Investigating the effects of herbaceous root systems on the soil detachment process at the species level.

Plant root growth significantly affect soil detachment process, whereas the mechanism of how roots affect the soil detachment process by overland flow at species level is not fully understood. This study was conducted to investigate the soil detachment rate responds to plant-induce soil properties and root traits at species level. Two typical herbaceous plants, Bothriochloa ischcemum (Linn.). Keng (BI; fibrous root system) and Artemisia vestita Wall. ex Bess (AG; tap root system), from the Loess Plateau were studies for one year under six planted densities of 5 plants m-2, 10 plants m-2, 15 plants m-2, 20 plants m-2, 25 plants m-2, and 30 plants m-2. In total, 24 steel tanks were planted, and two plots were used as bare soil controls. Their soil detachment rates were tested under a constant overland flow (1.5 l s-1) on a 26.2 % slope. The results showed that soil detachment rate under the six planted densities ranged from 0.034 kg m2 s-1 to 0.112 kg m2 s-1 for BI and was ranged from 0.053 kg m2 s-1 to 0.132 kg m2 s-1 for AG, which all greatly reduced soil detachment rate and were 68.17 % to 92.33 % and 69.20 % to 87.27 % less than that of the control. In general, BI was more effective in reducing soil detachment rate than AG, achieving a mean soil detachment rate that was 23.75 % lower. With increasing plant density, soil detachment rate decreased as a power function. The overland flow hydraulic characteristics, soil properties and root traits influenced by plant density were positively or negatively correlated with soil detachment rate. Specifically, soil detachment rate decreased with velocity, bulk density, root length density, and increased with shear stress and Darcy-Weisbach friction factor as power or exponential functions. On this basis, the soil detachment rate (Dr) can be satisfactorily estimated by overland flow velocity (v), soil bulk density (BD) and root length density (RLD) as a power function (Dr = 63.03v0.174 × BD-20.712 × RLD-0.233R2 = 0.65; NSE = 0.60; p < 0.01).

[Characteristics and factors influencing organic carbon decomposition in sediment in check dams]. / ååœ°å‰–é¢æ³¥æ²™æœ‰æœºç¢³åˆ†è§£ç‰¹å¾åŠå ¶å½±å“å› ç´ .

More than 56000 check dams have been built in the Loess Plateau, which capture around 0.95 Pg of organic carbon and act as an important carbon sink. However, the decomposition mechanism of organic carbon in the sediment in these dams is still poorly understood, and thus it is difficult to quantify their role in terrestrial carbon cycling. In this study, the mineralization culture was used as a simulated environment for the natural sediment environment. With the observations in the simulated environment, the decomposition rates of sediment organic carbon (SOC) were compared under different conditions to investigate the factors influencing the decomposition rate of SOC. The results showed that the average SOC decomposition rate of sediment under anoxic and aerobic conditions was (6.47±4.06) and (56.66±17.78) mg C·kg-1·d-1, respectively. The decomposition rate of SOC in dam sedi-ment under burial conditions was only 11.4% of that under the assumed aerobic condition, indicating that burial condition significantly reduced SOC decomposition. Under anoxic conditions, chemical compositions in the sediment had a greater effect on the decomposition rate of SOC than the microorga-nisms. In contrast, the effect of microorganisms on the decomposition rate of SOC was more significant under aerobic conditions. The physical properties of sediment had little effect on the decomposition rate of SOC under both anoxic and aerobic conditions. Under natural conditions, the siltation dam acted as a carbon sink. When the dam breaks, SOC stored in the sedimentary anoxic condition would be quickly exposed to the air, followed by a significant increase in the decomposition rate, and thus acting as a carbon source.

[Responses of soil erosion to changes in landscape pattern and its evolution in watershed in the loess hilly region under characteristic management and development]. / é»„ä¸˜åŒºç‰¹è‰²æ²»ç†å¼€å‘å°æµåŸŸåœŸå£¤ä¾µèš€å˜åŒ–å¯¹æ™¯è§‚æ ¼å±€æ¼”å˜çš„å“åº”.

Understanding the relationship between soil erosion and the changes in landscape patterns is important for guiding the management and development of watersheds. The Nangou watershed in Ansai County, Shaanxi on the Loess Plateau, is an area with the implement of "Grain for Green", ecological agriculture, ecological tourism and the demonstration of science and technology for landscape management. We quantified the spatial and temporal variations of landscape pattern and soil erosion from 1981 to 2018 using the GIS and the universal soil loss equation (USLE). The relationship between the soil erosion modulus and nine landscape pattern indices in three categories was analyzed using the principal component analysis at both plot and landscape levels. The results showed that, among the five landscape types, the spatial and temporal changes of cultivated land and woodland dominated the evolution of landscape patterns, which affected the concentration and distribution degree of the whole watershed. Soil erosion in the Nangou watershed decreased annually, with erosion area, erosion modulus and soil erosion intensity decreasing by 29.7%, 61.2%, and 73.4% from 1981 to 2018, respectively. The variation of cultivated land and forest land areas determined the changes of soil erosion modulus of the whole watershed. The change trend of landscape pattern index was consistent with that of soil erosion. "Grain for Green" Project was the major dri-ving force for the changes in the landscape pattern and for the reduction of soil erosion. The characteristic development and management could weaken soil erosion intensity in parts of the study area. The rational configuration of landscape types could effectively control soil erosion in a watershed. The combination of rational configuration and characteristic management could help achieve the goals for sustainable and high quality development of the watershed.

[Spatial variation and source identification of heavy metals in sediments in Shaanxi section of Weihe River, Northwest China.] / 渭河陕西段沉积物重金属空间分布及来源解析.

In order to understand the spatial variation of heavy metals in Shaanxi section of Weihe River, the contents and sources of Cd, Co, Cu, Pb, Sb, As, Ni, Cr, Zn, Mn in sediments at 17 sampling sites in Shaanxi section of Weihe River and its tributaries were analyzed. The results showed that the average contents of Cd, Co, Cu, Pb, Sb, As, Ni, Cr, Zn, Mn were 0.10, 1.24, 11.73, 11.95, 24.90, 24.91, 29.31, 54.18, 72.74, 626.85 mg·kg-1, respectively. Except for that of Cd being greater than 1, the coefficient of variation for each of other heavy metals was less than 0.5. The peak contents of Cd, Pb and Cr were found at the sampling site of Bahe River, of Co and Mn at Heihe River, of Cu and Zn at Qingjiang River, and of Sb, As and Ni at Shawang Ferry, Xianyang Railway Bridge and Linjia Village, respectively. According to the results of correlation analysis, principal component analysis and cluster analysis, the elements of Cd, Co, Cu, Pb, Ni, Cr, Zn and Mn mainly originated from industrial and domestic sources, but Sb and As mainly originated from agricultural and geochemical sources.

Effect of vegetation utilization on runoff and sediment production on grain-for-green slopes in the wind-water erosion crisscross region.

To effectively utilize the vegetation on grain-for-green slopes in the wind-water erosion crisscross region, it is necessary to determine the reasonable vegetation utilization intensity. We set up runoff plots on slopes which were not cultivated and were closed for many years in the Liudaogou catchment, a typical catchment in wind-water erosion crisscross region of the Loess Plateau. With artificial simulated rainfall experiments, the characteristics of runoff and sediment yield on slopes (10°, 20° and 30°) under different utilization intensity of vegetation were studied to select the reasonable utilization intensity. The results showed that the runoff rate in the process of rainfall simulation could be divided into two periods: rapidly increasing in the initial period and slow increasing or quasi-steady state in the middle and late periods. The variation of erosion rate during the rainfall was dependent on the slope. The utilization intensity had a significant effect on the runoff yield, which increased with the increasing utilization intensities. The slope gradient had a significant effect on the sediment yield, with the variation of sediment yield with slope gradient being: 20°>30°>10°. Compared with the unused (natural) plots, the relative runoff and sediment increased with increasing utilization intensities. Predicted based on the rainfall data, annual soil erosion amount on the slope would be basically lower than the tolerance level of soil loss when the vegetation cover on the slope surface reached 25% in 15 years after abandoning reclamation. More attention should be paid to the restoration and management of vegetation on the slope of 20° in this area.

Validating and improving interrill erosion equations.

Existing interrill erosion equations based on mini-plot experiments have largely ignored the effects of slope length and plot size on interrill erosion rate. This paper describes a series of simulated rainfall experiments which were conducted according to a randomized factorial design for five slope lengths (0.4, 0.8, 1.2, 1.6, and 2 m) at a width of 0.4 m, five slope gradients (17%, 27%, 36%, 47%, and 58%), and five rainfall intensities (48, 62.4, 102, 149, and 170 mm h(-1)) to perform a systematic validation of existing interrill erosion equations based on mini-plots. The results indicated that the existing interrill erosion equations do not adequately describe the relationships between interrill erosion rate and its influencing factors with increasing slope length and rainfall intensity. Univariate analysis of variance showed that runoff rate, rainfall intensity, slope gradient, and slope length had significant effects on interrill erosion rate and that their interactions were significant at p = 0.01. An improved interrill erosion equation was constructed by analyzing the relationships of sediment concentration with rainfall intensity, slope length, and slope gradient. In the improved interrill erosion equation, the runoff rate and slope factor are the same as in the interrill erosion equation in the Water Erosion Prediction Project (WEPP), with the weight of rainfall intensity adjusted by an exponent of 0.22 and a slope length term added with an exponent of -0.25. Using experimental data from WEPP cropland soil field interrill erodibility experiments, it has been shown that the improved interrill erosion equation describes the relationship between interrill erosion rate and runoff rate, rainfall intensity, slope gradient, and slope length reasonably well and better than existing interrill erosion equations.

[Study of immobilization of Aspergillus oryzae mycelium aided by artificial neural network].

Aspergillus oryzae mycelium pellets with abundant aminoacylase were cultured by liquid fermentation. Mycelium pellets were immobilized by crosslinking method with reagent of gelatin and formaldehyde. Basing on the orthogonal design table L16 (4(5)), artificial neural network(ANN) model with back-propagation(BP) of error structured 4-10-15-1 was used to optimize the immobilization conditions. And the optimal conditions were obtained. Then the activity of the immobilized cells prepared under the optimal conditions was assayed. Compared with the free mycelium activity of 1800 u, the residual activity rate was 83%, which was in good accordance with that predicted by ANN. It illustrated that artificial neural network can be used to find optimal conditions for cell immobilization.