The Temporal and Spatial Variation of Erosion and Sediment Yield on the Loess Plateau
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Collapsible loess is widely spread in Loess Plateau, northern Shaanxi province. The constructional damage due to side slope and irrigation will be caused if the loess doesn't deal with properly. Based on the analysis features of loess collapsibility and numbers of lab tests, this paper presents the relationship between loess structural parameters and confining pressure, as well water content and porosity ratio. The relevant loess structural parameters were obtained by fitting method. The loess collapsibility characteristics were analyzed with different confining stress, soil water content and porosity ratio. The main triggering factors of loess collapse were also analyzed. The results can further give the scientific evidence when dealing with the collapsible loess.
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The activity characteristics of the Plateau Low Vortex(PLV) in summer(from May to September) are investigatedby using the daily synopticcharts of 500 hPa at 08:00 and 20:00(BST) from 1980 to 2004.Some significant results areobtained as follows: The occurrence frequency of PLVs in summer has evident interdecadal,interannualand intraseasonal variation characteristics,and shows a decreasing tendency in the 1990s comparing with that in the 1980s.July is an active period of PLVs.The four sources of PLV forming in the Tibetan Plateau are between Shenzha and Gaize,northeastern Naqu,northeastern Dege,and Songpan.PLVs moving out of the Tibetan Plateau also have four sources: Northeastern Naqu,Qumalai,Dege and Maqin.Some PLVs can survive over 36 h in the Plateau and move eastward including three routes(northeast,southeast and east) that PLVs moving toward northeast are in the majority,but the routes out of the Plateau are different from those in the Plateau that most of PLVs are moving toward east first,then toward northeast and southeast.There are two main routes when PLVs are moving out of the Plateau,one is northeast to Hexi,Ningxia and Loess Plateau,the other is southeast to Sichuan Basin,and PLVs moving to Loess Plateauare the most.PLVs move out Plateau also has evident interannualand intraseasonal variation characteristics.Most of PLVs will weaken and vanish during 12 h after moving out of the Plateau,some can persist for 60 h,and only a few for 100 h,even 192 h.They would influence the precipitation in the vast area of east China,and maybe Korea peninsular and Japan.Warm PLVs are nearly two timesmore than baroclinic PLVs in the beginning state,while after moving out of the Plateau,the characteristics of PLVs change a lot during 12 h and most are baroclinic vortices.The occurring sources,removing routes and properties of PLVshave changed since the middle of 1980s compared with 1960s~1970s.
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Sichuan basin
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Loess plateau
Vegetation Cover
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There are some problems in the vegetation construction in the loess plateau region, such as the low rate of vegetation cover, the low survivorship and preservation rates of afforestation, and the low economic benefit. It can be done better if only the idea about ecological efficiency and tree species selection is changed. The great problems about vegetation construction are put forward.
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Afforestation
Vegetation Cover
Tree (set theory)
Forest cover
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By simulating the climate features on loess plateau,the loess ground thermal regime is deriked.By analyzing the calculated data and the tested data for the thermal regime,the changing law of the thermal regime caused by climatic change is explored.The relationship between loess temperature and loess depth in any month is given.It is pointed that the less the loess depth,the more the variation of temperature caused by climate change,and the more is the highest temperature and the less the lowest temperature.Further,this paper indicates that the more the loess depth is,the less is the variation of loess temperature caused by climate change.And the formula,by which the variation of loess temperature in any depth can be calculated,is arrived at.
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Variation (astronomy)
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Abstract In this study, distributing characteristics of five fluorine (F) species in loess in the Shaanxi Loess Plateau (SLP) were determined including unextractable residual F (F re ), extractable water-soluble F (F ws ), exchangeable F (F ex ), F bound to Fe-Mn oxides (F fm ), and F bound to organics (F or ). The results show that unextractable F re represents most percentage of F tf in loess. Of the four extractable F species, the content of F ws is higher than the other three extractable F species in most loess samples. The loess in the southeast SLP has the highest F ws content while the loess in the southwest has the highest F tf content. And the loess in the north SLP contains the lowest overall concentrations of F tf and F ws . Similar to F ws , the respective content of F ex , F fm , and F or in the loess is also very low. However, the total of them and F ws cannot be negligible for F mobility in loess. Overall, the loess in the SLP can be assessed as inferior quality in terms of F as a result of high F ws content in most samples. Based on the F speciation in the loess, F exposure to grazing animals and humans, in fact to children, was assessed, indicating that F in the loess in the southwest SLP might pose a much greater risk to grazing animals than in other part of SLP as the loess contains more F tf . However, there is no concern for the children’s exposure to loess F via ingestion in the study area in the present condition. As for the loess F risk to groundwater, it can be concluded that not only F ws but also the other extractable F including F ex , F fm and F or in loess may be responsible for the F enrichment in local groundwater in the area with the aid of the characteristics of F speciation in loess and distribution of local high-fluoride groundwater.
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Genetic algorithm
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Loess plateau
Vegetation Cover
Vegetation types
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Remarkable changes of vegetation cover in the Loess Plateau occurred in the latest 20 years. Land use/land cover (LULC) data of 1985, 1999 and 2009 were collected based on Landsat MSS, TM and MODIS remote sensing data. Results show that the widely implemented ecological restoration policies obtained a great success, achieving remarkable vegetation recovery and soil conservation in the Loess Plateau.
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Vegetation Cover
Land Cover
Restoration Ecology
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The loess tunnel, a kind of subground erosional geomorphy, is common in the loess plateau. Firstly, the classification of loess tunnels in the loess plateau is introduced. Secondly, based on field research, the distribution regularity of loess tunnels is discovered, that is, the density of loess tunnels is becoming lower from the north-west to the south-east. Thirdly, both the loess types and density differ in different depth; finally, the benefits and hazards of loess tunnels are analyzed. Results show that the loess tunnel has double significance: on the one hand, as a kind of geological hazard, it can not only result in serious water and soil loss, but also make damages to various constructions such as highway, railway, oil and gas conveying pipes and folk houses. On the other hand, it is a kind of important way that provides and discharges water for the effluent reservoirs in the loess plateau.
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