Abstract:The Yellow River Basin has a variety of sediment source areas, and the characteristics of water and sediment sources are prominent. Therefore, it is extremely necessary to study the Spatial equilibrium analysis of comprehensive control of soil and water conservation to optimize the spatial layout of soil and water conservation and to effectively and continuously reduce the sediment entering the Yellow River. Based on the analysis of the characteristics of the sediment source areas and the current situation of comprehensive control of soil and water conservation, we used statistical theory and methods to study the concept, principle and evaluation method of the spatial equilibrium of comprehensive control of the Yellow River soil and water conservation, and evaluated the equilibrium of control status. The results show that: (1) The spatial equilibrium of comprehensive control of soil and water conservation in the watershed refers to the control measures that corresponds to the spatial heterogeneity of soil erosion intensity and can effectively control the erosion and sediment yield intensity to a certain extent, and the degree of the control can be quantified by the effect; (2) The sediment reduction effects of different degrees of control are different, and the spatial equilibrium of control in the whole basin system can be identified by the differences in the degree of sediment reduction effect of different zoning control measures; (3) The evaluation method of spatial equilibrium of control is proposed, and the method mainly includes evaluation of watershed zoning, calculation of the degree of sediment reduction effect of soil and water conservation measures and spatial equilibrium coefficient of comprehensive control, and identification of weakly controlled areas; (4) At present, the spatial control of the Yellow River Basin is uneven, and the degree of sediment reduction effect of soil and water conservation measures and the spatial control equilibrium coefficient are very low in the Lanzhou-Toudaoquan area and the northern part of Shaanxi Province, which are typical weak control areas. The proposed method for evaluating the spatial equilibrium of comprehensive control of soil and water conservation can quantitatively identify weakly controlled areas and provide a new technical method for optimizing the development pattern of soil and water conservation.

Abstract:The construction spoil deposits have a unique material composition, and its soil erosion resistance is poor, which is easy to cause water and soil loss owing to rainstorm. Hence, it is important to explore the mechanism of flow reduction and sediment reduction of fine mesh net. To analyze the influence of rainfall duration dynamic changes on flow reduction and sediment reduction benefits of fine mesh net on construction spoil deposits, three rainfall intensities (60~120 mm/h) and four slope gradients (5°~35°) were considered on fine mesh net role of reducing soil erosion on spoil deposits. The results showed that: Under a rainfall intensity of 60 mm/h, covering with the fine mesh net has a significant inhibitory effect on the initial runoff time at 15°~35° (p<0.05), while it can significantly prolong initial runoff time (15°~25°) when a rainfall intensity more than 60 mm/h (p<0.05). There was a significant difference in the sediment reduction benefits of 60 mm/h and 90 mm/h (120 mm/h) rainfall intensity under different slopes (p<0.05). The flow reduction and sediment reduction benefits of fine mesh net were decreased with the prolonging of rainfall duration, and reached the threshold at a rainfall intensity of 90 mm/h. The power function can describe the relationship between the benefits of flow and sediment reduction with the rainfall duration well, and the benefit attenuation coefficient(b) increased sharply with the increase of rainfall intensity. The flow reduction and sediment reduction benefits of fine mesh net cover can be divided into high-efficiency stage, decreasing stage and stable stage with the change of rainfall duration. In general, considering the development of soil and water conservation work in production and construction projects, it is recommended to use temporary cover when a short-duration (< 30 min) and heavy rainfall (< 90 mm/h) is the main rainfall in the construction area of production and construction projects, which can effectively reduce soil erosion. The research results can provide reference for the supervision of soil and water conservation of production and construction projects.

Abstract:The Qingshui River Basin in Ningxia is located in the arid and semi-arid transition area of the Loess Plateau. This paper selected the daily runoff and precipitation data of the Quanyanshan hydrological station and meteorological station in the Qingshui River Basin from 1989 to 2019, and used the Chapman-Maxwell method to divide the daily runoff time series of the basin. The result of base flow segmentation was applied to separate runoff events to further explore the response law of runoff events to precipitation. The results showed that: (1) The precipitation, runoff and base flow of the Qingshui River Basin in Ningxia showed an upward trend as a whole. The Mann-Kendall test showed there was no significant mutation time point. The precipitation with a daily rainfall of less than 10 mm showed an increasing trend. The annual precipitation was mainly distributed in May-September, accounting for 81.72%. (2) Based on the daily runoff time series, a total of 58 runoff events were isolated in the Qingshui River Basin in the past 30 years. Under drought conditions, the total amount of precipitation was significantly related to rainfall intensity. Under the influence of soil moisture and water storage, the runoff process under drought conditions was more sensitive to the precipitation response in the early stage of the event. In the rainy season, the total amount of precipitation and the precipitation intensity were the main factors influencing surface runoff. (3) The influence of soil moisture on the characteristics of runoff events had a threshold change. When the precipitation in the previous 10 days was less than 5 mm, the peak flow was sensitive to its response.

Abstract:To investigate the effects of different plants on soil and water conservation in ephemeral gullies of agricultural fields in the black soil region of Northeast China, ephemeral gullies were modelled on bare slopes (LP) and slopes planted with both alfalfa (V₁) and Iris ensata Thunb (V₂). By simulating upper catchment, hydraulic erosion experiments were carried out on the slope surface of ephemeral gullies covered by different plants, and the characteristics of runoff and sediment yield as well as the spatial and temporal variation of hydrodynamic parameters were analyzed. The results showed that: (1) Under the same flow rate, the runoff generation time followed the order of LP < alfalfa < I. ensata Thunb, with significantly prolonged flow production and greater infiltration, sediment-reduction benefits of alfalfa (61%) was significantly better than that of I. ensata Thunb (29%), but the runoff reduction benefits of alfalfa (33%) was slightly weaker than that of I. ensata Thunb (38%). (2) Under the same flow rate, hydraulic friction coefficient (f) of alfalfa (2.3) was higher than that of I. ensata Thunb (0.8), while the average flow rate (u) of alfalfa was slightly lower than that of I. ensata Thunb, the Froude number (Fr) and the mean Reynolds number (Re) followed the order of alfalfa < I. ensata Thunb, and the overall flow was turbulent. (3) Analysis of the fitted functions showed that Reynolds number was positively correlated with flow rate and friction coefficient under the three sets of experiments, but the functional relationship was slightly different. Froude number was negatively correlated with friction coefficient, all in line with the law of logarithmic function change. The results showed that the reduction of runoff and sediment yield was due to the increase of friction and infiltration rate of the vegetation cover, and alfalfa was more effective in reducing runoff and sediment than I. ensata Thunb. With the increasing flow rate, the runoff and sediment reduction benefits of I. ensata Thunb decayed more rapidly than those of alfalfa. The critical flow rate for protection of I. ensata Thunb was 30~40 L/min, and alfalfa could meet the soil and water conservation needs at higher catchment flow.

Abstract:In order to explore the characteristics of runoff and sediment yield and the relationship between runoff and sediment yield on the slope under different antecedent soil moisture conditions, this paper took Ansai loessial soil as the research object, and systematically studied the influence of antecedent soil moisture on runoff and sediment on slope by setting six antecedent soil moisture treatments (5%, 10%, 15%, 20%, 25%, 30%). Two repetitions were set for each water content treatment, the slope gradient was 15°, the rainfall intensity were set to 90 mm/h, and the rainfall duration was set to 1 hour. The results showed that: (1) With the increase of antecedent soil moisture, the initial runoff time decreased as a power function, and the runoff increased linearly. (2) The amount of soil loss on the slope increased as a power function with the increase of antecedent soil moisture. The amount of soil loss in the high antecedent soil moisture group (29.3%) was 86.1 and 8.9 times that in the low water content group (5.8% and 10.6%) and the medium water content group (15.3%, 20.4% and 25.1%). When antecedent soil moisture was close to saturation, the slope erosion intensified and the amount of soil loss increased rapidly. (3) Under the conditions of different antecedent soil moisture, the relationship between slope runoff and sediment yield was a power function. When the runoff yield rate exceeded 1.4 L/min, the sediment yield increased rapidly or even doubled, showing the characteristics of "large water and more sediment". Antecedent soil moisture affected slope sediment yield by affecting infiltration runoff and changing the relationship between runoff and sediment. Therefore, for the loess slope, attention should be paid to preventing soil erosion caused by rainstorm or extreme rainstorm after continuous and lasting rainfall. Measures such as cultivation and vegetation cover can be taken to maintain appropriate soil water content and make the soil layer unsaturated to reduce erosion. The results provide a scientific basis for the protection and management of soil and water resources in the Loess Plateau.

Abstract:To explore the impact of grassy slope fire prevention project on runoff and sediment yield on grassy slope in arid valleys area, a series of sourcing experiments were conducted in three steep slopes of 27.5° in Liangshan Prefecture of Sichuan Province. The flow rates of sourcing experiments were 6, 9 and 12 L/min, respectively. The three slopes were treated as follows: (1) Remove vegetation and level the slope to represent the grassy slope fire passage; (2) Remove the aboveground part of the vegetation to represent the grassy slope fire isolation zone; (3) No treatment as a control. The effects of different grassy slope fire prevention project on water erosion under different scouring flow rates were studied by collecting the runoff and sediment at the slope outlet, respectively. The results showed that: (1) Due to the loose soil on the slope and the increase of water infiltration during the construction of the grassy slope fire prevention project, the initial runoff time of the grassy slope fire passage (20.33 min) was larger than that of the control slope (7.62 min) and the grassy slope fire isolation zone (5.22 min). (2) The order of the cumulative runoff and cumulative sediment yield under the three flow rates were as follow: grassy slope fire passage > grassy slope fire isolation zone > control slope. Moreover, the difference between the three slopes increased significantly with the increase of the flow rates. The construction of grassy slope fire prevention project had aggravated the water erosion on the steep slope. (3) There were linear relationships between the runoff and sediment yield on the control slope, while the relationships between the runoff and sediment yield were exponential, logarithmic, or linear for the grassy slope fire passage. The relationships between the runoff and sediment yield for the grassy slope fire isolation zone were logarithmic or linear. The construction of the grass slope fire prevention project has changed the original linear relationships between runoff and sediment yield. Therefore, more attention should be paid on soil erosion after the construction of grassy slope fire prevention project on steep slopes. This research can provide scientific reference for the impact of grassy slope fire prevention project on soil erosion in arid valleys and the implementation of preventive measures on steep slopes.

Abstract:In order to further explore the differences in accuracy of UAV-derived 3D models under different lighting conditions, four phases of digital surface models were constructed by UAV photography technology under sunny and cloudy conditions, and elevation points measured by RTK (real-time kinematic) and digital elevation model obtained by 3D laser scanner were taken as benchmark, respectively. At the typical section and the entire erosion gully scale, the difference in elevation accuracy of 3D reconstruction of erosion gully under different lighting conditions was analyzed. The results showed that: (1) At the typical section scale, the elevation accuracy of the model constructed on cloudy days was the highest, and the elevation accuracy of the model constructed at noon on sunny days was higher than that in the morning and afternoon, while the elevation error of the shaded area was 0.138~0.217 m higher than that in the non-shaded area. (2) At the entire erosion gully scale, the root mean square error of the aerial survey elevation model on cloudy days was only 0.155 m, which was the minimum. For different periods of sunny days, the elevation error of DSM obtained by UAV survey at noon was the lowest, but it was still 0.411 m higher than that of DSM on cloudy days. Based on the three elevation models of sunny days, the elevation error in the shaded area was 0.250~0.346 m higher than that in the non-shaded area. (3) From different slope aspects, the elevation error of sunny slope was the lowest, while the increasing of shadow area led to the further increase of other slope aspects errors. The results showed that the shadow caused by illumination significantly reduced the accuracy of the elevation model, which could provide a reference for the research of aerial mapping of erosion gully based on UAV.

Abstract:In order to find out the problem of soil and water loss on the slope side of oil and gas pipeline operation in fully weathered granite area, this paper adopted the methods of measuring the boundary conditions of typical slopes in the field, collecting the data of gully depth and gully sectional area of slope erosion characteristics, sampling and testing rock and soil mass, and the indoor model rainfall test. The results showed that rainfall, slope length, slope, catchment area and geotechnical characteristics all affected the slope erosion of backfill soil in fully weathered granite pipe trench. Sediment yield and flow yield increased with the increase of rainfall intensity. The slope length, slope and catchment area were positively correlated with gully depth and gully cross-sectional area, and the gully depth and gully cross-sectional area increased with the increase of slope length, slope and catchment area. Through sampling, it was found that the relative content of particle composition of undisturbed soil was different from that of backfill soil, and the particle size distribution of the initial backfill soil was good. At the initial stage of rainfall scouring, the runoff of backfill slope mainly carried away silt and clay particles. Compared with the original soil, the porosity of the backfill soil in five years increased to 1.13 times, the soil permeability coefficient increased by one order of magnitude, and the cohesion in saturated state and internal friction angle decreased to 67.6% and 87.5% of that of the original soil, respectively. By finding out the influencing factors and their effects on slope erosion of backfill soil in fully weathered granite pipe trench, it could provide a basis for the subsequent slope treatment.

Abstract:In order to explore the influence of climate and vegetation coverage changes on the shore slope of the fading zone of the Three Gorges reservoir area, the erosion laws and changing characteristics of different rainfall intensity and the vegetation coverage (0, 30%, 50%, 70%, 90%) were analyzed with artificial simulated rainfall experiments. The results show that: (1) Under different rain intensities, the accumulated sediment yield of vegetation slope erosion shows a downward trend with the increase of vegetation coverage, and the overall downward evolution trend can be divided into three stages rapid-gentle-stable, and the critical coverage of the shore slope of the Three Gorges Reservoir Area in the fading zone is 50%~70%, and maintaining vegetation coverage in this interval can effectively inhibit the sediment loss on the slope. (2) The relative coefficient of surface runoff under the same vegetation cover is positively correlated with rain intensity. The relative coefficient of surface runoff under the same rain intensity is negatively correlated with the vegetation coverage. It indicates that the vegetation on the slope can effectively block the surface runoff and have a certain inhibitory effect on soil erosion. (3) The Horton rainfall infiltration model was selected to analyze the influence of different vegetation coverage on the infiltration rate of rainfall. The analysis suyyests that the infiltration of rainfall on the slopes under different vegetation cover was roughly divided into three stages rapid decrease in the early stage of rainfall, slowing down in the midterm, and gradual stabilization in the later stage. The greater the vegetation coverage, the higher the stable penetration rate. The research results can provide a theoretical reference for soil erosion control on the slopes of the Three Gorges Reservoir Area and for promoting the protection and restoration of the ecological environment of the Yangtze River.

Abstract:By setting up erosion simulation plots, the change characteristics of soil nutrients in the process of quality degradation of the cultivated layer of purple soil sloping farmland were studied. In this paper, taking purple soil slope cultivated land in the Three Gorges Reservoir area as the research object, five erosion degrees (0, 5, 10, 15 and 20 cm) and two management measures (no fertilization (CK) and conventional tillage (F)) in situ experiments, using field in situ detection, soil chemical property analysis and other means were used to study the restoration effect of conventional tillage on soil nutrients in eroded topsoil and the interannual variation trend of soil nutrients. The results showed that: (1) All indicators of soil nutrients in the topsoil showed that F>CK, indicating that F was better than CK in improving soil nutrients, and it had a better effect on soil nutrients. The improvement effect of organic matter, total nitrogen and available phosphorus was obvious. (2) The soil nutrients of the arable layer of the purple soil slope farmland were mainly enriched in the topsoil layer of 0—20 cm. The soil nutrient content in the 30 cm soil layer increased significantly, and the effect on the increase of the organic matter content in the 10—20 cm soil layer was the best. (3) After a continuous 4 years positioning test, the organic matter, total potassium, alkali-hydrolyzed nitrogen, available phosphorus, and available potassium increased by 4.33%~15.89% under CK compared with the background value, the total nitrogen content did not change significantly compared with the background value, and the total phosphorus content decreased by 11.78% compared with the background value; the F soil nutrient increased by 4.51%~49.46% compared with the background value. The results provide basic parameters for the regulation of the plough layer and the improvement of land productivity.

Abstract:In order to explore the effects of biological crusts coverage, slope and flow rate on soil detachment capacity under freeze-thaw conditions when biological crusts existed, the algal crusts in the Dongliugou small watershed in the northern Loess Plateau were taken as the research object. A test method combining indoor freeze-thaw simulation and scour were carried out, and Taguchi method and Orthogonal design were used to analyze the effects of algal crust coverage, slope, flow and freeze-thaw on soil detachment capacity. The results showed that when the soil detachment capacity was the maximum, the crusts coverage, slope, flow was 10%, 20° and 24 L/min, respectively, while the number of freeze-thaw times was 1 and 10 in Taguchi method and Orthogonal design, respectively. Under freezing and thawing conditions, with the increasing of algal crust coverage, the soil detachment capacity gradually decreased. Soil detachment capacity increased with the increasing of slope and flow. In the orthogonal design, soil detachment capacity firstly decreased and then increased, but in the Taguchi method, the change of soil detachment capacity did not have had obvious law with the increasing of freeze-thaw times under the experimental conditions. Slope was the main factor affecting soil separation ability in the Orthogonal design, and the contribution rate of each factor was slope (15.08%)>coverage (14.38%)>flow (13.69%)>freeze-thaw (-13.23%). In Taguchi method, algal crust coverage was the main factor affecting soil detachment capacity, and the contribution rate of each factor followed the order of coverage (30.41%)>slope (25.32%)>flow (1.59%)>freeze-thaw (0.85%). The relative error of the soil separation ability predicted by the Taguchi method was small (CV=0.49), and the coefficient of determination was large (R²=0.961>0.958, p≤0.001). Taguchi method could be used to predict soil detachment capacity under certain experimental conditions. The results could provide a theoretical reference for soil erosion research on the northern Loess Plateau.

Abstract:Quantitative analysis of slope rill morphological characteristics is the basis of rill erosion research. The artificial rainfall simulation tests under the combinations of three rainfall intensities (30, 60 and 90 mm/h) and five slopes (2°, 5°, 10°, 15° and 20°) were conducted, and the effects of rainfall intensity and slope on rill morphology and its spatial change characteristics of saturated purple soil slope were quantitatively studied. The results showed that the average width, depth and ratio of width to depth of rill on the saturated purple soil slope was 3.44~9.64 cm, 1.01~8.14 cm and 1.18~3.87, respectively. The width and depth of rill increased first and then decreased from top to bottom along the slope surface, and the ratio of rill width to depth of rill along the slope surface followed the order of upper

Abstract:In order to study the law of rill erosion on the loess slope, and explore the indoor calculation method for the detachment capacity of water flow, this paper took loess soil as the research object, four flow rates (2, 4, 6, 8 L/min), and four slope gradients (5°, 10°, 15° and 20°) were set up, and the length of soil trough was 12 m. The critical rill length and sediment transport capacity of loess soil slope were obtained. Based on the functional relationship between the above two factors, the calculation formula of detachment capacity was deduced. According to this, the change rules of critical ditch length, sediment transport capacity and detachment capacity under different test conditions were analyzed, and the accuracy of this test method was verified. The results showed that under the designed hydraulic conditions, the critical rill length of rill erosion on loess slope varied from 5.33 to 11.12 m, and the critical rill length decreased with the increase of flow rates and slopes, and the sediment transport capacity increased with the increase of flow rates and slopes. There was an obvious linear relationship between detachment capacity and flow rate, and a logarithmic relationship between detachment capacity and slope. Compared with other methods, this test method had the advantages of convenient operation and high coincidence of results, and could better determine the denudation ability of rill erosion in loess area. The research results can further improve the theory of rill erosion on the loess slope.

Abstract:In order to explore the influence of different rock-soil cover patterns on soil erosion/loss in karst slope land, the artificially simulated rainfall experiment was used to study the characteristics of runoff and sediment yield on karst slope under three rock-soil cover patterns of mosaic pattern, transverse slope pattern and downslope pattern with bare slope as the control group. The results showed that: (1) The surface runoff yield of the downslope pattern was the largest, which increased by 88.6%, 67.1% and 576.1% compared with the mosaic pattern, transverse slope pattern and bare slope, respectively. At the same time, the underground runoff yield of the downslope pattern was the smallest, which was 37.5%, 36.1% and 39.2% lower than that of the mosaic pattern, transverse slope pattern and bare slope, respectively. (2) The surface sediment yield followed the order of downslope pattern > mosaic pattern > transverse slope pattern > bare slope, and the underground sediment yield followed the order of mosaic pattern > transverse slope pattern > downslope pattern > bare slope. The surface sediment yield of the three rock-soil cover patterns significantly increased compared with that of the bare slope, but the underground sediment yield increased relatively less. (3) Rock-soil cover pattern could the relationship between surface runoff and sediment. There was a power function relationship between surface cumulative runoff and surface cumulative sediment yield. Mosaic pattern significantly changed the relationship between surface runoff and sediment, and significantly improved the slope surface erosion. The results of this paper could further enhance the understanding of rainfall erosion law in karst slope land, and provide a reference for rocky desertification control in karst area.

Abstract:Rainfall runoff erosion transport capacity of high and steep slopes is an important scientific problem. The law of runoff erosion transport under the condition of the same rainfall intensity and different gradients and slope length was studied by indoor simulated rainfall experiment. The results showed that: (1) Under the test conditions, the flow depth was inversely proportional to the 1/3 power of hydraulic gradient and directly proportional to the 3/5 power of slope length, and the flow velocity increased in positive proportion to hydraulic gradient and flow depth. (2) Under the condition of bare slope with the same rain intensity, the runoff sediment concentration was directly proportional to the 1/2 power of hydraulic gradient, was proportional to the 4/5 power of the slope length. The sediment carrying capacity of water flow was directly proportional to the 1/2 power of hydraulic gradient. (3) The ratio of the turbulent diffusion effect of rainfall runoff to the effect of gravity was larger than that of open channel flow, indicating that the turbulent effect of raindrops is more obvious,the formula of sediment carrying capacity is given. Compared with the commonly used formula of river sediment carrying capacity, the coefficient was larger and the index smaller. The research results are of great significance for in-depth analysis of the mechanism of rainfall-runoff erosion and transport.

Abstract:In order to investigate the variation law and main driving factors of baseflow in the blown-sand region of Wuding River Basin, this study was based on the hydrological data of Zhaoshiyao hydrological station and precipitation data of several stations in the blown-sand region of Wuding River Basin from 1954 to 2018, compared the applicability of the three kinds of methods (HYSEP, Digital Filtering and BFI method) to segmentation baseflow, revealed the variation characteristics of river baseflow, analyzed the driving factors (precipitation, vegetation coverage and agricultural irrigation, etc.) which can cause changes of baseflow in this area. The results showed that the local minimum method in the HYSEP method is better than the other methods for the segmentation of channel basic flow in the blown-sand region. The average basic flow was 3.29×10⁸ m³ and the average basic flow index was 0.71 during 1954-2018. The basal flow showed a very significant decreasing trend in 1972 and 2000, and its periodic change was mainly controlled by the first main cycle (32 years). The variation of channel base flow in the blown-sand region area of the Wuding River Basin was the result of the comprehensive influence of precipitation, vegetation coverage, agricultural irrigation, etc. Compared with the first stage (1954-1972), in the second stage (1973-2000) and third stage (2001-2018) precipitation contributed 29.35% and 4.52% to the variation of baseflow, and the contribution rates of human activities (vegetation coverage and agricultural irrigation) were 70.65% and 95.48%, it indicates that human activities were the main driving factors of baseflow change. The research results can provide a basis for the rational development and utilization of water resources in blown-sand region of Wuding River Basin.

Abstract:In recent decades, global climate has changed abnormally and extreme hydrological events have occurred frequently. It is of great significance to understand the dynamic changes of extreme sediment and explore its possible influencing factors for preventing sediment disasters. In this study, the Wuding river basin in the middle reaches of the Yellow River was taken as the research object. From the four aspects of magnitude, time, intensity and frequency, eight extreme sediment indexes were established, including annual maximum 1-day sediment concentration (Sx1d), annual maximum 5-days sediment concentration (Sx5d), occurrence date of annual maximum 1-day sediment concentration (DSx1d), occurrence date of annual maximum 5-days sediment concentration (DSx5d), average annual sediment concentration (Sint), high sediment concentration (S95p), extremely high sediment concentration (S99p), and days of hyperconcentrated flows (S200). Mann-Kendall trend test and circular statistical approach were used to analyze the variation trend and time distribution characteristics of extreme sediment indexes. The change-point of indexes was determined based on Pettitt test, and the range of variability approach was used to quantitatively evaluate variation of each index. Finally, the influence of rainfall erosivity and ecological construction measures on extreme sediment changes are discussed. The results showed that: (1) From 1958 to 2018, all extreme sediment indexes of Wuding river basin showed a significant decreasing trend (p<0.05). (2) The rush period of Sx1d was from June 30 to August 18, and the rush period of Sx5d was from July 11 to August 17, which was more concentrated than that of Sx1d. (3) S200 reached moderate alteration, Sx1d, Sx5d, Sint, S95p and S99p reached high alteration, and S95p and S99p had the largest alteration, with alteration of -100%. The overall change of extreme sediment indexes was 83.72%, which belonged to high alteration. (4) During 1963—1966 period, the decrease of rainfall erosivity led to a reduction of extreme sediment in the Wuding river basin to a certain extent. During 1982—2018 period, NDVI and annual cumulative value of dam control area (A_d) were significantly negatively correlated with extreme sediment indexes (p<0.05), and path analysis indicated A_d had a greater direct effect on extreme sediment indexes than NDVI, which was the main factor affecting the change of extreme sediment. The research results are helpful to enhance the understanding of extreme sediment changes in Wuding river basin, and provide a theoretical basis for formulating sediment disaster prevention strategies.

Abstract:Habitat quality is an important reference index to measure the quality of a region’s ecological environment, and research on land use change can provide a scientific basis for evaluating the spatio-temporal dynamic evolution characteristics of regional habitat quality. Based on the land use data in 1980, 2000 and 2018, this paper analyzes and predicts the change of land use in Yulin City through the InVEST model, PLUS model, and geographic information map method, so as to explore the spatio-temporal evolution characteristics of habitat quality in Yulin City, Shaanxi Province. The conclusions are as follows: (1) The landscape matrix in Yulin City is mainly composed of grassland and cultivated land, followed by forest land and unused land, while water and construction land account for a relatively small proportion. The implementation of the policy of returning farmland to forest, the development of desertification control projects, and the development of construction land are the main driving factors of land use change. (2) From the overall analysis of the region, the average habitat quality in 1980, 2000, 2018 and 2030 is 0.502 8, 0.520 9, 0.518 3 and 0.525 9, respectively. The overall habitat value does not change much, showing a fluctuating trend of first increase, then decrease and then increase. From the analysis of the spatial pattern, the distribution of habitat quality in Yulin City has a certain regularity, and the overall pattern is high in the east and low in the west. The average value of habitat degradation in Yulin City is 0.029 8, 0.028 9, 0.029 2 and 0.028 3, respectively, indicating the threat of habitat degradation. The research results have theoretical support and policy significance for the protection of the natural environment and the improvement of habitat quality in Yulin City.

Abstract:Topography is the main factor influencing soil erosion, but the distribution pattern and influencing factors of topographic factors on the Qinghai-Tibet Plateau (QTP) need to be studied. Based on the 1 arc resolution SRTM (Shuttle Radar Topography Mission) elevation data, we calculated the slope, slope length and LS factor (slope length and steepness factors, LS), and studied the distribution pattern, statistical distribution characteristics and influencing factors of LS factors on the QTP in combination with area-elevation integration and Hack profile. The results show that: (1) The three topographic indexes of slope, slope length and LS factors all showed the pattern of that small in the center of the plateau and large in the around high mountains, and the average slope gradient of the inner flow area and the outer flow area was 6.55° and 14.3°, the average of slope length was 122.9 and 172.2 m, the mean LS factor was 4.8 and 12.7, respectively. (2) On the whole, the LS factor on the QTP was mainly affected by slope steepness, but the LS factor in the steep areas on the edge of the plateau was mainly affected by slope length. (3) The Hack profiles of the six main rivers in the QTP were convex, and the geomorphic evolution of the region was in its youth stage as a whole. (4) The distribution characteristics of LS factor on the QTP were consistent with soil erosion types and their combinations. The high value in the surrounding area corresponded to Glacier erosion-water erosion, the low value in the northwest corresponded to hydraulic freeze-thaw erosion and wind erosion, and the high value in the transition area from the southeast edge to the interior of the plateau corresponded to hydraulic gravity erosion. The distribution pattern and statistical characteristics of LS factor analyzed in this paper could provide theoretical and data support for the evaluation of soil erosion, and also had great significance for the study of material migration and transformation in the earth system of the QTP.

Abstract:The purpose of this study was to explore the co-evolution of soil erosion and rocky desertification and their interaction under driving factors and main driving factors in the karst region. In this study, Optimized RUSLE model was used to estimate soil erosion from 2005—2015 in the karst area of Guizhou Province, and the national rocky desertification census database was used to calculate the rocky desertification in the same period, and the Geographic detector was used to explore the interaction between the drivers and the main drivers. The results showed that soil erosion and rocky desertification from 2005 to 2015, karst area in Guizhou Province were mainly moderate and below, soil erosion accounted for more than 58%, and moderate and below rocky desertification accounted for more than 80%; In terms of time, there were similarities and differences in the occurrence time of these two, but during the research period, both of them tended to improve in varying degrees. The incidence of soil erosion in moderate and below rocky desertification was large, and the proportion of above moderate rocky desertification was very small, among which the incidence of soil erosion in no rocky desertification was more than 70%. The explanatory force of the soil erosion driver was the land use > slope > yearly precipitation > elevation > rock exposure rate > vegetation cover > lithology > soil thickness; The explanatory force of the rocky desertification driver was the rock exposure rate > soil thickness > yearly precipitation > elevation > lithology > land use > vegetation cover > slope. The explanatory force of factor combination (interaction) on soil loss and rocky desertification was enhanced compared with the single factor, in which the dominant factor of soil erosion was land use, and the dominant factor of rocky desertification was rock exposure rate; The results showed that the causal relationship between soil erosion and rocky desertification exists and soil erosion develops before rocky desertification, but the simple linear relationship cannot explain the two relationships, but a complex relationship with positive or negative correlation exist in stages. The results can provide theoretical reference for soil erosion and rocky desertification control in karst area.

Abstract:To explore the impact of land use change on carbon storage in Anhui Province, and reveal the spatial-temporal evolution and future trend of carbon storage, this study coupled carbon storage module of InVEST model and PLUS model to evaluate the spatial-temporal evolution characteristics of land use types and carbon storage in Anhui Province from 1990 to 2018, and to predict the change trend of carbon storage in Anhui Province in 2034 and 2050 from natural development and ecological protection scenarios. The results showed that the carbon storage of Anhui Province in 1990, 2000, 2010 and 2018 was 1 218.37×10⁶, 1 215.65×10⁶, 1 211.39×10⁶ and 1 206.18×10⁶ t, respectively. The carbon storage decreased year by year, which was caused by the occupation of cultivated land and forest land. In addition, the land use types in Anhui province varied spatially, and the overall carbon storage was much higher in the southern part than that in northern and central part. According to the results of scenario simulation, carbon storage in Auhui province under the natural development scenario would be 1 197.93×10⁶ and 1 196.08×10⁶ t in 2034 and 2050, respectively. Under the ecological protection scenario, the carbon storage would be 1 202.89×10⁶ and 1 200.37×10⁶ t in the same period. Compared with the natural development scenario, the expansion of construction land under the ecological protection scenario would be limited, and the high carbon density land types such as forests and grasslands would be protected, and the carbon storage capacity would be improved. These results could lay foundation for further clarifying the spatial and temporal pattern of carbon storage in Anhui Province and provide scientific references for further implementation of sustainable development strategy, acceleration of ecological province construction and "dual carbon" strategic planning in Anhui Province in the future.

Abstract:Exploring the response mechanism of water ecosystem services to the change of watershed landscape pattern in rapidly urbanization is of great significance to watershed landscape planning and ecosystem service improvement. This study took the Taihu Lake Basin as the research area, based on land use data, models and methods such as comprehensive landscape pattern index, SCS and InVEST model, and partial correlation analysis were applied. On the basis of depicted the landscape pattern and the spatial differentiation characteristics of three typical water ecosystem services, which were stormwater regulation, soil and water conservation and water quality purification, the response relationship of water ecosystem services to the characteristics of different landscape patterns at sub-watershed scale was mainly discussed. The results showed that: among the impact of the composition and configuration of the landscape on the three typical water ecosystem services, most of the conclusions were consistent with existing research conclusions or understanding. However, it was also found that the complexity of the shape of cultivated land and woodland landscape patches in Taihu Lake basin could improve the river water quality, and the wetland rare patches in the sub-basin were conducive to reducing non-point source pollution. The three kinds of water ecosystem services could be effectively improved by controlling the scale of cultivated land, optimizing the distance between cultivated land and water body and reducing slope cultivated land. Increasing forestland area in waterfront area and improving the density of patch edge, increasing the proportion of wetland and grassland in sub-basin were conducive to better control water pollution. Increasing the key landscape types such as wetlands and grasslands was the most effective way to improve water purification services. In order to more comprehensively and accurately depict the response relationship between pattern and water ecosystem service, it is also necessary to carry out in-depth research on ecosystem service flow, non-linear relationship and threshold, and the relative contribution of different pattern characteristics to service.

Abstract:Impervious surface expansion has a prominent impact on the process, function and service of urban ecosystem, so exploring its variation is of great significance to urban development. Based on the land use data from 2000 to 2020 in Nanjing, we integrated landscape spatial gradient analysis and pattern analysis method, setting radial gradient zones around the downtown by expanding outward at equal distances to analyze the spatial and temporal distribution and gradient characteristics of impervious surface. Meanwhile, the transects along and across the Yangtze River were set to analyze the driving forces behind the expansion scale and direction variation of impervious surface. It could provide policy suggestions for the landscape pattern optimization of Nanjing. Results showed that: (1) Impervious surface landscape dominance showed a downward trend along the gradient zone. The urban center was highly concentrated with well-shaped impervious surface. The peripheral urban area was the key regions of impervious surface expansion, accompanied with the reduction of arable land, forest land, water body and other natural landscape, so the landscape pattern of this area changed drastically. The suburban area impervious surface maintained slow and steady expansion. (2) Topography and river system significantly affected the expansion direction of impervious surface, planning policy would play a certain regulatory role. Economic development, population growth and industrial structure adjustment and optimization affected the expansion scale of impervious surface. (3) Nanjing should optimize the urban landscape pattern from three aspects improving the urban living space, transforming the mode of urban development and controlling the urban expansion.

Abstract:Constructing reliable precipitation datasets with high spatial and temporal resolution to reveal the temporal and spatial variation characteristics of precipitation in the context of global warming is crucial for water resources management and soil erosion prevention and governance. In this paper, a Combinedly Interpolated Precipitation (CIP) method was proposed. Using the daily precipitation data observed at more than 400 sites in Fujian Province from 1979 to 2018 as the data source, a 0.05°×0.05° high spatial resolution daily precipitation grid point dataset was produced in the study area. Based on this data set, eight extreme precipitation indices and three precipitation concentration indices were calculated, and the temporal and spatial variation characteristics of precipitation in Fujian Province were analyzed. The results showed that the CIP method proposed in this paper could effectively improve the accuracy of daily precipitation interpolation, and the data accuracy was far higher than that of the commonly used reanalysis and satellite remote sensing precipitation data products. The five extreme precipitation indicators of the maximum one-day precipitation, the maximum five-day precipitation, the heavy precipitation, the total precipitation and precipitation intensity in Fujian coastal areas and the lower reaches of the Minjiang River, had significant upward trend in a large area. The precipitation concentration period (PCP) in the whole region was bounded by the Jiufeng Mountains-the lower reaches of the Minjiang River-Daiyun Mountains strip, that was, PCP on the northwest side of the strip was before June 11, whereas the southeastern side was after June 11, which was basically consistent with the first rainy season in Fujian Province. The first rainy season in the northwest region had a backward trend, while the rainfall of the second rainy season in the southeast region had increasing trend.

Abstract:Dicranopteris dichotoma is the pioneer plant that invaded the degraded bare land of red soil, and its invasion process is of great significance to the change of soil environment in the process of ecological restoration of degraded land. Therefore, taking the eroded bare land of red soil in Changting County of Fujian Province as the research object, the soil physical and chemical properties, bacterial composition and diversity in the invasion and non- invasion areas of D. dichotoma were analyzed and determined. The results showed that the invasion of D. dichotoma significantly increased soil maximum water holding capacity, soil moisture, pH and the content of total carbon, total nitrogen, total potassium and organic matter, and significantly decreased soil bulk density (p<0.05). Compared with the non-invasion area, 14 dominant soil bacteria such as Rhizobiale and Bradyrhizobium added in the invasion area of D. dichotoma, the relative abundance of Proteobacteria and Alphaproteobacteria significantly increased (p<0.05), but the relative abundance of Chloroflexi and AD3 significantly decreased (p<0.05). The main functions of these soil bacteria were chemoheterotrophy, aerobic heterotrophy and cellulolysis. The invasion of D. dichotoma into bare land significantly increased the diversity of soil bacterial community structure (p<0.05). There were significant differences in soil bacterial community structure between invasion and non- invasion areas (p<0.05). The main influencing factors of soil bacterial community structure were soil moisture content, total carbon, organic matter, soil bulk density and pH. These influencing factors were positively correlated with Verrucomicrobia, Proteobacteria, Verrucomicrobiae and Alphaproteobacteria. In summary, D. dichotoma invasion could significantly improve soil physical and chemical properties, improve soil bacterial community composition, increase soil bacterial community diversity and dominant flora, and have a positive effect on soil bacterial community.

Abstract:To investigate the response of soil exchangeable salt-based ions and soil carbon and nitrogen content to nitrogen addition under two land use modes in the Three Gorges reservoir area, the changes of soil exchangeable Ca²⁺, Mg²⁺, Na⁺, K⁺ and NO₃^--N, DOC in forest and orchard soils in Zigui County, Hubei Province were investigated by indoor soil column leaching simulation experiments at four different nitrogen additions. The results showed that with the increasing of nitrogen addition amount, the leaching loss amount of exchangeable base cations in the forest soil increased significantly (p < 0.05), while that in the orchard soil did not change significantly. The total leaching loss amount of exchangeable base cations and the leaching loss amount of each base ion in the forest soil were higher than those in the orchard soil. Compared with the blank control (N0), in the forest soil under the three nitrogen additions (N1, N2 and N3), the total leaching loss amount of exchangeable base cations increased by 1.78%, 4.45% and 8.49%, respectively, and the leaching loss amount of NO₃^--N increased by 89.321%, 77.73% and 157.25%, respectively, indicating that nitrogen addition increased the leaching loss of NO₃^--N from the soil and thus took away exchange cations from the soil. The cumulative loss of DOC from forest soils decreased by 1.15% and 9.53% under N2 and N3 treatment, respectively, while it in orchard soils decreased by 15.55%, 5.88% and 17.16% under N1, N2 and N3 treatment, respectively. Compared with orchard soils disturbed by human, the leaching amount of exchangeable based cations in forest under a relatively natural state was more sensitive to nitrogen addition. The research showed that the increasing of nitrogen addition increased the leaching loss amount of exchangeable base cations and NO₃^--N in forest soil and decreased the leaching loss amount of DOC in forest and orchard soils.

Abstract:Taking the spruce-fir forest fire sites on the northeastern margin of the Qinghai-Tibet Plateau as the research object, the samples were collected from the burned sites. Ubed unburned natural forests in August 2020 and July-August 2021 based on the typical sampling method and indoor immersion method. Litter samples were measured and analyzed for indicators such as storage volume, water holding capacity, and effective storage capacity, to explore the hydrological effects of litter at different slope positions under the disturbance of forest fires, and to provide a basis for better-promoting forest water conservation and soil and water conservation functions. The results show that: (1) During the vegetation restoration process, the thickness and accumulation of litter increased, with the longer restoration years, and the thickness was 3.75~8.31 cm, and the accumulation iss 6.16~8.13 t/hm². The more thickness and volume of litter on the above-up-slope, mid-slope, and down-slope in the recovery 5 and 15 years fire sites were significantly different from those in the natural forest. (2) The maximum water-holding capacity of litter is 20.94~26.22 t/hm², and the difference between the maximum water-holding capacity of the litter in the 5 and 15 years of recovery and the natural forest reaches a significant level. Before the water-holding capacity of the litter reaches saturation, the water-holding capacity of the litter at each slope position has a logarithmic function relationship with the water immersion time, and the water absorption rate has a power function relationship with the water immersion time under different recovery years. (3) The effective storage capacity of litter is 14.58~16.95 t/hm², and the effective storage depth is 1.44~1.78 mm. The effective interception of litter in the restored 5 years burmed are shows the order of mid-slope > up-slope > down-slope, and the effective intercepted amount of the restored 15-year-burned area and the natural forest is down-slope > mid-slope > up-slope. To sum up, in the process of vegetation restoration, the thickness, volume and water-holding capacity of litter improved with the increase of the restoration period, showing that natural forest > restoration 15 years > restoration 5 years; The water performance and water holding process showed that the middle and lower slopes were larger than the upper slopes, that is, the hydrological effect of the litter was affected by the slope position and the disturbance of fire.

Abstract:The undisturbed soil columns were collected from different soil texture sample plots in Gongga Mountain primeval forest. The infiltration and outflow process and the stable isotope (δ¹⁸O) variation characteristics were monitored and analyzed during two rainstorms in summer of 2020. The results showed that: (1) The average total runoff (4.14 and 14.61 L, respectively) of gravel rich silty loam plot A at low altitude (2 649 m above sea level) after rainfall on August 6th and 11th was larger than that of silty loam sample plot B (3 000 m above sea level) (1.45 and 11.99 L, respectively). The outflow process of plot A was also more sensitive to rainfall. (2) The variation amplitude of isotope in outflow water was smaller than that in rainfall, and the new and old water were strongly mixed in the process of infiltration. (3) There were obvious differences in the variation patterns of the source and migration path of the outflow water between the two plots. Plot A showed extremely high rainfall contribution and fast triggered preferential flow path at the initial rainfall peak, and gradually showed the characteristics of plug flow when the outflow faded. Plot B was dominated by plug flow movement in the relatively slow infiltration process, and the exchange degree of new and old water was higher. Therefore, higher organic matter, gravel content and higher rainfall intensity were beneficial to the generation of preferential flow, and the generation and transformation process of preferential flow and plug flow had a rapid response to the change of rainfall intensity, which might have a further impact on aquifer recharge and solute transport in the basin.

Abstract:To explore the effects of typical Torreya grandis intercropping systems on soil carbon (C), nitrogen (N), and phosphorus (P) content and their stoichiometric characteristics on sloping farmland in the Three Gorges Reservoir Area, three typical intercropping systems, T. grandis (TG), T. grandis-Polygonatum sibiricum (TGP), and T. grandis-Glycine max (TGG), were selected in the T. grandis planting bases located in Baoping Town, Yunyang County, Chongqing. The contents of C, N, P in soil and their ecological stoichiometric characteristics under different models and soil depths were analyzed. The results showed that there was no significant difference in soil C content among different systems. Both N and P contents followed the order of TGG (0.80, 0.53 g/kg)>TGP (0.71, 0.40 g/kg)>TG (0.56, 0.39 g/kg), and compared with TG, N and P contents of TGG were significantly higher by 42.9% and 35.9%, respectively. Soil C and N mainly concentrated in the 0-10 cm soil layer, while P mainly concentrated in the 10-20 cm soil layer. Soil C∶N, C∶P and N∶P under the three systems was 8.39~10.73, 31.63~45.22 and 3.25~5.61, respectively, which were all lower than the national average values (14.4, 136.0, 9.3). And the N∶P ratio was less than 10, indicating that N was the limiting nutrient in the study area. The results of the correlation analysis showed that soil pH, bulk density and total porosity were also important indicators affecting soil C, N, and P contents and their ecological stoichiometry. T. grandis intercropping systems significantly enhanced the accumulation of soil nutrients. The content of C, N and P of TGG was higher than that of TGP and TG, and TGG showed better fertilizer cultivation effect.

Abstract:To study the influence of decomposition characteristics of litter on their water holding capacity under simulated nitrogen (N) deposition so as to provide a theoretical basis for the study of nutrient and water cycling in forest ecosystem under N deposition. The evergreen broad-leaved forest and Quercus semicarpifolia forest in central Yunnan Plateau were selected to conduct in situ leaf litter and twig decomposition experiment with four N treatment levels of 0 (control check CK), 10 (low nitrogen LN), 20 (medium nitrogen MN) and 25 (high nitrogen HN) g/(m²·a)N. Litterbag method and the laboratory immersion method were used to explore the variation characteristics of mass remaining rate, water holding capacity, water holding rate and water absorption rate of leaf litter and twig litter under different treatment. The results showed that: (1) The mass remaining rate of leaf litter and twig litter in two forest types decreased with the extension of decomposition time. Compared with the mass remaining rate of CK, LN treatment had no significant effect on leaf litter and twig litter in two forest types. MN and HN treatments increased leaf litter decomposition in evergreen broad-leaved forest at 16, 19, 23, 24 months and HN treatment increased leaf litter decomposition in Q. semicarpifolia forest at 16 months by 5.05%~7.45%, 7.88%~8.62% and 4.72%, respectively. (2) Compared with the CK, LN treatment increased the time required for 95% decomposition of leaf litter and twig litter in evergreen broad-leaved forest and twig litter in Q. semicarpifolia forest by 0.549, 0.366 and 0.402 years, respectively, while that of leaf litter in Q. semicarpifolia forest decreased by 1.011 years, and that of leaf litter and twig litter in two forest types under MN and HN treatment increased by 0.236~3.638 years. (3) The decomposition time, nitrogen deposition and their interaction significantly affected the maximum water holding capacity, maximum water holding rate, maximum water absorption of leaf litter and twig litter (p<0.001). Compared with the CK, the maximum water holding capacity, maximum water holding rate, maximum water absorption of leaf litter in evergreen broad-leaved forest under LN and MN treatments decreased by 21.99%,6.47%,54.47%,16.14%,4.15% and 1.25%, respectively, and those under HN treatment increased by 0.24%, 0.80%, and 0.96%, respectively, and in LN and MN and HN treatments, those of twig litter in evergreen broad-leave forest and leaf and twig litter in Q. semicarpifolia forest increased by 8.03%~38.22%, 5.47%~60.00% and 0.46%~5.72%, respectively. (4) The relationship between water holding capacity and the water holding rate of leaf litter and twig litter in two forest types and immersion time was a logarithmic function (m=a+bln t), and the water absorption rate was exponentially related to immersion time (v=at^-b). (5) The mass remaining rate of leaf litter in evergreen broad-leaved forest and that of twig litter in Q. semicarpifolia forest were significantly and positively correlated with their maximum water holding capacity, maximum water holding rate and maximum water absorption rate, respectively (p<0.05). In conclusion, the water holding capacity of litter was affected by the decomposition stage and nitrogen deposition.

Abstract:In order to investigate the changes in soil aggregates due to increased atmospheric nitrogen deposition and its effect on soil water infiltration, two kinds of nitrogen fertilizer ((NH₄)₂SO₄ and KNO₃) with four concentration levels (0, 10, 20, 40 kg/(hm²·a)N)were respectively added in mature and middle-aged coniferous forests at Mount Gongga, aims to investigate the effect of different forms of atmospheric nitrogen deposition on the structure of soil aggregates and the infiltration characteristics of soil water in a subalpine forest. The results showed that: (1) With the increase of nitrogen application, the proportion of large macroaggregate, soil water holding capacity, soil porosity and water stable infiltration rate in middle-aged stands gradually increased; the proportion of large macroaggregate, soil water holding capacity, soil porosity and water stable infiltration rate in mature stands showed a trend of first increasing and then decreasing; (2) The effects of different nitrogen forms on soil aggregate structure, soil porosity and water stable infiltration rate showed no significant difference; (3) Water infiltration was mainly affected by water holding capacity, soil porosity and aggregate formation. Nitrogen addition increased water holding capacity and soil porosity, and enhanced soil aggregation and water infiltration in middle-aged stands.

Abstract:To study the response difference of forest soil aggregate enzyme activity to nitrogen deposition and the influencing factors of aggregate enzyme activity, [JP2]taking the alpine P. yunnanensis forest and P. armandii[JP] forest in Central Asia of Yunnan Province as the research object, the field simulated nitrogen deposition test was conducted from June 2020 to May 2021. The settings were: control [CK, 0 g/(m²·a)N], low nitrogen [LN, 10 g/(m²·a)N], [JP2]medium nitrogen [MN, 20 g/(m²·a)N] and high nitrogen [HN, 25 g/(m²·a)N]. The[JP] soil samples in dry season (February 2021) and rainy season (August 2020) were collected respectively. The variation characteristics of urease(Vre), invertase(Inv) and acid phosphatase(AP) in soil aggregates and their interaction with environmental factors were analyzed to clarify the response characteristics of soil aggregate enzyme activity to nitrogen deposition under different screening methods. The results showed that: (1) Nitrogen deposition had no significant effect on the distribution of soil aggregates under the two stands, but different screening methods had significant effects; The activities of three enzymes in soil aggregates were promoted by LN and inhibited by MN and HN under different nitrogen deposition levels; (2) Compared with the dry sieving method, the enzyme activity in soil aggregates decreased significantly under the wet sieving method. The decline of enzyme activity in Inv and Ure aggregates was more than 20%, and the decline of AP was the highest, up to 57.55%; (3) The geometric mean GMea of soil dry sieve and wet sieve aggregate enzyme activity was higher than that of mixed soil, and the GMea under dry sieve condition was the highest, with an average increase of 50.35% compared with that under wet sieve condition. The stand among different factors had the greatest impact on Inv, while season had the greatest impact on Ure and AP. In conclusion, soil aggregates can isolate and protect soil enzyme activity. At the same time, the protection effect is jointly affected by season, stand type, screening method, and nitrogen application level. The research results provide a theoretical basis for the soil ecological process of regional forest ecosystem under nitrogen deposition and maintaining the stability of soil ecosystem.

Abstract:To study the disturbance effect of forest fire on the carbon cycle of coastal sandy forest ecosystem, taking Eucalyptus urophylla × Eucalyptus grandis plantation and Casuarina equisetifolia plantation as research objects, the LI-8100 soil CO₂ flux automatic measurement system was used to measure the soil CO₂ flux of burned and control plots in different plantations. At the same time, soil temperature and moisture, soil pH, total carbon, total nitrogen and mineral nitrogen contents in the sample plots were measured. The relationship between soil CO₂ flux and water and heat factors as well as the changes of soil physical and chemical properties were analyzed. The results showed that the soil CO₂ fluxes in the burnt plots were significantly lower than those in control plots, the monthly average of soil CO₂ fluxes in the E. urophylla × E. grandis forest burned plots and the control plots was 2.47 and 3.32 μmol/(m²·s), respectively, and that in C. equisetifolia forest was 2.48 and 3.28 μmol/(m²·s), respectively. After the forest fire disturbance, the soil temperature and moisture of the two shelterbelt forests were higher than those of the control plots, in the exponential function model, soil temperature at 10 cm of E. urophylla × E. grandis and C. equisetifolia forest explained 10.4%~21.4% of the total soil respiration. In the binomial function model, soil moisture at 10 cm in E. urophylla × E. grandis forest and C. equisetifolia forest explained 15.8%~29.4% of the total soil respiration. In the bivariate regression model, soil temperature and humidity and their interaction together explained 33.1%~66.8% of the total soil respiration. Mild fire disturbance had little effect on soil pH, total carbon, total nitrogen and mineral nitrogen content in E. urophylla × E. grandis and C. equisetifolia forest, the soil pH of the burned area in the two types of forest both increased, and the contents of NH₄⁺-N and NO₃^--N decreased. In summary, forest fire disturbance would significantly reduce soil carbon emission of two shelterbelt forests in the study area. The fitting effects of the bivariate model of soil temperature and humidity in different plots were all better than those of the single factor-model, indicating that soil carbon emission was affected by both, which could provide reference data and theoretical support for the research on the impact of forest fire disturbance on the soil carbon balance of coastal sandy shelter forests under the background of climate warming.

Abstract:Taking four grassland types in five forest areas in the Habahe region of the Altai Mountains as the research object, the change characteristics of species diversity of each grassland type in the five forest areas in Habahe region were analyzed. The regression analysis, correlation analysis, and VOR index were used to explore the influencing factors of species composition and diversity of different grassland types, and to evaluate the health status of their grassland ecosystems. The results showed that: (1) Among the different grassland types, the community similarity coefficient between desert steppe and mountain meadow steppe and mountain meadow steppe ranged from 0 to 0.25, and the heterogeneity was the large. The similarity coefficient between mountain steppe and mountain meadow steppe ranges from 0.50 to 0.75, with the small heterogeneity. (2) Among the four grassland types, the R² between the Margalef index, Simpson index, and Shannon-Wiener index of each grassland type was less than 0.75, and the quadratic term fitting showed a large difference, and the coverage and biomass were extremely significant correlated (p<0.01). (3) The relationship between altitude and biomass was poor, and R² was less than 0.40. Only the altitude and biomass of mountain meadow were significantly correlated (p<0.01), and the rest were not correlated. (4) Overall, the biomass of the five forest areas in September was less than that in June, but the biomass of the mountain steppe and the mountain meadow steppe in the Baihaba forest area in June was less than that in September, and the biomass of the desert steppe in the Hujierte forest area in June was less than that in September. (5) The average biomass of the five forest areas was fitted with the VOR index, and R² ranged from 0.118 to 0.712. The health level of grassland ecosystem in 5 forest areas was Naren (0.914) > Baihaba (0.863) > Tielieke (0.848) > Hujierte (0.845) > Qibaqilieke (0.827). The results provide an important basis for understanding the health status of grassland ecosystem in the Habahe region, and are of great significance for understanding the spatial distribution pattern and rational utilization of different grassland resources in the Habahe region of the Altai Mountains.

Abstract:Clarifying the impact of rainfall on soil moisture in the loess hilly area is great significance to accurately assess the impact of rainfall pattern changes on the structure and function of ecosystem. In this study, the artificial pure forest of Caragana korshinskii that had been abandoned for 23 years after being planted in the abandoned farmland in the loess hilly area of northern Shaanxi was taken as the research object. The soil moisture sensor was used to monitor the soil volume water content in different soil layers, and the responses of soil water supplement increment in different soil layers to rainfall characteristics (rainfall, rainfall duration and rainfall intensity) were discussed. The results showed that: (1) Soil water consumption and replenishment were mainly concentrated in the 0-500 cm soil depths, and the monthly variation in the vertical profile were "double peak" (April-May), "single peak" (June) and "double peak", and the change rate decreased with the increasing of soil depth. (2) When the rainfall was more than 4 mm, surface soil moisture could be effectively replenished. When it exceeded 142.8 mm, the replenishment depth could reach 200 cm soil layer. The soil moisture replenishment increment of the long-duration heavy rainfall was less than that of short duration heavy rainfall, however, the replenishment depth of long-duration heavy rainfall was deep and the peak time was long. (3) The influence of rainfall characteristics on soil moisture decreased with the increasing of soil depth. The influence of rainfall and rainfall duration was mainly in 0-50 cm soil layer, and the influence of rainfall intensity was in 0-30 cm soil layer. The logarithmic fitting of rainfall (rainfall duration) and soil water replenishment increment was the best. While the logarithmic fitting of rainfall intensity and soil water replenishment increment was the best, which could explain 39%~76% of soil water replenishment increment (rainfall), 0~97% (rain duration) and 1%~91% (rain intensity), respectively. To sum up, the greater the rainfall and the longer the rainfall duration, the greater the soil moisture replenishment increment. And the soil water consumption and rainfall replenishment was in 0-500 cm soil layer and 0-200 cm soil layer, respectively.

Abstract:To explore the differences in water sources and dynamic changes of major plants in shrub communities under climate change, the response characteristics of water use sources and growth of typical natural recovery plants (Artemisia ordosica, Medicago Sativa and Chenopodium album) to drought stress in the Loess Plateau were studied. And the droughts were controlled by reducing natural precipitation by 15% (moderate drought) and 30% (extreme drought). The potential water sources of vegetation communities were divided into shallow (0—20 cm), middle (20—60 cm) and deep (60—120 cm) soil water. The stable water isotope technique and MixSIAR model were used to quantitatively analyze the water absorption characteristics of vegetation roots under different drought stress levels (30%, 15% and the control). The results showed that: (1) The stable hydrogen and oxygen isotope values (δD and δ¹⁸O) of soil water and plant water were both located at the lower right of the local atmospheric precipitation line, which indicated that the isotope of soil water was enriched by evaporation. (2) Water sources of three typical plants could be flexibly converted to different soil layers under drought stress, specifically, the proportion of shallow soil moisture utilization decreased, while the proportion of middle and deep soil moisture utilization increased, which became more obvious with the increase of drought stress levels. (3) Different vegetation responsed to drought stress through different water use strategy, Artemisia ordosica mainly used shallow soil water (contribution rates were 48.2%, 52.7% and 57.6%, respectively) under flat land, rainfall reduction of 30%, 15% and CK treatments, while Chenopodium album mainly used middle (43.5%), shallow (49.6%) and shallow soil water (53.6%), respectively. In slope land, rainfall reduction of 30%, 15% and CK treatment, Artemisia ordosica mainly used shallow soil water (contribution rates were 42.5%, 44.5% and 58.1%, respectively), while Medicago Sativa mainly used the middle (40.9%), middle (46.7%) and shallow (53.9%) soil water. This indicated that the main species of vegetation community in semi-arid loess hilly region could respond to drought stress by converting water sources through plasticity. And the community water sources were divided in space to effectively reduce the competitive pressure on water resources, which would promote the coexistence of species through niche differentiation in water resources utilization.

Abstract:Pinus tabulaeformis is a typical species in the forest of northern China. The researches on the distribution, budget and transmission of radiant energy of P. tabulaeformis canopy are the theoretical basis for the building radiation transmission model and the ecological process model of the forest canopy, which are crucial for exploring the mechanism of energy flow and material circulation in forest communities. Based on the upwelling and downwelling of longwave and shortwave radiation, photosynthetically active radiation (PAR) and meteorological data obtained from the flux tower over the P. tabulaeformis communities in Helan Mountain forest ecosystem research station, the radiative energy interception and transmission characteristics of the P. tabulaeformis forest canopy under various weather and season conditions over the period of April to September 2021 were analyzed. The results showed that: (1) Under sunny condition, the diurnal variation of total solar radiation showed a smooth curve with a single peak, but an irregular curve with multiple peaks under cloudy condition, and the total solar radiation energy decreased by 48.3% to reach the top of the canopy. (2) The total solar radiation reaching the top of the canopy was dominated by the downwelling shortwave radiation. Although the diurnal variation of upwelling shortwave radiation showed a single peak curve under sunny condition, it only accounted for 8.1% of downwelling shortwave radiation. The longwave radiation of upwelling and downwelling fluctuated slightly with the alternation of day and night. (3) The seasonal dynamic characteristics of solar shortwave radiation revealed that both upwelling and downwelling shortwave radiation were the highest in June, while the highest upwelling and downwelling longwave radiation appeared in July. (4) The diurnal variation of PAR was a regular single peak curve above the canopy (25 m), but became irregular below the canopy (7 m) after interception and transmission by the canopy. The transmissivity of PAR ranged from 32.2% to 53.9%, and the highest value appeared in June. (5) The shortwave reflectance was over 7.8%~8.8% during the growing season from April to September, while the ratio of incoming and outgoing longwave radiation of surface ranged from 0.73 to 0.80. The above results showed that the P. tabulaeformis canopy in Helan Mountain had a large radiation interception effect, and the transmission of radiation through the canopy changed significantly in different weather conditions and seasons.

Abstract:In order to study the effect of amendments on infiltration characteristics and water and salt distribution of saline-alkali soil in Hetao Irrigation District, soil column experiment was carried out under five experimental conditions: control group and two contents (1% and 2%) of two modifiers (biochar and desulfurized gypsum). The results showed that: (1) Compared to the control group, 1% biochar made the infiltration time delay 8.9%, inhibited water infiltration, and reduced the amount of cumulative infiltration on the same time, while 2% biochar firstly inhibited and then promoted the process of infiltration, and it made the infiltration time shortened by 35.6%. Both desulfurized gypsum made the infiltration time shortened by 91.1%. They effectively promoted water infiltration and increased the amount of cumulative infiltration on the same time; Only 2% biochar significantly increased the final cumulative infiltration by 62.7%. (2) There was a power function relationship between the migration distance of wet front and time. Kostiakov model described the relationship between cumulative infiltration and time better than Philip model. (3) Compared to the control group, only 1% biochar reduced the soil moisture content by 2.7% after infiltration, while the other treatments had varying degrees of increase. The two application rates of biochar significantly reduced the soil salt content by 28.5% and 52.0%, respectively. However, the two contents of desulfurized gypsum significantly increased the soil surface salt content by 184.3% and 403.7%, respectively. The 2% application rate significantly increased the overall average soil salt content by 73.0%. By comprehensive consideration of the infiltration characteristics, soil moisture content and desalting effect of each treatment, biochar under the content of 2% is more suitable to improve saline-alkali soil in Hetao Irrigation District.

Abstract:In order to explore the differences in soil greenhouse gas emissions between Shihezi Irrigation Area, Xinhuzongchang Irrigation Area and Mosowan Irrigation Area, through long-term field observation and sample collection, adopts the static closed chamber-GC technique, daily observation was conducted to observe the soil greenhouse gases in Shihezi Irrigation District, Xinhuzongchang Irrigation Area and Mosowan Irrigation Area of Manas River Basin in 2019 at the seedling stage, flowering boll stage and spitting stage, and statistical methods were applied, and combined with soil temperature, water content, pH, organic carbon, ammonium nitrogen, nitrate nitrogen and other factors in the Manas River Basin. The results showed that: (1) Soil CO₂ and N₂O had obvious seasonal and daily changes, and the peak of soil CO₂ and N₂O emission fluxes appeared at the flowering boll stage, which were 527.160 and 1.713 mg/(m²·h). At the same time, the peak of the daily change of CO₂ emission flux appeared at 13:00, and the daily change peak of N₂O emission flux appeared at 17:00, which was manifested as a unipolar curve. The emission fluxes of the two soil greenhouse gases during the growth period were different between different irrigation areas, showing the irrigation area of Xinhuzongchang > Mosuowan> Shihezi. (2) Soil CO₂ and N₂O emission fluxes were more significantly affected by temperature, and soil CO₂ and N₂O were significantly positively correlated with temperature. The Q₁₀ of Shihezi Irrigation District, Xinhuzongchang Irrigation District and Mosowan Irrigation District were 1.31~1.82, 1.40~2.68 and 1.32~1.92, respectively. (3) The carbon reservoir reserves of cotton in Shihezi Irrigation District, Xinhuzongchang Irrigation Area and Mosowan Irrigation District were 3.34, 2.93 and 2.8 Tg, respectively.

Abstract:To determine the influence of biochar addition on maize yield and water-fertilizer use efficiency under limits of soil suction to trigger irrigation for mulched drip irrigation in saline-alkali areas, proposing the optimal irrigation schedule and biochar application rate, a field experiment from 2015 to 2016 was carried out in the maize growth stage of the salinized farmland in the Hetao Irrigation District. Three limits of soil suction to trigger irrigation [-15 (W15), -25 (W25), -35 (W35) kPa, and the irrigation quota was 22.5 mm] and three application rates of biochar were designed. Biochar was just only applied in the first year. Soil physochemical properties in top 15 cm layer, crop growth characteristics, water and nitrogen use efficiency and economic benefits of maize in the whole growth period were measured and analyzed. The results showed that the application of biochar at different irrigation water limits increased the soil water content, organic matter, and available nitrogen content in the whole growth period of maize. For same irrigation level, the higher the amount of biochar, the greater the improvements of these measurements. Application of biochar significantly increased the dry matter accumulation and grain yield of maize plants; the irrigation water use efficiency and the partial fertilizer productivity of nitrogen were also significantly improved. Compared with the control without biochar, under the conditions of W15, W25 and W35, B15 increased corn yield by 12.8%, 10.3% and 14.2%, irrigation water use efficiency increased by 14.2%, 10.4% and 12.9%, and nitrogen fertilizer partial productivity increased of 12.8%, 10.4% and 14.0%. For same irrigation treatment, the effect of B15 in saving water, enhancing yield was generally better than that of B30. It is suggested that the limit of soil suction to trigger irrigation is -35 kPa (22.5 mm for each irrigation) under mulched drip irrigation during the growth period of maize in salinized farmland, and the application rate of biochar is 15 t/hm².

Abstract:This study aimed to explore the effects of bio-organic fertilizer application on soil moisture, salinity, and soil nutrient properties in jujube fields under different irrigation levels, providing suitable water and fertilizer solutions for jujube cultivation. Two irrigation levels (W1 6 000 m³/hm², W2 6 600 m³/hm²), three basal application levels (S1-S2-S3: 1 200—1 650—2 100 kg/hm²) were set up with no bio-organic fertilizer as the control (W1CK, W2CK), totally eight treatments. A field experiment was conducted. Applying bio-organic fertilizer could increase soil water content, soil organic matter, and total carbon content at the same irrigation level. The increase in fertilizer application all showed that S3 > S2 > S1 > CK. At the W1 irrigation level, the water content, soil organic matter, and total carbon content of 0—150 cm soil increased by 3.20%~17.97%, 9.96%~20.31% and 2.03%~5.42% after the application of bio-organic fertilizer compared with the CK. At the W2 irrigation level, the above indices increased by 5.37%~20.19%, 6.55%~21.18% and 2.09%~6.34%, respectively. Application of bio-organic fertilizer could reduce the salinity content and soil pH of 0—150 cm soil at the same irrigation level. The increase in fertilizer application all showed that S3 < S2 < S1 < CK. At the W1 irrigation level, the salinity content and soil pH of the 0—150 cm soil decreased by 7.70%~15.74% and 0.86%~2.87% after the application of bio-organic fertilizer compared with the CK, while both indices were reduced by 8.90%~23.66% and 0.96%~2.52% respectively at the W2 irrigation level. In the comparison of different irrigation and fertlization (bio-organic fertilizer) treatments, the W1S3 treatment increased soil water content, soil organic matter, and total carbon content by 4.45%, 21.85% and 7.31%, respectively, compared with the local conventional irrigation treatment (W2CK) at 0—150 cm, soil salinity content and soil pH decreased by 2.59% and 2.08%, respectively. Considering the local water scarcity and easy loss of water fertilizer, and also the risk of groundwater pollution reduction, it is suggested that W1S3 treatment instead of the local conventional irrigation treatment (W2CK) should be a more appropriate irrigation and fertilization management.

Abstract:To clarify the characteristics of main grain yield, import and export, fertilizer consumption, this study analyzed the spatial and temporal variations of total yield, yield per unit area, sowing area, chemical fertilizer consumption and import and export of the five food crops (paddy, wheat, maize soybean and potato) in China during 2000-2020. The data of which were all from the China Statistical Yearbook (2000-2021). The results showed a progressive increase in the main grain yield of China for 17 years during the 2003-2020, the increase mainly presented in higher maize yield in northeast, north and northwest agricultural areas. In the past 20 years, grain crops yield of five crops showed an increasing trend, the highest yield per unit areas was paddy, but the highest increased was wheat (89.9%), while the lowest increased was paddy (12.3%). The sowing acreage of five grain sowing in China increased 10.4% in the past 20 years. Overall, the contribution rates of grain planting area and yield per unit area to grain yield increase in China were 19.9% and 80.1% respectively. In 2000-2020, the four kinds of crops paddy, wheat, corn and soybean imports increased, the highest was soyabean, which accounted for 82.6% of the four crops imports in 2020. The consumption of the fertilizer in China increased first and then decreased, which reached the peak in 2015 for 6 022.6 million tons. The amount of fertilizer application primarily centered in north China and the middle and lower reaches of the Yangtze River accounting for 55.1% of national total fertilizer consumption (51.465 million tons), while the largest fertilizer application intensity were the southeast and north China areas, which was 66.4 % and 25.7% higher than the national average (322.6 kg/hm²) respectively. Above all, in the past 20 years, the total output of major grain crops in China has shown an increasing trend, and the increase of grain yield per unit area was the main contribution factor, and China’s grain products trade changed from original regulator shortage to large-scale soybean import, while the amount of fertilizer consumption in China increased first until the peak in 2015 and then decreased gradually.

Abstract:Improving soil water use is an important goal to the sustainable development of agriculture in the dry loess plateau area. Through a four-year spring corn field experiment, the effects of deep burial of straw combined with nitrogen reduction on soil profile water consumption and water use distribution were studied, in order to provide a scientific basis for scientific management of water and fertilizer in dry farming areas on the Loess Plateau. The experiment was conducted at the Loess Plateau Agro-ecological Experiment Station of the Chinese Academy of Sciences in Changwu, Shaanxi from April 2017 to September 2020. Four treatments were set up: Constant nitrogen application (CON1, N250 kg/hm²), deep straw burial combined with constant nitrogen application (CON2, N250 kg/hm²+straw), reduced nitrogen application (CR1, N200 kg/hm²) and deep straw burial combined with reduced amount of nitrogen (CR2, N200 kg/hm²+straw). The results showed that: (1) The treatment of deep burial of straw increased the yield of spring maize by 9.8%~10.43%. Reducing nitrogen application to 200 kg/hm² did not reduce the crop yield, in the contrary, combined with the deep burial of straw, it would increase the yield of spring maize. (2) The fluctuation of soil water consumption mainly occurred in the 100—200 cm soil layer, and the soil water consumption in the 0—100 cm soil layer reached a dynamic balance. The deep burial of straw significantly reduced the total soil water consumption (p < 0.05). The total water consumption of the treated soil decreased by 10.86 and 20.31 mm under the deep burial of straw in 2017 and 2019 respectively. (3) The 4-year experimental data showed that the water use efficiency of the four treatments was CR2 > CON2 > CR1 > CON1, and the water use efficiency of deep burial of straw combined with reduced nitrogen application (N200 kg/hm²+straw) was the highest, which was 33.16 kg/(mm·hm²). In the loess dryland area, deep burial of straw combined with reduced nitrogen application to 200 kg/hm² is an effective measure to improve water use efficiency.

Abstract:Investigating the biochar and functional fungal agents to coordinate the regulation of desertified soil nutrients and microbial diversity and function can provide a theoretical basis for the fertility cultivation of desertified soil. The soil of the typical ecological and economic forest of the Mu Wusu Sandy Land was selected as the research object, and the effects of different amounts (2%, 4%, 8%) of biochar treatment and its combined application of quantitative functional agent treatment (Bacillus subtilis + Bacillus megaterium + Bacillus colloid) on soil chemical properties, bacterial diversity and function were analyzed by field positioning experiment and high-throughput amplification and sequencing technology. The results showed that: (1) Compared with the single biochar treatment, the soil available nitrogen and phosphorus nutrient contents of the biochar + functional agent treatment group increased by 44.71% and 187.36%, respectively. (2) The relative abundance of the Acidobacteria was significantly reduced by the single application or combination of functional agents of biochar, while the relative abundance of the phylum Firmcutes in the treatment of biochar + functional bacteria increased by 163.80%, 155.15%, and 100.21%, respectively, and the richness and diversity of soil bacterial species were increased to varying degrees. (3) The combined application of functional agents and biochar changed the carbon and nitrogen cycle function mediated by soil bacteria, such as significantly improving the decomposition function of organic matter of soil bacteria, and the decomposition process of chitosan and xylan increased by 186.54% and 242.46% respectively compared with the control group; enhanced the ammonization and respiratory function of bacteria; while single biochar treatment improved the denitrification and nitrogen fixation function of the bacteria. In summary, biochar with functional bacterial agents is better than single application of biochar treatment. Biochar and functional bacteria agents added to improve the soil available nitrogen and phosphorus nutrient content, significantly changed the soil bacterial community diversity and community function. These results can provide a scientific basis and theoretical reference for the selection of desertification soil improvement methods.

Abstract:In order to explore the improvement effects of the combined application of biological and chemical methods on saline-alkali soil in the Yellow River Delta, we first modified fly ash and isolated indigenous salt-tolerant bacteria, and then selected two strains of salt tolerant bacteria (BY-4 and BY-8) to carry out an indoor soil column leaching experiment in combination with a chemical compound amendment (i.e., modified fly ash+desulfurization gypsum+humic acid (FSZ)). The changes of base cations, dissolved organic carbon (DOC), sodium adsorption ratio (SAR) and soil organic matter in leachate and/or soil were studied. The results showed that the two strains BY-4 and BY-8 were salt tolerant and had the abilities to produce indole acetic acid and to solubilize phosphate or potassium. In compared with the treatment (CK), treatments with chemical compound amendments (FSZ) significantly promote the leaching of water-soluble Na⁺, reduced the total amount of water-soluble Na⁺ and SAR in soil, and increased the contents of DOC and organic matter in soil. The treatment of BY-8 combined with chemical compound amendment (FSZ8) performed the best. Compared with CK, soil total water-soluble Na⁺ under FSZ8 treatment decreased by 33.30%, SAR of arable soil decreased by 79.76%, DOC leaching loss decreased by 34.60% and organic matter content of arable soil increased by 79.47%. These findings were helpful to understand the role of salt-tolerant bacteria in soil improvement, and would provide theoretical and data reference for the development and utilization of biological and chemical composite amendments in the future.