In order to explore the effect of check dams on runoff process and elucidate the mechanismunderlying erosion reduction, we chose a representative basin in the first sub-region of the hilly and gully loess region with well-established check dam system as the research subject. Firstly, we analyzed the influence of check dams on runoff coefficient, sediment transport modulus and basin lag time. The result shows that the runoff coefficient of Jiuyuangou,Wangmaogou and Xiangtagou was reduced by 29.43%, 34.63% and 16.78% and the sediment runoff modulus was decreased by 28.09%, 67.75% and 27.75%, respectively, compared with Peijiamao, Lijiazhai and Tuanyuangou which were not governed. The basin lag time of Wangmaogou was 117 min, almost three times longer than that of Lijiazhai. Secondly, we analyzed the effects of the check dam siltation on flow discharging capacity through establishing the unit discharge concept. We defined the flow of cross section of any channel under 1 m water level as the specific rate of flow. A Chezy formula was used to calculate the flow through the channel unit. The results illustrated that the flow rate of natural channel unit was 41.82 m3 / s, while the flow rate of check dam was 17.13 m3 / s. With the dam siltation, deposition reduced the flow capacity of the channel, and the unit flow rate of channel was reduced to 40% of the original. Finally, we defined three kinds of the river nodes which are reach junction (river junction), reach barriers node (check dam) and reach feature transform node (the transition point of natural channel to siltation channel), and divided the reach barriers node into three sub.categories which are strong connectivity node (spillway), weak connectivity node (shaft and horizontal pipes) and disconnected node (check dam without water facilities) based on the category of water release works. According to the unit flow, we assigned weight to each kind of node, constructed the river tree graph of Wangmaogou watershed by graph theory, and calculated the weight value of the whole basin (0.21). By fitting the measured peak flow, we found that there is a good correlation between the weight value and peak flow. The results are of significance to analyzing the influence of check dams and other measures of soil and water conservation on hydrological process of watershed.

Studies of relief amplitude are of significance and practical application values not only to the sensitivity analysis of geological hazards like landslide and debris, but also to evaluation of the risk of geological hazards. However, little is known about relief amplitude in medium and small scale watersheds. Our objectives were to characterize the best relief amplitude of optimum statistical unit area of medium and small scale watersheds, learn geomorphic features of watersheds of such scales and figure out the reason of geological hazards. We chose the Wangmo River Watershed located in southwestern area of Guizhou Province and famous for its frequent landslides as our study area. We used a geographic information system (ArcGIS) and the DEM of 1:10000 scale to compute the optimum statistical relief amplitude unit of the watershed. Firstly, we adopted window analysis method and python module programming based on ArcGIS to automatically extract the different areas corresponding to the relief; condly, we employed mean change point analysis method and python module programming to automatically calculate the optimum statistical relief amplitude unit of the watershed.Finally, we analyzed the relief amplitude characteristics of the watershed and the relationships between relief amplitude, average slope and stream gradient factors. The results revealed that: 1) There was a significant logarithmic relationship between relief amplitude and average cell area of the watershed. 2)Based on python module programming we can automatically calculate the statistically optimum relief amplitude unit, that is 1.49 km², and the relief amplitude ranged between  0~648.23 m. 3) The reliefamplitude is higher in the middle of the areas where river networks are concentrated, while it is lower at the edge of the plateau, and the rivers are mainly distributed in the range of 200~500 m of the terrain. The landscape belongs to small relief mountain. 4) There is a significantly positive correlation between stream gradient and relief amplitude, that is, the stream gradient increased with the increase of the relief amplitude. These results show that the Wangmo River Watershed belongs to small mountain geomorphology, with cutting highlands and cutting mountains as well as serious soil erosion.

Soil erosion in sloping farmland is a key ecological and environmental issue that threats thesustainable agricultural development on the Loess Plateau of China. Knowledge of infiltration process is crucial for understanding and managing hydrological processes and soil erosion in sloping farmland. The objective of this study was to clarify the infiltration characteristics in sloping farmland at different stages of crop growth. The soybean (Glycine max L. ) was selected as our research object and its growth was divided into four stages: initial flowering stage (R₁ ), late flowering stage (R₂ ), pod bearing stage (R₄), and maturity starting stage (R₅ ). The bare sloping farmland was set as control (CK). Runoff from experimental plots was collected under the simulated rainfall condition, the infiltration processes and characteristics were analyzed, and the infiltration processes were simulated with the Horton and Kostiakov infiltration models. The following results were obtained. For the four growth stages of soybean, parameters such as initial infiltration rate, stable infiltration rate, cumulative infiltration amount and infiltration recharge coefficient presented generally the order as R₅ > R₄ > R₂ > R₁ > CK at different rainfall intensities and slope gradients. The recharge coefficient increased with growth stages but decreased with slope gradient. The crop coverage was the important factor for determining the recharge coefficient. Simulated infiltration processes with Horton and Kostiakov models showed that two models fit well with the infiltration and could reflect the infiltration characteristics while the fitting effect of Horton was better than Kostiakov. The results of our study are helpful for better understanding of the infiltration processes and characteristics in sloping farmland during the crop growth stages.

We studied soil profile characteristics, physico-chemical properties and nutrient distribution in wetland at different submerging depths in water of East Dongting Lake, central China. Results showed:1) The thickness of subsurface horizon and the depth of gley horizon increased as the wetland elevation increased,with soil types distributed as meadow soil and tidal soil. 2) The average soil particle density was 2.78 g/ cm³ and the soil bulk density varied between 0.71 1.41 g/ cm³. 3) The content of organic matters ranged from 1.78% to 5.07%. It decreased with the increase of soil depth. No change of organic matter content was found in subsurface horizon. 4) With the increase of wetland elevation, soil total P increased, but total K decreased. Total P in surface horizon were higher than that in subsurface horizon, but there were no significaut differences of total K between surface horizon and subsurface horizon. 5) The contents of Ca and Mg in gleyed meadow soil were higher than that in the other soil types, but there were no relationships between the depth of ground water and the conteuts of Ca and Mg.

By employing the method of using space as a substitute for time, we studied the characteristics of canopy structure and dynamic changes of forest communities at different restoration/ succession stages of degraded Karst forest, namely, shrub stage, shrub-tree stage, tree stage and climax stage, using a CI -110 Plant Canopy Imager. The results show that: 1) Among the changes of forest canopy structure in different succession stages, leaf area index ranged between 1.56 and 2.92, and its value initially decreased and then increased from shrub stage to top climax stage, and only at tree stage did it achieve extremely significant differences with that of other stages. 2) There were no significant differences in the variations of mean leaf angle at different succession stages. 3) The variations of canopy gaps were not significant among the shrub stage, the shrub-tree stage, and the climax stage. It reached the maximum value at the tree stage, and there existed extremely significant differences between the tree stage and other succession stages. 4) The correlation analysis of several indexes of canopy structure showed that there was a highly significant, negative correlation between leaf area index and canopy gap.

Partitioning soil respiration into root respiration, rhizomicrobial respiration and basal microorganism respiration is of important significance in ecological and pedological studies. The method of δ¹³C natural abundance is an ideal way in microbial biomass research to partition rhizosphere respiration into root respiration and rhizomicrobial respiration; however, it is difficult to be applied under field conditions. In this study, the method of nature ¹³C abundance was used to partition soil respiration into root respiration, rhizomicrobial respiration and basal micro-organism respiration in a Robinia pseudoacacia plantation in the Yellow River Xiaolangdi Ecology Research Station. The difficulties of separating root respiration and rhizomicrobial respiration by ¹³C natural abundance in the plantation have been solved in this study, which include: 1) the error caused by damage and disturbance, 2)ruling out δ¹³C difference caused by C3 and C4 photosynthetic pathways between soil and plant, and 3) the problem of soil CO² diffusion fractionation. The δ¹³C value of the soil ranged from - 19‰to - 23‰. It is suggested that carbon isotopic composition of soil organic matters in the deeper soil requires a long time to cycle so that the influence of returning maize cropland to plantation on soil carbon isotope would not vanish completely.The δ¹³C values of soil organic matters did not change significantly with soil depth, while the δ¹³C values of rootless soil organic matters had a significantly positive correlation with soil depth. Theδ¹³C fractionation of CO2 diffusion in the soil was about 2.0‰, suggesting that the root respiration and rhizomicrobial respiration of the R. pseudoacacia plantation has been successfully separated by ¹³C natural abundance in this study. The results showed that the proportions of root respiration ( f_R ) and rhizomicrobial respiration (f_M ) were about 43% and 57% in July, 52% and 48% in August,and 27% and 73% in September, respectively. f_R and f_M were influenced by soil temperature and their standard deviation (SD) was higher under a lower soil conductivity. The method of ¹³C natural abundance is proved to be a suitable approach for partitioning plantation soil respiration into root respiration, rhizomicrobial respiration and basal microorganism respiration.

In soil erosion area, land productivity and farmer爷s income can be raised obviously by carrying out the measures of soil erosion control and in the meantime increasing the amount of environmental human carrying capacity. As the most important and the largest soil erosion control project in the Yangtze River, also called “Yangtze River Harness冶project, it plays an important role for improving the environment and increasing human carrying capacity. Taking the fourth stage of the project in Sichuan Province as an example, we used cluster analysis method and divided the 72 controlled watersheds into 6 groups. The environmental human carrying capacity was calculated in terms of different consumption standards (food consumption and cash consumption). The results showed that the amount of the carrying capacity had been greatly increased after control. At the same level of harness investment, the small watersheds with higher population density and grain yield per hectare have more increment of carrying capacity. Based on analyzing the typical small watersheds, the proper value of investment for the fourth stage of the project is about RMB 110 000 to 120 000 yuan per square kilometer, at the investment level of the year 1997, for the purpose of increasing environmental human carrying capacity. In comparison, the amount of rational harness investment of the first stage of the project, which is similar to that of the fourth stage, is about RMB 315 000 yuan per square kilometer at present value of 2013.