Disaster characteristics and mitigation of Chutigang gully debris flow, Mangkang county, Tibet
[Background] There were many debris flow gullies along the Mangkang county section of the Jinsha River. The frequent debris flow activities had destroyed the roads along the river, and even blocked the river to form a dammed lake, which seriously threatens the normal life of people in this area. In order to clearly understand the formation law and disaster-causing characteristics of debris flows in this area, this study selects the representative Chutigang gully as the research object, and we conducted detailed field investigation and analysis for providing theoretical reference for the prevention and control of debris flow disasters in this region. [Methods] In this study, the peak discharge of the latest debris flow was calculated by using the cross-section survey method:firstly, a typical channel section was selected, and its geometric parameters, channel longitudinal gradient and debris flow's mud mark high were measured, secondly these parameters were substituted into the Manning formula to complete the calculation. The outbreak scales of debris flows under different rainfall frequencies were calculated by using the rain-flood method, and the calculation results were substituted into two empirical formulas of river blocking to analyze the river blocking probability by debris flows under different rainfall frequencies. [Results] After field investigation, the solid source reserve of Chutigang gully was 625.1×104 m3, among which solid source of slope erosion was 576.8×104 m3. The peak discharge of the latest debris flow activity was 122.92 m3/s, and its outbreak scale was close to the magnitude of once in 50-year period. According to two empirical calculation formulas about river blocking by debris flow, it was known that when a debris flow with a magnitude of once in 100-year period, it may cause serious blockage of the river, and a once in 50-year period debris flow may cause minor blockages in the river. It should be alerted to the risk of debris flow blocking the main river to form a dammed lake. [Conclusions] According to the field investigation, most of the solid source of Chutigang gully was located in the middle and lower reaches of the watershed, which was prone to cause blockage-collapse phenomenon and expands the magnitude of debris flow. Based on the disaster characteristics of debris flow in Chutigang gully, a "Reinforcement+Blocking" disaster mitigation project was proposed, of which the check-dams group were mainly arranged in the middle and lower reaches of the watershed, they were used to reduce the accumulation of loose solid materials from both sides of the hillslope, and to reduce the probability of the channel being blocked. Silt-trap dam can reduce the debris flow peaks discharge and thereby mitigate the degree of erosion on the downstream channel. The treatment project can provide reference for the management of debris flow disasters in this region.
LU Huiping, CHEN Jie, Lü Wenqiang, HE Youhua, DONG Yanli
Changes of water and sediment and soil erosion characteristics on the northern slope of Qilian Mountains in recent 20 years
[Background] The northern slope of Qilian Mountains is the source of many rivers in Hexi Corridor, as an important ecological security barrier in western inland area of China, which undertakes the diverse ecological functions such as water conservation, biodiversity protection. In recent 20 years, Qilian Mountain experienced a conversion from disordered exploitation of natural resources to the gradual restoration of ecological system. Our study was conducted to provide a technical basis to scientifically evaluating the effects of ecological restoration and effectively controlling the soil and water erosion in Qilian Mountain National Park. [Methods] In this study, five representative basins were selected, to investigate the spatial and temporal variations of runoff, sediment and intensity of soil erosion using the methods of anomaly analysis and variance analysis, based on the runoff, sediment and precipitation data measured at five hydrological stations including Zamusi, Jiutiaoling, Yingluoxia, Changmabao and Dangchengwan in 2002-2021. [Results] Compared to 2002-2011, the runoff in 2012-2021 observed from Zamusi station and Jiutiaoling station in Shiyang River Basin decreased respectively by 9.82% and 2.24%, while the runoff from Yingluoxia station in the Heihe River Basin increased by 11.88%, and the runoff from Changmabao station and Dangchengwan station in the Shule River Basin increased by 7.45% and 11.47%, respectively. Overall, the variations of runoff on the northern slope of Qilian Mountains showed the decreasing trend in the eastern yet the increasing trends in the middle and western, which were mainly caused by the regional climate change. Moreover, the sediment amounts at Zamusi, Changmabao, Dangchengwan station, decreased by 38.81%, 14.45%, and 40.16% respectively, yet at Jiutiaoling and Yingluoxia station increased by 79.35% and 63.96%, respectively. The intense rainfall may be the major driving force for the increasing sediment. Further, the average hydraulic erosion modulus for all the stations were less than 500t/(km2·a) in the last 20 years, and its intensities were within the allowable erosion amount, but the intensity of soil erosion at Changmabao station had the great risk to exceed the allowable limit. [Conclusions] The problems of ecological environment on the northern slope of Qilian Mountains has been initially settled, and the ecological environment has been improved. However, the Changma River basin is prone to the excessive soil and water loss and its effective control should be paid the great attention in future.
ZHOU Zhuoli, ZHANG Zhuodong, GAO Xiaofei, QU Xinmiao, HE Enpei
Comparison of centrifuge and pressure plate on soil water retention curve determination
[Background] Accurate and efficient determination of soil water retention curve is important for the study of soil water movement and soil erosion. Various measurement methods are based on different mechanisms and each method has different applicability. Comparing method differences across multiple soil types can reflect the influence of soil properties on measurement results of equipment and provide a reference for selecting suitable methods for determining soil water retention curve. [Methods] Centrifuge and pressure plate were used to determine the soil water retention curve of black soil, loessal soil, red soil, cinnamon soil and purple soil in the water erosion region. The determination range of 2 methods was 0-15300cm, and the data were divided into the low suction stage (0-1000cm) and the high suction stage (>1000-15300cm) to analyze the differences between the two methods. A paired samples t test was used to test the significance of the differences in soil volume water content determined by centrifuge and pressure plate. [Results] The water content of 5 soils measured by the centrifuge was lower than that of the pressure plate at low suction stage, contents while the result at high suction stage was the opposite pattern. The measurement results of black soil, loessal soil, cinnamon soil and purple soil had extremely significant differences (P<0.01) at high suction stage. The measurement difference of red soil was significant (P<0.05) at low suction stage, and the water contents measured by the 2 methods at high suction stage were very close. At high suction stage, soil types with high clay and silt content caused incomplete soil drainage due to insufficient balance time in the pressure plate, which was significantly different from the water content determined by the centrifuge. Soil types with high sand content were mainly affected by the change of bulk density at low suction stage, which obviously caused the centrifuge measurement result to be lower than that of the pressure plate. [Conclusions] Soil texture and pore distribution are the main reasons for the difference in measurement between the 2 methods for different soil types. For soils with high sand content, the soil volume is compressed obviously during the centrifuge determination process; for soils with high clay and silt content, the centrifuge method is relatively more suitable.
YU Haipeng, YANG Xiangwei, LI Jiazuo, ZHANG Chunping, YUAN Xigong, HUANG Yunan, LIU Xia
Analysis on spatial and temporal change of land use based on geo-information Tupu
[Background] Research on spatiotemporal land use variation characteristics carries great significance to capture the land resource deployment orientation and the impact degree on ecological environment. [Methods] Relying on the land use dynamic degree model and geographic information mapping theory, this paper investigates the characteristics of spatial and temporal variations on land use and the causes of mapping changes in two sequential cells from 2009-2013 and 2013-2018 in Mengyin County. [Results] 1) The land use structure for the study area was dominated by arable land and orchard land, representing over 56% of the total land area, with forest land being the second largest. During the decade, the decrease rate of land use quantity exhibited grassland > forest land > arable land, and the increase rate presented construction land > traffic land > water area > orchard land. 2) There were significant discrepancies in the type, quantity and area of major mapping units in both sequential cells. The mapping characteristics from 2009 to 2013 primarily featured the interchange of forest land and arable land, and the conversion of arable land into construction land, occupying 71.01% of the changed area. Spatially, the most significant patterns were found in forest land → arable land and arable land → construction land. From 2013 to 2018, the mapping was primarily characterized by the occupation and replenishment of arable land by construction land, the conversion of arable land to forest land, and the occupation of grassland by construction land, with an accumulated conversion ratio of 59.80%. In terms of space, the most significant were observed in arable land → construction land and arable land → forest land. 3) The pattern of arable land use change in the study area was predominantly prophase change and anaphase change, constituting 95.98% of its changing pattern; the pattern of forest land change was dominated by prophase change, accounting for 74.01%. [Conclusions] Significant discrepancies in the rate of land use change were identified over a 10-year period in Mengyin County. From 2009 to 2013, forest land declined and construction land expanded; from 2013 to 2018, there was a significant shrinkage of arable land, with a further expansion of construction land.
Dynamic change of vegetation cover and its driving factors in Wenshan of Yunnan over the past 20 years
[Background] Vegetation is the most active factor in the natural ecosystem and the inhibitory effect of surface vegetation cover on soil erosion has been well known. Existing studies have shown that under certain other conditions (precipitation, soil and topography), vegetation coverage has a significant negative correlation with soil erosion. Therefore, analyzing the dynamic changes of vegetation cover and its driving factors is critical to regional soil and water conservation, governance effectiveness evaluation and land space planning in mountainous areas. [Methods] Based on MOD13Q1 data, this paper systematically analyzed the temporal and spatial evolution characteristics of vegetation coverage in Wenshan from 2001 to 2020 using methods such as pixel dichotomy, one-dimensional linear regression equation, coefficient of variation, Hurst index and statistical methods. Spatial analysis was also employed by overlaying vegetation cover change information with land use during the past two decades to reveal the driving forces behind. [Results] 1) In the past 20 years, the annual vegetation coverage in the study area showed an upward trend of fluctuation, areas of extremely high vegetation coverage with FVC over 80% increased dramatically, ranging from 3997.22 km2 in 2001 to 15313.78 km2 in 2020. 2) Areas with improved and significantly improved vegetation coverage (84.51%) were more dominant than those areas of degraded and significantly degraded vegetation coverage (6.47%). About 80.98% of the total area was characterized by a stable vegetation coverage change, only 0.50% of the area showed a strong variability in vegetation coverage change, with a scattering distribution. However, the average Hurst index for 71.14% of Wenshan was <0.5, which indicated that there will be a certain degree of reverse decline for the future vegetation coverage change. 3) Based on overlay analysis, the dynamic change ratios of cultivated land, forest land and artificial surface were 38.14%, 35.01% and 27.67%, respectively, which were the major factors responsible for the vegetation coverage change. [Conclusions] The method mentioned in this study provides a reliable estimation, due to the consideration of time series images and multi-perspective analysis, which are potentially transferable to other mountainous areas as a robust approach for rapid assessment of vegetation coverage, as well as soil erosion control efforts. Overall, the status of vegetation coverage, the ecological environment has been continuously improved during the past 20 years, as well as the construction of ecological civilization.
HONG Qian, CHEN Xiaofeng, YU Weiqing, LI Xi, LIU Qing, WANG Xijin
An expevimental study on improvement of residual soil and the plant growth in transmission line tower foundation construction
[Background] Disposal of residual soil and vegetation restoration in damaged areas emerged during transmission line tower foundation construction are the main factors restricting the project compliance of soil and water conservation. Unreasonable disposal scheme of residual soil and inadequate vegetation restoration effect would cause soil erosion during the construction period of transmission line project, and it is very difficult to rectify before soil and water individual acceptance. In order to solve the problems above, and to promote the acceptance of water and soil conservation of power transmission and transformation construction projects, it is of great significance to study the method of improving construction residual soil into planting soil. [Methods] Experiment methods were determined by searching the keywords of "soil water and fertilizer conservation" "soil improvement materials" and "plant growth promotion", consulting the relevant literature and the actual situation of transmission line tower foundation construction, excluding the relevant research of tall trees, and focusing on the soil improvement methods for the growth of herbal plants. Indoor two factor gradient experiments were carried out to improve the residual soil by the mixed application of super absorbant polymer and organic fertilizer by setting nine improvement groups and one control group (CK), improvement groups were as follows:25/50 (A1B1), 50/50 (A2B1), 100/50 (A3B1), 25/100 (A1B2), 50/100 (A2B2), 100/100 (A3B2), 25/150 (A1B3), 50/150 (A2B3), 100/150 (A3B3) according to the added grams of "super absorbant polymer/organic fertilizer", and the mechanism of soil improvement and plant growth was analyzed by principal component analysis method, in which nine indexes representing soil improvement and vegetation growth selected in this study were recombined into a group of unrelated comprehensive indexes through dimension reduction transformation. [Results] 1) Soil improvement by using super absorbant polymer combined with organic fertilizer was significant, the content of soil organic matter increased synchronously with the increment of super absorbant polymer amount, and super absorbant polymer was conducive to improving the rapid degradation of nitrogen, phosphorus and potassium within organic fertilizer, but excessive application of super absorbant polymer would lead to the opposite effect. 2) Organic fertilizer promoted plant growth directly. With the increment of organic fertilizer addition, the plants aboveground and underground biomasses increased simultaneously. The aboveground and underground biomasses of plants decreased inversely with super absorbant polymer used excessively. And the effect of soil mixed improvement was more significant in the early period of vegetation restoration. 3) Through principal component analysis, it can be seen that the best effect of mixed application of super absorbant polymer and organic fertilizer on vegetation restoration was in A2B2 group, followed by A1B3 and A2B3 groups. 4) The outdoor experiment further confirmed that the vegetation restoration of the improved group was significantly better than that of the control group, and the vegetation restoration effect of the experimental group was basically consistent with the comprehensive score of the indoor experiment, which confirmed the reliability of the indoor experiment results. [Conclusions] The results of this study reached the original goal in the background by providing an important reference for synchronously solving the two big problems of residual soil disposal and vegetation restoration of transmission line tower foundation construction. It also has found an appropriate theoretical and practical basis for improving the one-time success rate of water and soil conservation acceptance of power transmission and transformation construction projects.
SHEN Faxing, ZHENG Taihui, DUAN Jian, HU Rui, YU Ronggang
Feasibility on artificial cultivation of bryophytes in rare earth tailings in southern Jiangxi
[Background] A large number of mine tailings have been generated by the excessive mining of rare earth ores. These tailings are characterized by low acidity, poor water storage capacity, low nutrient content, and high contents of rare earth and heavy metal elements, which seriously restrict the growth of plants. Biological soil crusts (BSCs) (associations of soil particles with mosses, fungi, algae, cyanobacteria, or lichens) are distributed extensively in South China, which can adapt to the arid and barren environment. Therefore, it may be used as an option for ecological restoration of mine tailings. However, limited information is available about the growth and influencing factors of artificial cultured BSCs in rare earth tailings.[Methods] Indoor incubation experiments of BSCs in the rare earth tailings were conducted to investigate the development characteristics of BSCs artificially cultivated in the rare earth tailings. Nine experimental treatments with 5 replications, including two factors (e.g. light intensity and soil water content) and three levels were randomly arranged. During the cultivation period (from November 2019 to July 2020), the coverage, plant density, and biomass of BSCs were dynamically monitored. The coverage, plant density, and biomass of cultivated BSCs were further statistically analyzed by univariate multivariate analysis of variance of a general linear model.[Results] 1) The indoor incubation experiment showed that the coverage of BSCs reached 100% in 80d, and the plant density was more than 54.8plants/cm2 in 140d, under the condition of high moisture (28%-30%). No significant differences in plant coverage and density existed among different light intensities.2) Also under the condition of high moisture, significant differences in moss biomass were observed among different light intensities in a decreasing order as follows:86.79mg/cm2 (at a medium light intensity of 5900lx), 70.15mg/cm2 (at a high light intensity of 5900lx), and 36.18mg/cm2 (at a low light intensity of 1900lx) (P<0.05). Under the conditions of medium soil moisture (13%-15%) plus medium light intensity, the coverage of BSCs was 54.07%, which was significantly higher than those under the conditions of medium soil moisture plus high light intensity and medium soil moisture plus low light intensity (P<0.05). Under the conditions of low soil moisture (5%-8%), BSCs could not grow and develop normally under all light intensities.[Conclusions] The obtained results indicate that BSCs could be used as a measure of ecological restoration in the rare earth tailings mining areas. Several moss species such as Trichostomum brachydontium, Trichostomum involutum, Anoectangium stracheyanum, and Brachymenium exile have good adaptability in vegetation restoration of rare earth tailings. Soil moisture is the most important factor affecting the development of BSCs. The optimal conditions for the growth of BSCs in rare earth tailings are soil water content of 28%-30% and light intensity of 5900lx.
Effects of exogenous calcium under deficient irrigation on the drought resistance of tomato seedlings in greenhouse
[Background] Drought, desertification and land degradation have become global environment problems for centuries, which lead to unsustainable development in agriculture. As tomato is one of the representative economic crops in northwest arid region, the study on its drought resistance has become a hot topic in recent years. Knowledge of physiological adaption of tomato to soil water deficit is well understood, but little is known about the effect of exogenous calcium (Ca2+) against drought at the seedling stage of greenhouse tomato. The study is aimed to investigate drought-induced physiological and morphology changes in tomato, as well as drought relief using exogenous Ca2+. [Methods] The experiment set 3 water stress levels (W90:90% FC; W60:60% FC; and W30:30% FC, FC refers to the field capacity) and 3 Ca2+ application levels (Ca0:0; Ca1:50mg/kg and Ca2:100mg/kg). The changes of soil basic physicochemical properties and the physiological characteristics of greenhouse tomato were investigated, including stomatal characteristics, root morphogenesis, protective enzyme activities, and the osmotic regulatory substance content. The desert soil in arid regions and the tomato cultival "Fenbaoli" were taken as the experimental materials. [Results] 1) The concentration of total salt, alkali-hydrolyzale nitrogen, available phosphorus and potassium in soil solutions of deficient irrigation were significantly higher than that of conventional irrigation (P<0.05). 2) Deficient irrigation inhibited the growth of tomato seedlings, significantly reduced the plant moisture content, dry weight, total root length and root surface area (P<0.05). Without additional Ca2+, the root shoot ratio (R/S) of tomato was negatively correlated with the irrigation quota. Compared with W90Ca0, R/S of W30Ca0 increased by 68.9%. Meanwhile, the antioxidative enzyme (catalase) activities and the osmotic substances (proline and soluble protein) contents of the deficient irrigation treatments were evidently higher. 3) Under mild deficient irrigation, 50mg/kg Ca2+ increased leaf stomata opening degree, the number of starch grains in the mesophyll cells and the activities of antioxidant enzyme (superoxide dismutase) in the leaves. Furthermore, in terms of severe deficient irrigation, the mesophyll cell structure was severely damaged, chloroplast membrane collapsed, grana lamella disintegrated, and Ca2+ had no significant effect on the regulation of stoma and chloroplast structure. [Conclusions] Ca2+ is involved in the defense regulation of membrane lipid peroxidation in tomato seedlings induced by drought stress. Therefore, it is possible to improve the drought tolerance for tomato in arid regions by the addition of Ca2+ during the seedling stage. The inhibition of mild drought stress for greenhouse tomato seedlings on the desert soil could be alleviated by foliar spray of 50mg/kg Ca2+.
