Regional differences in gully network connectivity based on graph theory:a case study on the Loess Plateau,China

Material exchange frequently occurs in gullies,and thus the relationship between a gullynetwork structure and sediment transport potential has attracted considerable interest.However,previous researches ignored the difficulty of material transport from sources to sinks,and did not quantify the connectivity of a network structure.In this study,we used a graph model structure to model gully networks of six typical sample areas in the Loess Plateau of China and quantified gully network connectivity using four indexes:average node strength,accessibility from sources to sinks,potential flow,and network structural connectivity index.Results show that:(1)Reflected by different quantitative indexes,the trends of gully network connectivity in different regions are similar.From north to south,the connectivity of a sample area first increases and then decreases.(2)The more mature gullies have stronger network connectivity.Small resistance is conducive to material transport in the gullies.(3)The node connectivity index of the gully network shows a significant aggregation distribution in space,and node connectivity on the main channel is often stronger than that on the branch trench.These results not only deepen the understanding of the process and mechanism of loess gully geomorphic development and evolution but also provide a reference for geomorphic studies.

Diurnal and seasonal dynamics of soil respiration in a Platycladus orientalis forest stand on the semiarid Loess Plateau, China

Forest ecosystems on China's Loess Plateau are receiving increasing attention because of their special importance in carbon fixation and conservation of soil and water in the region.Soil respiration was investigated in Platycladus orientalis forest stands of the region at diurnal and seasonal scales.The daily and seasonal average values of soil respiration were 2.53μmol·m^(-2)·s^(-1)and 3.78μmol·m^(-2)·s^(-1),respectively.On a diurnal and seasonal scale,the variations of soil respiration in the P.orientalis forest show a one-peak pattern.The diurnal dynamics of soil respiration were mainly driven by soil temperature.However,the relationship between soil respiration and soil temperature was not significant,mainly because of the hysteresis effect of soil respiration on soil temperature.Soil moisture plays another dominant role in the ecosystem carbon balance,but was not affected by soil temperature in P.orientalis forest on the semiarid Loess Plateau.

Study on the Climate Changes Characteristics in the Hilly Region of the Loess Plateau and Its Influence on Agricultural Production

[Objective] The aim was to study the climate changes characteristics in the hilly region of the loess plateau and its influence on agricultural production.[Method] Taking Yan’an City as an example,and by dint of temperature and precipitation in nine meteorological stations from 1957 to 2007 and accumulated anomaly curve,linear regression and relevant analysis,the climate changes characteristics in 51 years in Yan’an were expounded.The climate changes in the hilly region of the loess plateau were studied and its influences on agricultural production were concluded.[Result] The characteristics of climate changes in the hilly region were as follow:high temperature in winter and warm winter trend was clearly;the temperature in spring enhanced fast and the drought disaster was increasing worse;rainy days occurred now and then in autumn.The climate changes had different levels of influences on agricultural production in Yan’an City.Because of rising temperature in winter,facility agriculture was vigorously developed and the apple range expanded;in the meantime,because of rising temperature in spring,drought was worsen and sowing in spring can not proceed;constant rain in autumn damaged the quality of date.[Conclusion] The study provided theoretical basis for the regional agricultural production and agricultural structure adjustment.

Land-use changes in the small watershed of the Loess Plateau,hilly-gully region, China

As more and more farmland is converted to forestry, the need for effective decision support regarding the use of land in the fragile ecological environment of the Loess Plateau hilly-gully area. The Luoyugou watershed was chosen as the study area to calculate the single dynamic degree, integrated dynamic degree, and change indexes of land use, as well as the land-use type transition matrix. This was done by interpreting the TM and SPOT images of the Luoyugou watershed in 1986, 1995, and2004 and making statistical analysis. The results of ou statistical analysis show that the conversion of slope farm land to terrace and forest land plays a dominant role in land-use changes in the Luoyugou watershed from 1986 to2004. The land-use changes are mainly driven by popula tion growth, socio-economic development, consume spending, and investment in forest ecology.

Dynamic Land Use /Cover Change and Analysis of Landscape Pattern in the Hilly and Gully Region of Loess Plateau: A Case Study of Pengyang County in Southern Ningxia

The quantitative evaluation on land use /cover change as well as its influence on landscape pattern under the background of returning grain plots to forestry is significant to the sustainable utilization of land resources and ecological environment reconstruction in the southern Ningxia.Based on multi-temporal remote sensing data from four periods of Landsat TM /ETM,and combination of ecological quantity analytical method with GIS,the change of land use /cover and landscape pattern in Pengyang County of Ningxia Province were analyzed.The conclusions showed that the amount of each land use type was changed with different degrees,the area of forest /grass land increased,while farmland and unused land decreased.The change of landscape pattern was characterized as that the degree of landscape fragmentation,mixed distribution of patches,diversity index and evenness index increased gradually and then decreased,the connectivity between patches decreased gradually and then increased,and landscape shape presented irregular.

Autumn Daily Characteristics of Land Surface Heat and Water Exchange over the Loess Plateau Mesa in China

The Loess Plateau, located in northern China, has a significant impact on the climate and ecosystem evolvement over the East Asian continent. In this paper, the preliminary autumn daily characteristics of land surface energy and water exchange over the Chinese Loess Plateau mesa region are evaluated by using data collected during the Loess Plateau land-atmosphere interaction pilot experiment （LOPEX04）, which was conducted from 25 August to 12 September 2004 near Pingliang city, Gansu Province of China. The experiment was carried out in a region with a typical landscape of the Chinese Loess Plateau, known as ＂loess mesa＂. The experiment＇s field land utilizations were cornfield and fallow farmland, with the fallow field later used for rotating winter wheat. The autumn daily characteristics of heat and water exchange evidently differed between the mesa cornfield and fallow, and the imbalance term of the surface energy was large. This is discussed in terms of sampling errors in the flux observations-footprint; energy storage terms of soil and vegetation layers; contribution from air advections; and low and high frequency loss of turbulent fluxes and instruments bias. Comparison of energy components between the mesa cornfield and the lowland cornfield did not reveal any obvious difference. Inadequacies of the field observation equipment and experimental design emerged during the study, and some new research topics have emerged from this pilot experiment for future investigation.

Quantitative analysis of the dynamic change and spatial differences of the ecological security: a case study of Loess Plateau in northern Shaanxi Province

Using the theory and method of the ecological footprint, and combining the changes of regional land use, resource environment, population, society and economy, this paper calculated the ecological footprint, ecological carrying capacity and ecological surplus/loss in 1986-2002 on the Loess Plateau in northern Shaanxi Province. What is more, this paper has put forward the concept of ecological pressure index, set up ecological pressure index models, and ecological security grading systems, and the prediction models of different ecological footprints, ecological carrying capacity, ecological surplus and ecological safety change, and also has assessed the ecological footprint demands of 10,000 yuan GDE The results of this study are as follows： （1） the ecological carrying capacity in northern Shaanxi shows a decreasing trend, the difference of reducing range is the fastest; （2） the ecological footprint appears an increasing trend; （3） ecological pressure index rose to 0.91 from 0.44 during 1986-2002 on the Loess Plateau of northern Shaanxi with an increase of 47%; and （4） the ecological security in the study area is in a critical state, and the ecological oressure index has been increasing rapidlv.

A GIS-based Modeling Approach for Fast Assessment of Soil Erosion by Water at Regional Scale, Loess Plateau of China

The objective of this study is to develop a unique modeling approach for fast assessment of massive soil erosion by water at a regional scale in the Loess Plateau, China. This approach relies on an understanding of both regional patterns of soil loss and its impact factors in the plateau area. Based on the regional characteristics of precipitation, vegetation and land form, and with the use of Landsat TM and ground investigation data, the entire Loess Plateau was first divided into 3 380 Fundamental Assessment Units （FAUs） to adapt to this regional modeling and fast assessment. A set of easily available parameters reflecting relevant water erosion factors at a regional scale was then developed, in which dynamic and static factors were discriminated. Arclnfo GIS was used to integrate all essential data into a central database. A resulting mathematical model was established to link the sediment yields and the selected variables on the basis of FAUs through overlay in GIS and multiple regression analyses. The sensitivity analyses and validation results show that this approach works effectively in assessing large area soil erosion, and also helps to understand the regional associations of erosion and its impact factors, and thus might significantly contribute to planning and policymaking for a large area erosion control in the Loess Plateau.

Dynamic Simulation of Land Use in the Southern Loess Plateau

To study the dynamic changes of land use and predict the future land use scenarios based on the current land use,this paper uses Cellular Automata- Markov( CA- Markov) model to simulate the landscape pattern in 2030. The results show that in the study area during the period 1980- 2005,grassland and construction land increased,and woodland increased slightly; waters and unused land decreased,and arable land underwent dramatic changes. The simulation precision of CA- Markov model is 87. 28%,indicating that the use of it for simulation is reliable. The land use of the study area will be changed greatly in the future. This method provides a reference for the regions to carry out land prediction,and the research results can provide a basis for the study of optimization of land.

Deep profile soil moisture distribution characteristics for different microtopographies on the semi-arid Loess Plateau, China

Soil moisture is a limiting factor for vegetation restoration on the Loess Plateau, China. Micro-topography may cause heterogeneities in the distribution of soil moisture, but little is known about its effect on deep soil moisture. Our study aims to explore the distribution and impact of soil moisture within the upper 10 m of soil for different microtopographies. Taking undisturbed slope as the control, five micro-topographies were selected. Soil moisture over a depth of 0-10 m from 2017 to 2019 was investigated, and soil particle size and soil organic matter were measured. Variance analysis and multiple comparisons were used to analyze the difference in soil moisture for different microtopographies and multiple-linear regression was used to analyze the influence of micro-topography on soil moisture. There are significant differences in soil moisture within the different layers underlying the examined micro-topographies, while the inter-annual variation in soil water storage for the selected microtopographies increase with increased rainfall. The depth of influence of micro-topographic vegetation on soil moisture exceeded 1000 cm for a gully(GU), 740 cm for a sink hole(SH), 480 cm for a scarp(SC), 360 cm for an ephemeral gully(EG) and 220 cm for a platform(PL). Micro-topography will cause the heterogeneous distribution of soil moisture in the shallower layers, which changes the vegetation distribution differences between micro-topographies. This may be the survival strategy of herbaceous vegetation in response to climate change in the Loess Plateau. For future vegetation restoration efforts, we need to pay attention to the influence of microtopography on soil moisture.

The influence of plant root system architectural properties upon the stability of loess hillslopes,Northeast Qinghai,China

To investigate the influence of root system architectural properties of three indigenous （cold- adapted） shrubs on the hillslope stability of loess deposits in the Xining Basin, northeast part of Qinghai-Tibet Plateau （QTP）, indoor direct shear tests have been conducted on the remolded rooted soil of three shrubs. Test results show that root system architectural indices （root area ratio （RAR）, root length density （RLD） and root density （RD）） of the shrubs decline with depth and the relationship between RAR, RD and depth is exponential, while a power relationship describes the relationship between RLD and depth. The cohesion force of remolded rooted soil for the shrubs initially increases with depth, but it then demonstrates a slightly decreasing trend, which can be described with a power relationship. Power relationships also describe relationships between cohesion force and RAR, RLD and RD for the shrubs. As the growth period increases from lO to 17 months, the incremental increase in RAR is 48.32% ~ 21o.25% for Caragana korshinskii Kom and 0.56% ~ 166.85% for ZygophyUum xanthoxylon （Bunge） Maxim. This proportional increase is notably larger than that for RLD and RD. The increment in RAR is marginally greater for C. korshinskff than it is for Z. xanthoxylon. Correspondingly, the cohesion force incremental rates of remolded rooted soil for C. korshinskii and Z. xanthoxylon are 12.41% ~ 25.22% and 3.45% ~ 17.33% respectively. Meanwhile, as root content increases, the contribution by roots to cohesion force increases markedly until a threshold condition is reached.

Spatial-temporal Pattern and Population Driving Force of Land Use Change in Liupan Mountains Region, Southern Ningxia, China

The Liupan Mountains is located in the southern Ningxia Hui Autonomous Region of China, which forms an important dividing line between landforms and bio-geographic regions. The populated part of the Liupan Mountains region has suffered tremendous ecological damages over time due to population pressure, excessive demand and inappropriate use of agricultural land resources. In this paper, datasets of land use between 1990 and 2000 were obtained from Landsat TM imagery, and then spatial models were used to characterize landscape conditions. Also, the relationship between the population density and land use/cover change (LUCC) was analyzed. Results indicate that cropland, forestland, and urban areas have increased by 44,186ha, 9001ha and 1550ha, respectively while the grassland area has appreciably decreased by 54,025ha in the study period. The decrease in grassland was most notable. Of the grassland lost, 49.4% was converted into cropland. The largest annual land conversion rate in the study area was less than 2%. These changes are attributed to industrial and agricultural development and population growth. To improve the eco-economic conditions in the study region, population control, urbanization and development of an ecological friendly agriculture were suggested.

Study on Rural Domestic Waste Treatment in Loess Plateau Region——Taking Longfang Town in Shaanxi Province as Example

With the continuous development of economy and changes in people’s lifestyle,rural domestic waste brought about serious harm to water,air,human health,ecological landscape and so forth.In this paper,taking Longfang Town in Loess Plateau region as example,the source,amount and harms of rural domestic waste were analyzed firstly,as well as the current situation and existing problems of treatment,and then a suitable waste disposal technology for the town was chosen,finally the reasonable treatment methods combining new countryside and non-new countryside with township was summed up,so as to realize the reduction,harmless and resource treatment of rural domestic waste.

THE SYSTEMATIC DYNAMIC EMULATION ON THE AGRICULTURAL DEVELOPMENT ON THE LOESS PLATEAU

The Loess Plateau, covered with thick loess, lies in the middle reaches of the YellowRiver to the west of the Taihangshan Mountains, east of the Wuqiao Mountains south ofYinshan Mountains and north of the Qinling Mountains with a total area of 56×10~4km^2.The plateau is 1000--2500m above sea level and has loess as thick as 100--200 metres, be-

High-frequency climatic fluctuations over the past 30 ka in northwestern margin of the East Asian monsoon region, China

Whether millennial-to centennial-scale climate variations throughout the Holocene convey universal climate change is still widely debated.In this study,we aimed to obtain a set of high-resolution multi-proxy data(1343 particle size samples,893 total organic carbon samples,and 711 pollen samples)from an alluvial-lacustrine-aeolian sequence based on an improved age-depth model in the northwestern margin of the East Asian monsoon region to explore the dynamics of climate changes over the past 30 ka.Results revealed that the sequence not only documented the major climate events that corresponded well with those reported from the North Atlantic regions but also revealed many marked and high-frequency oscillations at the millennial-and centennial-scale.Specifically,the late stage of the last glacial lasting from 30.1 to 18.1 cal.ka BP was a dry and cold period.The deglacial(18.1-11.5 cal.ka BP)was a wetting(probably also warming)period,and three cold and dry excursions were found in the wetting trend,i.e.,the Oldest Dryas(18.1-15.8 cal.ka BP),the Older Dryas(14.6-13.7 cal.ka BP),and the Younger Dryas(12.5-11.5 cal.ka BP).The Holocene can be divided into three portions:the warmest and wettest early portion from 11.5 to 6.7 cal.ka BP,the dramatically cold and dry middle portion from 6.7 to 3.0 cal.ka BP,and the coldest and driest late portion since 3.0 cal.ka BP.Wavelet analysis results on the total pollen concentration revealed five substantially periodicities:c.5500,2200,900,380,and 210 a.With the exception of the c.5500 a quasi-cycle that was causally associated with the Atlantic meridional overturning circulation,the other four quasi-cycles(i.e.,c.2200,900,380,and 210 a)were found to be indirectly causally associated with solar activities.This study provides considerable insight into the dynamic mechanism of the Asian climate on a long-time scale and future climatic change.

Vegetation and environmental changes in western Chinese Loess Plateau since 13.0 ka BP

Pollen records from the Chinese Loess Plateau revealed a detailed history of vegetation variation and associated climate changes during the last 13.0 ka BP. Before 12.1 ka BP, steppe or desert-steppe vegetation dominated landscape then was replaced by a coniferous forest under a generally wet climate （12.1-11.0 ka BP）. The vegetation was deteriorated into steppe landscape and further into a desert-steppe landscape between 11.0 and 9.8 ka BP. After a brief episode of a cool and wet climate （9.8-9.6 ka BP）, a relatively mild and dry condition prevailed during the early Holocene （9.6-7.6 ka BP）. The most favourable climate of warm and humid period occurred during mid-Holocene （7.6-4.0 ka BP） marked by forest-steppe landscape and vegetation alternatively changed between steppe and desert-steppe from -4.0 to -1.0 ka BP.

Changes in Land Use and Agricultural Production Structure Before and After the Implementation of Grain for Green Program in Western China–Taking Two Typical Counties as Examples

Soil erosion becomes a serious environmental problem in the world, especially in western China. An effective management practice called the Grain for Green Program(GGP), which was launched in 1999, aims to reduce soil and water loss and alleviate the ecological environment problem in western China. Two typical counties in western China, the Zhongxian(in Chongqing Municipality) and Ansai(in Shaanxi Province) were chosen to evaluate the dynamic changes of land use and agricultural production structure before and after the implementation of the Program in this paper. The results showed that the cultivated land area was reduced by 7.08% from 1989 to 2003. The cultivated land per person was decreased by 8.42% during 1999-2003. Moreover, the stability index of the secondary sector of the economy was increased from 0.91 in the period 1990-1999 to 0.94 in the following ten years. In addition, the stability index of tertiary economic sector increased from 0.88 to 0.92 in Zhongxian county. Meanwhile, the cultivated land area was reduced by 15.48% from 1990 to 1999. The soil erosion modulus was decreased by 33.33% from 1999 to 2006. Also, the stability index of secondary and tertiary economic sectors was 0.86 in the period 1998-2002. However, it decreased by 77% during 2002 to 2007 in Ansai County. These results imply that the Grain for Green Program had different impact on the two regions. Several effective strategies of soil and water conservation have been carried out to ameliorate the sustainable development of ecological environment and economy in these two counties of western China.

Review on Regional Climate Change Induced by Qinghai-Tibet Plateau Uplift

[Objective]The aim was to study the influence of Qinghai-Tibet Plateau uplift on regional climate in China.[Method] Trough relevant study of Qinghai-Tibet Plateau and its surrounding movement,the tectonic movement of the Qinghai-Tibet Plateau and its surrounding areas,especially the case of the impact caused by plateau phased uplift were studied based on paleomagnetic measurements.[Result]The increasing Qinghai-Tibet Plateau led to obvious transition from dry to cold in northwest China and it became dry quickly,which led to loess accumulation,replacement of vegetation types and human activity.Meanwhile,it was dry,and there was certain degree of climate changes in the area.[Conclusion] Qinghai-Tibet Plateau had far-reaching significance on basic climate characteristics in northwest China.

Spatial distribution of surface rock fragment on hillslopes in a small catchment in wind-water erosion crisscross region of the Loess Plateau

The cover and size distributions of surface rock fragment in hillslopes were investigated by using digital photographing and treating technique in a small catchment in wind-water erosion crisscross region of the Loess Plateau. The results indicated that the maximal cover of rock fragment was pre-sented at mid-position in steep hillslope. Rock fragment presented a general decreasing-trend along the hillslope in gentle hillslope. Rock fragment cover was positively related to gradient, rock fragment size decreased generally along the hillslope, and the size reduced with the gradient. The mean size of rock fragment was at a range of 6―20 mm in the steep hillslope, rock fragment size > 50 mm was rarely presented. The covers of rock fragment at different positions were markedly related to the quantities of rock fragment < 40 mm. The area of rock fragment of 2―50 mm accounted for 60% or more of the total area, dominating the distribution of rock fragment in the hillslopes.

The effect of environmental factors on spatial variability in land use change in the high-sediment region of China＇s Loess Plateau

In areas with topographic heterogeneity, land use change is spatially variable and influenced by climate, soil properties, and topography. To better understand this variability in the high-sediment region of the Loess Plateau in which soil loss is most severe and sediment diameter is larger than in other regions of the plateau, this study builds some indicators to identify the characteristics of land use change and then analyze the spatial variability as it is affected by climate, soil property, and topography. We build two indicators, a land use change intensity index and a vegetation change index, to characterize the intensity of land use change, and the degree of vegetation restoration, respectively. Based on a subsection mean method, the two indicators are then used to assess the spatial variability of land use change affected by climatic, edaphic, and topographic elements. The results indicate that： 1） Land use changed significantly in the period 1998-2010. The total area experiencing land use change was 42,302 km2, accounting for 22.57%of the study area. High-coverage grassland, other woodland, and forest increased significantly, while low-coverage grassland and farmland decreased in 2010 compared with 1998.2） Land use change occurred primarily west of the Yellow River, between 35 and 38 degrees north latitude. The four transformation types, including （a） low-coverage grassland to medium-coverage grassland, （b） medium-coverage grassland to high-coverage grassland, （c） farmland to other woodland, and （d） farmland to medium-coverage grassland, were the primary types of land use change, together constituting 60% of the area experiencing land use change. 3） The spatial variability of land use change was significantly affected by properties of dryness/wetness, soil conditions and slope gradient. In general, land use changed dramatically in semi-arid regions, remained relatively stable in arid regions, changed significantly in clay-rich soil, remained relatively stable in clay-poor soil, changed dramatically in steeper slopes, and remained relatively stable in tablelands and low-lying regions. The increase in vegetation coincided with increasing changes in land use for each physical element. These findings allow for an evaluation of the effect of the Grain to Green Program, and are applicable to the design of soil and water conservation projects on the Loess Plateau of China.