LI Xiaofei, GUO Xiaoping, LI Pengfei, XUE Dongming, XUE Guolian, YUE Liling
Evaluation of ecosystem service value for gangue dump field in Lingwu mining areas
[Background] Coal mining has caused a severe impact on the ecological environment of Lingwu area, and its ecological restoration work has been widely concerned. In order to study the restoration effects of the gangue discharge slope under different ecological restoration projects, the restoration effects were evaluated by quantitatively estimated the ecosystem service value and taking the typical gangue dump in Lingwu Coal Mine Area as the research objects.[Methods] According to the principle of restoration ecology, based on the UAV remote sensing images to classify the land uses in the study area, the revised equivalent factor method was used to analyze the representative gangue dumps in the Lingwu coal base among pre-occupation, before and after implementing restoration measures. And the value of ecosystem services per unit area of the three scenarios was estimated and studied to quantitatively evaluate the ecological restoration effects.[Results] The unit area ecosystem service value in Lingwu gangue dump experienced a sharp decline and gradual improvement before mining, before and after implementing restoration measures.Among them, the highest value was Meihuajing gangue dump in 2020 (13372 Yuan), which recovered to 78.02% of the original one, and climate regulation and hydrological modulation were the main single ecosystem services.[Conclusions] The ecological restoration effect of Meihuajing gangue dump is better than those of the same area. It is revealed that the appropriate ecological restoration project in the ecological restoration process in the arid desert coal mine area of Northwest China is an important reason for the ecological restoration and the improvement of ecosystem service value.
MA Han, FU Suhua, DONG Lixia, JIANG Guangyi, ZHANG Zhilan, ZHAO Hui
Analysis of key affecting factors in soil erosion spatial differentiation based on GeoDetector
[Background] Soil erosion is one of the environmental problems worldwide. Chongqing is located in the southwest purple soil area, with severe erosion. Exploring the possibility of using GeoDetector to determine the leading factors of soil erosion spatial differentiation in county-level administrative regions, and mastering the leading factors affecting the spatial heterogeneity of soil erosion in each district and county is the basis for effective soil loss control.[Methods] In this study, China Soil Loss Equation (CSLE) model was used to calculate soil erosion intensity in Hechuan district and Yunyang county of Chongqing, and GeoDetector was used to explore the dominant factors and interaction factors affecting the spatial heterogeneity of soil erosion. The CSLE model is based on the USLE and RUSLE. It is widely used because of its simple structure and easy access to parameters. GeoDetector is a statistical model based on spatial autocorrelation, which detects and analyzes spatial heterogeneity. It has four functions of factor detection, interaction detection, risk detection and ecological detection. This article used factor detection and interaction detection for analysis. Factor detection was used to reveal the influence of each factor on dependent variables. Interaction detection was used to judge the relationship between two different factors acting together on the dependent variable.[Results] 1) The slope and biological measure factor were the leading ones for the spatial variability of soil erosion in Hechuan district and Yunyang county, respectively. The affecting factors of the spatial differentiation of soil erosion in Hechuan district were ranked in descending order of explanatory power, namely, slope factor S, slope length factor L, tillage measure factor T, biological measure factor B, engineering measure factor E, soil erodibility factor K, and rainfall erosivity R. The affecting factors of Yunyang county were ranked in descending order of explanatory power, namely, the factor B, L, T, S, E, K, and R factor. 2) The interactive detection results showed that the effect of any two factors on the spatial difference of soil erosion was enhanced. The largest interaction q values were terrain factors interacting with other factors in the two counties. The top three interaction types in Hechuan district were L∩B (60.1%), S∩B (56.5%), and L∩S (54.1%). The top three interaction types in Yunyang county were L∩B (78.5%), L∩E (59.0%), and S∩B (56.9%).[Conclusions] These results suggest that GeoDetector can be used to identify key factors in the spatial differentiation of soil erosion in county-level administrative regions. Due to the different geographical environments in different regions, the dominant factors affecting the spatial differentiation of soil erosion were regionally different. The determination of the dominant factors can provide targeted opinions for different districts and counties to control soil erosion.
WU Ke, LI Zhen, QI Zhiguo, LI Wei, FENG Tian, QIN Zhanfei
Estimation model for gully volume in the basin of Northwest Hebei mountains
[Background] Gully erosion is an important environmental hazard in the basin of Northwest Hebei mountains, which produces a tremendous amount of sediment-inducing siltation of downstream reservoirs and causes some flooding and pollution. Therefore, the prevention and control of gully erosion have become the top priority of soil and water conservation in recent years. Moreover, the erosion prone gully area and control gully erosion can be determined by modeling and mapping the gully erosion over a large scale, and the estimation model of the gully volume is the basic issue in the research of gully erosion. However, little research on modeling gully volume in this area has been published. The objective of this study is to develop a model to assess the gully volume using the morphological parameters of gullies.[Methods] In order to measure the morphological parameters of 17 gullies located at Yangyuan county, Hebei province, a 3-D laser scanner (Rigel) was used to obtain the point cloud data, and then the digital elevation model (DEM) with the pixel size of 0.15 m×0.15 m was created based on Delaunay triangulate irregular network (TIN) using ArcGIS 10.3. The morphological parameters were extracted from DEM and finally the gully length (L, m), area (A, m2), top width (TW, m), bottom width (BW, m), depth (D, m), cross-sectional area (CSA, m2) and volume (V, m3) were calculated.[Results] 1) The development of gullies were imbalance in this study area. The lengths, areas and volumes of gullies varied greatly, however the parameter values of the same parameter at each section just had little difference. 2) The Pearson correlation analysis showed that there was significant positive relationship between V and L, A and D, and the Pearson's correlation coefficient were 0.949, 0.870 and 0.814, respectively, indicating that L, A and D can be used to estimate the gully erosion amount at the large spatial scale. 3) There was power function relationship between V and L and A, and the determination coefficients of the regression equation were 0.770 6 and 0.915 9, respectively. Furthermore, the RMSE and MAE between the measured and predicted gully volumes suggested that the V=0.046 53A1.499+24.08D1.916-44.26(R2=0.974 8) was more preferred for predicting the volume of a gully, compared with the V-L and V-A relation.[Conclusions] Above results V(A, D) relationship can be used to assess the gully volume in the basin of Northwest Hebei mountains. The results of this study may provide a method and basis for assessing the gully volume over a large scale, and will be greatly helpful to assess the soil and water conservation.
WANG Zuoxiao, JIA Hongwen, MA Xinyao, LI Yuanhang, LIN Sha, ZHANG Jing, HE Kangning
Comparison of stability of typical artificial water conservation forest in eastern Qinghai
[Background] The eastern Qinghai Province is located in the transition zone between the Loess Plateau and the Qinghai-Tibet Plateau, and due to its unique geographical location and natural environmental conditions, the regional forest ecosystem is sensitive and fragile, and once damaged, it is extremely difficult to recover. Meanwhile, Qinghai province is the plateau water tower of China. It is very important whether the forest in the region can play its water conservation function stably for a long time. Study the stability of artificial water conservation forest and clarify the main factors limiting can provide scientific basis for the regulation and function improvement of the forest structure.[Methods] From May to September 2019, the experiment was carried out in the Tagou watershed of Datong county, Qinghai province. Six typical artificial water conservation forest of Picea crassifolia, Populus cathayana, Betula platyphylla, P. cathayana& B. platyphylla, P. crassifolia & B. platyphylla, P. crassifolia & P. cathayana, were selected as research objects. Stand density, soil moisture and other indicators were measured. The stability evaluation index system was constructed from four aspects:forest structure stability, biological stability, resistance stability and functional stability, and the combined weights of each index were calculated by combining the analytic hierarchy method and fuzzy matter element method, and the comprehensive evaluation method was used for analysis and evaluation.[Results] 1) The annual net growth of mixed forests was greater than that of pure forests, and the annual net growth of coniferous pure forests was significantly greater than that of broadleaf pure forests (P<0.05). 2) The natural regeneration of the mixed forest of P. crassifolia & B. platyphylla, was significantly higher than that of other stand types, and there was no natural regeneration of the P. cathayana pure forest. 3) The soil moisture of P. cathayana was significantly lower than that of other forest (P<0.05), the soil nutrient content of mixed forest was higher than that of pure forest, the maximum soil nutrient of P. crassifolia & B. platyphylla was 37.77 g/kg. 4) The overall stability of the mixed forest was greater than that of the pure forest. The best stability forests were P. crassifolia & B. platyphylla, and the worst stability forest were P. cathayana. 5) The combined weighting results showed that the weight values of stand density, soil moisture and biodiversity were relatively large.[Conclusions] The most stable stand type in the region is P. crassifolia& B. platyphylla. Stand density, soil moisture and biodiversity were the main limiting factors for stand stability. In the process of vegetation reconstruction, it is necessary to adjust the stand structure and density, increase the biodiversity of shrub and herbaceous layer, and create conifer and broadleaf mixed forest with different age.
Remote sensing analysis of temporal and spatial evolution trend of loose material sources in meizoseismal area, Baisha River Basin, Dujiangyan, China
[Background] Baisha River Basin is the main drinking water source in the main urban area of Chengdu. The "5·12" Wenchuan earthquake led to the accumulation of a large number of collapse and landslide debris on the steep slopes, resulting in serious soil and water loss during rainstorm, which has a serious impact on the water supply of the water source. The investigation and change trend analysis of loose material sources in the basin have important guiding significance for the comprehensive control of soil and water loss in the basin.[Methods] Four periods of high-resolution remote sensing images one year before the earthquake and 10 years after the earthquake were selected. The loose material source was extracted by using object-oriented remote sensing automatic interpretation combined with human-computer interaction. The spatial distribution and dynamic change characteristics of material source were analyzed by GIS spatial analysis method.[Results] Before the "5·12" Wenchuan earthquake in 2008, the loose material sources area of the basin was only 20.05 km2, accounting for 5.57% of the total area of the basin. The "5·12" Wenchuan earthquake caused a large number of new loose material sources in the basin, with a total area of 106.31 km2, accounting for 29.52% of the total area of the basin. At 10 years after the earthquake, the total material source area decreased by 66.95 km2. There are still a few new sources in the basin after the earthquake, and the new sources in the 5 years after the earthquake are mainly distributed in the lower reaches of the basin due to human activities such as post disaster recovery and reconstruction, river dredging and mining. At 5-10 years after the earthquake, the newly added sources decreased, which was mainly caused by the expansion of the source range of some slopes in the upper reaches of the basin or the newly added collapse and landslide sources. The earthquake caused the average source center of the basin to move about 6.7 km downstream as a whole, and the average source center gradually moved back at 10 years after the earthquake.[Conclusions] Although the ecological restoration of the basin is obvious, there is still a certain gap from that before the earthquake. The material sources in the three directions of southwest by west, northwest by west and northwest by north of the upstream are still in an unstable state, which is the area to be treated in the next step.
CHEN Hao, ZHANG Xiaoping, WANG Doudou, GUO Jinwei, YAN Rui, AI Juehao
Analysis of soil erosion changes and its influencing factors in the upper reaches of Beiluo River watershed
[Background] The upper reaches of Beiluo River watershed, located in the hinterland of the Loess Plateau, is one of the main source districts of coarse sediment of the middle Yellow River, and is also the key area for soil erosion control and ecological construction in China. The Grain for Green (GFG) project implemented in 1999, resulting in soil erosion process in the upper reaches of Beiluo River watershed changing greatly. Clarifying soil erosion changes and driving factors in the upper reaches of Beiluo River watershed before and after the GFG project is of great significance for promoting green development and health management of the Yellow River watershed.[Methods] The revised universal soil loss equation was combined with GIS spatial analysis to study the spatial and temporal characteristics of soil erosion, rainfall erosivity and vegetation coverage before and after the GFG project (1991-2000 and 2001-2010) in the upper reaches of Beiluo River watershed. And the contribution rates of the GFG project and precipitation change on soil erosion change in the watershed were analyzed.[Results] 1) The results showed that the mean annual rainfall erosivity decreased from 1 390.2 MJ·mm/(hm2·h·a) before the GFG project to 1 260.7 MJ·mm/(hm2·h·a) after the GFG project, a decrease of 9.3%. Rainfall erosivity decreased in 99.3% of the whole watershed. The decrease of rainfall erosivity reduced the intensity of soil erosion in the watershed. 2) The vegetation coverage of the watershed increased from 30.8% before the GFG project to 47.6% after the GFG project, with an increase of 54.5%. About 88.3% of the area showed an increasing trend of vegetation coverage. The vegetation coverage in Wuqi county of the southeast was significantly higher than that in Dingbian county of the northwest. The increase of vegetation coverage greatly weakened the intensity of soil erosion in the watershed. The combined effect of the GFG project and the change in precipitation resulted in soil loss decreased from 8 078.9 t/(km2·a) before the GFG project to 3 060.7 t/(km2·a) after the GFG project, with a decrease of 62.1%. 3) The contribution rate of the GFG project and precipitation change to reducing soil erosion in the watershed was 85% and 15% respectively. The contribution rate of the GFG project to reducing soil erosion in Wuqi county and Dingbian county was 86% and 82% respectively.[Conclusions] The degree of soil erosion reduction in the watershed is dominated by the GFG project characterized by vegetation coverage change. The results provide valuable data for evaluating the benefits of soil and water conservation of ecological restoration on the Loess Plateau.
HE Xiangchang, WANG Yunqi, LI Tong, LI Yaoming, WANG Yujing, QI Zihan, LI Kewen
Root-soil plate characteristics of three typical lodging trees in Jinyun mountain, Chongqing
[Background] Root-soil plate is an important module for mechanical analysis and modeling of slope forest trees and understanding the mechanical mechanism of forest lodging. The purpose of this study is to predict the geometric parameters of root-soil plate based on the easily observed indexes of aboveground parts of plants, and to analyze the main influencing factors of the morphological characteristics of root-soil plate.[Methods] In this study, the field investigation was carried out on the lodging trees in the forest of Jinyun Mountain. The tree height, crown height, crown width, windward radius, leeward radius, lateral diameter, root-soil plate depth, root quantity and topographic slope of Cunninghamia lanceolata, Machilus nanmu and Gordonia acuminata were counted. The root tensile strengths of the root-soil plates of the three tree species were measured. Finally, the survey data were statistically fitted and PCA analysis was carried out.[Results] 1) G. acuminata had the largest lateral diameter and the smallest root-soil plate depth, and the number of surface roots was more than that of C. lanceolata and M. nanmu, and the whole root-soil plate of G. acuminata was in the shape of wide and shallow disc. C. lanceolata had the smallest lateral diameter and the largest root-soil plate depth, and the number of deep roots was more than that of G. acuminata and M. nanmu, and the whole root-soil plate of C. lanceolata was in the shape of narrow and deep cylinder. 2) The lateral diameter, windward radius and leeward radius of the root-soil plate of the three tree species had a strong positive correlation with the DBH (R2>0.452), while the correlation between the depth of the root-soil plate and the DBH was weak (R2<0.047). 3) The results of PCA analysis showed that there was a strong positive correlation between the lateral diameter of root-soil plate and the number of roots and topographic slope, and there was a strong positive correlation between the root-soil plate depth and the crown width and crown height ratio.[Conclusions] The indicators of the lateral diameter, windward radius and leeward radius can be predicted relatively well by the DBH, but the prediction of the depth of the root-soil plate is poor. The shapes of root-soil plates of lodging plants are mainly determined by the number of roots and the crown height ratio. More number of roots and larger topographic slope lead to greater lateral diameter of root-soil plate, and trees with larger crown height and crown width lead to greater root-soil plate depth.
LI Pengfei, LI Weiguang, WENG Xuexian, HU Jinfei, GAO Chendi, LI Yancheng, GAO Jianjian, DANG Tianmin
Unpaved road erosion in the hilly-gully region of Loess Plateau and its impacting factors based on LiDAR
[Background] Unpaved roads, widespread in the hilly and gully of Loess Plateau, China, have been suffering from severe soil erosion, adversely impacting the traffic and transportation as well as threatening socio-economic development. However, little was known about the spatial development and underlying mechanisms of unpaved road erosion, largely constraining the control of road erosion.[Methods] Using various methods such as unmanned aerial vehicle (UAV) light detection and ranging (LiDAR), UAV photogrammetry and field survey, this study investigated the morphological pattern of unpaved road erosion in a small catchment (Qiaogou) of the hilly and gully Loess Plateau and explored the relationship between road erosion intensity (E) and associated impacting factors. Road erosion models were then established and validated using the field data from another catchment (Yangou catchment) in the hilly and gully Loess Plateau.[Results] 1) The slope gradient of each road segment and gullies decreased significantly (P<0.05), while the ratio of width to depth and density of gullies as well as erosion intensity did not change significantly (P>0.05) from the head to the outlet of the Qiaogou catchment. 2) The major influencing factors of unpaved road erosion were catchment area (R2=0.60, P<0.01) and slope gradient of road segment (R2=0.54, P<0.01), followed by road segment length (R2=0.20, P<0.05), and visible-band difference vegetation index (R2=0.01, P<0.67) and slope gradient of drainage area (R2=0.02, P=0.53) were of the least influence. 3) The road erosion intensity model was constructed based on individual road segment slope (Gr) and drainage area (Ac) factors as well as their combination respectively. The developed models were expressed as E=0.87Ac+77 759.67 (R2=0.60, P<0.01), E=8 707.23Gr-49 252.46 (R2=0.54, P<0.01) and E=-0.56Ac+5 783.06Gr-11 748.78 (R2=0.80, P<0.01). The accuracy of the road segment slope model was verified using the available road erosion measurements in the Yangou catchment to be satisfactory (R2=0.92, P<0.01), demonstrating the applicability of the established models in the hilly and gully Loess Plateau.[Conclusions] The achieved results enhanced current understanding on the processes and mechanisms of unpaved road erosion and provided a useful reference for the prediction and control of road erosion on the Chinese Loess Plateau.
Distribution and landscape structures of ancient terraces in southern China
[Background] Terracing is an important measure for soil and water conservation,in the southern region of China, the ancient terraces have become a model for the harmonious development of human activities and the natural landscape structure of the mountains during the development of farming culture for hundreds and thousands of years. And the water and soil conservation role of terraces and the sustainable development of ecosystems are of great significance to maintain the sustainable development of mountain agriculture in China.[Methods] Taking 12 typical ancient terraces in southern China as the research objects, we combined Landsat 8 OLI image data and DEM data, visually interpreted and extracted the landscape elevation data of each ancient terrace and the slope and slope direction data of the terrace subsystem using ArcGIS technology, and calculated the landscape pattern index of each ancient terrace using the principle of landscape ecology and Fragstats software to analyze its distribution characteristics and landscape features.[Results] 1) The ancient terraces in southern China are mainly located in Yunnan province, Sichuan province, Guizhou province, Guangxi Zhuang autonomous region, Hunan province, Jiangxi province, Fujian province and Zhejiang province, with a total area of over 2 600 km2.Representative famous terraces include:Hani Terraces, Longji Terraces, Ziquejie Terraces, Shangbao Terraces, Yunhe Terraces, etc. 2) The ancient terraces in southern China are located in the subtropical mountainous and hilly areas between E 101°48'-119°29' and N 22°33'-29°46'. The altitude range is about 150-3 000 m.Moreover,they are most distributed on the sunny slope, second on the semi-sunny slope and semi-shady slope, and least on the shady slopein the range of 6°-25°. 3) The ancient terraced ecosystems in southern China mainly consist of forest land and cultivated land (terraces), with the percentage of area occupied by forest land from 53.77% to 86.36% and the percentage of area occupied by cultivated land (terraces) from 6.59% to 35.66, and the ratio of forest to field area is 1.62-13.42. Forests provide a constant source of water for the terraces. 4) The vertical landscape structure of ancient terraces in southern China is dominated by "four-elements isomorphism" and "multi-elements isomorphism" from the mountain top to the river valley, in which the landscape structure of "four-elements isomorphism" is characterized as follows:Forest-village-terraces-river. The landscape structure of "multi-elements isomorphism" is characterized as:Forest-village-terraces-town-river. The unique landscape structure has formed the self-flow irrigation system from the forest at the top of the mountain to the village on the mountainside and the terraces to the river valley and the nutrient input system of the terraces with the help of the irrigation canal system, which guarantees the longevity of the terraces.[Conclusions] The study of ancient terraces in southern China clarifies their distribution, landscape structure and common features of their formation.It provides a basis for improving the soil and water conservation function of terraces, promoting the sustainable development of mountain agriculture and the construction of modern terraces.
Calculation and validation of the constitutive relation for root-soil composite based on representative volume element method
[Background] Tree roots can inhibit shallow landslides. Quantitative evaluation of the effect of root reinforcement is a key step for assessing the effectiveness of vegetation in slope stabilization. The traditional calculation method of root-soil composites did not consider the influence of roots on the elastic parameters of root-soil composites. Meanwhile, it is difficult to calculate a slope with a large number of roots. In fact, trees are often planted in a spatial layout of regular planting arrangement on slopes to create plantations; thus, this research treats periodically arranged tree roots and the surrounding soil as a periodic composite.[Methods] The representative volume element (RVE) method was introduced to directly construct the three-dimensional constitutive relation of root-soil composites. The theoretical results obtained by the RVE method were verified by direct shear tests and repeated shear tests with length-varied roots. The roots and soil used in the test were collected in Jixian, Shanxi. The application feasibility of the equivalent mechanical properties of the root-soil composite obtained by the RVE method to evaluate the slope stability was verified by numerical simulation.[Results] The RVE method can be used to accurately evaluate the equivalent elastic properties of root-soil composites, and the improvement rate of the shear elastic modulus is only 0.24% higher than the repeated shear test. The difference for cohesion c and internal friction angle φ is only 2.45 kPa and 3°, respectively. The cohesion calculated by the Wu model is overestimated about 5 times compared to the test results. Compared with the pure soil slope, the safety factor of the vegetated slope with the test data increases by 7.20% and the RVE slope model increases by 9.78%, while the safety factor of the slope with the Wu model increase by 29.33%. The Wu model has the risk of overestimating the slope stability compared with the RVE model.[Conclusions] The RVE method can accurately predict the alterations of the elastic parameters and strength parameters c and φ of the root-soil composite. The strengthening effect of roots on the soil not only improves the cohesion, but also changes the internal friction angle and elastic parameters. RVE method combined with numerical simulation provide new method and technical means to realize the stable calculation of the slope with a large number of roots.
DUAN Jian, WANG Lingyun, WANG Ling, YANG Jie, WANG Jian, TANG Chongjun, ZHENG Haijin
A review of researches on plant root channel architecture and soil preferential flow process
[Background] Root channels formed by the alive roots and rotten roots play an important role in increasing preferential flow and altering hydrological processes such as soil infiltration. The root channel architecture characteristics are very complex and difficult to describe accurately and quantitatively. The influence mechanisms of root channels on preferential flow infiltration process are theoretically beneficial to water resources management, groundwater pollution, landslides and mudslides prevention.[Methods] In view of this research hotspot, numerous literature retrieval were carried out with "root channels" "architecture characteristics" "preferential flow" "matrix infiltration" "soil infiltration" and "soil moisture" as keywords in the Web of Science and China National Knowledge Infrastructure (CNKI) databases. These keywords appeared very frequently in relevant fields. Representative literatures were selected for analysis and integration in the previous studies by the end of 2020. The influencing factors, quantitative measurement methods of plant root channel architecture were in detailed described, and the influences of root channel architecture on soil preferential flow infiltration process were discussed.[Results] 1) The biological and abiotic factors, such as plant species, planting time, soil properties, and management measures significantly influence root channel architecture and the mechanism of each influencing factor are still unclear. In the past, due to technical methods and other limitations, soil macropores from different sources were often studied together during the study of preferential flow, without separately considering the characteristics of plant root channels and their importance. 2) In recent years, it has become a trend to use CT scanning imaging technology to obtain three-dimensional parameters of root channel architecture, which can characterize the network structure of large pores from different sources (biopores and non-biopores) as a whole. 3) Preferential flow and soil matrix infiltration are the two forms of soil water infiltration. During soil infiltration process, preferential flow must be accompanied by soil matrix infiltration. Previous quantitative research methods of preferential flow cannot quantitatively partition the temporal preferential flow and matrix infiltration, resulting in very little quantitative research of preferential flow infiltration process. However, the macropore connectivity blocking method provide a practical solution for quantitatively partition the temporal preferential flow and soil matrix infiltration. 4) Plant root system may improve soil infiltration properties by forming root channels through its own decay and decomposition. The values of root channel numbers, area, volume, and diameter are significantly and positively correlated with the soil infiltration rates and preferential flow flux.[Conclusions] Therefore, in the future, the three-dimensional quantitative index system for root channel architecture should be established to reveal development mechanism and architecture characteristics of plant root channel. More efforts should be focused on the influence mechanisms of root channel architecture on soil preferential flow infiltration process. It will be an important research direction to deeply reveal the mechanism of soil preferential flow movement and its contribution to water infiltration.
CHEN Qitao, WANG Tian, LI Zhanbin, ZHANG Jiao, LI Peng, CHENG Shengdong
Research progress in fingerprint technology identifying sediment source in the past 30 years
[Background] Soil erosion is one of the major global environmental issues. As one of the core contents of soil erosion research, the source of sediment in watersheds has received widespread attention and research. The identification of sediment sources has an important role and significance for the analysis of the temporal and spatial distribution characteristics of soil erosion and the benefit evaluation of soil and water conservation measures. Fingerprint recognition technology has been developing for many years, and various research methods have emerged in an endless stream. Understanding the development process of research and cutting-edge hotspots has become an important prerequisite for technological development.[Methods] To grasp the frontiers and application hotspots of fingerprint identification of sediment sources at home and abroad, mathematical statistics and bibliometric methods were used to analyze the journal papers published in the field of fingerprint identification of sediment sources for 30 years from 1991 to 2021, based on the core papers of Web of Science and CNKI database, CiteSpace software.[Results] The fingerprint technology to identify the source of sediment has started to grow rapidly since 1997, reached a high fever period in 2013-2019, and reached a peak of 150 articles in 2019. China, the United States, and the United Kingdom were the main research countries at this stage. The cumulative number of papers published by the three was more than 60% of the total number of statistics. China accounted for 19.2%, the United States accounts for 23.88%, and the United Kingdom accounts for 20.85%. In particular, the United States accounted for 32.67% of the highly cited papers selected. The United Kingdom, France, and Germany were pioneers in the study of fingerprint identification of the source of sediment. In terms of cooperative research, the U.S. Geological Survey has close cooperative ties with four major global centers (Chinese Academy of Sciences, Lausanne Research Institute, Spanish Research Council, and the University of Paris-Saclay). The research mainly was involved the three fields of environment, ecology, and geology. The specific research content was the selection of fingerprint factors, the analysis method of evaluating and judging the contribution rate of sediment, and the research area was mainly concentrated in the watershed near the agricultural area. The current research frontiers in this field were the consideration of uncertainty (identification and classification of potential sources, sample collection, variation of fingerprint properties, etc.), and the improvement of analytical models.[Conclusions] The current research frontiers in this field are the consideration of uncertainties (identification and classification of potential sources, sample collection, variation of fingerprint properties, etc.), further improvement of fingerprint factors, diverse regions and larger watershed scales, and transformation to practical tools cutting edge research will be broader in scale, the research perspective will be more thorough and in-depth, and the accuracy of the research data will be higher and more accurate. How to reduce the cost of this method is also one of the key research directions in the future.
CHEN Yulan, HAN Jianqiao, JIAO Juying, XU Qian, CHEN Tongde, LI Jianjun, WANG Nan, BAI Leichao
A review on the layouts of rainwater storage and drainage measures in small watersheds
[Background] Due to the impact of global climate change, the frequency of extreme weather events increased, leading to flood and drought disaster frequently occurred and water shortage. With the growth of population and economy, water consumption increases greatly and water pollution is serious, which aggravated the contradiction between supply and demand of water resources. How to coordinate rainwater storage and drainage in a small watershed for alleviating water resource shortage and flood disaster is a scientific and practical issue to be solved urgently.[Methods] We collected all relevant literatures with the keywords of "storage and drainage measures" and "rainwater resource utilization", which come from CNKI, ScienceDirect, Springer and others. Based on those literatures at home and abroad, this paper summarized the types and regulating effects of existing storage and drainage measures in small watershed. This paper also sorted the methods and objectives in existing layout of storage and drainage measures, and analyzed their shortcomings and challenges.[Results] 1) Storage and drainage measures can be divided into intercepting, diversion, storage and drainage measures, which have different ways and effects on runoff regulation. It is necessary to optimize the layout of storage and drainage measures in order to effectively control rainfall runoff, achieve rainwater resource utilization and sustainable development in a small watershed. 2) The existing layout methods of storage and discharge measures mainly include experiential layout, multi-criteria decision making, machine learning and model simulation. However, in addition to empirical layout, other layout methods mostly focused on the optimal layout of intercepting and storage measures, and there was a lack of research on the optimal layout of diversion and drainage measures. 3) At present, there are some problems in the layout of storage and drainage measures, such as "insufficient cognition of layout mechanism and quantification of model simulation" "emphasizing storage and neglecting drainage, process separation and terminal treatment coexist". At the same time, it is faced with challenges of intensified contradiction between water supply and demand and the frequent occurrence of extreme climate events.[Conclusions] Therefore, the layout of storage and discharge measures should be based on the water cycle process under the contradiction between water supply and demand and extreme climatic events, and the characteristics of different dimensions such as time, space, process, factors and measures. Then the hydrologic and hydraulic model of small watershed and multi-objective constraint evaluation model of storage and drainage measures are established to provide technical support for constructing the network system of intercepting-diversion-storage-drainage. In this way, the effects of storage and drainage measures on the accumulation, storage, dispersion, and utilization of runoff can be realized, and the purpose of storage and drainage coordination and rainwater resources can be achieved. Finally, water resources shortage and rainstorm flood disaster will be alleviated, so as to improve the watershed's ability to cope with global climate change and human activities and promote the sustainable development of society, economy and ecology in small watershed.
Spatial and temporal scale effect on runoff in China: A review based on literature statistical analysis
[Background] Scale effect on runoff is a frontier and hot issue in the field of hydrology and water resources. Since the end of the 1980s, many researchers in China have carried out a wide range of related studies across the country. However, the existing relevant review articles have not yet systematically and quantitatively analyzed the study of the scale effect on runoff in China from the overall progress and regional distribution.[Methods] Based on the 517 pieces of literature in six bibliometrics databases and through the method of word frequency analysis, we reviewed the studies of the scale effect on runoff in China. Specifically, we summarized the studies from the development history, research topics, research institutions, distributions of spatial and temporal scale, study areas, research methods, and mathematical models. The searching pattern in the CNKI database was Title=(((runoff OR hydrolog* OR flood OR "overland flow" OR "base flow" OR "stream flow" OR "river flow) AND (*scale OR *scaling) NEAR/1 (*temporal OR time* OR spatial* OR spatio* OR different OR multi* OR effect OR affect OR impact OR influence OR dependent OR transf* OR convers* OR analy* OR issue)).[Results] 1) The development history of relevant research could be divided into three stages:the initial stage from 1989 to 2000, the rapid development stage from 2001 to 2006, and the stable development stage after 2007. 2) Inter-yearly scale and rainfall event scale predominated in the temporal scales; watershed-scale predominated in the spatial scales. 3) Regarding the river basins, the Yellow River and Yangtze River were the main study areas. Regarding the soil and water conservation zones, considerable studies were conducted in the northwestern Loess Plateau, and then followed by the southwestern purple soil region, southern red soil region, and northern hilly and mountainous region. Regarding the terrain types, many studies were clustered in the plateau, and then followed by mountain, hill, and plain. Regarding the climate zones, most study areas were located in humid and semi-humid areas that had adequate rainfall as well as in warm temperate, subtropical, and mid-temperate zones that had a suitable temperature. 4) There were a wide variety of research methods, and different research methods and numerical models were applicable to different temporal and spatial scales.[Conclusions] Overall, the scale issue of runoff or hydrology still has an urgent need for further exploration and discussion. Research on the spatio-temporal scale issues of flood processes regarding extreme rainstorms should be further strengthened. Also, attention should be paid to the subjects of scale effect on hydrological connectivity, variable-scale hydrology model, and scale conversion. This review may provide basic data for a systematic understanding of the research status quo of the scale issue in hydrology in China, as well as directions for future research and work in the fields of hydrology and soil and water conservation.
