[ Background ] Soil erosion is an important cause of soil nutrient loss, river channel sedimentation and many other ecological environment problems in the Three Gorges Reservoir Region. And severe soil loss in the Three Gorges Reservoir Region is in a widespread. [Methods] Taking the Reservoir Region as the study area, based on Geographical Information System, the Revised Universal Soil Loss Equation(RUSLE) was used to calculate the soil erosion of the five years, 1990, 1995, 2000, 2005 and 2010, in the Three Gorges Reservoir Region. ANOVA was used to analyze the significant impact on soil erosion in different land use. In addition, quantitative analysis was used to investigate the temporal and spatial variation of soil erosion intensity from 1990 to 2010; then the spatial distribution rules and spatial temporal characteristic of soil erosion under the different types of land use were studied.And all of above aimed to provide the supports for the sustainable development of the Three Gorges Reservoir Region. [ Results] During the period of 1990—2010, the value of average soil erosion modulus and the amount of soil erosion in the Three Gorges Reservoir Region were generally in a decreasing trend with the amount of 183.564 507 million tons, and it was graded as medium eroded area, in 2005 there was a certain degree of rebound with 19 282.74 million tons. From space, the slight and light erosion were the most widely distributed grades of soil erosion in this study area. The annual modulus of soil erosion of six different land use types in the same year was as: dry farmland > grassland > forestland > unused land > paddy field > construction land; one-way ANOVA revealed the soil erosion under different land use patterns, with a very significant difference,and there was solid difference in contribution rate of soil erosion by different kinds of land uses. The area of slight erosion in all 6 land use types gradually increased. Concurrently, erosion areas in moderate-and higher-erosion level transferred to the lower level at varying degree. [Conclusions] These above findings demonstrate that with returning farmland into forest and grass as well as large transferring of rural labor, the soil erosion in the Three Gorges Reservoir Region shows an improving trend as a whole, but the governance work in some parts of the Region still needs to be strengthened. The result of this study will be helpful to establish the quantitative relationship between land use and soil erosion, and also helpful in the adjustment of land use type in the future.

[Background] Soil water is the main factor limiting the recovery of vegetation and thesustainable development of agriculture and forestry in the region of the Loess Tableland. Soil watercontent in 9-year apple orchard, 19-year apple orchard, corn field, and wheat field was investigated in the Changwu Tableland to define the soil hydrological characteristics and soil drying state of main cropland and orchard on the Loess Plateau. [Methods] The water storage capacity of soil in a profile of 600 cm was measured using a neutron probe (CNC503B) from April to October in 2014. [Results] 1)The 9-year orchard had the largest soil water storage in 0 -600 cm soil profile, followed by the corn field, wheat field and 19-year orchard in which soil water storage averaged 186.5, 183.6, 158.6 and 132.8 cm, respectively. There was no significant difference between the corn field and 9-year orchard, but significant differences existed among other fields. 2) Soil water content in shallow soil layer (0 - 200 cm) for the 4 fields showed medium variation (10% < CV < 100%), while soil water content in deep soil layer was relatively stable (CV <10%). 3) The depth of soil water depletion for the 19-year orchard was 500 cm, while the depths for the 9-year orchard, corn field and wheat field were all 300 cm. The rain replenishment depth of the 19-year orchard was 250 cm, while the depths for the 9-year orchard, corn field and wheat field were all deeper than 600 cm. 4) Compared with other fields, soil desiccation in the 19-year orchard occurred most severely. Specifically, the 0 -200 cm soil layer dried seasonally, the 200 - 250 cm and 250 - 320 cm soil layers dried severely, and the 320 - 600 cm soil layer dried extremely. Thus, a persistent soil dry layer formed. Soil desiccation in the corn field and 9-year orchard occurred easonally, and a temporary soil dry layer formed in the shallow soil layer in the case of water shortage. [Conclusions] It is scientific to transfer the agricultural structure of Changwu Tableland from field crops to apple economic forest, but the soil-moisture storage will be absent and the soil drying will be severe after the apple forest reaching the later stage of full fruit period, as a result, the economic value and ecological effect of apple forest will be restricted, thus scientific methods shall be taken such as reasonable water management measures and adjusting stand density to realize the sustainable development of economy and ecology in the region of Loess Tableland.

[Background] The Loess Plateau, which is characterized by weak ecological environments and scarce water resources, is located in the Northwest of China. Due to the development of economy and increment of population, this region has been faced with the increasing pressure of water resources shortage. In order to achieve the scientific allocation and efficient utilization of water resources in watershed, it is of great significance to conduct the investigations on characteristics of waters transformation in the area. [Methods] As typical case for study, the Jiuyuangou Watershed, which is located in Suide County, Yulin City of Shaanxi Province, was selected to investigate the characteristics of waters transformation in the loess hilly and gully regions. Precipitation samples, gully-channel water samples and well water samples were collected and tested to quantify the compositions of the hydrogen and oxygen isotopes in each water during Sept. 15 to 19, 2014. [Results] By analyzing the relationships between δD and δ¹⁸ O in the gully-channel water and well water of Jiuyuangou, it was found that the evaporation line equation of gully-channel water was EL-1: δD = 5.40 δ¹⁸ O - 20.34(n = 13, R² = 0.99), and the evaporation line equation of the gully-channel water and well water was EL-2: δD = 5.33δ¹⁸O - 20.89(n = 19, R² = 0.98). Additionally, the temporal and spatial variations of δ¹⁸ O in gully-channel water and well water were illustrated in the paper. It was visualized that the δ¹⁸O in gully- channel water on Sept. 16 was the lowest during the period of sampling, and the δ¹⁸ O in gully-channel water increased progressively from the upper to the lower reaches of Jiuyuangou Watershed. The δ18 O of well water tended to be more positive and more stable than that of gully-channel water. The impacts of rainfall, air temperature and wind speed on the variation of δ¹⁸O in gully-channel water was greater than that on the variation of δ¹⁸O in well water. It was concluded that the surface water and ground water in Jiuyuangou Watershed were both supplied by atmospheric precipitation. The weighted average value of hydrogen and oxygen stable isotopes in precipitation which could effectively recharge the ground water was δ¹⁸O = -11‰and δD = -79.80‰respectively. Besides, the gully-channel water and well water in the upper reaches presented a similar evaporation trend with similar slope and intercept, implying that there was some degree of transformation between them. Furthermore, the main transformation relationship between the gully-channel water and well water was characterized by unidirectional recharge from the gully-channel water to the well water with a slow recharge rate, indicating that the retention time of the water in Jiuyuangou Watershed was longer. [Conclusions] Finally, based on the above results, water loss caused by evaporation in the transformation process between the gully-channel water and well water is also calculated using Rayleigh distillation model and regression equation between absolute temperature T and fractionation factor 18αw - v and 2αw - v with an assumption that the water vapor exchange is equilibrated. The estimated result shows that the gully-channel water will lose 7% during the transformation process.

[Background] The Taihu Lake basin, covering the Taihu Lake watershed and the River Area of southeastern China, is the highly developed region in China, and the soil loss caused by intensive human activities have been received much attentions in recent years. [Methods] To study the soil erosion situation of the Taihu Lake basin in the last 10 years, this article analyzed the soil erosion situation and its spatial distribution based on the remote sensing survey data of two periods by the Ministry of Water Resources, acquired the change trend during 2002 to 2011, and evaluated quantitatively the soil erosion situation with erosion index (EI) in the Taihu Lake basin. [Results] The total soil erosion area of the Taihu Lake basin in 2011 was 22 872.59 km², among it Taihu Lake watershed accounted for 1 064.58 km² and the River Area of southeastern China for 21 808.01 km². The main erosion intensity was light erosion in the Taihu Lake basin. However, the Taihu Lake watershed had the more percentage of slight erosion area, while the River Area of southeastern China had more percentage of strong, ultra strong and severe erosion area. From the administrative division perspective, Fujian Province had the most soil erosion area in the Taihu Lake basin. Zhejiang Province took the second place in soil erosion area and the main erosion was light and medium erosion. Anhui Province had the most erosion area of strong, ultra strong and severe relatively, which accounted for 23.42% of the soil erosion. Jiangsu Province and Shanghai had the least soil erosion area and there were nearly only light and medium erosion. From 2002 to 2011, the soil erosion area of the Taihu Lake basin had a decreasing trend in general. The total decrement area was 10 811.14 km² and annual average decrement area was 1 201.24 km². However, the area of light, moderate and severe erosion decreased and the area of very severe and extremely severe erosion increased. EI is a comprehensive index to assess soil erosion degree. The larger index value indicates more serious erosion. The EI in Taihu Lake watershed was 0.33, while it in the River Area of southeastern China was 1.65 in 2011. The EI was much higher in the River Area of southeastern China, indicating that the soil erosion was more serious as a whole. From 2002 to 2011, EI in the Taihu Lake basin decreased, which explained the soil erosion situation improved in general. But the EI obviously increased in a few areas, such as Zhuji, Taizhou, Wenling of Zhejiang Province and Minqing, Minhou, Putian, Xiamen of Fujian Province, exceeding 1.5 units. [Conclusions] Taihu Lake watershed showed less serious erosion than the River Area of southeastern China. It was also obvious to know that in the most areas of the Taihu Lake basin, the soil erosion area decreased from 2002 to 2011. However, there still were some areas where the erosion area and degree increased. Therefore, we suggested that these areas should be key controlling regions and there should be the countermeasures to prevent further soil erosion.

[Background] Forest vegetation plays a key role in soil erosion in Danjiangkou Reservoir area, and different vegetation has different ability on soil infiltration. Soil hydraulic properties drive water distribution and availability in soil. There exists limited knowledge of how plant growth especially surface root might influence soil hydraulic properties. Roots growing near the soil surface may influence soil detachment, and modify the properties of soil in their immediate vicinity. [Methods] To investigate the effects of root on soil infiltration capacity, the soil and root (two layers of 0 -10 cm and 10 -20 cm) of 35 samples representing the main vegetation types in Danjiangkou Reservoir area were surveyed and analyzed. The root structure characteristics and its influence on soil infiltration were studied, and the methods of modeling, correlation analysis and regression were introduced. [Results] The soil infiltration capacity of 0 - 10 cm soil layer of different vegetation types were higher than that of 10 - 20 cm. Soil initial infiltration rate and soil steady infiltration rate of 0 -10 cm and 10 -20 cm soil layer showed the same trend of the broadleaf forest > coniferous and broadleaf mixed forest > shrub > coniferous forest. Soil infiltration rate and soil steady infiltration rate had significant linear correlation with root length density and root surface area density among different vegetation types. The index of soil infiltration had significant correlation with root structure parameters of different root diameter ranged from 0.5 to 5 mm (P < 0.05). Kostiakov infiltration model, Philip infiltration model and Horton infiltration model stimulated the soil infiltration processing, and in Kostiakov infiltration model, root length density and root surface area density of different root diameter ranged from 0.5 to 5 mm presented the positive correlation with b values and negative correlation with a value. Root length density, root volume density and root biomass had significant correlation relation with the indexes of soil infiltration, which could be used to study the relation of root distribution and soil infiltration. The results indicated that vegetation types significantly affected soil infiltration, and coniferous and broadleaf mixed forest as well as broadleaf forest were better in soil infiltration and root structure. Root at diameter of 0.5 -5 mm played the key role in the root system on soil infiltration capacity. [Conclusions] The study promotes better understanding of surface root in different vegetation types and its influence on the soil infiltration, and suggests that coniferous and broadleaf mixed forest, and broadleaf forest should be protected, and shrub and coniferous forest should be transformed to promote the soil and water onservation capacity in Danjiangkou Reservoir area.

[Background] In the early last century, the problem of soil erosion has been quite serious, thus it is urgent to carry out scientific and effective soil and water conservation work for preventing soil erosion. China is a country with one of the most serious soil erosion, the Loess Plateau is the most serious soil erosion area in the world, and it is also the main source of the Yellow River sediment area; the Loess Plateau region of soil erosion cause not only the deterioration of ecological environment, but also a serious threat to the lower reaches of the Yellow River ecological security. [Methods] In order to explore the hydrodynamics characteristics of rill flow, the dynamics characteristics of rill flow from the perspective of hydraulics and rivers movement mechanics were studied under the combined scouring test condition of 6 slopes (2°, 4°, 6°, 8°, 10°, and 12°) and 5 discharges (8, 16, 24, 32, and 40 L/ min). [Results] Results indicated that the average velocity of rill flow was in power function relationship with discharge.However, the there was no correlation between the velocity and slope, which was because the development of drop pits was more mature with the increase of the slope, resulting in the growth of rill flow path. The thickness of the viscous sub-layer was in negative correlation with slope and discharge, and presented an essential effect on rill flow resistance. Resistance coefficient varied from 0.16 to 1.45 and increased with the increase of the slope and showed no correlation with Reynolds number, meaning that the flow regime belonged to the turbulent rough area, this was because the morphology of bed surface developed significantly, i. e. , the dissipation capacity of the flow increased significantly, with the increase of the intensity of rill flow. [Conclusions] The experimental results showed that the bed morphology of loess slope had great influence on the velocity of rill flow. By reasonably changing the bed morphology of loess slope, the flow velocity can be decreased and onsequently the soil erosion on the Loess Plateau region can be controlled. In this experiment, the height of bed surface bump was several times higher than the viscous sub-layer because the thickness of viscous sub-layer was thin. The resistance resulted from the small vortexes formed while turbulent flow was bypassing the bump. The result of this study has certain theoretical value to the exploration of the dynamics of rill flow, and has certain guiding significance to control the soil erosion on loess slope and to restore eco-environment.

[Background] Soil erosion harms the development of national economy. Water erosion is the most important form of soil erosion in China. Overland flow is the main driving force of water erosion and main carrier of sediment transport which is a key factor of water erosion. Reynolds number, Froude number and resistance coefficient of overland flow are important parameters reflecting overland flow characteristics. [Methods] To investigate mechanical properties of overland flow, the study on the dynamic changes of Reynolds number, Froude number and resistance coefficient with 3 plant density (0, 20, and 30 plants/ m² ), 2 vegetation distributions (row arrangement and random arrangement), two slopes (5°and 10°) and 3 scouring flow (1, 2, 3 m³ / h) were studied by field scour simulation experiment. [Results] The results showed that effect on Reynolds number of inflow section by plant coverage density and slope was not significant, and only effected by flow rate. Dynamic changes on Reynolds number of inflow section remained stable over time, while that in outflow section showed an increasing trend which was affected by plant density. And the increasing rate of dynamic changes in outflow section slowed down with the increase of the plant density, however, influence by plant arrangement was not significant. Compared to the inflow section, Reynolds number of outflow section was smaller, indicating that the kinetic energy of the overland flow reduced during scouring process. Froude number was both less than 1 in two observation section, which were slow flow. Froude number of inflow section only increased with flow rate increasing, and the influences on Froude number of inflow section by lant coverage density and slope were not significant. The same as Reynolds number of inflow section, Froude number of inflow section also remained stable over time. The dynamic change of Froude number in outflow section decreased with time slowly, which was effected by plant densiy significantly, and the influence on it by plant arrangement was not significant. The dynamic changes of Froude number leveled off even plant density increased. Effect on resistance coefficient by slope was not significant, which was effected by plant density and flow rate, and the influence of plant arrangement was not significant. Stepwise regression analysis on resistance coefficient showed that f = 2.350t0.012q-3.178 c0.084, indicating that dynamic changes of resistance coefficient showed an increase trend that could be controlled by increase of slope and plant density. [Conclusions] Dynamic changes of resistance coefficient on bare slope had greater increase rate than slopes covered by vegetation, and resistance coefficient changing with time tend to be gentle with the plant density increased. Meanwhile, change range of resistance coefficient in plant random arrangement slope was smaller than slope in plant row arrangement.

[Background] The purpose of the study is to understand the situation of water conservation of forest resources in Fengning County of Hebei Province. [Methods] We studied the water conservation ability of 4 different types of forest land for water source by collecting soil and litter samples and comparing the difference of litter amount determination, the litter water-holding capacity, water determination process and soil moisture and physical properties. [Results] The forest litter water-holding capacities of 4 types of forest land for water source followed the order: Populus simonii forest land > Larix gmelinii *Armeniaca sibirica forest land > Pinus tabuliformis *A. sibirica forest land > P. tabuliformis forest land, and the maximum water-holding capacity of P. simonii forest land and the ffective water-holding one were 29.79 and 4.01 t/ hm² respectively. In terms of water-holding capacity in soil porosity, total porosity followed the order: P. simonii forest land > grassland > cultivated land > L. gmelinii *A. sibirica forest land > P. tabuliformis *A. sibirica forest land > P. tabuliformis forest land, and the value ranged in 43.49%—34.96%. Regarding soil bulk density, there was an order: grassland > P. tabuliformis forest land > cultivated land > P. simonii forest land > P. tabuliformis * A. sibirica forest land > L. gmelinii *A. sibirica forest land. Considering the soil water constant within 0 -30 cm soil layer, the maximum soil water constant of L. gmelinii *A. sibirica forest land, P. tabuliformis *A. sibirica forest land, and P. tabuliformis forest land existed within 10 -20 cm soil layer. The maximum soil water constant of P. simonii forest land existed within 20 - 30 cm soil layer. The maximum soil water constant of grassland and cultivated land existed within 0 to 10 cm soil layer. [Conclusions] According to the above analysis, the difference of water conservation capacity in different water source forest is obvious. Under the condition of the same site, broadleaf conifer mixed forest has better water conservation function; in order to fully explore the water conservation function of the water source forest in the north of Hebei Province, we should strengthen the management and protection of the existing water source forest, and construct a more reasonable water source forest.