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In order to improve the leaf color and optimize the facility of cultivation system of Aglaonema commutatum ‘Big apple', its hydroponic seedlings were used as the test material in this study, six light qualities(white light, R:B = 1:1, R:B = 1:2, R:B = 2:1, R:B = 1:3, R:B = 3:1, in which R and B represent red light and blue light, respectively)and two photoperiods(8 h·d-1, 12 h·d-1)were cross cultured to determine the growth amount, biomass, soil and plant analyzer development(SPAD)value, anthocyanin content and leaf color parameters(hue value a*, hue value b*, luminosity L* and hue angle h*), and to investigate its response to red and blue light qualities and photoperiodic interactions. The results were as follows:(1)The dry weight and fresh weight of A. commutatum seedlings treated with LP11(R:B=1:3×12 h·d-1)were the highest, which was most conducive to plant growth and biomass accumulation; followed by LP5(R:B=1:3×8 h·d-1)treatment.(2)Under the same light quality condition, the SPAD value of 8 h·d-1 photoperiod was higher than that of 12 h·d-1 photoperiod, the anthocyanin content of 12 h·d-1 photoperiod was higher than that of 8 h·d-1 photoperiod, the SPAD value of LP11 treatment was the lowest and the anthocyanin content was the highest. The leaf color parameters a* and b* of A. commutatum cultured in 12 h·d-1 photoperiod were higher than those in 8 h·d-1 photoperiod, and the value of h* was lower than that in 8 h·d-1 photoperiod.(3)The principal component analysis showed that the LP11 treatment was the most effective in promoting the growth and leaf color improvement of A. commutatum. In conclusion, 12 h·d-1 photoperiod is more conducive to the growth and leaf color change of A. commutatum, and LP11 treatment is the best combination of light quality and photoperiod. [ABSTRACT FROM AUTHOR]

Sediment connectivity is closely related to geomorphology, topography, ecological hydrology, soil erosion, nutrient and pollutant movement, and water quality conservation. As one of the hot topics in soil erosion research during the past decade, sediment connectivity is required to be fully examined from the perspective of soil erosion. Sediment connectivity describes the interactions of sediment cascades between different topographical and landscape units in a system which is usually quantified with the structural connectivity and functional connectivity in four dimensions, i.e.,lateral, longitudinal, vertical and temporal. Its impacting factors include climate, lithology, geomorphology, watershed characteristics, topography, soil properties, vegetation, hydrological processes, soil erosion and human activities as well as their temporal and spatial variations. The specific influencing mechanisms vary among these factors and among different spatial scales, therefore resulting in distinct responses of sediment connectivity. Field survey and mapping, graph theory, index and model simulation are frequently applied to investigate and quantify sediment connectivity. The theories behind these methods are different, so do the required data, specific procedures, and the corresponding results. The index of connectivity（IC） is the most widely employed in the quantification of sediment connectivity. Nevertheless, IC well reflects the structural connectivity, rather than the functional connectivity. From the perspective of soil erosion, future studies regarding sediment connectivity should focus on the concept, influencing factors and their dynamic mechanisms, method comparison and index optimization, relationships of sediment connectivity with hydrological connectivity, soil erosion and sediment delivery ratio, as well as the effects of soil conservation measures on sediment connectivity and the corresponding mechanisms. [ABSTRACT FROM AUTHOR]

The most striking characteristic of an arid climate is a lack of moisture with the low precipitation, while strong evaporation, particularly in northwest China. In the natural lake wetland, the growth state of natural vegetation and the quality of basic farmland are strongly dependent on the groundwater burial condition. Therefore, this study aims to propose a set of groundwater function evaluation and zoning, to establish a novel evaluation system for the groundwater function in arid area. 4 layers were divided, including from high to low (marked as the system target layer), criterion function layer, attribute index layer, and factor index layer. Specifically, 14 indicators were set in the evaluation system. A step to build the system was as follows: To combine the logic and multi-objective indicators, attributes classification, function aggregation, and unique system, called “dry area system” for short. The requirement and standard for the evaluation of the groundwater condition were generally associated with “Technical requirements for evaluation and zoning of groundwater functional zones” released by China Geological Survey Bureau in 2006, where the indicators are guiding the evaluation and division of groundwater function in North China, northeast China, Shanxi great Basin and northwest China. Compared with the previous edition, the “dry area system” mainly expressed the indexes of “Arid area system”, representing the essential characteristics of groundwater in northwest China, further to pose the new connotation on the attribute indexes of a system, with the removal the number of less common indexes. Specifically, 22 indicators were reduced to 14 factors, with the addition of some new indexes, including the attribute index of “natural wetland landscape maintenance”, the factor indexes of “wetland environment and groundwater correlation”, “oasis coverage and groundwater correlation”, and “desertification and groundwater correlation”. In this study, an index weight method of “Arid area system” was proposed using the sequence synthesis mathematical theory, and the analytic hierarchy process as the theoretical framework. The original data was selected to serve as the basis of weight evaluation, according to the principle of index weight analysis, including the critical, correlation, systematic evaluation. The index weights of 14 factors were then analyzed in factor index layer. Based on the indexes of possession, renewal, availability, and ecological function of groundwater resources, the weight of groundwater resources function and ecological function in arid area was elucidated to fit in the northwest inland groundwater function of the natural properties. The application in Shiyang River Basin showed that the “Arid area system” was feasible for the groundwater function evaluation in arid area. The evaluation data was also suitable for the essential characteristics of groundwater resources and ecological function in different areas. The finding can provide a sound theoretical basis for fine management groundwater and ecological protection, and thereby to support rational development of groundwater and targeted management of ecological protection in arid areas. [ABSTRACT FROM AUTHOR]

Aggregate stability (MWD) is an important indicator of soil structure stability, and closely correlated to the processes of slope hydrology and soil erosion. Up to date, few studies are conducted to investigate the variation of MWD and influencing factors on the regional scale. In order to study the variation characteristics of MWD and influencing factors in the Loess Plateau, a 508 km long transect including seven sampling sites along the precipitation gradient was laid out in this study. The MWD of cropland, grassland and woodland on each sampling site were measured, in the meantime soil mechanical composition, bulk density, soil organic matter, root mass density and vegetation coverage of each sampling site were also measured. The results indicated that there existed significant (P<0.05) difference between the MWD of cropland and the MWD of grassland and woodland. Cropland had the largest mean MWD, followed by woodland; the cropland had the lowest mean MWD. The ratios of the mean MWD of grassland and woodland to the mean MWD of cropland were 2.94 and 2.39, respectively. The reason why the mean MWD of cropland was lowest could be explained by the fact that the lower soil organic matter and root mass density of cropland, and the disturbance of MWD induced by the frequent tillage operations. The MWD of cropland showed a decreasing trend from south to north along the precipitation gradient. The changing trends of the MWD of grassland and woodland were similar, which could be attributed to the similarity of the near surface characteristics (such as non-disturbance, high plant residue return) of grassland and woodland. The MWD of the Yijun was slightly lower than the MWD of Fuxian, and then the MWD of sampling sites showed a generally decreasing trend from Fuxian to Erdos. The MWD of cropland, and grassland and woodland were all influenced by soil organic matter, annual average precipitation and annual average temperature. In addition, there existed a significant (P<0.05) relationship between the MWD of cropland and soil mechanical composition, however the MWD of grassland and woodland were closely related to root mass density. The poor relationship between the MWD of cropland and root mass density were attributed to its low root mass density and frequent tillage operation. The fact that grassland and woodland had high soil organic matter and root mass density which masked the influence of soil mechanical composition well explained that no significant (P>0.05) relationship was found between the MWD of grassland and woodland and soil mechanical composition. The annual average precipitation and annual average temperature influenced the MWD of cropland, grassland and woodland by affecting root mass density and soil organic matter. No-linear regression demonstrated the MWD of cropland could be satisfactorily simulated by median soil grain size and annual average precipitation with the coefficients of determination (R2) of 0.95 and the Nash-Sutcliffe efficiency (NSE) of 0.99. The MWD of grassland and woodland could be simulated by soil organic matter, root mass density and annual average temperature. The simulated result of grassland and woodland was not as good as that of the cropland with the coefficients of determination (R2) of 0.64 and the Nash-Sutcliffe efficiency (NSE) of 0.64, which under-predicted low measured MWD and over-predicted high measured MWD. The results of this study will be of great significance in understanding the spatial variation of aggregate stability (MWD) along the precipitation gradient and its influencing factors, and analyzing the regional change law of hydrological and erosional processes. [ABSTRACT FROM AUTHOR]

Sediment transport capacity of overland flow, which is the maximum equilibrium sediment load that a flow can transport, is a key concept for developing process-based soil erosion models because it plays a pivotal role to determine soil detachment rate and sediment transport. Few studies have been conducted to investigate the mechanism of sediment transport capacity by overland flow on steep slopes. In this paper, based on the systematic definition of sediment transport capacity of overland flow, the influences and their mechanisms of hydraulic properties of overland flow and sediment characteristics on sediment transport capacity were deeply analyzed. Sediment transport capacity of overland flow has great spatial and temporal variations due to the comprehensive effects of precipitation, topography, soil, vegetation, land use, sealing formation, rill development, and gravel covering. Therefore, it is very difficult to measure sediment transport capacity of overland flow directly in field conditions. The commonly used methods to determine sediment transport capacity of overland flow can be categorized into the modification from river sediment transport capacity formula, the rational method, the model simulation, and the direct measurement. The advantages and disadvantages of each method were compared and analyzed. Further studies should be focus on the measuring methodology and techniques for sediment transport capacity of overland flow, the hydro-dynamic mechanism of sediment transport process, sediment transport capacities of typical soil types, transport capacity formula development and performance evaluation, and sediment transport capacity of overland flow under changeable conditions. It is helpful to summarize the conclusions of different studies, promote the research on sediment transport capacity of overland flow, and improve the prediction precision of the process-based soil erosion models for better service to water and soil conservation planning and design. [ABSTRACT FROM AUTHOR]

Plant litter has been accumulated greatly along with vegetation restoration on the Loess Plateau. Besides covering soil surface, plant litter can be incorporated into topsoil under natural circumstances by soil splash, sediment deposition, and soil-dwelling animal activities. The distribution (covering soil surface or incorporated into surface soil) and the decomposition of plant litter can modify soil physical properties (including soil detachment capacity and soil erosion resistance) which are closely related to soil detachment process by overland flow. This study was conducted to investigate the effect of vegetation restoration on soil detachment process for black locust (Robinia pseudoacacia L.) stand with different ages of returning farmland on the Loess Plateau. The experiments were performed in the Zhifanggou small watershed (36°46'28"-36°46'42"N, 109°13'46"-109°16'03"E) in August, 2015. After a complete watershed survey, altogether 6 sampling sites were selected, including 1 corn (Zea mays L.) field and 5 black locust stands of 10, 15, 20, 30, and 40 years. Soil samples were collected from the top 5 cm soil layer using a circular steel ring with 10.0 cm diameter and 5.0 cm depth. Soil detachment was measured in a 4.0 m long, 0.35 m wide flume. Prior to the test of soil detachment capacity, soil samples were saturated in a container for 8 h and drained for 12 h. Then the soil samples were inserted into a hole (0.5 m away from the outlet of flume) on the flume bed and were scoured by flowing water under designed flow shear stress. A total of 180 soil samples were collected from different aged black locust stands and scoured under 6 flow shear stresses. In this study, 6 combinations of flow rates and slopes were applied to obtain 6 different flow shear stresses (5.4-17.4Pa) with similar intervals. Rill erodibility is defined as the increase in soil detachment capacity per unit increase in flow shear stress. Critical shear stress is a threshold parameter defined as the value above which a rapid increase in soil detachment capacity per unit increase in shear stress occurs. When the measured detachment capacity was plotted against the flow shear stress, rill erodibility and critical shear stress could be determined from the slope of the fitted straight line and its intercept on the X axis. The results showed that the density of plant litter in 0-5 cm surface soil was 0.065, 0.175, 0.316, 0.289 and 0.171 kg/m2 for 10, 15, 20, 30, and 40-year-old black locust stands, respectively, with the mean value of 0.20 kg/m2. The 40-year-old black locust stands had more capillary porosities, soil organic matter, and water stable aggregates, and smaller soil bulk density. Soil detachment capacity decreased by 49.8%, 73.9%, 85.0%, 86.0%, and 87.0% for 10, 15, 20, 30, and 40-year-old black locust stands, respectively, compared to the control. The soil detachment capacity decreased significantly over time as an exponential function (R2=0.97, P=0.006). The control (corn field) had the biggest rill erodibility (0.29 s/m), and the 40-year-old black locust stand had the smallest rill erodibility (0.04 s/m). Compared to the control, the rill erodibility for 40-year-old black locust stand was reduced by 86.3%. The black locust stand with 20 years had the biggest critical shear stress (4.78 Pa), and the control had the smallest critical shear stress (4.15 Pa). The critical shear stress increased by 10.1% for 40-year-old black locust stand compared to the control. The critical shear stress increased significantly with litter density as a linear function (R2=0.67, P=0.046). Rill erodibility was better than critical shear stress in the respect of reflecting the variation of soil detachment. The soil-plant litter system has a larger erosion resistance to flowing water than the control. Importantly, the soil-root system may have a larger structural stability and erosion resistance to flowing water than soil-plant litter system. [ABSTRACT FROM AUTHOR]

Shallow groundwater, which is in over-exploitation, is the main water source of farm irrigation in the agricultural areas of the central Hebei piedmont plain. According to the dynamic monitoring data of shallow groundwater level from long-time observation hole in the different agricultural areas of the central Hebei piedmont plain, variable characteristics of shallow groundwater level response to the successive years with less rainfall were studied. The results show that large-scale and intensive shallow groundwater exploitation during spring irrigation periods of successive years with less rainfall mainly causes the continuous decline of shallow groundwater level in the agricultural areas of the central Hebei piedmont plain; the decline amplitude of shallow groundwater level during spring irrigation period is related closely with the precipitation from January to June of the previous year and the same year; when the annual precipitation is less than the local annual average precipitation (528. 4 mm), the effect of agricultural water exploitation on the decline of shallow groundwater increases significantly with the decrease of precipitation; when the annual precipitation is more than the local annual average precipitation, even more than 630 mm. the effect of agricultural water exploitation on the decline of shallow groundwater decreases significantly; adjusting and controlling rationally the exploitation intensity of shallow groundwater in the agricultural areas is important for improving the sustainable utilization of shallow groundwater in the agricultural areas of the central Hebei piedmont plain. [ABSTRACT FROM AUTHOR]

Gully erosion is one of the major contributors to severe land degradation in the Yuanmou Dry-hot Valley Region of Southwest China, due to the frequent erosive precipitation events in the rainy season and special lithological conditions. Most active gullies in the study area are characterized by steep gully headcut, and headward erosion has been recognized as the main process of gully expansion. In particular, scour holes are often developed in the open side of gully headcut, which cause the frequent collapse of overhanging layers of gully heads in the process of headward erosion, and thus accelerate gully headward development. It is, therefore, of great significance to carry out the study on the collapse of overhanging layers of gully heads during the gully headward processes. In this study, based on the field investigations, a generalized physical model of active gully head was established. Then, the stability of overhanging layer of active gully head was studied by the momental analysis method, considering the main factors i.e. headcut height, the shape of scour hole and the development of tension crack at gully head. The results showed that the stability of overhanging layer of gully head was affected by various factors, such as the soil water content, the height of scour hole, the location and depth of tension crack. The results also indicated the difficulty in studying the mechanism of the gully head collapse process. When other parameters were assigned with default values, the stability of overhanging layer of gully head was decreased with soil water content and depth of tension crack (p<0.001) as an exponential function, and decreased with height of scour hole (p<0.001) as a linear function. As the distance between the tension crack and the headcut wall increased, the stability of overhanging layer increased significantly (p<0.001). Furthermore, to test the reliability of the evaluation of stability of overhanging layers, 4 gully heads molded by man with scour holes and the flow scouring experiments were employed in the field. When the collapse of overhanging layers of gully heads occurred, soil water contents of the whole collapse soil and the collapse surface soil were determined by oven-dry method with 6 repetitions. The results showed that the measured soil water contents of the whole collapse soil and the collapse surface soil were 69.8%-87.6% and 82.0%-95.5% of the model estimated values, separately. The small difference in soil water contents between the measured values and estimated values also indicated that this evaluation model was very valuable for the prediction of the collapse of overhanging layers of gully heads in the Yuanmou Dry-hot Valley Region. Moreover, the soil water content of the collapse surface soil was much closer to the model estimated value, which demonstrated that the development of tension crack on the overhanging layers of gully heads did affect their stability. These results are helpful to supplement meaningful theories to the erosion mechanism study and conservation practices implementation of active gully heads in the Yuanmou Dry-hot Valley Region. However, due to the complexity and uncertainty of the collapse of overhanging layers, further studies are needed to focus on the process of collapse of active gully heads, which can further improve the evaluation reliability of the stability model. [ABSTRACT FROM AUTHOR]

Well recharging is an important recharge mode using for controlling groundwater overdraft. And it has advantages of covering a small area and high recharge efficiency. However, water infiltration characteristics in different layer sands are various. Based on the sand characteristics in typical area of the North China Plain, using the developing fan sand box model of emulational well recharging, laboratory experiments were carried out under conditions of different constant water levels and quantities of flow in coarse, medium and fine sands. The data of temporal and spatial variation of groundwater level and its quantity were comprehensively analysed and compared. The results show as follows. The groundwater level decreases along the water flow direction in coarse, medium and fine sands under conditions of different constant water levels. The reducing scale in coarse sand is the biggest and the smallest in fine sand. The process of water level decreasing can divide into speediness and low speed stages in the three kinds of sands. Distances from well wall to demarcation points of two stages in coarse, medium and fine sands are smaller and smaller. When water level in recharging well increases, the quantity of water recharge appears quadratic growth in medium and fine sands, which appears linear growth in fine sand. The flow rate changes most obviously when water level changes in coarse sand. Well recharging processes include three stages: storing water around well, diffusing out into the distance and stabilization. The time of stages of storing water around well and diffusing out into the distance in coarse and medium sands is short and reaching stability of water level spent 600 s. The time of them is long in fine sand and reaching stability of water level spent 9 500 s. The study has a certain degree of guiding significance for selection of artificial recharging site, optimization of recharging sands and layout of recharging wells. [ABSTRACT FROM AUTHOR]

A stabilizing and tracking control strategy of using a strapdown inertial navigation system (SINS) to measure the pointing direction and angular rate of gun barrel is proposed to enable the marching guns to track targets and stabilize at a large fire angle, in which the stabilizing and tracking control are accomplished in the geodetic coordinate system. The conventional three-loop control is applied and improved, and the reference and feedback values of position loop and velocity stabilization loop are given in the'geodetic coordinate system. As the position feedback, the azimuth and pitch angular rales of SINS are resolved based on the geodetic coordinate system. The measured values of gyros in SINS mounted on the gun are transformed to the azimuth and pitch angular rates in the geodetic coordinate system, and re multiplied by the drive ratios of drive mechanisms as the feedback of velocity stabilization loop. A dynamic coupling model of gun, turret and carrier is established using Lagrange equation in consideration that the rotary center of turret and carrier is misaligned, and the carrier moves in six degrees of freedom.The simulation validation of the proposed control scheme is conducted based on SINS measurement model, two-motor drive model and control model of motor servo system. The result shows that the two-channel independent control, the high-accurate stabilizing control of pointing direction of gun at a large fire angle, the high tracking performance in a certain range of firing angle, and the isolation of wider frequency hand disturbance from carrier can be realized. [ABSTRACT FROM AUTHOR]