaceae families the mostly predominant. Cynodon dactylon, Rubus lambertianus Ser., and Lindera glauca were the dominant species of herbs, shrubs, and trees, respectively. The highest number of species were found on lower slopes, slopes with semi-sunny aspects, slopes with gradients 30-50°, elevation below 500 m, and on slopes with at least five years since restoration. The plant diversity H' and R tended to be higher on lower slopes than on upper slopes, and higher on slopes with semi-shady aspects than on slopes with semi-sunny aspects (P < 0.05). Vegetation diversity increased with the years since restoration. Slope position and slope aspect were identified as the primary influencing factors, and the H' and R indexes were major indicators of changes in plant diversity on mountainous slopes.

Study on the improvement of clay properties by xanthan gum and its application on ecological slope protection engineering.

Traditional substrate binder releases greenhouse gases during the production and application processes, and is detrimental to the vegetation restoration on slopes. To develop a new environmentally friendly soil substrate, this paper conducted a serial of experimental studies on the ecological function and mechanical properties of the xanthan gum (XG)-amended clay by plant growth tests and direct shear tests. The improvement mechanism of the xanthan gum (XG)-amended clay has also explored through microscopic examinations. Experimental results of plant growth tests show that the germination of ryegrass seeds and growth of seedlings can be effectively promoted by adding a proper content (≤2%) of XG into clay. Plants in substrates with 2% of XG grew best, while a high content (3-4%) of XG has an inhibitory effect on the plant growth. The results of direct shear tests illustrate that the shear strength and cohesion both increase with the increase of XG contents, while the internal friction has an opposite trend. The improve mechanism of the xanthan gum (XG)-amended clay were also explored by XRD tests and micro-scopic examinations. It is found that shows that XG does not react chemically to form new mineral components after mixing with clay. The mechanism of XG improving clay is mainly because the XG gel can fill the pores between clay particles, and enhance the cementation between clay particles. XG can enhance the mechanical properties of clay and offset the deficiencies of traditional binder. It can play an active role in the ecological slope protection project.

Effect of Cementitious Capillary Crystalline Waterproofing Materials on the Mechanical and Impermeability Properties of Engineered Cementitious Composites with Microscopic Analysis.

Building structures are prone to cracking, leakage, and corrosion under complex loads and harsh marine environments, which seriously affect their durability performance. To design cementitious composites with excellent mechanical and impermeability properties, Engineered Cementitious Composites (ECCs) doped with ultrahigh molecular weight polyethylene short-cut fibers (PE-ECCs) were used as the reference group. Different types (XYPEX-type from Canada, SY1000-type from China) and doses (0%, 0.5%, 1.0%, 1.5%, 2.0%) of Cementitious Capillary Crystalline Waterproofing materials (CCCWs) were incorporated. The effect of CCCWs on the mechanical and impermeability properties of PE-ECCs, and the microscopic changes, were investigated to determine the best type of CCCW to use and the best amount of doping. The results showed that with increasing the CCCW dosage, the effects of both CCCWs on the mechanical and impermeability properties of PE-ECC increased and then decreased, and that the best mechanical and impermeability properties of PE-ECC were achieved when the CCCW dosing was 1.0%. The mechanical properties of the PE-ECC were more obviously improved by XYPEX-type CCCW, with a compressive strength of 53.8 MPa, flexural strength of 11.8 MPa, an ultimate tensile stress of 5.56 MPa, and an ultimate tensile strain of 7.53 MPa, which were 37.95%, 53.25%, 14.17%, and 21.65% higher than those of the reference group, respectively. The effects of the two CCCWs on impermeability were comparable. CCCW-PE-ECC(X1.0%) and CCCW-PE-ECC(S1.0%) showed the smallest permeation heights, 2.6 mm and 2.8 mm, respectively. The chloride ion diffusion coefficients of CCCW-PE-ECC(X1.0%) and CCCW-PE-ECC(S1.0%) exhibited the smallest values, 0.15 × 10-12 m2/s and 0.10 × 10-12 m2/s, respectively. Micromorphological tests showed that the particle size of the XYPEX-type CCCW was finer, and the intensity of the diffraction peaks of C-S-H and CaCO3 of PE-ECC increased after doping with two suitable doping amounts of CCCW. The pore structure was improved, the surface of the matrix was smoother, and the degree of erosion of hydration products on the fiber surface was reduced after chloride ion penetration. XYPEX-type CCCW demonstrated a more obvious improvement in the PE-ECC pore structure.

Growth characteristics of Cynodon dactylon and mechanical properties of slope with different sludge contents.

The utilization of dredged sludge can reduce environmental pollution and save land resources. To explore using sludge resources in ecological slope-protection projects, dredged sludge was incorporated into ecological slope-protection soil. Cynodon dactylon was planted to analyze the effect of sludge content on its growth. Direct-shear tests on the slope-protection soil with and without Cynodon dactylon were conducted to elaborate on the effect of sludge content, water content, and roots on the mechanical properties of the sludge-clay mixture. When the sludge content was <50%, Cynodon dactylon's growth improved with the sludge content increase, but at >50%, the sludge content's effect was meagre. As the sludge content increased, the cohesion and internal friction angle of the sludge-clay mixture without roots decreased, lowering the shear strength. The soil's cohesive force and internal friction angle follows the sequence: natural state with roots > natural state without roots > saturated state with roots > saturated state without roots. The cohesion and shear strength of the sludge-clay mixture with roots increased at first before decreasing with an increase in sludge content, optimized at 50% sludge content. Here, the ecological slope stability was the best, meaning that the optimum sludge proportion was 50%.

Drone-based investigation of natural restoration of vegetation in the water level fluctuation zone of cascade reservoirs in Jinsha River.

The reservoir water level fluctuation zone (WLFZ) is a new and fragile ecosystem that is gaining attention with the construction of large and medium-sized hydropower plants. Compared to the natural riparian zone, it has a greater drop in water level, longer inundation time, more intense impact from alternating wet and dry conditions, and a wider impact on ecological security. The Jinsha River basin is located in the upper reaches of the Yangtze River in China, and several world-class large-scale hydropower projects with dam heights over 100 m have been built, forming a large area of reservoir WLFZ, however, due to the short time since their construction, there are few related studies. In this paper, fixed sample plots were set up in the typical WLFZs of each large reservoir in the Jinsha River basin. In response to the problem of the precipitous terrain and poor accessibility of the Jinsha River basin, a combination of small UAV surveys and field research in July 2020 was used to draw vegetation cover maps and extract topographic data for each site, and quantitatively analyse the community composition, dominant species types, area, coverage, spatial distribution patterns and environmental factors of tolerant vegetation using spatial superposition analysis, neural network models, landscape pattern indices and typical correlation analysis. The results showed that the original drought-tolerant vegetation in the arid river valley WLFZ has evolved into amphibious herbaceous vegetation, with trees and shrubs disappearing and species composition tending to be simpler. 44 species of plants, mainly in the Asteraceae and Gramineae families, were extant, 61% of which were also reported in the Three Gorges Reservoir WLFZ. The water level variation showed convergence in the natural screening process of suitable species in the WLFZ. Moreover, even in the dry valley WLFZs, flood stress showed a more significant filtering effect on vegetation species than drought stress. The vegetation in the WLFZ showed an obvious band-like aggregated distribution along the water level elevation gradient, and the vegetation coverage along the flooding gradient is as follows: upper part of the WLFZ >> middle part > lower part, and mainly concentrated in the gentle area with slope less than 35°. Flooding stress, drought stress and soil substrate deficiency were the main limiting factors for vegetation recovery in the WLFZ. The vegetation restoration of the WLFZ should be adapted to local conditions, and the dominant role of native species should be emphasized. At the early stage of the restoration of the WLFZ, native species should be selected for artificial planting to accelerate the formation of vegetation cover, and gradually advance downwards along the gradient of water level elevation, while for areas of the WLFZ with slopes greater than 35° and large topographic relief, biological engineering measures should be used to help plant establishment, and after a certain stable cover has been formed, natural restoration should be the main focus.

The Triaxial Test of Polypropylene Fiber Reinforced Fly Ash Soil.

Recently, soil reinforcement using arranged or randomly distributed fibers has attracted increasing attention in geotechnical engineering. In this study, polypropylene (PP) fibers with three lengths (6, 12, and 24 mm) and three mass percentages (0.5%, 1%, and 1.5%) were used to reinforce a coal fly ash soil (FAS) mixture. Unconsolidated, undrained triaxial tests were carried out in order to study the mechanical properties of the polypropylene fiber-reinforced FAS mixture and evaluate the impact of fiber on the shear strength of the FAS mixture. It is found that the fiber length of 12 mm could significantly improve the shear strength of the polypropylene fiber reinforced FAS mixture, and little effect is shown on the shear strength while using a fiber length of 24 mm. Additional fibers enhance the energy absorption capacity of the FAS specimens and therefore the highest energy absorption capacity occurs when the fiber content is 1% and the fiber length is 12 mm. The peak deviator stress enhances impressively with the addition of polypropylene fiber. The impact of fiber on the peak deviator stress is the largest when fiber content is within 1.0%. The fiber length has little effect on the peak deviator stress when it exceeds 12 mm.

Experimental and Numerical Studies on the Direct Shear Behavior of Sand-RCA (Recycled Concrete Aggregates) Mixtures with Different Contents of RCA.

Recycled concrete aggregate (RCA) is a typical construction and demolition (C&D) material generated in civil engineering activities and has been widely used as the coarse-grained filler added to sand for roadbed fillings. The effect of RCA content on the mechanical behavior of sand-RCA mixtures is complicated and still not fully understood. To explore the effect of RCA content on the macroscale and microscopic behavior of the sand-RCA mixtures with various RCA contents, laboratory direct shear tests and numerical simulations using the 3D discrete element method were performed. Experimental direct shear tests on sand-RCA mixtures with different contents of RCA were first carried out. Numerical direct shear models were then established to represent the experimental results. The particle shape effect was also considered using a new realistic shape modeling method to model the RCA particles. Good agreement was observed between the DEM simulation and experimental results, verifying the ability of the numerical direct shear models to represent the direct shear behavior of sand-RCA mixtures. The macroscopic responses of both experimental and numerical tests showed that all samples presented an initial hardening followed by a post-peak strain softening. The peak-state friction angles increased with the RCA content for samples under the same vertical stress. The effect of RCA content on the microscopic behavior based on DEM simulation was also found. The microscopic properties of RCA-sand mixtures, such as coordination numbers, PDFs and contact force transformation features, were analyzed and related to the macroscopic results.

Occurrence and ecotoxicological risk assessment of perfluoroalkyl substances in water of lakes along the middle reach of Yangtze River, China.

Polyfluoroalkyl substances (PFASs) are widely distributed in aquatic environment, and the potential ecological risk of PFASs has become a new challenge in recent years. But there were few integrated studies about the distribution, source appointment and risk assessment of PFASs in water of lakes along the middle reach of Yangtze River, China. Hence, this study investigated the pollution characteristics, source apportionment, ecological risks assessment of eleven PFASs from the surface water in this region. The total concentrations of PFASs (∑PFASs) ranged from 12.43 to 77.44 ng L-1 in this region. The ∑PFASs in Hong and Poyang Lakes were higher than those in Dongting Lake and middle reach of Yangtze River (p < 0.05). The compositions of PFASs in the middle reach of Yangtze River and along three lakes were similar, being with a larger proportion of short-chain PFACs. The food packaging and metal plating sources were identified as the main sources by two models. The total risk quotients (∑RQs) showed the ecological risk for algae in the middle reach of Yangtze River, Dongting and Poyang Lakes were negligible, but the low risk in some sites of Hong Lake. The EDIs of ∑PFASs were much lower than the tolerable daily intake recommended by the European Food Safety Authority. The results of this study were significant for developing effective strategies (e.g. short-chain substitution and restriction) of controlling PFASs pollution in the middle reach of Yangtze River and along lakes.

Composition and distribution of vegetation in the water level fluctuating zone of the Lantsang cascade reservoir system using UAV multispectral imagery.

With the development of a large number of tall dams and large cascade reservoir projects in the Lantsang River Basin, a large water level fluctuating zone (WLFZ) containing cascading reservoirs has formed. This newborn ecosystem is related to the sustainable development of hydropower projects, and has become a new problem to be studied urgently. Taking WLFZs in the Huangdeng, Xiaowan and Nuozhadu Reservoirs in the Lantsang River Basin as study areas, this study used multi-spectral remote-sensing field data obtained with unmanned aerial vehicles (UAVs) to ascertain the species types, coverage, distribution characteristics, dominant species and pioneer species of naturally restored vegetation. The considered data were subjected to UAV data processing, vegetation classification using multi-spectral images and a geographic information system (GIS) terrain-distribution analysis. Results show that: Polygonum Plebeium, Cynodon dactylon, Xanthium sibiricum, Ageratum conyzoides, Eleusine indica, Digitaria sanguinalis and Verbena officinalis are the dominant species of vegetation that could be naturally restored in the WLFZ; the vegetation coverage and the number of species are significantly positively correlated with the age and restoration periods of the WLFZ; the vegetation coverage of each study area increases at first, and then decreases, as a function of elevation; gentle slopes about 0-25°are more suitable for vegetation restoration. This study provides first-hand data on the natural restoration of vegetation in WLFZs, and gives a useful reference for its ecological restoration as a consequence of hydropower cascade development in the Lantsang River Basin. Finally, the study demonstrates that light UAV remote sensing is an attractive choice for investigating vegetation in reservoir WLFZs.

Study on the mechanical properties of flax fiber-reinforced silty clay contaminated by zinc-ion solution.

Mechanical properties of fiber-reinforced soil after soaking in heavy metal ion solution have great influences on safety and stability of the reinforcement, herein the mechanical properties of optimum moisture content of different concentrations of zinc ions contaminated soil were studied through shear test, compression test and triaxial test. The compressive modulus, compression coefficient and porosity ratio of different concentrations of the zinc-ion contaminated soil under different pressure were studied, and the variation characteristics of internal friction angle and cohesion were also investigated, thereafter, the causes of the change of cohesion and internal friction angle were analyzed from the microscopic perspective. The results show that the shear strength of contaminated reinforced soil increases with the increase of confining pressure at the same zinc ions concentration. And at the same confining pressure, with the increase of zinc ions concentration, the shear strength of contaminated reinforced soil first increases and then decreases. With the increase of zinc ions concentration, the internal friction angle and compression coefficient increase, the cohesion and the modulus of compression decrease. With the increase of normal stress, the compression coefficient decreases firstly and then increases, and the compression modulus increases and then decreases. With the concentration of zinc ions increases at lower normal stress, the amount of shrinkage increases and the compression coefficient decreases. While at higher normal stress, the compressive modulus decreases and the compression coefficient increases.

Transformation of sulfadiazine in humic acid and polystyrene microplastics solution by horseradish peroxidase coupled with 1-hydroxybenzotriazole.

Enzyme catalyzed coupling with redox mediators are considered as great interesting and viable technologies to transform antibiotics. This work demonstrated the horseradish peroxidase (HRP) was effective in transforming sulfadiazine (SDZ) transformation coupled with 1-hydroxybenzotriazole (HBT) at varying conditions. The removal of SDZ was independent of Na+ and its ionic strength, but Ca2+ could enhance transformation efficiency by increasing the enzyme activity of HRP. The presence of humic acid (HA) and polystyrene (PS) microplastics showed inhibition on the transformation of SDZ, and the transformation rate constants (k) decreased with the concentration of HA and PS particles increased. These primarily attributed to covalent coupling and electrostatic interaction between SDZ and HA, SDZ and PS, respectively, which reduced the concentration of free SDZ in the reaction solution. The presence of cation recovered the inhibition of SDZ transformation by HA and PS particles, which ascribed to compete between cation and SDZ. The divalent cations (Ca2+) showed more substantial competitiveness than mono (Na+) due to more carried charge. Eight possible transformation products were identified, and potential SDZ transformation pathways were proposed, which include δ-cleavage, γ-cleavage, carbonylation, hydroxylation, SO2 extrusion and SO3 extrusion. In addition, HA and PS particles couldn't affect the transformation pathways of SDZ. These findings provide novel understandings of the transformation and the fate of antibiotics in the natural environment by HRP coupled with redox mediators.

Effect of microstructure change on permeability of flax-fiber reinforced silty clay soaked with zinc-ion solution.

With the application of fiber-reinforcement technology, the mechanical properties of silty clay are improved with fiber reinforcement. However, the variation of permeability coefficient and other parameters of flax-fiber reinforced silty clay have not been sufficiently studied. In this study, the permeability of flax-fiber reinforced silty clay soaked with zinc-contaminated solution under different osmotic pressure was tested by a flexible-wall permeameter, and the effects of zinc-ion concentration and confining pressure on the permeability of flax-fiber reinforced silty clay were studied. Genius XRF was employed to detect the types and quantity of metal elements in the specimens, thereafter, the reasons for the change of permeability were explained from chemical and microscopic perspective. The results showed that the permeability coefficient of flax-fiber reinforced silty clay decreased significantly with the increase of zinc-ion concentration in a low concentration (about 1-10 mg L-1). While in a high concentration (about 100 mg L-1), the permeability coefficient of flax-fiber reinforced silty clay changed little with the increase of zinc-ion concentration. While the flax-fiber reinforced silty clay was not soaked with zinc-ion solution, the permeability coefficient of the specimen increased with the increase of confining pressure. However, when the flax-fiber reinforced silty clay was soaked with zinc-contaminated solution, the permeability coefficient first decreased and then tended to be constant with the increase of confining pressure. With the increase of confining pressure, the porosity of flax-fiber reinforced silty clay decreased, and with the increase of zinc-ion concentration, the porosity of flax-fiber reinforced silty clay first increased and then decreased.

Transformation mechanisms of tetracycline by horseradish peroxidase with/without redox mediator ABTS for variable water chemistry.

The threat of antibiotics in the environment causing antibiotics resistance is a global health concern. Enzymes catalyze pollutant transformations, and how commercially available enzymes like horseradish peroxidase (HRP), with or without a redox mediator, may be used to degrade antibiotics in water treatment is of great interest. This work demonstrates tetracycline transformation by HRP, and how it is significantly enhanced by free radicals created from the mediator 2,2-Azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). Water temperature and pH strongly influence the tetracycline removal rate due to their correlation with the enzyme activity, abundance and stability of ABTS•+. Four transformation products were identified in the pure HRP system using a liquid chromatography tandem mass spectrometry hybrid quadrupole-orbitrap mass spectrometer system. Addition of 25 µmol L-1 ABTS not only accelerated the degradation of tetracycline, but also expanded the range of degradation pathways. Potential tetracycline transformation pathways are proposed based on these observations, which include a range of mechanisms such as hydroxylation, demethylation, dehydration, decarbonylation and secondary alcohol oxidation. Despite of decreased efficiency, the HRP/ABTS system was able to degrade tetracycline in a domestic wastewater treatment plant effluent matrix, which demonstrates the potential of the system to be utilized in wastewater treatment.

Tetracyclines, sulfonamides and quinolones and their corresponding resistance genes in coastal areas of Beibu Gulf, China.

As the rapid development of aquaculture in the Beibu Gulf, large number of antibiotics was released into marine aquatic environment. But little integrated studies concerned on the occurrence and correlation of antibiotics with their corresponding ARGs in this region. We investigated the abundance of three prevalent categories of antibiotics and corresponding antibiotic resistance genes (ARGs), analyzed the potential correlation among antibiotics, ARGs and sediment properties in eight terminal rivers, nine semi-closed sites and eight nearshore areas from Beibu Gulf. Residual concentrations of total antibiotics ranged from 51.04 to 137.64 µg/kg, TETs had higher concentrations than FQs and SAs. Conventional PCR of ARGs revealed intI1, sul2, tetB, tetC and tetG had 100% detection frequency in all samples. Quantitative analysis showed sul genes were dominant compared to tet genes. The abundance of antibiotics and ARGs were decreased from river to open sea. Significant correlations (p < .05) between intI1 and ARGs (sul2 and tetG) were revealed by Pearson analysis, indicating that intI1 gene played a significant role in the occurrence and diffusion of ARGs. Significant correlations among the ARGs, the corresponding or irrelevant residual antibiotics and sediment characteristics were observed by redundancy analysis and network. Due to the potential health risks of antibiotics with corresponding ARGs, the control and treatment measures should deserve wide attention.

Experimental Investigations on the Pull-Out Behavior of Tire Strips Reinforced Sands.

Waste tires have excellent mechanical performance and have been used as reinforcing material in geotechnical engineering; however, their interface properties are poorly understood. To further our knowledge, this paper examines the pull-out characteristics of waste tire strips in a compacted sand, together with uniaxial and biaxial geogrids also tested under the same conditions. The analysis of the results shows that the interlocking effect and pull-out resistance between the tire strip and the sand is very strong and significantly higher than that of the geogrids. In the early stages of the pull-out test, the resistance is mainly provided by the front portion of the embedded tire strips, as the pull-out test continues, more and more of the areas towards the end of the tire strips are mobilized, showing a progressive failure mechanism. The deformations are proportional to the frictional resistance between the tire-sand interface, and increase as the normal stresses increase. Tire strips of different wear intensities were tested and presented different pull-out resistances; however, the pull-out resistance mobilization patterns were generally similar. The pull-out resistance values obtained show that rubber reinforcement can provide much higher pull-out forces than the geogrid reinforcements tested here, showing that waste tires are an excellent alternative as a reinforcing system, regardless of the environmental advantages.

Bioremediation of heavy metal contaminated aqueous solution by using red algae Porphyra leucosticta.

Bioremediation is an effective process for the removal and recovery of heavy metal ions from aqueous solutions. In this study, red algae Porphyra leucosticta was examined to remove Cd(II) and Pb(II) ions from wastewater through biological enrichment and biological precipitation. The experimental parameters that affect the bioremediation process such as pH, contact time and biomass dosage were studied. The maximum bioremediation capacity of metal ions was 31.45 mg/g for Cd(II) and 36.63 mg/g for Pb(II) at biomass dosage 15 g/L, pH 8.0 and contact time 120 minutes containing initial 10.0 mg/L of Cd(II) and 10.0 mg/L of Pb(II) solution. Red algae Porphyra leucosticta biomass was efficient at removing metal ions of 10.0 mg/L of Cd(II) and 10.0 mg/L of Pb(II) solution with bioremediation efficiency of 70% for Cd(II) and 90% for Pb(II) in optimal conditions. At the same time, the removal capacity for real industrial effluent was gained at 75% for 7.6 mg/L Cd(II) and 95% for 8.9 mg/L Pb(II). In conclusion, it is demonstrated that red algae Porphyra leucosticta is a promising, efficient, cheap and biodegradable sorbent biomaterial for reducing heavy metal pollution in the environment and wastewater.