WANG Yujing, ZHOU Lijun, WANG Yunqi, LI Hongfei, LI Tong, WANG Xinhao
Effect of soil moisture content on root failure mode in direct shear test
[Background] The stress state and failure mode of plant roots in the shearing process will affect the root's ability of reinforcing soil,which is usually neglected in the classical models when quantifying the shear strength increment provided by roots and results in the overestimation of root reinforcement. [Methods] Aiming to explore the resistance behaviors and failure model of roots in the unsaturated soil under shearing condition, the large scale direct shear test for Vetiver root-soil composite, root tensile and pullout test were conducted based on the various soil moisture content and root quantity gradient. And the fractured or pulled out root ratio of each treatment shearing sample were observed simultaneously. Based on which the shear strength increment by roots are calculated by a revised model considering effect of soil moisture and root failure. [Results] 1) Under the condition of the same moisture content, the increased root shear strength was positively correlated with the root density. Under the condition of a certain root density, the increased root shear strength had a negative correlation with the moisture content. 2) The tensile force Tr and strength t with diameter 0.2-2.2 mm was 3-19 N and 5-29 MPa, and can be described as a negative power function and a positive power function with the increase of diameter D respectively (Tr=11.514D-0.885,t=9.5763D1.095). Root pullout force p also followed the positive power function with diameter (p=αDβ,α>0,β>0) and higher the moisture content, smaller the α value. 3) Among the four water moisture contents, Wu model values was 1.834, 1.864, 1.889, and 1.873 times of test values respectively, however the model value was 1.337, 1.028, 0.788, and 0.481 times of test values respectively when taking the root failure mode into account. [Conclusions] 1) Under unsaturated conditions, the reinforcing soil capacity of the root system is mainly related to the ratio of the number of roots extracted during the shearing process. The higher the water content during the direct shear test, the lower the extraction strength of the root system, and the root extraction. The larger the ratio of number of the extract roots, the smaller the amount of roots that can fully contribute to the tensile strength, and thus the weaker the root system's ability to stabilize the soil. 2) The root tensile strength, pull-out force and diameter are all in a power-exponential function relationship, and as the moisture content increases, the fitting attenuation coefficient of the pull-out force increases. 3) After taking moisture content and root failure mode into account, the estimated value of the obtained root shear strength is closer to the experimental value than that by the Wu model.
BAI Yijing, LIU Yanling, LI Yu, HUANG Xingcheng, ZHANG Yarong, JIANG Taiming, QIN Song
Effect of long-term different tillage and fertilization measures on aggregates composition and organic carbon in yellow soil slope cultivated land
[Background] The findings demonstrated the suitable tillage measures and rational application of fertilizer could effectively prevent and control regional soil erosion. Soil properties that affect soil erosion are mainly anti-erodibility and impact resistance, and soil aggregates are their characteristic form. Stabilization of soil aggregation is considered to be the most important mechanism for soil carbon sequestration. The effects of conservation tillage and optimized fertilization on the soil aggregates composition and soil organic carbon were compared in this paper, and it can be used as a better combination of farm and fertilization for slope land in karst area. [Methods] The long-term positioning monitoring of agricultural non-point source pollution in Guizhou province was taken as the experimental platform. The dry sieve method (mechanically stable aggregates) and the wet sieve method (water stable aggregate) were used to compare and study the effects of 6 treatments on the aggregate composition and organic carbon content of yellow soil,6 treatments referred to no fertilization + downslope conventional tillage (T1), conventional fertilization + downslope conventional tillage (T2) as the control, optimized fertilization + downslope conventional tillage (T3), optimized fertilization +cross ridge tillage (T4), optimized fertilization +cross ridge tillage + straw mulching (T5), and optimized fertilization + cross ridge tillage + straw mulching + contour hedgerow (T6). [Results] 1) The compositions of mechanically stable and water stable aggregates by each treatment were mainly composed of large aggregates of ＞0.25 mm. Under the same tillage conditions, the mean weight diameter (MWD), geometric mean diameter (GMD) and aggregates size of ＞0.25 mm(R0.25) of T3 increased by 14.22%,25.74% and 5.24% compared to T2, respectively. 2) Compared with other treatments, the soil of percentage of aggregate destruction (PAD), unstable aggregate index (ELT) and fractal dimension (D) of T6 were the lowest,the organic carbon content of T1 was the lowest in water stable aggregates of different particle sizes. The organic carbon content of T3 increased by 1.88%-26.32% compared to T2 in the aggregate sizes of >5.00, 5.00-2.00, 0.50-0.25, and <0.25 mm under the same tillage conditions. The organic carbon content of T5 and T6 increased by 3.21%-17.20% and 0.26%-10.19% compared to T4 in the aggregate sizes of >5.0, 5.0-2.0, 2.0-1.0, and 1.0-0.5 mm, respectively under the same fertilization conditions. The contents of soil aggregate organic carbon was mainly in the size of ＞0.25 mm, and the >5.00 mm aggregates were the highest contribution rate of organic carbon in T2, T3, T4, T5 and T6,which were 27.04%,31.51%,30.89%, 33.61% and 31.63%, respectively. Furthermore, soil aggregate organic carbon showed a positive correlation with soil total organic carbon.[Conclusions] Long-term optimized fertilization and conservation tillage may effectively improve the aggregates and its stability and soil organic carbon content, and can be used as a better combination of tillage and fertilization for slope land in karst areas of China.
WANG Tianle, GUO Qingxia, WANG Haibin, DING Yi, DU Yi, CHEN Shuiying
Analysis of soil nutrient in different lands after Returning Farmland to Forests in Chakou Watershed
[Background] The project of Returning Farmland to Forests is the largest ecological project in China and even in the world. The study on the soil nutrient characteristics of different land after Returning Farmland to Forests will provide the basis for soil remediation and improvement of different land where Returning Farmland to Forests is conducted.[Methods] In order to explore the characteristics of soil nutrient in different lands where Returning Farmland to Forests was conducted, taking the different lands after Returning Farmland to Forests in the Chakou Watershed in the loess hilly and gully region as study object, soil samples of ecological forest land (Robinia pseudoacacia, Platycladus orientalis) and economic forest land (Juglans regia) were collected. Taking soil samples of existing slope cropland as the reference substance, multiple comparisons of nutrients in soil layers of 0-20 cm and 20-40 cm in the different plots were conducted by one-way ANOVA, correlation analysis of soil nutrients by Pearson correlation coefficient, and the modified Nemerow formula was used to evaluate the soil nutrients in different plots.[Results] 1) The soil nutrient contents of lands after Returning Farmland to Forests in Chakou Watershed was mostly moderate variation, variation coefficient of each nutrient content was concentrated in 20%-30%, nutrient content in the topsoil (0-20 cm) was higher than that in the 20-40 cm soil layer, reflecting the surface aggregation effect of forest soil, among them, the surface aggregation effect of organic matter and available nutrients were more obvious, the soil nutrient content of 0-20 cm soil layer was generally 30% more than that of 20-40 cm soil layer. 2) Soil nutrient content in different plots ranked in the order of ecological forest > economic forest > slope cropland on the whole, however, we found that there was no significant difference in total phosphorus content among different plots, it may be related to the parent material in the soil. 3) The correlation between the contents of total nitrogen, available nitrogen and potassium with organic matter was positively significant. 4) The soil comprehensive fertility index of R. pseudoacacia, P. orientalis and J. regia were 0.9 (intermediate level), 0.85 (intermediate level), and 0.74 (low level),this showed that the soil nutrient status of ecological forest was better than that of economic forest.[Conclusions] On the whole, the benefit of soil nutrient conservation for land where Returning Farmland to Forests was conducted were better than those of existing slope cropland in Chakou Watershed, however, the characteristics of soil nutrients in different plots varied. The comprehensive study on soil nutrients of ecological forest and economic forest will provide basis for soil ecological restoration of different models of returning farmland to forest.
Evaluation on eco-environmental damage of human-caused soil erosion for production and construction projects
[Background] Human-caused soil erosion in production and construction projects is a typical modern accelerated erosion type by human-being. For different production and construction projects, there exists an internal and necessary relationship between human-caused soil erosion and eco-environmental damage where express great differences among disturbed geomorphic units, soil erosion characteristics and hazards. [Methods] Taking various disturbed underlying surfaces of production and construction projects as examples, we studied the characteristics of disturbed surface, soil and vegetation by field investigation and in-situ observation methods, and put forward an evaluation paradigm of eco-environmental damage human-caused soil erosion from the view of hazards of human-caused soil erosion. Economic methods of soil and water conservation were used to calculate the value of eco-environmental damage, and two cases were also used to verify this procedure. [Results] 1) Eco-environmental damage from human-caused soil erosion manifest the destruction of soil structure and land resources, degradation of land vegetation, changes of water resources circulation system, decline of ecosystem service functions and the increasing risk of rain-induced floods, landslides, and debris flows. 2) The key links for the evaluation system of eco-environmental damage include 4 aspects such as the judgment on soil and water damage and eco-environmental thresholds, establishment of an index system for identification of soil erosion hazards, causal link analysis of eco-environmental damage, and quantification methods and standards for the value of eco-environmental damage. The damage degree to ecological function of disturbed landform in real estate construction project sorted by loose engineering accumulation > slope green belt > construction access road. 3) The eco-environmental damage for mining projects are the destruction of surface groundwater circulation system, artificial landslide occurred in accumulation body rain-induced conditions. Damage for real estate construction projects is the collapse of high and steep slopes, destruction of topsoil structure and nutrients, decrease of water conservation function caused by increased hardened pavement, etc. The value of soil environmental loss for mining projects and real estate construction projects accounted for 77.27% and 60.35% separately. [Conclusions] The paper may provide some appraisal ideas and methods for evaluation of eco-environmental damage human-caused soil erosion. Furthermore, eco-environmental damage induced from production and construction projects mainly focus on man-made collapses, rain-induced landslides, regulation of runoff on hardened road, water retention function and destruction of the groundwater circulation system especially, which can provide some practical support for damage evaluation and ecological restoration.
BI Huaxing, HOU Guirong, YUAN Pujin, ZHOU Lianxiong, GONG Yaguang
Forest and grass coverage calculation and acceptance criteria for production and construction projects involving urban representing requisitioned land: Taking Beijing as an example
[Background] It is easy to calculate the water and soil loss control indicators for general production and construction projects according to the GB/T50434—2018, however, the calculation of forest and grass coverage index becomes extremely complex when representing requisitioned land (refers to the land which a construction organization represents government to requisition) is included into production and construction project. According to statistics by Beijing Soil and Water Conservation Center, the probability of representing requisitioned land included in the production and construction project is very high and there are different scenarios for representing requisitioned land in Beijing.Therefore, the calculation method and formula of forest and grass coverage rate is becoming a very important issue for different scenarios of representing requisitioned land in production and construction projects. [Methods] First we summarized 4 classification conditions of representing requisitioned land from the practical experiences. Then we calculated the forest and grass coverage rates of 6 scenarios based on the 4 classification conditions. The forest and grass coverage rate was the area of forest and grass vegetation, i.e., all artificial and natural woodland and grassland areas within the scope of prevention and control responsibility of production and construction projects divided by the area of responsibility for prevention and control, i.e., where the production and construction organization should undertake the obligation to prevent and control soil and water loss according to law, including land of requisition, occupation, use and jurisdiction of the project.[Results] 1) Four classification land conditions are ① whether representing requisitioned land has been constructed already or not when a production and construction project starts to build; ② whether representing requisitioned land will be constructed by construction project organization or not; ③whether representing requisitioned land has been transferred to the ownership organization or not when soil and water conservation measures are checked(whether forest and grass coverage rate meet the acceptance criteria for soil erosion control or not) for the production and construction project; and ④ whether representing requisitioned land has been disturbed during the construction of the project or not. 2) Correspondingly,the calculated results of forest and grass coverage rate in this project case were from 24.44% to 33.3% in the 6 scenarios of representing requisitioned land. i.e., some were lower than the acceptance standard 25% of forest and grass coverage required in this project, implying that forest and grass coverage of some scenarios was not acceptable. [Conclusions] The calculated values of forest and grass coverage vary in different scenarios of the representing requisitioned land, which causes the conflict of the acceptance conclusion on soil and water conservation. Therefore,it is necessary to classify different scenarios of representing requisitioned land in the compile of water and soil conservation plan for production and construction projects and calculate the corresponding forest and grass coverage, which may allow us to accurately grasp whether the project’s forest and grass coverage rate has reached the acceptance standards or not.
XU Hongjiao, HU Haibo, CHU Lei, YAN Chao, WANG Chaoqi
An analysis on runoff interception and sediment reduction effect by litter in Cinnamomum camphora forest
[Backgrounds] The deterioration still exists partially though the situation of soil erosion in red soil regions of South China has been generally improved in recent years, and the reduction of soil erosion is not proportional to the magnaged area. The undergrowth litter layer is generally considered to be useful in reducing the damage of soil from rainfall. Therefore, the aim of this study is to reveal the mechanism of slope erosion by analyzing the effects of undergrowth litter of Cinnamomum camphora forest on runoff interception and sediment reduction. [Methods] There are two independent variables in this study, rainfall intensity and litter coverage. Simulated rainfall experiment was undertaken in order to simulate different rainfall intensities (30, 60, and 90 mm/h),and litter coverage was also set to be 0, 50, 100 and 250 g/m2. The dependent variables are runoff yield and sediment yield. Significance analyses and regression analyses were undertaken on these variables by using SPSS 18.0 software in order to demonstrate the effects of undergrowth litter on runoff interception and sediment reduction. Fitting analyses were also conducted by Matlab software to illustrate the relationship between sediment yield and runoff yield.[Results] Under the same rainfall intensity and litter coverage, the runoff yield increased rapidly at the beginning for a short period then remained stable, while the sediment yield also increased rapidly at the beginning but decreased afterwards, then stayed stable. More specifically, the runoff reduction rate ranged from 4.06% to 34.21% under different rainfall intensities and litter coverage. At the same condition and the same period, the sediment reduction rate ranged from 25.78%-96.73%. Additionally, the runoff yield and sediment yield both decreased with the increase of the biomass of litter under the same rainfall intensity in this experiment. Moreover, the comparison between the effects of litter coverage on the runoff yield and on the sediment yield showed that, litter cover was more effective in reducing the sediment. [Conclusions] The effect of runoff interception and sediment reduction by litter cover decreases when rainfall intensity increases;however, the litter cover can still intercept runoff and reduce sediment considerably compared to bare slope under the same rainfall intensity. That is to say, the ground litter layer can effectively mitigate soil erosion caused by rainfall because it can reduce the rainfall energy by covering bare slope therefore prevent it from direct rainfall splash. There is a clear quadratic relationship between the runoff yield and the sediment yield in this study.
LU Xue, ZHANG Yunqi, LONG Yi, PEI Zengli, WU Zhehong, XU Mingyang, ZHANG Decheng
Modeling sediment yield using WaTEM/SEDEM for a small catchment of karst depression in the Three Gorges Reservoir region: A case study of the Changjiawa depression catchment of Wushan county
[Background] In karst area, the soil formation rate is low, and soil layer is thin and shows great spatial heterogeneity. The Three Gorges Reservoir region is the ecological security barrier in the middle and upper reaches of the Yangtze River. Karst landscape is wide in this region. In general, the karst land has complex terrain, and is subjected to intensive human disturbance and increasing rocky desertification. Reliable data of specific sediment yield (SSY) from small catchment is essential to our understanding of the process of rocky desertification. [Methods] The WaTEM/SEDEM was used to analyze the effects of multiple factors on soil erosion, to simulate the interception of sediment by water bodies such as reservoirs, ponds, dams and river sections in the southwest karst area. The WaTEM/SEDEM model was used to assess the SSY of Changjiawa catchment, a typical karst depression catchment in the Three Gorges Reservoir region. The SSY was determined by 137Cs dating to calibrate the model parameters and verified by the reported data of SSY from karst catchment. [Results] 1) The sedimentation rate in the Changjiawa depression was 0.27 cm/a, and the SSY was 155 t/(km2·a). The simulation results were corrected using the SSY determined by 137Cs dating in the depression, and the optimal combination of the minimum and maximum KTC values of WaTEM/SEDEM were 18 and 7, with the highest cNS (Nash-Sutcliffe coefficient) of 0.79, it showed that the model simulation effect was the best. 2) Using the WaTEM/SEDEM model, the total sediment deposition and SSY of Changjiawa small catchment since 1963 were 557 t and 122.91 t/(km2·a), which was higher than that in most karst catchments, which was mainly related to the lithology of the basin and the intense human activities. 3) WaTEM/SEDEM model simulation results were verified by published erosion and sediment modulus data. The correlation coefficients of the simulation results of SSY and sediment yield (SY) were 0.93 and 0.94, implying the simulated data reflected the actual erosion and sediment modulus situation in this area, and 137Cs data had good correction effect on WaTEM/SEDEM model parameters. [Conclusions] The combination of nuclear tracer dating technology and the WaTEM/SEDEM model may produce reliable SSY from small catchment of peak cluster depression, which is useful in karst areas lacking monitoring data. In the future, the WaTEM/SEDEM model may be used to assess sediment yield at the scale of depression catchment in this region.
Construction and application of soil and water conservation supervision and management technology system based on the “air-ground integration”
[Background] In recent years, with more and higher requirements for water and soil conservation informationization supervision of production and construction projects, traditional methods of follow-up inspection and supervision and management of production and construction projects are of inefficiencies, limitations, and blindness, which are difficult to meet the high requirements, high performance, and high precision requirements of supervision work under the new situation. In order to make up for the inadequacy of traditional supervision methods and meet the demand for supporting technology in the supervision work under the new situation, there is an urgent need to explore new technologies and new methods. This article mainly discusses the soil and water conservation supervision and management technology system based on the "air-ground integration", and its applicability in the supervision, inspection and management of soil and water conservation.Taking the Datengxia Water Conservancy Project as a case, the application process and effects of the supervision technology system in actual work are explained in detail.[Methods] The soil and water conservation supervision and management technology system based on the "air-ground integration" uses modern information technologies and equipment, such as high-frequency remote sensing census technology, high-precision remote sensing detailed survey technology, unmanned aerial vehicle field survey technology, supervision system and mobile information collection handheld terminal. The project supervision technology system can ascertain the construction status of the production and construction project, the disturbed area and the disturbed type, determine the implementation of soil and water conservation measures, the use and protection of the soil disposal, the key parts that need on-site supervision and inspection, and the implementation of the last supervision and inspection opinions.[Results] 1) After practice, the soil and water conservation supervision and management technology system in construction projects based on the "air-ground integration" met the needs of supervision under the new situation,which applies modern information technology and equipment. 2) Using the project supervision technology system, we have mastered the construction stage, disturbed area, water and soil conservation measure system, location and protection of waste soil disposal, and the implementation of previous supervision, inspection, rectification, etc. of the Datengxia Water Conservancy Project. These regulatory results provided effective support for the water administrative department to carry out supervision and inspection. 3) After calculation, compared with the traditional way, the use of the project supervision technology system to carry out the supervision and inspection of water and soil conservation of 2017-2018 production and construction projects in Pearl River Basin saved an average of 55% in economic costs per project time compared, and the efficiency of supervision increased by 4 times, which had outstanding economic and social environmental benefits.[Conclusions] Soil and water conservation supervision and management technology system based on the "air-ground integration" meets the needs of supervision under the new situation, and at the same time full coverage, high frequency, and refined coordinated supervision are achieved.
Ecological stoichiometry characterization of soil carbon, nitrogen, and phosphorus of Pinus tabuliformis plantations at different stand ages
[Background] This work is to investigate the effects of concentrations and stoichiometric of soil organic C(carbon), total N (nitrogen) and total P (phosphorus) in Pinus tabuliformis plantation at different age stages, and to provide theoretical guidance for the regulation of the growth environment of forests and a reference for the management of soil fertility in forests. [Methods] In June 2018, a survey was conducted in Wendao Forest Farm, Fushun county, Liaoning province, and Pinus tabulaeformis plantations of different forest ages (42, 65, and 85 years) were selected as the research objects. Three plots with a total area of 20 m×20 m (9 plots in total) were set up respectively, and took three soil sample collection points (27 sampling points in total) according to the upper, middle and lower routes. The sampling points were more than 5 m from the boundary. Sampling was conducted according to soil depth of 0-20, >20-40, >40-60 cm at the sampling point. Soil organic C was determined by potassium dichromate oxidation-heating method, soil total N was determined by potassium dichromate sulfuric acid digestion method, the determination of soil total P was determined using a Mo-Sb molten NaOH anti colorimetry. [Results] 1) The contents of soil organic C, total N and total P in 0-60 cm soil layer of P. tabuliformis plantation were 15.73-47.67, 0.40-1.58 and 1.11-2.27 g/kg, which were statistically affected by different stand age and soil depth (P<0.01). Soil organic C and total N increased at initial and then decreased with stand age, and decreased with increasing of soil depth. 2) The C:N, C:P and N:P in 0-60 cm soil layer of P. tabuliformis plantation were 36.19-42.43, 10.40-39.44 and 0.26-1.33. The stand age and the soil depth presented an extremely significant influence on soil C:P and N:P (P<0.01), but no significant influence on soil C:N (P>0.05). 3) There was significant correlation between soil C:N and soil total N, and there was no correlation with soil organic C. Soil C:P was significantly correlated with soil organic C and total P. N:P was significantly correlated with soil total N and total P. [Conclusions] The soil organic C and total N contents in P. tabuliformis plantation in this study increased with the stand age, but they decreased when the stand age reached a certain stage. The mineralization ability of soil N is weak and the soil N is poor, this is very important for the regulation of forest growth environment, and provides a reference for the future management of forest soil fertility.
Impacts of types and depth of substrates on quantity and quality of runoff from green roofs
[Background] As an important measure of sponge city, green roofs have been wildly adopted in urban water resource management in recent years. However, few researches focus on both water quantity and quality of green roof runoff in North China. Substrate is one of the key components of green roofs, thus it is important to clarify how substrate influences runoff quantity and quality from green roof. [Methods] We set up 6 extensive green roofs with 3 types (i. e., local planting soil, engineered soil, and light growing medium) and 2 depths (15 cm and 10 cm) of substrates in Beijing. In order to analyze the influences of type and depth of substrates on the water quantity and quality of green roof runoff, we used a weather station (HOBO U30) and rain gauges to monitor the rainfall and runoff processes of green roofs under natural rainfall conditions during the rainy season in 2017. The nutrients (NH4+-N, NO3--N, NO2--N and PO43--P) and dissolved heavy metals (DCr, DCd, DCu, and DNi) in the rainwater and runoff were analyzed by Automatic Discrete Analyzer (SmartChem 200) and ICP-MS. [Results] 1) The average runoff reduction rates of green roofs with local planting soil and engineered soil were significantly higher than the that of green roofs with light growing medium (P<0.05). The local planting soil, engineered soil and light growing medium green roofs with a substrate thickness of 15 cm provided higher runoff reduction rates (67.8%, 60.3%, and 46.6%, respectively) than the those with a substrate thickness of 10 cm (55.6%, 53.0%, and 41.5%, respectively). 2) The experimental green roofs were the sinks of NH4+-N, NO3--N and NO2--N, the mean pollution load reduction rates were (86.8±15.6)%, (69.4±17.1)% and (58.5±24.1)%, respectively. The engineered soil green roof with a substrate thickness of 15 cm and the light growing medium green roof with a substrate thickness of 10 cm were the sinks of PO43--P, the reduction rates of pollution loads were 21.8% and 7.8%, respectively, but the other green roofs were all the sources of PO43--P. 3) The experimental green roofs were the sinks of DCd, and the mean reduction rate of pollution load was (52.4±8.8)%. Except for the engineered soil green roof with a substrate thickness of 15 cm was the sink of DCr (the reduction rate of pollution load was 18.6%), the other 5 green roofs were all the sources of DCr, and all of the 6 experimental green roofs were the sources of DCu and DNi. [Conculsions] The runoff reduction rates of local planting soil and engineered soil green roofs are significantly higher than that of the light growing medium green roofs. Green roofs with 15 cm depth have better performance in runoff management than green roofs with 10 cm depth. The substrate type and depth also affect pollution loads in runoff from green roofs, and all the 6 experimental green roofs were the sinks of NH4+-N, NO3--N, NO2--N, and DCd, but were the sources of DCu and DNi. The results of this experiment provide scientific reference for the water quality evaluation and hydrologic design of green roofs in North China.
ZHOU Lianxiong, DING Guodong, YANG Zhiheng, LI Danxiong, WU Yanan, SAI Shuo, WANG Jinhui
Construction of eco-clean small watershed in the middle section of Yanshan Mountains: A case study of Anchungou small watershed in Luanping county, Chengde city, Hebei province
[Background] The middle section of Yanshan Mountains is an important water source and water conservation area of Beijing. The quality of its ecological environment directly affects the safety of water sources in Beijing. The purpose of this research is to explore the construction characteristics and governance models of eco-clean small watersheds in the middle section of Yanshan Mountains, and to provide reasonable suggestions for further promoting the construction of eco-clean small watersheds in the region.[Methods] Taking Anchungou small watershed as an example, this paper focused on the analysis of small watershed construction objectives, the layout of governance measures and specific governance measures. Then the paper analyzed the application of Beijing standard and landscape ecology theory and near-natural governance principles in small watershed construction. Finally, the paper summarized the characteristics of eco-clean small watershed construction in the middle section of Yanshan Mountains from several aspects, such as the formulation of construction objectives, the application of landscape ecology theory, near-natural governance, encouraging public participation, and the integration of Mountains-Rivers-Forests-Farmlands-Lakes-Grasslands. [Results] Anchungou small watershed is located in the middle section of Yanshan Mountains, northwest of Luanping county, Hebei province, with a watershed area of 115.2 km2. The analysis results show that: 1) Anchungou small watershed is based on Beijing standards and combined with local conditions to formulate construction goals, which meets the development needs of the small watershed in the middle section of Yanshan Mountains. 2) The construction of Anchungou small watershed pays attention to the landscape and implements near-natural management according to local conditions, which improves the landscape pattern of the watershed while improving the ecological environment. 3) The construction of Anchungou small watershed has formed a comprehensive management system through measures such as closure management, water and soil conservation forests, terraces, village beautification, and wetland restoration. 4) The goals of controlling soil erosion, protecting and using water and soil resources in the basin, and coordinated development of population, resources and environment have been achieved. [Conclusions] The construction of eco-clean small watershed in the middle section of Yanshan Mountains should be based on Beijing standards. and combined with local conditions and the principle of landscape ecology to carry out near-natural management of landscape forests and lakes in the watershed, and construct a comprehensive protection system for points, lines and surfaces. Ultimately, the purpose has been achieved that preventing soil erosion, protecting water sources, improving the ecological environment of the river basin, and enhancing the landscape pattern of the river basin.
ZHAO Shuai, CAI Xiongfei, WANG Ji, LI Xiaoyan, LI Ding, ZHAO Shijie, YU Xinjie, XU Die
Research progress on the effects of raw and modified biochar on soil heavy metal pollutants
[Background] Duo to the rapid development of modern society, soil heavy metal pollution becomes increasingly prominent, which seriously threatens the security of ecological environment. Biochar comes from a wide range of biological sources and of a low cost. It has a huge specific surface area, complex pore structure and abundant functional groups. With its excellent performance, it can effectively renovate soil heavy metal pollution, making it a research hotspot in a variety of environmental functional materials. With the complexity of soil heavy metal pollution types, it is necessary to modify biochar to achieve the purpose of improving the remediation effect. [Methods] In view of this research hotspot, numerous literature retrieval were carried out with "biochar", "soil heavy metal pollution", "passivation remediation" and "modified biochar" as keywords. These keywords appeared very frequently in relevant fields. Representative literatures were selected for analysis and integration. The characteristic and applications of biochar were briefly described, the remediation effects of biochar on heavy metal pollutants were summarized, and the modified biochar was emphatically discussed, and the properties of modified biochar and the changes of its effects on heavy metals were discussed. [Results] Biochar comes from a wide range of sources (agricultural wastes, sludge, fruit shells, and poultry dung), it is mainly prepared by low-temperature anoxic slow-speed pyrolysis technology. Its properties mainly depend on the types of biomass raw materials and pyrolysis conditions. The adsorption mechanism of biochar for heavy metals can be divided into surface adsorption (physical adsorption), surface complexation or precipitation, ion exchange and electrostatic attraction, which can effectively reduce the availability and migration of heavy metal pollutants in soil. After modification, the application performance of biochar is enhanced,for example, functional groups are introduced, impurities are removed and surface performance is improved. Remediation effect of heavy metal pollutants in soil is significantly improved. [Conculsions] The treatment of heavy metal contaminated soil by modified biochar has been quite effective, but at present, it is mainly in the laboratory stage or small-scale test stage, and there is a lack of large-scale in-situ experiments. The aging and final flow direction of biochar are not studied deeply enough. The selection of raw materials of biochar should follow the principle of taking local materials, and the secondary pollution of soil environment should be avoided in the process of treatment. Green environmental protection and efficiency is the development trend of biochar field.
HE Tao, SHI Yangzi, YANG Yang, HUANG Tingting, BAI Xue, LIU Baoyuan, LIU Yingna
Research progress on gully erosion measurement methods
[Background] Gullies are defined as the channels that are too deep to cross or to fill with normal tillage operations. Gully erosion, literally, is the soil detachment and transportation that occurs during the development of gullies, and serves as a major source of soil loss at the catchment scale. Accurate and suitable monitoring techniques are required in the quantitative study of gully erosion and therefore in the establishment and improvement of gully erosion models. During recent decades, more and more effort has been made to improve the previous monitoring methods as well as to develop new efficient methods. [Methods] The advanced searches provided by the Web of Science were applied to explore the major gully erosion measurement methods employed in the previous studies by the end of 2019. The application trends and characteristics of these methods were analyzed quantitatively, and the primary advantages and disadvantages of each method were discussed. [Results] The results manifest 2 classes of gully erosion monitoring methods, which are contact and non-contact methods. Therefore, the class of the contact method includes erosion pins, tape method, volume replacement method, total station and GPS; and the class of the non-contact method consists of laser scanning, stereo-photogrammetry and remote sensing. According to the supporting platform, these methods are further subdivided into 14 specific types, among which the aerial and satellite remote sensing have been so far applied most frequently. The corresponding publications account for 39.6% and 12.8%, respectively, of the total publications directly measuring gullies. Since 1980s, increasing attention has been paid to the quantitative research of gully erosion. Three typical trends in general are identified for the applications of the 14 gully measurement methods, which are rapid increase represented by the airborne structure from motion (SfM) stereo-photogrammetry, slow followed by fast increase represented by the satellite remote sensing, and slow increase represented by the airborne laser scanning. Different methods are applicable for different research objects and purposes. According to the 9 indices used for method evaluation, the tape method possesses rather low accuracy, but it is simple and efficient, and serves as a great tool for rapid gully survey in the field. The real-time kinematic (RTK) GPS is usually the optimal choice for field gully monitoring as it has a rather high accuracy but low time cost. The newly-developed SfM photogrammetry exhibits significant superiority over the traditional stereo-photogrammetry; whereas, the remote sensing is suitable for large-scale research on temporal and spatial distribution of gullies. [Conclusions] These findings hold important implications for selecting gully erosion measurement methods. To ensure the consistency and comparability of measurement results, standard procedures need to be established for each method in the future. It remains a challenge to integrate different techniques to realize the comprehensive gully erosion monitoring at multiple spatial and temporal scales.
