Analyze on soil erodibility of different land uses in southern Qinghai-Tibet Plateau
[Background] Erosion is one of the main causes of soil degradation worldwide. The Qinghai-Tibet Plateau is a vast area with obvious differences in topography, climate, and vegetation in different areas, covering almost all terrestrial soil erosion types. This brings a huge risk of erosion to the soil, which will seriously threaten its ecological barrier function. Quantitative assessment of soil erosion risk in the southern Qinghai-Tibet Plateau, so as to fully understand the status quo of soil erodibility in the study area, and put forward reasonable suggestions, which will help reduce the risk of soil erosion in the study area. [Methods] In this study, a large-scale sampling was carried out in the southern Qinghai-Tibet Plateau, and four typical land use patterns (Farmland, grassland, woodland, and shrubland) in this area were taken as the research objects. The composition of soil particles and organic carbon mass fraction were measured, and the soil fractal dimension was calculated. Quantitatively assess the soil erosion risks of different land use types and different soil layers, and analyze the impact of soil particle size characteristics on soil erodibility. [Results] The K value of soil erosion in the study area ranged from 0.022-0.036 t·hm2·h/(hm2·MJ·mm), the proportion of soil above medium erosion (K＞0.033 t·hm2·h/(hm2·MJ·mm)) was 43.19%, and the risk of soil erosion in the southern Qinghai-Tibet Plateau was higher. There were general differences in soil erosion among different land use types, soil erodibility was as follows: farmland＞shrubland＞grassland＞woodland, and the soil erosion of farmland was significantly higher than that of the other three land use types (P<0.05). In the soil vertical profile, the proportions of sample points with above-medium erosion (K＞0.033 t·hm2·h/(hm2·MJ·mm)) for the three soil layers (0-10, 10-20, and 20-30 cm) were 26.47%, 47.22% and 55.89%, respectively. Conversely, the proportions of sample points with below-medium and low erosion (K≤0.033 t·hm2·h/(hm2·MJ·mm)) were 73.53%, 52.78% and 44.11%, respectively. As soil depth increases, soil erodibility also increases, and soil erosion resistance decreases. Regression analysis revealed that the K value of soil erosion exhibited an exponential negative correlation with sand content and an exponential positive correlation with clay content and fractal dimension, both correlations being highly significant (P<0.001). [Conclusions] These results indicate that the soil erosion risk in the southern Qinghai-Tibet Plateau is relatively high, especially in farmland. We should start with the adjustment of land use, implement the policy of returning farmland to woodland and grassland, and increase vegetation coverage to reduce the risk of soil erosion in the study area and improve the benefits of soil and water conservation. The relevant research results can provide data support for the rational use of soil resources and ecological protection under different land use patterns in the southern Qinghai-Tibet Plateau.
ZHANG Zheng, XIANG Qiansheng, ZHANG Dengshan, WANG Li, SHI Wenjun
Response of soil moisture of sand barrier in alpine region to rainfall events of different grades
[Background] In order to explore the response mechanism of soil moisture to rainfall under different vegetation restoration measures in alpine sandy land, the optimum soil layer for sand-fixing plants to plant and better play its role in soil and water conservation.and its response to different rainfall events under three years' planting in Gonghe Basin, Qinghai province, including high vertical net cage sand barrier, wheat straw checkered sand barrier+Hedysarum scoparium, wheat straw checkered sand barrier+Caragana korshinskii, wheat straw checkered sand barrier+Artemisia desertorum, and wheat straw checked sand barrier+Helianthus tuberosus, so as to provide theoretical basis for scientific planting of soil depth of sand-fixing plants. [Methods]Taking the three-year-old high net cage sand barrier, wheat straw checkered sand barrier+Hedysarum scoparium, wheat straw checkered sand barrier+Caragana korshinskii, wheat straw checkered sand barrier+Artemisia desertorum. and wheat straw checkered sand barrier+Helianthus tuberosus planting in Gonghe Basin, Qinghai Province as the research objects, the rainfall and sand barrier types of 0-140 cm(10, 20, 40, 60, 80, 100 cm) in the study area were measured by 2900ET weather station and ECH2O respectively. [Results] 1) From August 2020 to August 2021, the rainfall in the study area was mainly concentrated in April to September, with low-frequency light rain as the main event, and the rainfall event <2 mm accounted for the highest of the total rainfall events (38.98%) and the lowest contribution rate (6.12%). The types of sand barriers can be divided into slow accumulation period (January-April), consumption period (May-June), accumulation period (July-September) and stable period (October-December) according to the monthly change of total soil water storage capacity, and all of them reach the peak in August, among which the soil water storage capacity of the vertical sand barrier is the highest (47 563.54 mm), and that of H. tuberosus sand barrier is the lowest (25 564.09 mm). 2) When the rainfall is less than 5 mm, the soil moisture of H. tuberosus sand barrier 0-10 cm, flower stick sand barrier and A. arenaria sand barrier 0-20 cm fluctuates. When the height is 5-18 mm, the vertical sand barrier is 0-10 cm, the Caragana sand barrier, A. arenaria sand barrier and H. tuberosus sand barrier are 0-20 cm, and the water content of the flower bar sand barrier is 0-100 cm. ＞18 mm, the vertical sand barrier is 0-10 cm, Caragana sand barrier, A. arenaria sand barrier and H. tuberosus sand barrier are 0-60 cm, and the soil moisture of the flower bar sand barrier is 0-140 cm. [Conclusions] Based on the response of soil moisture to rainfall and the characteristics of soil moisture replenishment in the process of desertification land control under different vegetation mapping measures in this area, it is suggested to repair it from May to June.
Effects of nitrogen addition on vegetation characteristics and soil properties in desert steppe
[Background] Desert steppe is an important natural barrier in Ningxia, but its soil is barren, vegetation composition is simple, and most of them are in nitrogen restricted state, thus its response to various environmental disturbance factors is obvious. In recent years, abundant nitrogen has entered grassland ecosystems through nitrogen settlement. Therefore, the method of simulating nitrogen settlement is adopted to study the effect of nitrogen addition on desert steppe vegetation characteristics, soil nutrients and enzyme activity, which may provide a theoretical basis for the dynamic changes of desert steppe ecosystem structure under nitrogen settlement. [Methods] Taking grassland as the research object in desert steppe of Ningxia, urea as nitrogen source, setting four pure nitrogen added treatment: CK (0), LN (5 g/(m2·a)), MN (10 g/(m2·a)) and HN (15 g/(m2·a)). The short-term effects of nitrogen addition on vegetation and soil characteristics in the desert steppe were studied from three aspects: Vegetation characteristics, soil nutrients and enzyme activities. In August 2020, soil samples of 0-20 cm were collected to determine the physical and chemical properties of the soil, and vegetation survey was carried out. [Results] 1) With the increase of nitrogen addition, the vegetation species composition of the desert steppe changed, important values for grasses and legumes increased and cruciferous plants decreased. The coverage and aboveground biomass increased first and then decreased. The grassland coverage of MN treatment was significantly higher than that of CK treatment (P<0.05). The aboveground biomass of LN and MN treatments was significantly higher than that of CK and HN treatments (P<0.05). 2) With the increase of nitrogen addition, the height and density of herbaceous plants in the desert steppe gradually increased, Simpson index and Pielou index decreased first and then increased, Simpson index in LN treatment was significantly lower than that in CK, MN and HN treatment(P<0.05). Pielou index of MN treatment was significantly lower than that in CK treatment (P<0.05). 3) Nitrogen addition had no significant effect on soil total nutrients(P>0.05), but significantly reduced SAK in desert steppe(P<0.05). Compared with CK, SAK (soil available potassium) in LN, MN and HN treatments decreased 30.82%, 31.35% and 32.13%, respectively. 4) Redundancy analysis showed that pH value, urease and catalase were the main factors affecting vegetation characteristics in the desert steppe. [Conclusions] LN and MN treatment could increase aboveground biomass in the desert steppe in the short term. Their soil moisture content was higher, nutrient content and enzyme activity increased to varying degrees. Under HN treatment, soil nutrient and water content in the desert steppe were generally lower, and above ground biomass of vegetation decreased, but the growth of dominant species was promoted. The results showed that low and medium nitrogen addition levels were beneficial to vegetation restoration and soil environment improvement in the desert steppe, but high nitrogen addition levels weakened the favorable effects.
LI Qiqi, XU Qijing, HOU Lei, WANG Runliu, WANG Keqin
Structure evaluation of the improved soil with contour reverse-slope terrace based on soil aggregates property
[Background] Yunnan is situated in a mountainous area, and there are only two seasons, rainy season and dry season. In rainy season, concentrated and heavy rainfall increases a great probability of soil erosion. As the main type of arable fields, sloping farmland is regarded as the key cultivated land type for soil and water loss. The contour reverse-slope terrace (CRT) increases soil water storage, root exudation, enzyme activities and reduces soil surface runoff and moisture loss, erosion and degradation, which improves the soil environment through changes of runoff and sediment yield, has been well documented, but the reasons remain unclear. In this study, we aim to elucidate the mechanisms of soil structure improvement and ecological remediation with the CRT in sloping farmland. [Methods] A field location experiment was conducted in the watershed of Yizhe in Songhua dam in Yunnan with two measures: Above and below the terrace in CK sloping farmland (CK-A, CK-B), above and below the terrace in CRT sloping farmland (CRT-A, CRT-B). The composition and stability were analyzed by measuring 0-5, 5-10, 10-20 and 20-40 cm soil mechanical-stable aggregates, physical property and constructed minimum data set to evaluate soil structure. In order to evaluate the effect of CRT on soil structure improvement in sloping farmland, a soil structure evaluation index system based on aggregates properties was constructed. [Results] 1) CRT measures improved the soil pore status, aggregates composition characteristics and stability significantly. 2) Six indicators including soil bulk density, soil porosity, geometric mean diameter (GMD), stable aggregates (R0.25), total aggregates (At) and ＞2-5 mm soil aggregates were identified as the main indicators for soil structure evaluation in the minimum data set. The verification of total data set suggested that the minimum data set reflected the effective information and accuracy evaluation for soil structure. 3) The soil structure index in CRT, compared with CK, ranging from 0.26 to 0.58, increased by 23.1% and 36.2%, indicating that soil structure was on the middle level; meanwhile, below the terrace in CRT, soil structure index in the 0-5, 5-10 and 10-20 cm soil layer increased by 25.2%, 27.3% and 25.7% compared with that in CK, respectively. It is mainly due to the erosion protection from both the upper and lower steps. [Conclusions] The CRT measures promotes soil structure via increasing the proportion of soil total aggregates and soil porosity, improving soil structure and therefore is the optimal ecological restoration measure of degraded soil ecosystem in sloping farmland. The soil structure evaluation method based on the minimum data set is applicable in this area of research and can represent the soil structure performance of sloping farmland with CRT measures accurately.
Changes in soil conservation function before and after the Grain for Green project in the Weihe River Basin
[Background] Soil conservation function plays an important role in soil formation, vegetation fixation and water conservation. Since the implementation of the Grain for Green project (GFGP), soil erosion in China has been effectively controlled. The change of soil conservation function in Weihe River Basin (WRB) before and after the GFGP was quantitatively evaluated in this study. [Methods] Based on the Sediment Delivery Ratio (SDR) module of the InVEST model, the soil conservation function of the WRB in 1980 and 2020 was evaluated using the data of rainfall erosivity (R), soil erodibility (K), vegetation coverage factor (C), DEM, and soil and water conservation measures factor (P). And the soil conservation amount under different land use types and slopes were counted in ArcGIS 10.2. [Results] 1) After the GFGP, the soil erosion of the WRB was significantly improved. Compared with 1980, the actual amount of soil erosion in 2020 decreased by 1.40×108 t, the average soil erosion modulus decreased by 1 033.51 t/(km2·a). The total amount of soil conservation increased from 48.60×108 t to 53.73×108 t. The soil erosion intensity has generally changed from a stronger level to a weaker level. The proportion of slight erosion increased from 60.75% to 77.43%. 2) Among different land use types, grassland had the largest soil conservation amount, accounting for ＞40% of the total, while the largest amount of soil conservation per unit area was forestland. The soil conservation function of water area and unused land was relatively low. 3) The amount of soil conservation per unit area increased with the increase of slope within a certain range. The soil conservation amount in 0-5° micro slope area was the lowest. The area with >15°-25° steep slope has the largest amount of soil conservation, accounting for more than one third of the total soil conservation amount. [Conclusions] After the implementation of GFGP, the soil conservation function of the WRB has been significantly improved. Land use and slope were two important factors affecting the soil conservation function. With the progress of vegetation restoration, the soil conservation function of different land use types and different slopes is gradually strengthened. The results provided a reference for quantitative evaluation of vegetation restoration effect and soil conservation function in the basin.
LU Jiefeng, ZHAO Qing, LI Ruidong, WANG Wenlong, LOU Yibao
Effects of plant root systems on runoff and sediment yield characteristics of dump slopes in the Erdos mining area
[Background] Planting Elymus dahuricus and Artemisia ordosica plays an important role in controlling soil erosion on dump slopes in open-pit mining area. However, the influence of root systems of E. dahuricus and A. ordosica, as well as their mixed root systems, on the runoff and sediment yield characteristics of rill erosion on dump slopes in the Erdos mining area is still unclear. [Methods] The field simulated scouring experiment was conducted to study the hydrodynamic characteristics of rill erosion and characteristics of runoff and sediment yield on the dump slope with different plant root types (fibrous root system of E. dahuricus, tap root system of A. ordosica, mixed root systems of E. dahuricus and A. ordosica). [Results] The runoff velocity, drag coefficient, runoff shear force and runoff power of different plant root types on dump slopes showed different change trends with runoff scouring time. The fibrous root system of E. dahuricus and the tap root system of A. ordosica both reduced the runoff velocity, runoff shear force and runoff power, while the two plants had different effects on the drag coefficient. Specifically, the fibrous root system of E. dahuricus increased the drag coefficient on dump slopes, while the tap root system of A. ordosica is the opposite. The average runoff yield rate reached its minimum value on the test plot of the fibrous root system of E. dahuricus. The sediment yield rates of the test plots of different plant root types decreased compared with the CK, and the average sediment yield rate had decreased by 51.28% to 69.40%. The presence of the three plant root systems effectively reduced the soil detachment rate on dump slope, among which the maximum erosion reduction rate of the fibrous root system of E. dahuricus was as high as 71.1%. The critical runoff shear force and critical runoff power of the test plots of three plant root types were 0.04-1.28 N/m/s and 0.02-0.25 Pa, respectively, and the two critical values were ranked from largest to smallest in the fibrous root system plot, mixed root system of fibrous root system and tap root system, the taproot system plot, and the bare plot. [Conclusions] The presence of three plant root systems changed the hydrodynamic characteristics during the rill erosion process on the dump slopes under runoff scouring conditions, effectively reduced the amount of soil erosion. Among them, the E. dahuricus with fibrous root system had the best effect of reducing erosion, while the effect of A. ordosica with tap root system and the mixed planting of E. dahuricus and A. ordosica with mixed root system on reducing erosion is relatively poor. The results can provide a theoretical basis for the prevention and control of soil erosion on the dump slopes in the Erdos mining area.
DA An, HAN Hairong, LI Huayi, WU Huifeng, CHENG Xiaoqin
Plant-litter-soil stoichiometric characteristics of typical plantation forests and their interaction in loess hilly and gully region
[Background] The ecological environment of the Loess Plateau is fragile and its soil fertility is quite low, the "Grain for Green Project" is a key measure for soil and water conservation and restoration of degraded land in this region. The study of the plant-litter-soil stoichiometric characteristics of typical plantation forests and their interrelationships may reveal the limiting elements of vegetation growth. Comparing differences in ecological stoichiometric characteristics between pure and mixed forests can help to find out which of the two silvicultural modes is the better choice in the process of vegetation restoration in the region and provide scientific support for the reconstruction mode of vegetation on the Loess Plateau. [Methods] We selected four types of plantation forests (pure Pinus tabuliformis forest, P. tabuliformis + Caragana korshinskii mixed forest, pure Larix principis-rupprechtii forest, and L. principis-rupprechtii + C. korshinskii mixed forest) in Jingle county, Shanxi province, and set up 3 sampling sites in each forest. We collected tree layer organs (leaves, branches, stems and roots), litter, and soil (0-30 cm) samples and determined the C, N and P content using potassium dichromate oxidative heating and AA3 continuous flow analyzer. We used ANOVA, correlation analysis and structure equation modelling to analyze the ecological stoichiometric characteristics and their interactions among tree layer organs (leaves, branches, stems and roots), litter, and soil (0-30 cm). [Results] 1) The changes of C, N and P contents of trees in 4 plantation forests were in the form of leaf>branch>sti>root. Only L. principis-rupprechtii leaf N content significantly increased by 3.18 g/kg after mixing, leaf C∶N and C∶P decreased, and regional tree growth showed P limitation. 2) Only L. principis-rupprechtii litter N content increased significantly by 1.35 g/kg after mixing, while litter C∶N was reduced, and there were no significant changes in litter of P. tabuliformis forests. 3) The C and P contents of plantation forest soil both decreased with increasing soil depth, in which the C and P contents of 0-10 cm soil layer were significantly higher than those of other soil layers, which were 8.92 and 0.31 g/kg, respectively. Mixing increased the C contents of each soil layer of L. principis-rupprechtii, in which the 0-10 cm soil layer increased the most significantly, with a significant increase of 49.15%. 4) Pearson and SEM analyses showed that the N contents of the litter layer directly influenced the soil layer C∶N, which in turn influenced the nutrient pattern of the arbor layer, which in turn positively influenced the litter layer. [Conclusions] Mixing can effectively improve the nutrient status of plantation forests. However, the introduction of the same hybrid shrubs varied significantly among tree species, while the L. principis-rupprechtii + C. korshinskii mixed forest is optimal. In the future, mixed afforestation should be preferred for vegetation restoration in loess hilly and gully region.
GAO Lianwei, MA Ziao, LIU Chunhe, ZHAO Lili, WANG Ao, ZHA Tonggang
Response of tree stem sap to soil moisture stress in typical plantations in the low mountainous area of Beijing
[Background] Drought and water shortage are important factors limiting the ecological construction in North China. Soil moisture is an important factor affecting tree stem sap, which determines the overall level of tree stem sap and its response sensitivity to environmental factors. The main factors of tree stem sap are different under different soil moisture conditions. The variations of tree stem sap and the response mechanism to meteorological factors under different soil moisture stress are important contents of understanding the adaptation mechanism of trees to environmental change and the water cycle mechanism. [Methods] The representative plots of Acer truncatum and Pinus tabuliformis, two typical tree species in the low mountainous area of Beijing were selected. The thermal diffusion probe technique was used to monitor the yearly change of tree stem sap density of A. truncatum and P. tabuliformis. The time domain reflect system was set up in two plots to monitor soil moisture. The automatic weather station was used to monitor weather factors in real time. The tree stem sap density and environmental factors under different soil water stress were analyzed by regression analysis. The yearly change of tree stem sap density and its driving factors under different soil moisture conditions were investigated. [Results]1) The tree stem sap density of A. truncatum and P. tabuliformis demonstrated "unimodal" type yearly changes, and the number of days with soil moisture stress in 2022 accounted for 76.2% of the whole year. 2) The tree stem sap density of both A. truncatum and P. tabuliformis decreased significantly with the increase of moisture stress (P<0.05). Soil relative water content had a substantial influence on tree stem sap density per unit of vapor pressure deficit (VPD) under soil moisture stress (P<0.05), but not under no soil moisture stress. Under severe soil moisture stress, soil relative water content explained 62.2% and 54.3% of tree stem sap density per unit of VPD of A. truncatum and P. tabuliformis. 3) Multiple stepwise regression analysis showed that the dominant factor of tree stem sap density was meteorological factor under no soil moisture stress, and tree stem sap density was governed by meteorological factors and soil moisture under mild soil moisture stress, while the only dominant factor was soil moisture under severe soil moisture stress. [Conclusions] We investigated the changes of tree stem sap and the dominant factor of the typical plantations in the low mountainous area of Beijing under different soil moisture stress. The results elucidate the response law of sap of typical artificial forests to soil moisture conditions in low mountain areas of Beijing. The results may provide technical guidance for the nurturing and management of artificial forests in this area.
Ecological restoration design of mine landscape conforming to topographic gradient: Taking the design of Weihai Huaxia city as an example
[Background] As a model of mine restoration and ecological civilization construction, the restoration model of mining sites in Huaxia city, Weihai, Shandong province, is highly instructive in protecting the ecological environment and improving social and economic benefits. Mining caused many ecological and environmental problems in mining sites, also restricted regional economic development. Currently, research on ecological restoration of mine landscapes is mostly carried out with a single element such as soil restoration, ecological governance, and landscape reconstruction, lacking a multi-functional coupling of various elements and an overall grasp of ecology, economy, landscape, and culture.[Methods]Taking the Huaxia city of Weihai as the object, the terrain of the mine footprint as the research base, and various landscape elements as the research patches, an ETZLM design model for ecological management of the mine landscape was established. Then, we designed elements from aspects such as terrain, base, vegetation, etc., and carried out functional design of different elements in combination with horizontal and vertical spatial layout design, internal and external network connectivity design. We proposed and built a strategic and technical framework for ecological restoration of mine landscapes, and developed design and practical research on ecological restoration of mine landscapes that conformed to terrain gradients. [Results]In terms of element design, the terrain structure design that conforms to the terrain and surface undulation perfectly integrates the natural environment and landscape design, while saving development costs and avoiding resource waste caused by transitional excavation. The base reconstruction design of slopes and ponds, taking into account the back-end benefits after restoration, provides a high-quality platform for later vegetation growth and biological reproduction. The vegetation restoration design of the mountain has constructed a diverse and ornamental landscape environment, providing support for tourism development. In terms of structural design, the spatial layout of the horizontal structure of the site should grasp the spatial configuration of various elements as a whole, which is conducive to maintaining the consistency between the landscape and the environment. While the ecological spatial layout of the vertical structure of the vegetation community, which combines different types of plant communities in a hierarchical manner, is crucial to protecting the habitat of animals and plants and stabilizing the stability of the slope. As an important node of the regional ecological network, the landscape ecological restoration of Huaxia city mining pits provides good support for regional soil and water conservation, water conservation, and climate regulation. The combination of elements and structural design improves the functional requirements of Huaxia city from different perspectives such as soil, vegetation, landscape, and economy. [Conclusions]The practice of mine restoration based on environmental factors, structures, and functions has made the scenic area of Huaxia city excellent in ecology and beautiful in scenery after completion, realizing a virtuous cycle of ecological, economic, and social benefits, and playing a exemplary role in the restoration of the mine ecological environment and greening landscape design practice.
Changing trend of soil erodibility factor based on two national mappings of it
[Background] The soil erodibility (K factor) is one of the key factors in calculating soil erosion modulus using the Chinese soil loss equation (CSLE). Therefore, obtaining an accurate distribution map of K factor is necessary for the national monitoring of soil and water loss in China. The current available Chinese K factor map was made during the soil and water conservation measures survey in the first national census in 2011, based on soil type maps of provinces (autonomous regions and municipalities) and soil profile data from the second national soil survey (K value in version 2011 for short). It is necessary to update the K value in the version 2011 and study the changing characteristics of K factor from the version 2011 to the version 2022 (see below). [Methods] In order to increase the accuracy and reliability of soil erosion assessment, an updated K factor map was completed in 2022, using the random forest prediction method and soil profile data from the "Investigation of Chinese Soil Series" (K value in version 2022 for short). The K factor maps in the version 2011 and 2022 were chosen as the research projects, and their value size and spatial distribution in the major river basins and soil type of China were compared. [Results] 1) The mean value of the national K value in the version 2022 (0.029 8 t·hm2·h/(MJ·mm·hm2)) was slightly lower than that in the version 2011 (0.032 3 t·hm2·h/(MJ·mm·hm2)), indicating a positive trend in the development of soil erosion control in China. Except for the Haihe River Basin and Songliao River Basin, the K value in the version 2022 in each basin increased when compared to the K value in the version 2011. Among them, the K factor of castanozems, dark brown earths, saline soils and other soil type decreased the most, while the K factor of fluvo aquic soils, cinnamon soils, yellow earths and other types of soil increased. 2) The trend of changes in the national mean value of K factor was consistent with the dynamic trend of a decrease in the area and degree of soil erosion nationwide. The decrease in K factor was mainly related to reasons such as Returning Farmland to Forests and soil amendment, while the increase in K factor was related to intensive cultivation and slope erosion. [Conclusions] This study may provide a basis for dynamic monitoring of soil erosion and evaluation of the effectiveness of soil and water conservation management. In the future, it is necessary to strengthen ecological protection, improve soil quality and its ability to resist erosion.
ZHANG Junbin, ZHANG Yan, LI Kunheng, CHEN Chang, LIANG Yanrong, YANG Runze
Accessing accuracy of extracting gully and ephemeral gully in the Songnen typical black soil region based on GF-7 satellite images
[Background] Gully erosion, as an extreme form of land degradation, causes a potential danger for both local ecological security and food security. Gully measurement with high-efficiency and high-precision has important significance for gully erosion monitoring in the black soil area of Northeast China. This study aims to explore the applicability of satellite remote imagery Gaofen-7 for monitoring gully erosion in the black soil area. [Methods] A typical watershed with area of 4.2 km2 in Binxian county, Heilongjiang province, was selected as the study area to analyze the accuracy of extracting ephemeral gully (EG) and permanent gully (PG) parameters by visually interpretation using GF-7 stereoscopic satellite images (multispectral data of 0.8 m resolution and panchromatic data of 0.65 m resolution) with unmanned aerial vehicle (UAV) measurement data as a reference. [Results]1) The 64 ephemeral gullies were interpreted from UAV imagery, with a density of 15.23 gullies/km2 and an average length of 83.43 m. The 80 ephemeral gullies were extracted from GF-7 with only 42 were the same as those from UAV images. The error in the number and density of ephemeral gullies interpreted using GF-7 images was larger than 50%, with many cases of misinterpretation. Using GF-7 images, the water flow paths, plot boundaries, and field roads may be misidentified as ephemeral gullies. It is inappropriate to be used for monitoring EG erosion at the small watershed scale. The 17 permanent gullies were interpreted from UAV images, with a density of 4.04 gullies/km2 and a gully density of 2.02 km/km2. The measurement in linear and areal density of the permanent gullies with GF-7 was reliable with the errors were 1.00% and 5.62%, respectively. 2) Comparing the length of the 42 EGs interpreted from both GF-7 and UAV images, the average error of gully length using GF-7 images was 4.54 m, with the relative error below 10% accounted for 40.48%. However, there was no statistically significant difference (P＞0.05) between the gully length measurements of the GF-7 and UAV and a good linear relationship was fitted (R2=0.93). 3) There was high reliability of gully length, width and area of permanent gullies extracted using the GF-7 images with the mean errors were 2.89%, 14.92% and 16.02%, respectively. The average error of the gully depth of the permanent gullies was 1.24 m, with a relative error of 24.46%, and the average error of gully gradient was around 7%, and the average relative errors of the permanent gullies' volumes were 69.95%, indicating the three-dimensional morphological parameters of permanent gullies from GF-7 were not reliable. [Conclusions] There is high accuracy in the measurement of density and two-dimensional parameters of permanent gullies at the scale of small watershed using GF-7 images, while there is a large error in extraction of three-dimensional parameters of permanent gully. This study may provide an important reference for the investigation and monitoring of gullies in Chinese black soil area.
QI Zihan, WANG Yunqi, LI Tong, LI Kewen, YAN Xiangjun, MA Lei, WANG Taiqiang, LIU Yufang
Effects of root distribution on soil water characteristics and conductivity of typical forest land in Jinyun mountain
[Background] Soil-water characteristic curve and hydraulic conductivity of forest soil are important mathematical models, which play conversion roles in coupling analysis of water force coupling in porous media, but it is not deeply understood yet when the existence of plant roots was taken into account. [Methods]The soil water characteristics and hydraulic conductivity based on VG model of undisturbed soil for four stands (coniferous and broad-leaved mixed forest, evergreen broad-leaved forest, Phyllostachys pubescens forest, and shrub forest) were studied by centrifuge test and variable head permeability test. Meanwhile, the normalized mathematical model of unsaturated hydraulic conductivity versus soil root was established. [Results] 1) P. pubescens forest has the most root amount especially in the aspect of coarse roots; the broad-leaved mixed forest has the widest distribution range of each diameter class, but the number of roots in each layer is not much, the number of roots in each layer of shrubbery is large, and the shrubbery has considerable. 2) The saturated conductivities of four forests surface soil are 7.00 μm/s (coniferous and broad-leaved mixed forest), 7.04 μm/s (evergreen broad-leaved forest), 0.69 μm/s (P. pubescens forest) and 3.70 μm/s (shrub forest), respectively. And it is a decreasing tendency with soil depth, except for the second layer in P. pubescens forest. 3) The air entry parameter of four forest stands increased firstly and then decreased with the soil depth, while the pore diameter parameter n decreased with the soil depth. The saturated conductivity of forest soil versus the number of roots can be regressed as power law function, R2≥0.959 76. [Conclusions] The saturated conductivity ks of soil in mixed coniferous and broad-leaved forests, evergreen broad-leaved forests, P. pubescens forests and shrub forests are closely related to the root distribution, and the saturated conductivity and root number are in the form of power function. The unsaturated conductivity of forest soil can be described and predicted by normalized model when plant roots are taken into account.
TAN Lu, GUO Hongli, LIU Xia, WU Fang, ZHANG Xue, MENG Wenting, CHEN Jianpeng
Layout of vegetation coverage monitoring sites based on the soil and water conservation region in China
[Background] Vegetation coverage is an essential factor in monitoring and assessing soil erosion. It is critically impacted by the spatial heterogeneity of vegetation characters such as vegetation types, forest category and tree species. Although remote sensing is considered as an effective way to monitor the dynamic change of vegetation coverage in large area, field survey at fixed monitoring site is still necessary especially for understory vegetation. [Methods] The purpose of this study is to localize a set of vegetation coverage monitoring sites in Jiangsu province. Multi-source data was used including map of vegetation regionalization, map of tree species, map of soil and water conservation, remote sensing images and digital elevation model. Spatial heterogeneity of vegetation characters was analyzed by taking the third-level soil and water conservation regions as the control units. On the basis of this, monitoring sites were sampled through stratified sampling and flitted according to observations through field survey. [Results] 1) Ⅲ-4-2t, Ⅲ-5-3fn and Ⅲ-5-4nt belongs to the warm-temperate deciduous broad-leaved forest, with oak deciduous forest as zonal vegetation. V-1-2nt, V-1-1ns, V-1-5nr and the north V-1-4sr belongs to north-subtropical mixed evergreen and deciduous broad-leaved forest, the zonal vegetation of which changes from deciduous broad-leaved forest with evergreen shrubs to mixed evergreen and deciduous broad-leaved forest. The south of V-1-4sr belongs to the mid-subtropical evergreen broad-leaved forest, with evergreen broad-leaved forest as zonal vegetation. 2) Timber forests, shelter forests and economic forests are predominant in the study area. However, the proportion of each forest category and tree species varies among different soil and water conservation regions. From the north to the south, the dominant tree species of timber forests and shelter forests change from Populus spp. and Platycladus orientalis to Pinus massoniana, Cunninghamia lanceolata, Cinnamomum camphora and broad-leaved forest, while the dominant tree species of economic forests change from Malus pumila, Pyrus spp., Castanea mollissima and Ginkgo biloba to Camellia sinensis, Amygdalus perisica and Citrus reticulata. 3) Considering the spatial heterogeneity of forest category and tree species among the third level of soil and water conservation regions, 96 monitoring sites were sampled from 17 sampling area. According to field survey, 49 vegetation coverage monitoring sites were located, which including the dominant forest categories and tree species in each soil and water conservation region. [Conclusions] Vegetation category, forest category and tree species exhibit significant spatial heterogeneity in Jiangsu Province. The proposed layout of monitoring sites provides a technical support for vegetation coverage monitoring in Jiangsu province. It also provides useful reference for the layout of vegetation coverage monitoring sites in other similar regions.
LIU Xinyue, CAI Youzhu, ZHAO Lijuan, CHENG Chang, CHEN Xiao, HE Kangning
Difference analysis of soil organic carbon density distribution characteristics of Picea crassifolia and Betula platyphylla forest: Taking the Ta'ergou watershed of Datong county, Qinghai province as an example
[Background] Forest is the most important carbon storage pool in the terrestrial ecosystem. Studying the spatial distribution pattern of soil organic carbon density (SOCD) in forest land and understanding its influencing factors contribute to enhancing soil fertility, thereby promoting the stability of forest stands and improving vegetation productivity in ecosystems. Due to the fact that the Ta'ergou small watershed in Datong county, northeastern Qinghai province is a typical representative area for implementing the Grain for Green Project in the Qilian Mountains region, this area has been selected as the research area. [Methods] This study selected three typical forest types, namely Picea crassifolia forest, Betula platyphylla forest, and Picea crassifolia & Betula platyphylla forest, in the Ta'ergou watershed of Datong county, Qinghai province. Set up 5 plots in each forest type, totaling 15. Sampling was conducted on soil layers (0-20, 20-40, and 40-60 cm) at different depths under different forest types, the organic carbon content was measured to calculate the SOCD, and the grey correlation analysis method was used for research and analyze the distribution characteristics and influencing factors of soil organic carbon density in the forest land. [Results] The findings indicated that the soil organic carbon density (SOCD) content in different forest land types demonstrated that the P. crassifolia & B. platyphylla was higher than the B. platyphylla (P<0.05), and the P. crassifolia was the lowest. The organic carbon density on the vertical profile decreased with the increase of soil depth and was significantly positively correlated with the shrub biomass and canopy density in the vegetation layer factors, while significantly negatively correlated with the angular scale. Among the three forest types, the correlation between available phosphorus (AP) and soil organic carbon density is the highest in the P. crassifolia forest at 0-20 cm (correlation degree is 0.92). In the B. platyphylla forest, the factors with strong correlation with organic carbon density are 0-20 cm alkaline nitrogen (AN), 0-40 cm available phosphorus (AP), and average tree height (H); In the P. crassifolia & B. platyphylla, the correlation between canopy density (CD) and organic carbon density is the highest (correlation degree is 0.95). [Conclusions] The P. crassifolia & B. platyphylla has the best comprehensive properties, which is more favorable for the storage and buildup of soil organic carbon. It has important guiding significance for the improvement of forest stand function in the region.
