Hydro-fluctuation Belt Research Articles

A modified Hoek-Brown failure criterion considering the damage to reservoir bank slope rocks under water saturation-dehydration circulation

After water is impounded in a reservoir, rock mass in the hydro-fluctuation belt of the reservoir bank slope is subject to water saturationdehydration circulation (WSDC). To quantify the rate of change of rock mechanical properties, samples from the Longtan dam area were measured with uniaxial compression tests after different numbers (1, 5, 10, 15, and 20) of simulated WSDC cycles. Based on the curves derived from these tests, a modified Hoek- Brown failure criterion was proposed, in which a new parameter was introduced to model the cumulative damage to rocks after WSDC. A case of an engineering application was analyzed, and the results showed that the modified Hoek-Brown failure criterion is useful. Under similar WSDC-influenced engineering and geological conditions, rock mass strength parameters required for analysis and evaluation of rock slope stability can be estimated according to this modified Hoek-Brown failure criterion.

Seasonal variations of carbonic anhydrase activity in Chongqing urban section of Jialing River and its influencing factors

Carbonic anhydrase (CA) is an enzyme in algal carbon-utilization that plays an important role in the formation of algal blooms. A year-long monitoring program in the shore area of Chongqing Urban Section of the Jialing River (JR) was launched to determine the variations in carbonic anhydrase activity (CAA) and its change mechanism in the hydro-fluctuation belt of the tributaries in the Three Gorges Reservoir (TGR) area. The variations in basic water quality parameters, different carbon forms, and CAA were investigated from November 2013 to October 2014. Results showed that the mean CAA value in JR was 0.67 ± 0.31 EU/106 cells. CAA was high during the flood stage, low during the impounding stage, and peaked on April 3, 2014 during the discharging stage. No significant difference was observed in the CAA of different sampling sites in JR. However, a significant difference was observed between the CAA of JR and that of the Yangtze River. Correlation analyses showed that water temperature, pH, algal cell density, and dissoluble organic carbon were positively correlated with CAA, whereas CO2 and dissoluble inorganic carbon were negatively correlated with CAA. A model for CAA and related parameters was built through principal component regression. The equation was expressed as follows: CAA = 0.116T + 0.00746Cells+0.0156pH−0.0157CO2−0.0150DIC+0.0135DOC+0.565. Results revealed that CAA in JR was controlled by multiple factors, which could be used for CAA monitoring. The model demonstrated a potential value in controlling algal blooms.

三峡库区消落带重建植被下土壤微生物生物量碳氮含量特征

PDF HTML阅读 XML下载 导出引用 引用提醒 三峡库区消落带重建植被下土壤微生物生物量碳氮含量特征 DOI: 10.5846/stxb201610272191 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 重庆市林业重点科技攻关项目（渝林科研2016-8；2015-6）；国家国际科技合作专项（2015DFA90900）；中央财政林业科技推广示范项目（渝林科推[2014-10]）；重庆市研究生科研创新项目（CYS2015068）；重庆市研究生科研创新项目（CYB16066） Characteristics of soil microbial biomass C and N under revegetation in the hydro-fluctuation belt of the Three Gorges Reservoir Region Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为探究三峡库区消落带植被重建后，土壤微生物生物量含量特征及影响因素，对忠县消落带人工重建植被土壤及裸地土壤（作为对照）微生物生物量碳氮含量进行了调查研究。结果表明：（1）在消落带165-175 m高程土壤微生物生物量碳含量草地>林地>农耕地>裸地，微生物生物量氮含量规律与微生物生物量碳一致，农耕地明显提高；土壤微生物生物量总体呈现出草地最高、林地和农耕地次之，裸地最低的趋势，表明进行消落带植被恢复对土壤微生物生物量有显著的促进作用。（2）不同植被类型下，土壤微生物生物量碳氮比变化范围为8.02-10.25，土壤微生物生物量碳、氮占土壤有机碳、全氮的百分比范围分别是2.40%-4.60%和2.13%-3.58%，其中林地对土壤碳、氮库贡献显著高于裸地（P < 0.05）。（3）土壤微生物生物量碳、氮与土壤有机碳、全氮和pH值呈现显著相关性，与土壤含水量呈现极显著相关性，说明消落带重建植被土壤的这些理化性质对土壤微生物生物量碳、氮含量有强烈的影响。因此，在三峡库区消落带进行植被恢复重建能显著提高土壤微生物生物量及土壤质量，对加强三峡库岸生态系统的稳定性具有重要意义。 Abstract:Operation of the Three Gorges Dam Reservoir on the Yangtze River, China, has formed a hydro-fluctuation belt with an annual water level change of near 30 m spanning and an area of 350 km2. Such a change in water level has led to a direct shift in plant community composition within the hydro-fluctuation belt. Different vegetation types alter the riparian soil environment to varying extents, via their influence on the biogeochemical cycles of materials such as soil microbial biomass carbon and nitrogen. Accordingly, by determining the relationship between soil physicochemical properties and soil microbial biomass under different vegetation types, we can provide useful information for vegetation restoration in the hydro-fluctuation belt of the Three Gorges Reservoir Region. To explore the changes in re-vegetated soil quality in the hydro-fluctuation belt of the Three Gorges Reservoir, we examined the contents of soil microbial biomass carbon (SMBC) and soil microbial biomass nitrogen (SMBN) in this region. Soils under four typical vegetation types (natural grassland, artificial timber forest, crop land, and unplanted soil) were investigated in the reservoir riparian region of Zhong County (107°32'-108°14'E, 30°03'-30°35'N), located in the center of Chongqing Municipality. The results showed that both SMBC and SMBN content was the highest in natural grassland and the lowest in unplanted soil. Under different types of vegetation, the ratio of SMBC/SMBN ranged from 8.02 to 10.25, the ratio of SMBC/soil organic carbon (SOC) was 2.40%-4.60%, and the ratio of SMBN/total nitrogen (TN) was 2.13%-3.58%. The SMBC/SOC and SMBN/TN ratios of forest soils were significantly higher than those of the unplanted soil (both P < 0.05). Soil microbial biomass was significantly correlated with SOC, TN, and soil pH, and very significantly correlated with soil moisture. Our study showed that the physical and chemical properties of soil under revegetation had a significant impact on both SMBC and SMBN. Thus, revegetation facilitated an increase soil microbial biomass and enhanced soil quality in the hydro-fluctuation belt of the Three Gorges Reservoir Region. 参考文献 相似文献 引证文献

水位变化对三峡库区消落带落羽杉营养特征的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 水位变化对三峡库区消落带落羽杉营养特征的影响 DOI: 10.5846/stxb201606211213 作者: 作者单位: 西南大学生命科学学院,西南大学生命科学学院,西南大学生命科学学院,西南大学生命科学学院,西南大学生命科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家国际科技合作专项（2015DFA90900）；三峡后续工作库区生态与生物多样性保护专项项目（5000002013BB5200002）；重庆市林业重点科技攻关项目（渝林科研2015-6）；中央财政林业科技推广示范项目（渝林科推[2014-10]）；重庆市研究生科研创新项目（CYB16066） Effect of water-level change on nutritional characteristics of Taxodium distichum in the hydro-fluctuation belt of the Three Gorges Reservoir Author: Affiliation: College of Life Science,Southwest University,College of Life Science,Southwest University,College of Life Science,Southwest University,College of Life Science,Southwest University,College of Life SCience, Southwest University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:三峡大坝建成蓄水后，其独特的水位调度节律对水库消落带植物的生境造成巨大干扰。为了解落羽杉在消落带特殊生境下的生理生态过程，探究其水淹耐受机制，在三峡库区消落带植被修复忠县示范基地建立3 a后，对试验样地内种植于消落带海拔175-165 m范围的落羽杉进行叶片、根系样品采集，并调查其生长情况，测定分析落羽杉营养元素含量及其与植株生长和土壤养分间的关系。结果表明：（1）水位变化对适生树种落羽杉营养元素吸收造成了明显影响。随着淹水深度和淹水时间的延长，落羽杉根系能量代谢受阻，根系功能紊乱，营养元素吸收与运输受到抑制，落羽杉N、P、K、Ca、Zn吸收减少；水淹导致土壤中Fe2+、Mn2+含量升高，落羽杉Fe、Mn吸收增加。（2）相关性分析表明，落羽杉株高与N、K、Mg含量呈极显著正相关关系，与P含量呈显著正相关关系，而与Fe、Cu含量呈极显著负相关关系，与Mn含量呈显著负相关关系；落羽杉冠幅与植株N、P、K、Mg含量呈极显著正相关关系，而与Fe、Cu含量呈极显著负相关关系；落羽杉营养元素含量与土壤元素含量无显著相关性。（3）消落带不同海拔落羽杉营养元素的积累量均不低于植物正常生长水平，未见严重的缺素状况。研究结果表明，落羽杉对三峡库区消落带水位变化具有很好的适应能力，能够对水位变化做出积极的响应，平衡各元素的积累量，维持植株正常生长。 Abstract:The construction of the Three Gorges Dam reservoir spans the Yangtze River, China, forming a hydro-fluctuation belt with a water level drop of nearly 30 m and an area of 300 km2. The unique anthropogenic hydrological regime of the Three Gorges Dam has had significant negative impacts on the reservoir's riparian ecosystem. Some flooding-intolerant plants living within the belt gradually died off, which exacerbated vegetation habitat fragmentation and deleteriously affected the biological diversity, ecosystem structures, and functions of the water-fluctuation zone. Therefore, a pressing scientific challenge is to recover and restore the vegetation there and ensure proper ecological function. Previous studies have shown that Taxodium distichum is a flooding-tolerant plant and has been used for vegetation reconstruction. The nutritional characteristics of plants in a particular area can reflect the eco-physiological processes of plants, and can serve as crucial indicators of the structure and function of the local ecosystem. The nutritional characteristics play a key role in adaptation to anti-seasonal flooding, and might reveal clues about the adaptation mechanisms of plants in the hydro-fluctuation belt of the Three Gorges reservoir area. To contribute to this understanding, the nutritional characteristics of T. distichum growing in the reservoir riparian region of Zhongxian county, which had been planted in 2012, were studied. Element contents of three sample zones in low water elevation (165 m)-SD, high water elevation (170 m)-SL, and the control-CK(175 m) were determined in 2015. The macroelement, secondary element, and micronutrient contents in root and leaves of plants were measured. The results showed that:(1) Concentrations of N, P, K, Ca, and Zn in leaves and roots of T. distichum under flooding significantly decreased compared to CK, whereas Fe and Mn contents significantly increased. (2) Some nutrient concentrations of T. distichum under flooding decreased, but still maintained their normal performance. (3) Correlation analysis showed that plant heights were positively correlated with the concentrations of N, P, K, and Mg; plant heights were negatively correlated with the concentrations of Fe, Cu, and Mn; canopies of plants were positively correlated with the concentrations of N, P, K, and Mg, but negatively correlated with Fe and Mn. This investigation indicates that water level change had significantly influenced the nutritional characteristics of T. distichum in water-level-fluctuating zone of the Three Gorges Reservoir. T. distichum had good adaptability to the changed water habitat. 参考文献 相似文献 引证文献

Multi-Functional Dike-Pond SYSTEM Adaptive to Water Level Change: Application of Pond-Based Ecological Wisdom in Ecological Restoration of the Hydro-Fluctuation Belt of the Three Gorges Reservoir

There are many ponds with different sizes and shapes in nature, providing a variety of ecological services. In the era of traditional farming, people created pond systems with ecological wisdom, such as Beitang ponds, multi-pond system, mulberry-based dike fish pond, etc., which perform ecological functions including water storage, stormwater regulation, pollution purification, micro-climate adjustment, and habitat provision. Due to global climate change and human interference, problems such as the surface water shortage, water pollution and water ecosystem destruction are becoming more and more serious. To deal with the changing environment, restore ecology, and construct landscape effectively, we not only could be inspired by the natural pond system, but also need to learn from the traditional cultural heritage, such as the ecological wisdom of the various pond systems. The multi-functional dike pond system plays an important role in dealing with the environmental changes and optimizing the ecological services. On the basis of clarifying the composition, structure and function of ponds in nature, this article explores the ecological wisdom of the pond systems in traditional villages, taking the design and practices of the Three Gorges Reservoir as an example to discuss the application of the multi-functional dike pond in the ecological restoration and landscape optimization of the hydro-fluctuation belt with seasonal water level fluctuation.

Creep degradation mechanism by water-rock interaction in the red-layer soft rock

Bank slope stability has become a great concern, while the impoundment of Three Gorges reservoir. The bank slope composed of red-layer soft rock has exhibited distinct deformation and failure. Therefore, a typical red-layer soft rock around Three Gorges reservoir area was selected to demonstrate the process of cyclic changes at the reservoir level and immersion-air-dry cyclic action of water-rock inside hydro-fluctuation belt. To meet the objective of this study, a series of creep tests were conducted on the rock specimens at different water-rock interaction stages. The following points were noticed based on the laboratory results: (1) the creep fracture strength and long-term strength of red-layer soft rock degraded significantly during the process of water-rock interaction. For the first three water-rock interaction circulations, the strength of red-layer soft rock degraded quickly and then gradually became stable. (2) During the creep test, the lateral expansion of red-layer soft rock increased significantly regarding to the number of cycles. (3) The creep curve includes three typical stages at failure stress level—primary (damped) stage, secondary (steady-state) stage, and tertiary (nonlinear accelerated) stage. As the number of cycles increased, the percentage of secondary stage diminished gradually. However, the tertiary stage showed a gradual increment, since the plasticity of the specimens was strengthened by water-rock interaction. (4) The shear failure characteristics of the specimens became highly considerable during the process of water-rock interaction, and there have been a gradual increment of shear rupture zone. (5) The SEM results showed that the specimen microstructure changed its state from dense to loose and porous. The findings of this research provide a good basis for long-term stability analysis of bank slope.

Effects of Soil Moisture and Temperature Variations on Organic Carbon Mineralization of Purple Soil in the Hydro-fluctuation Belt of the Three Gorges Reservoir

Soil sampling in the field and an incubation experiment in the laboratory was conducted to investigate the effects of soil moisture and temperature on soil organic carbon (SOC) mineralization of purple soil in the hydro-fluctuation belt of the Three Gorges Reservoir. Three incubation temperatures (10, 20 and 30℃) and four moisture levels (40% water holding capacity (WHC), 70% WHC, 100% WHC and submerged condition) were used in the experiment. In the entire incubation period (66 d), the SOC cumulative mineralization reached the maximum at 100% WHC, but there was no significant difference between 100% WHC and submerged condition (P>0.05). At 10℃ and 20℃, the SOC cumulative mineralization at 100% WHC and under submerged condition was not significantly different from that at 70% WHC treatment, but significantly higher than that at 40% WHC treatment. While the cumulative mineralization of organic carbon at 100% WHC and under submerged condition was significantly higher than that at 70% WHC and 40% WHC when the temperature was 30℃ (P<0.05). The results indicated that compared with 70% WHC treatment, the higher moisture content (100% WHC and submerged condition) had no negative effects but rather promotion effects on the mineralization of SOC at high temperature (30℃). Under the same soil moisture conditions, the SOC cumulative mineralization of purple soil in the hydro-fluctuation belt increased as temperature increased. Moreover, the analysis of variance showed that SOC cumulative mineralization was significantly affected by temperature and soil moisture, and there was a significant interaction with temperature and soil moisture (P<0.05). Fitting of two-pool first-order model was performed to indicate that temperature and soil moisture influenced the contents of labile SOC fraction and the mineralization rates of recalcitrant SOC fraction, which led to the differences of SOC cumulative mineralization under the different treatments. With the increasing temperature, the temperature sensitivity was significantly decreased in the 40% WHC treatment, but there was no obvious difference when the soil moisture content was not less than 70% WHC.

桑及菌根桑在库区消落带的生态重建功能及应用潜力

PDF HTML阅读 XML下载 导出引用 引用提醒 桑及菌根桑在库区消落带的生态重建功能及应用潜力 DOI: 10.5846/stxb201408211660 作者: 作者单位: 南方山地园艺学教育部重点实验室,南方山地园艺学教育部重点实验室,南方山地园艺学教育部重点实验室,南方山地园艺学教育部重点实验室,西南大学蚕学与系统生物学研究所,西南大学蚕学与系统生物学研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 现代农业产业技术体系专项(CARS-22-ZJ0503);重庆市研究生教育教学改革研究项目(yjg143028) Ecological reconstruction function and potential application of mulberry and mycorrhizal mulberry in the Three Gorges Reservoir area Author: Affiliation: Key Laboratory of Horticulture Science for Southern Mountainous Regions,Ministry of Education,College of Horticulture and Landscape Architecture,Department of Agriculture,Southwest University,Key Laboratory of Horticulture Science for Southern Mountainous Regions,Ministry of Education,College of Horticulture and Landscape Architecture,Department of Agriculture,Southwest University,Key Laboratory of Horticulture Science for Southern Mountainous Regions,Ministry of Education,College of Horticulture and Landscape Architecture,Department of Agriculture,Southwest University,Key Laboratory of Horticulture Science for Southern Mountainous Regions,Ministry of Education,College of Horticulture and Landscape Architecture,Department of Agriculture,Southwest University,Institute of Sericulture and Systems Biology,Southwest University,Institute of Sericulture and Systems Biology,Southwest University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:三峡工程在提供丰富水电资源造福人类的同时,也引发了一些生态环境问题,对库区环境、生物、气候以及人们的生活都产生了不同程度的影响。桑树休眠和生长发育节律与库区水体涨落规律的反向偶联,桑的菌根结构在改善根际土质量,促进桑树水分和养分吸收,增强桑树对盐碱、干旱、重金属的耐受性,提高幼苗的存活率,促进桑苗生长,促进植物群落正向演替等生态过程中发挥着重要的作用。分析了三峡库区消落带周期性水淹的生态特征和岸生植物生态恢复障碍,综述了桑及菌根桑在消落带的生态特性和应用潜力,最后提出了菌根桑生物技术的应用所面临的新课题和挑战。 Abstract:The construction of the Three Gorges Dams in the Yangtze River in the 1990s has induced profound impacts on the environment and biodiversity in the reservoir region, although these hydroelectric dams have supplied an enormous amount of hydropower resources and electricity to all of China. One main example of such environmental effects is the gradual degeneration or death of plants under waterlogging or flooding along the reservoir areas after implementation of the dams. The river banks, which serve as hydro-fluctuation belts, have been annually fluctuated for three to six months at a time, leading to low soil fertility and high erodibility. Meanwhile, some adaptive vegetation with low water-holding capacity has persisted in the drought soil. However, these distinctive characteristics are major restoration obstacles in the hydro-fluctuation belt area, even for plants with strong vitality. Mulberry (Morus alba L.), a plant native to China, has not only economic importance to the Chinese silk industry but also ecological benefits to its plantation regions in China. Studies have shown that mulberry trees have strong ecological adaptation ability and ecological restoration potential, as they are able to hold water and prevent soil erosion with their extensive root systems. These traits facilitate mulberry survival in harsh environments, particularly when they have established symbiotic associations with beneficial soil microorganisms such as arbuscular mycorrhizal (AM) fungi. On the other hand, the application of AM fungi to ecological restoration has been recently proposed. In general, AM fungi and their massive underground hyphal networks could enhance the uptake of plant nutrients and water, formation of soil aggregates, and resistance to biotic and abiotic stresses. Studies have further shown that AM fungi have significant impacts on the soil microflora community and on plant community compositions. As a result, mulberry trees colonized by AM fungi could have the capacity to improve the soil rhizosphere quality, promote the uptake and transportation of minerals and water, and enhance the tolerance to drought and waterlogging. Therefore, mycorrhizal mulberry could promote leaf development and tree performance for the food resource of silk worms as well as function in ecological restoration on the river bank areas of the Three Gorges Reservoir. As the growth rate of mulberry is inversely related to fluctuations of water level in the reservoir, the planting of AM fungi-colonized mulberry trees is considered to be a potential ecological restoration strategy to deal with both the waterlogging in winter or early spring and the drought in summer at the fluctuation belts or in other fragile ecosystems of the Three Gorges Reservoir. In this paper, we review the ecological characteristics and plant growth obstacles faced during the water fluctuation period on the river banks along the Three Gorges Reservoir areas of the Yangtze River, and then propose the potential application of the mycorrhizal mulberry for ecological reconstruction of the hydro-fluctuation belts of these areas. 参考文献 相似文献 引证文献

Macro/Microtesting and Damage and Degradation of Sandstones under Dry-Wet Cycles

In terms of the degradation of mechanical parameters of rock mass in the hydrofluctuation belt of a reservoir bank slope arising from rainfall and the reservoir level fluctuation, the moderately weathered sandstone in a side slope of the Three Gorges Reservoir Region is selected as a research object to carry out “drying-saturation-drying” tests for disks with two thicknesses (h=25 mm,h=50 mm) in different cycles; a spiral CT machine, an ultrasonic velocity meter, and a light Schmidt hammer are utilzed to conduct nondestructive testing on dry-wet cycles; through the Brazilian splitting test, the uniaxial tensile strength of “dry” and “saturated” sandstones under different dry-wet cycles is obtained. The research shows that, with the increase of the dry-wet circles (n), the longitudinal wave velocity and the rebound strength of sandstones are linearly decreased withn; the uniaxial tensile strength of sandstones and the mean CT number of cross sections are logarithmically decreased withn; the fitting equation of macro/micromechanical parameters and dry-wet cycles (n) of sandstones is raised, which is provided as a reference basis for the weathering process of sandstones under dry-wet cycles.

Soil stability characteristics of mulberry lands at hydro-fluctuation belt in the Three Gorges Reservoir area, China

The hydro-fluctuation belt in the Three Gorges Reservoir area is a typical seasonal and artificial wetland system and ecologically fragile zone. Using the widely existing mulberry forest lands in the hydro-fluctuation belt as an example and the 180-m water-level forest land as a control, this paper analyzes the soil stability of mulberry forestlands at different water levels in the hydro-fluctuation belt by analyzing and comparing the changes between soil physical and mechanical properties. The results indicated that (1) water-level changes, such as rising, flooding, draining, and exposure, affect the soil structure in mulberry forestlands. The soil agglomeration statuses for the soil layers decreased from 180 > 175 > 170 > 165 m, and the soil agglomeration statuses at a depth of 0∼20 cm decreased by 43.79, 44.95, and 57.45% compared with the control. (2) The soil water stability index decreased as follows: 180 > 170 > 175 > 165 m, which only accounted for 50.00, 47.73, and 40.91% of the control. In addition, the soil water stability indexes for the topsoils at various water levels were 1.87 (180 m), 1.67 (175 m), 2.92 (170 m), and 1.86 (165 m) times greater than those of the subsoils; thus, the resistance to hydraulic dispersion and disintegration were greater in the topsoil than in the subsoil. (3) The soil aggregate stability index decreased from 180 > 165 > 170 > 175 m and by 22.75, 23.53, and 35.29% compared with the control. (4) The soil shear strengths (composed of the cohesive force C and the internal friction angle φ) of the topsoils at water levels of 175, 170, and 165 m were significantly lower than in the control, and the internal friction angles decreased by 10.52, 19.08, and 43.25% and the cohesive force decreased by 9.88, 16.36, and 27.51%, respectively. The stability of the soil structure was greatly influenced by the soil clay content, soil organic matter content, and waterlogging duration. The study results could provide scientific support for soil and water conservation in the hydro-fluctuation belt and for biological filter construction in the Three Gorges Reservoir area to control the transport of sediment and non-point source pollutants.

Leaf gas exchange, chlorophyll fluorescence, non-structural carbohydrate content and growth responses of Distylium chinense during complete submergence and subaerial re-emergence

We examined outdoor effects of submergence and subaerial re-emergence on photosynthesis, non-structural carbohydrate content and growth of Distylium chinense, an evergreen shrub used in restoration programs under way at the hydro-fluctuation belt of the Three Gorges Reservoir Region. Two-year-old D. chinense seedlings were completely submerged for 150 days, then drained and held for a further 60 days. All the seedlings survived the flooding period. The biomass, root/shoot ratio, net photosynthetic rate, stomatal conductance, maximal photochemical efficiency (Fv/Fm), photochemical quenching (qP) and electron transfer rate (ETR) of submerged seedlings were significantly depressed in relation to control seedlings. We also observed increases in chlorophyll content and reductions in non-photochemical quenching (qN) during submersion. The contents of carbohydrates (soluble sugars and starch) in leaves and roots decreased significantly during submergence, but the levels (especially of starch) gradually stabilized toward the end of the submersion period. All seedlings survived for 60 days after drainage. Biomass had almost completely recovered by the end of the experiment, and the net photosynthetic rate, stomatal conductance, Fv/Fm, qP, qN and ETR increased gradually after draining, rising to the values similar to those of controls by the end of the experiment. Carbohydrate content also recovered to the level of controls by the end of the experiment, although starch and soluble sugar contents decreased and increased, respectively, 30 days into the recovery period. We therefore conclude that D. chinense seedlings are flood-tolerant and have excellent post-submergence recovery abilities that make this a suitable candidate species for vegetation restoration at the hydro-fluctuation belt of the Three Gorges Reservoir Region.

三峡水库奉节以东秭归和巫山段消落带植物群落动态特征

三峡水库奉节以东秭归和巫山段消落带植物群落动态特征

Response of primary vectors and related diseases to impoundment by the Three Gorges Dam

To investigate the impact of the Three Gorges Dam on the local ecological environment. We conducted a 3-year cross-sectional survey of natural focus infectious diseases in the area before and after the water level rose to 156 m to evaluate the dam's health impacts. Direct and indirect immunofluorescence methods were applied to detect rat antigen and antibody of haemorrhagic fever with renal syndrome (HFRS). Fresh rat kidneys were inoculated in Korth's culture medium to detect Leptospira. A group of captured crabs were ground to observe the metacercariae of Paragonimus. Serum samples were collected from healthy local individuals. ELISA kits were used to detect human antibody against HFRS and paragonimiasis. Human Leptospira infections were detected by a microscopic agglutination test. Upstream rodent density increased significantly with Rattus flavipectus and Apodemus agrarius as the major pathophoric genera. The infection rate of human HFRS and Leptospira in the upstream human population samples was significantly higher than in the downstream samples and correlated with the increase in rodent density. Paragonimus infection rates remained at a low level during the study. Culex pipiens fatigan and Armigeres obturbans were the dominant species of mosquito. The creation of the Three Gorges Dam changed the proliferation of intermediary agents of diseases, but not notably. However, the ecological effects on the environment may require a prolonged period of time to manifest themselves; thus, long-term and effective surveillance of vectors and related diseases needs to be established.

Prospects for cultivating white mulberry (Morus alba) in the drawdown zone of the Three Gorges Reservoir, China

Restoration of vegetation is the most viable management approach for restoring ecological functions in the drawdown zone (hydro-fluctuation belt) of the Three Gorges Reservoir. The selection of plants for this purpose is therefore critically important. Most indigenous plants are not adapted, however, to the counter-seasonal fluctuation of water levels and rapid changes of up to 30 m in water depth that characterize the management of the reservoir. As a result, the reservoir drawdown zone tends to be vegetation deficient. Mulberry (Morus alba L.) has attracted attention as a suitable woody plant for restoring woody vegetation because of its strong adaptation to environmental stresses and the finding that it survives up to 7 m of flooding in parts of the drawdown zone. Comprehensive evaluation of research is therefore required in order to provide guidance for the rational use of mulberry in vegetation restoration strategies for the drawdown zone. Knowledge of the physiology of mulberry adaptation to stress is reviewed here, along with a detailed review of the ecology and agricultural benefits and limitations of mulberry in the context of the Three Gorges Reservoir. It is proposed that a cultivation model for mulberry plants based on ecological principles should be adopted for use within the drawdown zone and that a wider range of biophysical and socio-economic research to develop this model further should be conducted in the future.

EXPERIMENTAL RESEARCH ON CHANGES IN THE MECHANICAL PROPERTY LAW OF RESERVOIR BANK SANDSTONE UNDER "IMMERSION-AIR DRY" CIRCULATION

During the normal operating of reservoir, the rock mass quality in hydro-fluctuation belt of reservoir bank will degrade gradually under the water-rock interaction because of the periodically impoundment and drainage. In this article, with the consideration of the change of water pressure, an experiment was performed to simulate the process of immersion-air dry cycles with sandstones selected from the hydro-fluctuation belt of Three Gorges reservoir area. Test results indicates that the change of water pressure and immersion-air dry circulation caused cumulative and irreversible damage to the sandstone samples. The compressive strength, cohesion force and internal friction angle all deteriorated gradually. Moreover, the more immersion-air dry cycles, the more serious damage to the rock mass. The research results have great reference value for studying the deterioration law of the rock mass in hydro-fluctuation belt of reservoir bank as well as provide favourable evidences for the long-term stability analysis of reservoir bank.

The response of mulberry trees after seedling hardening to summer drought in the hydro-fluctuation belt of Three Gorges Reservoir Areas

Interest has developed in the potential of mulberry (Morus alba), a woody perennial, for revegetating the hydro-fluctuation belt of the Three Gorges Reservoir due to its resistance to water-logging stress. To be useful, the trees must also be able to withstand dry conditions in summer when temperatures can be very high and droughts become severe quickly. Here, we report a study in which mulberry seedlings were grown in a greenhouse under a variety of simulated soil water conditions reflecting potential summer scenarios in the hydro-fluctuation belt of the Three Gorges Reservoir Area. We compared the responses of two pretreatment groups of mulberry seedlings to different levels of drought stress. The pretreatment groups differed with respect to drought hardening: the daily-managed (DM) group had relative soil moisture held constant in the range 70-80 %, while the drought-hardened (DH) group had relative soil moisture held constant at 40-50 %. Following the month-long pretreatment of seedlings, the two groups of young trees (DM and DH) were then respectively subjected to three levels of drought stress for a month: normal watering, moderate drought stress, and severe drought stress. A series of measurements comparing the physiological status of the plants in the two groups were then made, and the following results were obtained: (1) As drought stress increased, the heights, base diameters, root surface areas, photosynthetic rates (Pn), stomatal conductances (Gs), and transpiration rates (Tr) of the mulberry trees in both groups (DM and DH) decreased significantly, while the specific root area and abscisic acid (ABA) contents had increasing trends. Root activity and instantaneous water use efficiency of mulberry trees in both groups (DM and DH) were all raised under drought stress conditions than under normal watering, but the root/shoot ratio and leaf water potential were lowered. (2) At the same level of soil water content, the heights, base diameters, root/shoot ratios, root surface areas, specific root areas, photosynthetic rates (Pn), stomatal conductances (Gs), and transpiration rates (Tr) of the young mulberry trees in the DH were all significantly higher than those of the control group (DM). Leaf water potential, instantaneous water use efficiency, and abscisic acid content of DH were all significantly lower than DM. Under different degrees of drought stress, the growth of mulberry trees will be inhibited, but the trees can respond to the stress by increasing the root absorptive area and enhancing capacity for water retention. Mulberry trees demonstrate strong resistance to drought stress, and furthermore drought resistance can be improved by drought hardening during the seedling stage.

Photosynthetic physio-response of Taxodium ascendens seedlings to different soil water gradients

Four different kinds of water treatments were applied to study the photosynthetic eco-physiological characteristics of Taxodium ascendens seedlings in the environment of the Three Gorges hydro-fluctuation belt. The four kinds of water treatments were: normal growth water condition (CK), light drought stress (T1), soil water saturation (T2), and soil submersion (T3). The results showed that different water treatments could effectively influence the content of the photosynthetic pigment, leaf gas exchange and apparent resources use efficiency of T. ascendens seedlings. It was also demonstrated that the T. ascendens seedlings could not only tolerate water submersion and wet conditions but also endure a certain degree of drought. To establish a protection forest system in the hydro-fluctuation belt in the Three Gorges Reservoir Area, the species T. ascendens is suitable for planting in conditions of root submersion or water-saturated soil. In case it is planted in drought conditions, this tree species should be watered appropriately in order to keep its normal net photosynthetic rate.

Effect of soil water changes on photosynthetic characteristics of Taxodium distichum seedlings in the hydro-fluctuation belt of the Three Gorges Reservoir area

Four different kinds of water treatment were applied to examine the photosynthetic characteristics of baldcypress (Taxodium distichum) seedlings in the hydro-fluctuation belt of the Three Gorges Reservoir area. The aim was to shed light on the physio-ecological adaptation of this species to changing water levels for revegetation purposes. The water treatments were normal growth water condition (CK), light drought water stress (T1), growth under soil water saturation (T2) and growth with soil submersion (T3). T3 had the lowest content of photosynthetic pigment; T1 and T2 did not differ from CK in the content of chlorophyll and carotenoid. The ratio of chlorophyll a to b in the four groups ranged from 2.04 to 2.69 and the ratio of chlorophyll to carotenoid from 3.08 to 4.51. In group T1, the seedling of baldcypres had lower apparent light use efficiency, lower apparent CO2 use efficiency and a lower net photosynthetic rate, with the net photosynthetic rate 24.9% lower than that of group CK. However, T2 and T3 did not differ from CK in apparent light use efficiency, apparent CO2 use efficiency and net photosynthetic rate. Water use efficiency of the four treatments consistently increased as treatment was prolonged; the average water use efficiency of T3 was the lowest while that of CK was the highest. Correlation analysis showed that the net photosynthetic rate of baldcypress seedlings was positively related to transpiration rate, stomatal conductance, water use efficiency, apparent light use efficiency and apparent CO2 use efficiency, but highly negatively related to the ratio of chlorophyll a to b. Net photosynthetic rate was not significantly related to the contents of chlorophyll and carotenoid, the ratio of chlorophyll to carotenoid, relative air humidity and intercellular CO2 concentration. The transpiration rate was positively correlated with stomatal conductance and negatively related to water use efficiency. The results showed that different water treatments could effectively influence the baldcypress seedlings’ content of photosynthetic pigment, leaf gas exchange and apparent resources use efficiency. The results verified that the species T. distichum takes on the features of a water-tolerant and hydrophilic plant, which can be considered as one of the species for the building of a forest protection system for the hydro-fluctuation belt in the Three Gorges Reservoir area. Baldcypress should not be planted in drought-stricken soils.