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1.
Flood control of the Yangtze River is an important part of China’s national water security.In July 2020,due to continuous heavy rainfall,the water levels along the middle-lower reaches of the Yangtze River and major lakes constantly exceeded the warning levels,in which Taihu Lake exceeded its highest safety water level and some stations of Poyang Lake reached their highest water levels in its history.In August 2020,another huge flood occurred in the Minjiang River and the Jialing River in the upper Yangtze River,and some areas of Chongqing Municipality and other cities along the rivers were inundated,resulting in great pressure on flood control and high disaster losses.The 2020 Yangtze River flood has received extensive media coverage and raised concerns on the roles of the Three Gorges Dam and other large reservoirs in flood control.Here we analyze the changes in the pattern of the Yangtze River flood control by comparing the strategies to tackle the three heavy floods occurring in 1954,1998,and 2020.We propose that the overall strategy of the Yangtze River flood control in the new era should adhere to the principle of"Integration of storage and drainage over the entire Yangtze River Basin,with draining floods downstream as the first priority"by using both engineering and non-engineering measures.On the basis of embankments,the engineering measures should use the Three Gorges Dam and other large reservoirs as the major regulatory means,promote the construction of key flood detention areas,keep the floodways clear,and maintain the ecosystem services of wetlands and shoals.In terms of non-engineering measures,we should strengthen adaptive flood risk management under climate change,standardize the use of lands in flood detention areas,give space to floods,and promote the implementation of flood risk maps and flood insurance policies.The ultimate goal of this new flood control system is to enhance the adaptability to frequent floods and increase the resilience to extreme flood disasters. 相似文献
2.
The soil Microbial Carbon Pump as a new concept for terrestrial carbon sequestration 总被引：1，自引：0，他引：1
Soil is a huge terrestrial carbon pool, which has higher carbon storage than the sum of atmospheric and terrestrial vegetation carbon. Small fluctuations in soil carbon pool can affect regional carbon flux and global climate change. As soil organic carbon plays key roles in soil carbon storage and sequestration, studying its composition, sources and stability mechanism is a key to deeply understand the functions of terrestrial ecosystem and how it will respond to climate changes. The recently-proposed concept of soil Microbial Carbon Pump(MCP) emphasizes the importance of soil microbial anabolism and its contributions to soil carbon formation and stabilization, which can be applied for elucidating the source, formation and sequestration of soil organic carbon. This article elaborates MCP-mediated soil carbon sequestration mechanism and its influencing factors, as well as representative scientific questions we may explore with the soil MCP conceptual framework. 相似文献
3.
Based on deep geophysical detections, we have reconstructed the crustal structure from the eastern margin of the Tibetan Plateau to the Jiangnan-Xuefeng orogenic belt. The results suggest that the Yangtze Block was overthrusted by crustal materials in its NW direction from the eastern Tibetan Plateau but in its SE direction from the Jiangnan orogen. These overthrusting effects control the crustal structure from the western Sichuan to the western area of the Jiangnan orogen-Xuefeng orogenic belt. The eastward extruded materials from the eastern Tibetan Plateau were blocked by the rigid basement in the Sichuan Basin, where upper-middle crust was overthrusted whereas the lower crust was underthrusted beneath the Sichuan Basin. The underthrusted unit was absorbed by crustal folding, shortening and thickening in the Yangtze Block, forming the Xiongpo and Longquan Mountains tectonic belts and resulting in the NW-directed thrusting of the Pujiang-Chengdu-Deyang fault, and the western hillsiden fault in the Longquan Mountain. These results provide resolution to the controversy where the eastward extrusion material from the Qinghai-Tibet Plateau had gone. Overall, that Yangtze Block was subjected to thrusting of the crustal materials from the orogenic belts over its both sides. This finding has implications for the study of the intracontinental orogenic mechanism in South China, the reconstruction of tectonic evolutionary history and the kinematics processes during the lateral extrusion of the Tibet Plateau. 相似文献
4.
The two leading modes of winter surface air temperature(SAT) over China during 1961–2017 are a spatially consistent pattern and a north-south dipole pattern. Based on the two leading modes, the characteristics of the extreme cold and warm days in the two patterns, defined by the standard deviation larger than 1.28 or smaller than-1.28 in the time series of the two leading modes, are analyzed. With the increase of winter SAT during 1961–2017, the number of spatially consistent extreme cold days decreased and their occurrence was restricted to late December to early January, whereas the number of spatially consistent extreme warm days increased significantly in January and February. Global warming is associated with an increase in the spatially consistent extreme warm days and a decrease in spatially consistent extreme cold days, but has little relation to the sum of extreme cold and warm days of either the spatially consistent or north-south dipole pattern. The Siberian High(SH) is the main factor controlling the sum of spatially consistent extreme warm and cold days. The strong(weak) SH before(after) the1990 s corresponds to an increase(decrease) in the sum of the spatially consistent extreme warm and cold days. The occurrences of extreme south-cold-north-warm and extreme south-warm-north-cold days are related to the north-south difference of the SH.When the center of the SH is in mid-high latitudes, the extreme south-warm-north-cold(south-cold-north-warm) days occur more(less) often. During the winters of 1961–2017, the total number of extreme cold and warm days of the north-south dipole pattern changes negligibly. The North Atlantic meridional overturning circulation(AMOC) may be the main factor affecting the sum of the extreme cold and warm days of the two types of SAT pattern in China. 相似文献
5.
Numerical modeling of free-surface flow over a mobile bed with predominantly bedload sediment transport can be done by solving the shallow water and Exner equations using coupled and splitting approaches.The coupled method uses a coupling of the governing equations at the same time step leading to a non-conservative solution.The splitting method solves the Exner and the shallow water equations in a separate manner,and is only capable of modeling weak free-surface and bedload interactions.In the current study,an extended version of a Godunov-type wave propagation algorithm is presented for modeling of morphodynamic systems using both coupled and splitting approaches.In the introduced coupled method the entire morphodynamic system is solved in the form of a conservation law.For the splitting technique,a new wave Riemann decomposition is defined which enables the scheme to be utilized for mild and strong interactions.To consider the bedload sediment discharge within the Exner equation,the Smart and Meyer-Peter&Müller formulae are used.It was found that the coupled solution gives accurate predictions for all investigated flow regimes including propagation over a dry-state using a Courant-Friedrichs-Lewy(CFL)number equal to 0.6.Furthermore,the splitting method was able to model all flow regimes with a lower CFL number of 0.3. 相似文献
6.
Zhaode YUAN Jing LIU-ZENG Xue LI Jing XU Wenqian YAO Longfei HAN Tao LI 《中国科学:地球科学(英文版)》2021,64(1):127-147
Large-scale detailed mapping plays a key role in revealing the rupture characteristics and mechanisms of strong earthquakes.Relatively few studies have been performed on the surface ruptures of large earthquakes in central and western Tibet due to its remote nature and high elevation.Based on high-resolution unmanned aerial vehicle(UAV)photography,we mapped the coseismic surface rupture of the 2014 Yutian M_s7.3 earthquake.Along the western Altyn Tagh fault system,the earthquake produced~37 km of surface rupture along the South Xor Kol fault(southern section S1),Xor Kol fault(central section S2)and Ashikule fault(northern section S3).Section S1 has a 16-km-long surface rupture with an average sinistral offset of 52±25 cm and a maximum offset of~90 cm,while section S3 has a 14.2-km-long surface rupture with an average sinistral offset of 36±21 cm and a maximum offset of~84 cm.A compilation of 5308 cracks yields an average crack width along the southern section of 85±71 cm and a maximum width of~700 cm;the average width along the central section is 39±21 cm,and the maximum width is 243 cm;and the average width along the northern section is 61±44 cm with a maximum of~340 cm.In addition,the average cumulative opening across rupture zone is 3.4±2.9 m along the southern section,with a maximum of~17 m;4.3±3.6 m along the central section,with a maximum of~13 m;and 1.7±1.6 m along the northern section,with a maximum of~6 m.Evidently,the average crack width and cumulative opening decrease towards bends and steps along the fault.A global synthesis of surface rupture distributions corresponding to strike-slip earthquakes indicates that the rupture zone is wider near the complex parts of fault geometries(such as bends,steps and fault bifurcations)than along straight sections,suggesting that the fault geometry has an obvious control on the surface rupture width.The widespread cracks at the intersection between the Xor Kol and South Xor Kol faults may indicate that an extensional regime is more likely to produce distributed offfault deformation,which provides an observational constraint for the numerical simulation of dynamic rupture on a fault.In addition to coseismic surface rupture,the Yutian earthquake also produced a large number of gravity-driven slides on alluvial fans with gentle slopes.The friction efficiency of the water-bearing salt layer beneath fans could decrease the sliding threshold and trigger instability under surface shaking.These distributed deformations and gravity-driven slides reflect the coupling between the rupture propagation and fault geometry and indicate that the rupture may have propagated in two directions along the Ashikule fault after passing through a step.Therefore,the investigation of coseismic surface rupture provides important observational constraints on the dynamic rupture process. 相似文献
7.
Numerical simulations of shake-table experiment for dynamic soil-pile-structure interaction in liquefiable soils 总被引：5，自引：4，他引：1
A shake-table experiment on pile foundations in liquefi able soils composed of liquefi able sand and overlying soft clay is studied. A three-dimensional(3D) effective stress fi nite element(FE) analysis is employed to simulate the experiment. A recently developed multi-surface elasto-plastic constitutive model and a fully coupled dynamic inelastic FE formulation(u-p) are used to model the liquefaction behavior of the sand. The soil domains are discretized using a solid-fl uid fully coupled(u-p) 20-8 noded brick element. The pile is simulated using beam-column elements. Upon careful calibration, very good agreement is obtained between the computed and the measured dynamic behavior of the ground and the pile. A parametric analysis is also conducted on the model to investigate the effect of pile-pinning, pile diameter, pile stiffness, ground inclination angle, superstructure mass and pile head restraints on the ground improvement. It is found that the pile foundation has a noticeable pinning effect that reduces the lateral soil displacement. It is observed that a larger pile diameter and fi xed pile head restraints contribute to decreasing the lateral pile deformation; however, a higher ground inclination angle tends to increase the lateral pile head displacements and pile stiffness, and superstructure mass seems to effectively infl uence the lateral pile displacements. 相似文献
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Historical biome changes on the Tibetan Plateau provide important information that improves our understanding of the alpine vegetation responses to climate changes.However,a comprehensively quantitative reconstruction of the historical Tibetan Plateau biomes is not possible due to the lack of quantitative methods that enable appropriate classification of alpine biomes based on proxy data such as fossil pollen records.In this study,a pollen-based biome classification model was developed by applying a random forest algorithm(a supervised machine learning method)based on modern pollen assemblages on and around the Tibetan Plateau,and its robustness was assessed by comparing its results with the predictions of the biomisation method.The results indicated that modern biome distributions reconstructed using the random forest model based on modern pollen data generally concurred with the observed zonal vegetation.The random forest model had a significantly higher accuracy than the biomisation method,indicating the former is a more suitable tool for reconstructing alpine biome changes on the Tibetan Plateau.The random forest model was then applied to reconstruct the Tibetan Plateau biome changes from 22 ka BP to the present based on 51 fossil pollen records.The reconstructed biome distribution changes on the Tibetan Plateau generally corresponded to global climate changes and Asian monsoon variations.In the Last Glacial Maximum,the Tibetan Plateau was mainly desert with subtropical forests distributed in the southeast.During the last deglaciation,the alpine steppe began expanding and gradually became zonal vegetation in the central and eastern regions.Alpine meadow occupied the eastern and southeastern areas of the Tibetan Plateau since the early Holocene,and the forest-meadow-steppe-desert pattern running southeast to northwest on the Tibetan Plateau was established afterwards.In the mid-Holocene,subtropical forests extended north,which reflected the“optimum”condition.During the late Holocene,alpine meadows and alpine steppes expanded south. 相似文献
10.
Much effort has been made in investigating the seismic response and failure mechanism of rectangular subway stations,however,the influence of earth retaining systems has generally been ignored in previous studies.This paper presents a numerical study on the seismic performance of a rectangular subway station with/without earth retaining systems by taking fender piles as the example,and aims to illustrate how the existence of fender piles affects seismic responses on subway stations.The loading conditions of subway stations and their surrounding soils prior to earthquakes are discussed.Next,seismic responses of subway stations with or without fender piles were simulated.Afterward,earthquake-induced deformations of stations and surrounding soils,as well as the internal forces and damage modes of the structural components,were systematically studied.Consequently,the seismic performance of the stations was affected by the existence of fender piles.In addition,earthquake intensity is illustrated.The study showed that deformation modes of surrounding soils and damage modes of stations were different with regard to the existence of fender piles.Meanwhile,earthquake intensity influencing the seismic performance of stations with or without fender piles were found to be opposite. 相似文献
11.
舌状叶镖水蚤(Phyllodiaptomus tunguidus)是我国特有的大型哲水蚤,主要分布在我国华南地区.根据2000年对广东省19座典型大中型水库的2次采样和2002年对流溪河水库和新丰江水库的5次采样,重点测定了流溪河水库、新丰江水库和鹤地水库等3座大型水库中舌状叶镖水蚤个体体长及形态参数,分析了广东省大中型水库中舌状叶镖水蚤的种群与个体大小的分布特征.在对19座水库的2次采样中,11座水库发现该种成体,其中5座水库在丰水期没有出现该种的成体,6座水库在丰水期和枯水期都有该种类成体的出现.丰水期与枯水期舌状叶镖水蚤的平均丰度分别为0.465ind./L和0.996ind./L.舌状叶镖水蚤主要出现在大型水库中,特别是贫营养的大型水库,其丰度主要由食物数量、质量与捕食压力所决定.2002年,流溪河水库丰度和新丰江水库舌状叶镖水蚤全年的平均值为1.308ind./L和0.294ind./L,丰水期高于枯水期.在个体大小和形态特征上,2座贫营养水体——流溪河水库、新丰江水库的舌状叶镖水蚤的体长与第一触角长度均大于中营养水体——鹤地水库,这种形态上的差异是由鱼类捕食方式(滤食或选择性捕食)所决定. 相似文献
12.
鄱阳湖流域干旱气候特征研究 总被引：2，自引：1，他引：1
本文利用鄱阳湖流域127个站点1960-2007年逐日降水和温度资料,选用Z指数对鄱阳湖流域的气象干旱进行分析,并将干旱分为偏旱、大旱和特旱三个等级.研究结果表明鄱阳湖流域干旱基本呈现出南少北多、南强北弱的空间分布形式.鄱阳湖流域7-12月发生的干旱以偏旱为主,大旱和特旱主要出现在1-6月.线性趋势变化分析表明,2000年以来干旱范围和干旱强度均呈现出增加的趋势,其中,2003、2004和2007年的干旱较为严重.2003年大部分月份偏旱范围广、强度大,全年大旱和特旱出现的范围均较小,但3-4月和6-7月的大旱和特旱强度较大;2004年大部分月份偏旱范围和强度均相对较小,但在3月和6月出现范围较大且强度较强的大旱和特旱;2007年干旱分布更为极端,仅在7、10和11月出现范围较广或强度较大的偏旱,而在5月集中出现面积超过80%的大旱和特旱. 相似文献
13.
Structure and Significance of S-wave Velocity and Poisson’s Ratio in the Crust beneath the Eastern Side of the Qinghai-Tibet Plateau 总被引：2，自引：0，他引：2
The receiver functions of body waves of distant earthquakes obtained for the regions beneath 41 digital stations (Lhasa and
GANZ in Tibet, Mandalay and Rangoon in Myanmar, SHIO in India, CHTO in Thailand, and station network in Sichuan and Yunnan)
were used to invert for S-wave structure in the crust and upper mantle in Sichuan, Yunnan, and their surrounding areas. Meanwhile
the distribution characteristics of the Poisson’s ration and the crustal thickness in Sichuan and Yunnan areas were also obtained.
Results indicate that the depth of Moho beneath the eastern side of Qinghai-Tibetan plateau varies strikingly. It is obvious
that the greatest changes in crustal thickness occur in a north-south direction. The crustal thickness decreases from north
to south, being as thick as 70 km in eastern Tibet, the northern portion of our area of interest, and less than 30 km in Chaing
Mai and Rangoon, the southern portion of our area. There are, however, exceptions regarding the trend. The thickness exhibits
an east-west variation trend in the area from Ma’erkong-Kongding in Sichuan to Lijiang in Yunnan. In general the Jinpingshan-Longmenshan
fault and Anninghe fault can be taken as the boundaries of this exception area. The thickness in Kongding in the west is 68 km,
while it is only 39 km in Yongchuan in the east. Moreover the Poisson’s ratio values in the blocks of central Sichuan and
Sichuan-Yunnan Diamond are high, and a low velocity layer in the crust of this area can be obviously detected. The distribution
characteristics of the high Poisson’s ratio and the low velocity of the crust in this block correspond to the tectonic structure,
being in contrast with the surrounding areas. Combining with the distribution features of the modern tectonic stress field,
it is deduced that the Sichuan-Yunnan area is probably the channel through which the materials of the lithosphere flow eastward. 相似文献
14.
This study investigated the subcellular distribution of Cu, Zn, Cd and Ag in liver of mallard (Anas platyrhynchos), spot-billed duck (A. poecilorhyncha) and great cormorant (Phalacrocorax carbo) to better understand metal fractionation and dynamics in avian liver. Most of the total Cu, Zn, Cd and Ag were present in hepatocytosol, and their concentrations increased with total hepatic levels in all the three avian species. Copper, Zn and Cd in hepatocytosol were present mostly in metallothionein fractions (MTs), and Cu and Cd contents in this fraction were positively correlated with hepatocytosol levels in all the species. Silver was observed mostly in both high-molecular weight and MT fractions in hepatocytosol in mallard and great cormorant, whereas it was present in both low-molecular weight and MT fractions in spot-billed duck, suggesting that distribution of Ag in the hepatocytosol was species-specific. The elution profile of metals in MT fractions revealed six metallic peaks in mallard and spot-billed duck, and three peaks in great cormorant, implying the presence of multiple MT isoforms in the liver of these avian species. The present study demonstrated that MTs are closely associated with metal regulation, especially Cu and Cd, in these three aquatic birds. 相似文献
15.
Residues of selected antibiotics in water and mud from shrimp ponds in mangrove areas in Viet Nam 总被引：1，自引：0，他引：1
In recent years, antibiotics have been used widely in intensive shrimp culture and this may lead to their contamination of the environment. Surveys on residues of trimethoprim (TMP), sulfamethoxazole (SMX), norfloxacin (NFXC) and oxolinic acid (OXLA) in water and mud in shrimp ponds in mangrove areas were conducted in the north as well as in south of Viet Nam in July and August, 2002. The results show that these antibiotics are found in all samples in both shrimp ponds and surrounding canals. The highest concentrations of TMP, SMX, NFXC and OXLA are 1.04, 2.39, 6.06, and 2.50 ppm in water samples; and 734.61, 820.49, 2615.96, 426.31 ppm (based on wet mud weight), respectively. The comparison of antibiotics residues between study sites and types of shrimp ponds will be discussed in this paper. The results also suggest that antibiotics residues may cause harmful effect on ecosystems in the study sites. 相似文献
16.
We apply a geospeedometer previously developed in this lab to investigate cooling rate profiles of rhyolitic samples initially held at 720–750°C and quenched in water, liquid nitrogen, and air. For quench of mm-size samples in liquid nitrogen and in air, the cooling rate is uniform and is controlled by heat transfer in the quench medium instead of heat conduction in the sample. The heat transfer coefficient in ‘static’ air decreases with increasing sample size. For quench of mm-size samples in water, heat transfer in water is rapid and the cooling rate is largely controlled by heat conduction in the sample. Our experimental results are roughly consistent with previous calculations for cooling in air and in water (although constant heat transfer coefficients were used in these calculations), but cooling rate in liquid nitrogen is only 1.8–2.3 times that in ‘static’ air, and slower by a factor of 2 than calculated by previous authors. Cooling rate in compressed airflow is about the same as that in liquid nitrogen. The experimental results are applied to interpret cooling rates of pyroclasts in ash beds of the most recent eruptions of the Mono Craters. Cooling rates of pyroclasts are inversely correlated with sample size and slower than those in air. The results indicate that the hydrous species concentrations of the pyroclasts were frozen in the eruption column, rather than inside ash beds or in flight in ambient air. From the cooling rates, we infer eruption column temperature in a region where and at a time when hydrous species concentrations in a pyroclast were locked in. The temperature ranges from 260 to 570°C for the most recent eruptions of Mono Craters. These are the first estimates of temperatures in volcanic eruption columns. The ability to estimate cooling rates and eruption column temperatures from eruptive products will provide constraints to dynamic models for the eruption columns. 相似文献
17.
Regolith surface characteristics and response were examined over a three‐year period in a badland area in a Mediterranean middle‐mountain zone near Vallcebre (Eastern Pyrenees). Preliminary work carried out in this area indicated clear seasonal patterns of regolith properties driven by frost heaving in winter and crusting and erosion in the rest of the year. Rainfall simulations were performed with a small portable nozzle simulator in order to study seasonal changes in runoff generation, erosion rates and raindrop effect on bulk density changes. The results showed large seasonal variations in runoff and erosion responses. In?ltration rates after runoff start were correlated with precipitation depth before runoff start; runoff generation was therefore related to regolith saturation only to a very limited extent. Erosion rates were more controlled by runoff rates than by the weakness of regolith against raindrop splash, and sediment grain size increased with concentration. The combined role of antecedent regolith moisture and bulk density explained most of the seasonal variability in in?ltration, bulk density changes during rainfall and erosion rates, but some seasonal differences in sediment detachability were not explained by these variables and may be attributed to changes in roughness. Overall, runoff and erosion responses were relatively stable during spring and autumn, whereas wide variations in in?ltration rates and sediment detachment occurred in winter and summer respectively. Experiments conducted in a single season would have produced poorly representative, if not erroneous, results. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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The haematological, biochemical, and enzymological alterations produced on exposure of Channa punctatus to LC50 (11.2 mg/L) for 96 h and to a sublethal concentration (1.12 mg/L) of cadmium (Cd2+) for 15, 30, 60, and 120 days have been studied. The fish were hypoglycemic and hypolactemic. The pyruvate content of blood and liver decreased in acute and all stages of chronic exposure except for 30 days where significant increase was recorded. Depletion was noted in the total protein and glycogen content of liver and muscle, and the level of lactate in liver in the two types of exposure. The levels of muscle lactate and pyruvate increased in both exposures. The activities of hexokinase, glucose-6-phosphatase, and lactate dehydrogenase decreased in liver after 96 h and all stages of chronic exposure except 30 days. The activities of hexokinase and lactate dehydrogenase in muscle and glutamate-oxalacetate transaminase and glutamate-pyruvate transaminase in serum, liver, and muscles increased in all exposures. The activities of succinate and malate dehydrogenases in liver and muscles decreased after acute and all stages of chronic exposure. The above results suggest that glycolysis and gluconeogenesis were impaired in liver but glycolysis prevailed in muscle. Aerobic oxidation is adversely affected in metal exposed fish, while proteolysis was increased. 相似文献