Arsenic and fluoride co-enrichment of groundwater in the loess areas and associated human health risks:A case study of Dali County in the Guanzhong Basin

This study aims to reveal the occurrence and origin of typical groundwater with high arsenic and fluoride concentrations in the loess area of the Guanzhong Basin—a Neogene faulted basin.Key findings are as follows:(1)Groundwater samples with high arsenic and fluoride concentrations collected from the loess area and the terraces of the Weihe River accounted for 26%and 30%,respectively,of the total samples,with primary hydrochemical type identified as HCO_(3)-Na.The karst and sand areas exhibit relatively high groundwater quality,serving as preferred sources for water supply.It is recommended that local governments fully harness groundwater in these areas;(2)groundwater with high arsenic and fluoride concentrations in the loess area and the alluvial plain of rivers in Dali County is primarily distributed within the Guanzhong Basin,which represents the drainage zone of groundwater;(3)arsenic and fluoride in groundwater originate principally from natural and anthropogenic sources;(4)the human health risk assessments reveal that long-term intake of groundwater with high arsenic and fluoride concentrations pose cancer or non-cancer risks,which are more serious to kids compared to adults.This study provides a theoretical basis for the prevention and treatment of groundwater with high arsenic and fluoride concentrations in loess areas.

Characteristics of root pullout resistance of Caragana korshinskii Kom.in the loess area of northeastern Qinghai-Tibet Plateau,China

Roots exert pullout resistance under pullout force,allowing plants to resist uprooting.However,the pullout resistance characteristics of taproot-type shrub species of different ages remain unclear.In this study,in order to improve our knowledge of pullout resistance characteristics of taproot systems of shrub species,we selected the shrub species Caragana korshinskii Kom.in different growth periods as the research plant and conducted in situ root pullout test.The relationships among the maximum pullout resistance,peak root displacement,shrub growth period,and aboveground growth indices(plant height and plant crown breadth)were analyzed,as well as the mechanical process of uprooting.Pullout resistance of 4-15 year-old C.korshinskii ranged from 2.49(±0.25)to 14.71(±4.96)kN,and the peak displacement ranged from 11.77(±8.61)to 26.50(±16.09)cm.The maximum pullout resistance and the peak displacement of roots increased as a power function(R^(2)=0.9038)and a linear function(R^(2)=0.8242)with increasing age,respectively.The maximum pullout resistance and the peak displacement increased with increasing plant height;however,this relationship was not significant.The maximum pullout resistance increased exponentially(R^(2)=0.5522)as the crown breadth increased.There was no significant relationship between the peak displacement and crown breadth.The pullout resistance and displacement curve were divided into three stages:the initial nonlinear growth,linear growth,and nonlinear stages.Two modes of failure of a single root occurred when the roots were subjected to vertical loading forces:the synchronous breakage mode and the periderm preferential breakage mode.These findings provide a foundation for further investigation of the soil reinforcement and slope protection mechanisms of this shrub species in the loess area of northeastern Qinghai-Tibet Plateau,China.

Study on Function of Vegetation's Preventing Soil Erosion in Small Watershed of the Loess Area

This paper analyzes the function of preventing soil erosion of the different woodlands according to a long-term fixed-position observation, and points out that the steep slope plantation of uncontrolled measures for soil and water conservation is apt to produce sediment Forestland has very strong effect in soil and water conservation when the biomass of arbor in the hillslope is over 1 4.51t/ha. Through analyzing the function of soil and water conservation about forestland (arbor, bush and the mixed woo...

Selection of Indigenous Plants in Roads in Northwestern Loess Plateau Area

[Objective] The aim was to study on resource utilization of indigenous plants in roads in order to solve resource shortage of indigenous plant in bioengi- neering. [Method] Based on northwestern loess plateau area, we conducted research on selection of indigenous plants and survey on the species which could live in adverse condition, mainly by surveying, with frequent tests as a supplement, to make a comprehensive observation and evaluation on plant combinations which are to be extensively applied. [Result] The research indicated that in central dividing strips, four arbors, including Platycladus orientalis （Linn.）Franco, Sabina chinensis, Sabinachinen- sis（Linn.）Ant., and Ulmus purnila L., and nine frutices, including Lycium chinense, Tamarix austromongolica, Rosa xanthina Lindl., Forsythia suspense, Atriplex canescens, Amygdalus triloba, Hippophae rharnnoides Linn., Arnorpha fruticosa L., and Syzygium aromaticum could be planted. In addition, Gleditsia sinensis Lain, Robinia pseudoacacia L, Elaeagnus angustifolia L., Rhus typhina, Salix babylonica, Salixmatsudana and Fraxinus chinensis, tall and strong, are suitable to be planted as border trees, presenting a good vision. Frutices, limited by height, are usually with more branches, which will provide a good landscape if grown with tall plants. Prunus dacidiana and Ulmus pumila L., prone to be damaged by insects, should be planted with other species to stop the infestation in space. [Conclusion] The research laid foundation for selection of indigenous plants in roads, providing references for resource shortage of indigenous plant for bioengineedng.

Effects of loading rate on root pullout performance of two plants in the eastern Loess Plateau,China

Root pullout performance of plants is an important mechanical basis for soil reinforcement by plant roots in the semi-arid areas.Studies have shown that it is affected by plant factors(species,ages,root geometry,etc.)and soil factors(soil types,soil moisture,soil bulk densities,etc.).However,the effects of loading rates on root pullout performance are not well studied.To explore the mechanical interactions under different loading rates,we conducted pullout tests on Medicago sativa L.and Hippophae rhamnoides L.roots under five loading rates,i.e.,5,50,100,150,and 200 mm/min.In addition,tensile tests were conducted on the roots in diameters of 0.5-2.0 mm to compare the relationship between root tensile properties and root pullout properties.Results showed that two root failure modes,slippage and breakage,were observed during root pullout tests.All M.sativa roots were pulled out,while 72.2%of H.rhamnoides roots were broken.The maximum fracture diameter and fracture root length of H.rhamnoides were 1.22 mm and 7.44 cm under 100 mm/min loading rate,respectively.Root displacement values were 4.63%(±0.43%)and 8.91%(±0.52%)of the total root length for M.sativa and H.rhamnoides,respectively.The values of maximum pullout force were 14.6(±0.7)and 17.7(±1.8)N under 100 mm/min for M.sativa and H.rhamnoides,respectively.Values of the maximum pullout strength for M.sativa and H.rhamnoides were 38.38(±5.48)MPa under 150 mm/min and 12.47(±1.43)MPa under 100 mm/min,respectively.Root-soil friction coefficient under 100 mm/min was significantly larger than those under other loading rates for both the two species.Values of the maximum root pullout energy for M.sativa and H.rhamnoides were 87.83(±21.55)mm•N under 100 mm/min and 173.53(±38.53)mm•N under 200 mm/min,respectively.Root pullout force was significantly related to root diameter(P<0.01).Peak root pullout force was significantly affected by loading rates when the effect of root diameter was included(P<0.01),and vice versa.Except for the failure mode and peak pullout force,other pullout parameters,including root pullout strength,root displacement,root-soil friction coefficient,and root pullout energy were not significantly affected by loading rates(P>0.05).Root pullout strength was greater than root tensile strength for the two species.The results suggested that there was no need to deliberately control loading rate in root pullout tests in the semi-arid soil,and root pullout force and pullout strength could be better parameters for root reinforcement model compared with root tensile strength as root pullout force and pullout strength could more realistically reflect the working state of roots in the semi-arid soil.

Effect of Vegetation and Precipitation upon Runoff and Sediment Production on Slope Lands of the Loess Area in China

According to fixed-position data for 1992-2003 from 16 runoff plots of Caijiachuan watershed which lie in Jixian County, Shanxi Province, in the loess area, this paper studied the relationship between vegetation and runoff and sedimentproduction on slope lands. The results showed as follows: 1) Runoffand sediment production in Robinia pseudoacacia forestand Pinus tabulaeformis forest had a high correlation with precipitation amount and rainfall intensity, but the correlation decreased gradually with the increase of canopy density; 2) The secondary forest had better function of soil and water conservation than artificial R. pseudoacacia forest, and runoff and sedimentproduction in the former in an individual rain event was 65%-82% and 23%-92% lower than thosein the latter, respectively;3) The difference ofrunoff and sediment production in several land uses was very distinct. Runoff and sediment production in Ostryopsisdavidiana forest and the secondary forest were the least; runoff and sediment production in artificial R. pseudoacacia forest and P. tabulaeformis forest were 5-fold as much as those in O. davidiana forest. Besides, runoff and sediment production in mixed stand of apple trees and cropswere 16.14-fold and 2.96-fold higher than that in O. davidiana forest, respectively, but theamount decreased obviously after high-standard soil preparation for theformer;4) Based on gray correlation analysis of variousfactorsaffecting runoffand sedimentproduction on slope lands, it can be seen that stand canopy density and herb and litter biomass werethe most significant ones, whosegray correlation valuesall exceeded 0.6. Therefore, mixed forest with multi-layer stand structure and shrub forest should be developed in vegetation reconstruction of the loess area, which help to increase coverage and litter thicknessto cut down the runoffand sediment production dramatically on slope lands.

The carbon isotope composition of C3 herbaceous plants in loess area of northern China

13C of 367 C3 herbaceous plants was measured in loess area in northern China. Their δ13C values vary between ?21.7%. and ?30.0%., with a mean of ?26.7%.. In the center of Loess Plateau (semimoist area) with annual precipitation of 400–600 mm, the δ13 C values of C3 herbaceous plants range from ?24.4%. to ?28.5%., with a mean of ?27.5%.. In the west of Loess Plateau (semiarid and arid area) with annual precipitation less than 400 mm, they range between ?21.7%. and ?30.0%., with a mean of ?26.2%.. Annual precipitation is the main factor that makes δ13C values of C3 herbaceous plants in the west greater than those in the central Loess Plateau. The composition of δ13C in C3 plants increases with deceasing annual precipitation, and the mean change is ?49%./100 mm.

Carbon isotope ratios of C_(4) plants in loess areas of North China

Carbon isotope ratios (δ^(13)C) of 89 C_4 plant samples were determined fromthe loess area in North China. δ^(13)C values vary between -10.5per thousand and -14.6per thousandwith a mean of -12.6per thousand. Along a precipitation gradient from the semi-moist area to thesemiarid area, then to the arid area, the δ^(13)C values of C_4 plants show a slight decreasingtrend. The δ^(13)C values of C_4 plants in the dry season are found lower than those in the wetseason. These trends are opposite to those observed for C_3 species.

Mechanism of formation of sliding ground fissure in loess hilly areas caused by underground mining

Based on a shallow-buried coal seam covered with thick loose layers in hilly loess areas of western China,we developed a mechanical model for a mining slope with slope stability analysis, and studied the mechanism of formation and development of a sliding ground fissure by the circular sliding slice method.Moreover, we established a prediction model of a sliding fissure based on a mechanical mechanism,and verified its reliability on face 52,304, an engineering example, situated at Daliuta coal mine of Shendong mining area in western China. The results show that the stress state of a mining slope is changed by its gravity and additional stress from the shallow-buried coal seam and gully terrain. The mining slope is found to be most unstable when the ratio of the down-sliding to anti-sliding force is the maximum, causing local fractures and sliding fissures. The predicted angles for the sliding fissure of face 52,304 on both sides of the slope are found to be 64.2° and 82.4°, which are in agreement with the experimental data.

Relationship Between Agriculture and Ecological Deterioration,Restoration and Reconstruction in Loess Plateau Areas of Northwest China

A comprehensive analysis was conducted on the current situation as well as historic succession processor agriculture and ecological conditions in Northwest China, in particular in the Loess Plateau, by means of a inter-disciplinary approach of ecology, agro-geohistory, and agronomy. It was concluded that the fundamental causes responsible for the ecological deterioration, signed by the poor agro-productivity and serious soil erosion, had been the extensive cropping system by ever-increasing reclamation on semi-drought slope land, where initiated a natural vegetation of brushy grasses with sparse trees, thus suitable only for animal husbandry. Based on an identification of specific actual status of China, several countermeasures of correctly dealing with the relationship between agricultural development and the ecological restoration and reconstruction were proposed, including to get breakthrough first in the transection area by means of the rational use of resources and the raising of agro-system productivity, to promoting 'water conservancy-type ecological agriculture' through the radical shift of traditional production pattern, and the adoption of a policy of proper degree of grain self-reliance, as well as to construct livestock industry base in Northwest China.

Impacts of Sloping Land Conversion Program on the vegetation in loess hilly and gully area of northern Shaanxi

Aiming at alleviating the serious soil erosion, the Chinese government initiated the Sloping Land Conversion Program （SLCP） in 1999. Now; after 8 years of project implementation, the ecological recovery effects of the SLCP have become the hot issue of academic circle. This paper; raking the loess hill and gully area of northern Shaanxi as an example, presents a methodology for assessing the vegetation restoration effect of SLCP with normalized difference vegetation index （NDVI）. The key components include calculation of the Growing Season NDVI （GSNDVI）, and estimation of the NVDI change induced by climate and SLCP, respectively. Based on the method, the NDVI change between 2000 and 2006 was obtained using the GSNDVI that excluded the noise from snow and ice. After the part of total NDVI change caused to： climate variation was estimated using empiric formulae, we obtained the part induced by human factors, i.e. the SLCP The human induced part of ND VI change was considered as an approximation indicating the effect of the SLCP on the vegetation. Finally, we analyzed the ND VI change characters of the whole study area, different slope lands and different land use types by spatial statistics method. Results show that the vegetation condition is significantly improved by the SLCP, particularly land types that directly involved in the SLCP, such as steeply slope farmlands, degraded grasslands, etc.

Erosion environment in the sediment-rich area on the Loess Plateau

Based on the investigation and analysis of characteristics of precipitation, natural environment, socio-economic factors and soil erosion, this paper indicates that the precipitation is the main driving force for the soil erosion in the sediment-rich area, its variability determines the characteristics of soil and water loss; the natural conditions such as the drainage systems, geological and topographic features, the composition of soil and land surface materials, vegetation and climate determine the seriousness of soil and water loss; irrational socio-economic activities of human beings usually accelerated soil and water loss; meanwhile, the low preservation rate and inferiority of soil and water conservation measures made it impossible to make rapid progress on soil and water loss control. Furthermore, the characteristics of erosion environment endowed this area with more sediment that is the main reason for the flooding disasters by the Yellow River. Therefore, more emphasis should be placed on the enhancement of soil and water conservation. The soil loss prediction models will provide scientific basis for the planning of soil and water conservation, the designing of soil and water conservation measures and the valuation of effects of soil and water loss control. According to the analysis of the previous studies on soil loss prediction, and the water-sediment variation features, it is thought that study on soil loss prediction under various rainfall conditions and soil-water conservation measures should be carried out.

Combining gradual and abrupt analysis to detect variation of vegetation greenness on the loess areas of China

The annual peak growth and trend shift of vegetation are critical in characterizing the carbon sequestration capacity of ecosystems.As the well-known area with the fastest vegetation growth in the world,the Loess Plateau(LP)lands find an enhanced greening trend in the annual and growing-season.However,the spatiotemporal dynamics of vegetation peak growth and breakpoints characteristics on time series still needs to be explored.Here,we performed tendency analysis to characterize recent variations in annual peak vegetation growth through a satellite-derived vegetation index(NDVI_(max),Maximum Normalized Difference Vegetation Index)and then applied breakpoint analysis to capture abrupt points on the time series.The results demonstrated that the vegetation peak trend had been significantly increasing,with a growth rate at 0.68×10^(-2)·a^(-1) during 2001-2018,and most pixels(70.81%)have a positive linear greening trend over the entire LP.In addition,about 83%of the breakpoint type on the monthly NDVI time series is a monotonic increase at the pixel level,and most pixels(57%)have detected breakpoints after 2010.Our results also showed that the growth rate accelerates in the northwest and decelerates in the southeast after the breakpoint.This study indicates that combining abrupt analysis with gradual analysis can describe vegetation dynamics more effectively and comprehensively.The findings highlighted the importance of breakpoint analysis for monitor timing and shift using time series satellite data at a regional scale,which may help stakeholders to make reasonable and effective ecosystem management policies.

Soil erosion types in the loess hill and gully area of China

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SOC Vertical Distribution Pattern of Economic Plants in the Loess Gully Areas of China

Three economic plants from the loess gully areas in China to explore the changing vertical distribution characteristics of soil organic carbon.The results showed that:(1) with the increase of depth,the average SOC content of economic plants decreased from 13.98 to 1.39 g/kg on the 0-100 cm soil profile,in the form of a power function;(2) the constructed depth spatial distribution models for different plants could help accurately assess the spatial distribution pattern of soil organic carbon;(3) compared with traditional agricultural planting,the carbon sink function for walnut and grape at a soil depth of 100 cm increased by 92.8±8.98 t/hm^(2) and 45.7±7.7 t/hm^(2),respectively.The adjustment of agricultural planting structure increases the content of soil organic carbon,and economic plants are of great significance to enhance the carbon sink function of the agricultural ecosystem in the loess gully area.

富水沟谷区浅埋煤层导水裂隙演化特征

富水沟谷区域下浅埋煤层赋存条件特殊,采场上覆岩层导水裂隙发育演化特征复杂。为了揭示沟谷区浅埋煤层在回采扰动作用下覆岩裂隙演化规律,以朱家峁煤矿1305-2工作面过沟谷区回采阶段为工程背景,采用理论分析、物理相似模拟、数值模拟与现场效果验证的方法,建立了覆岩裂隙−渗流场概念模型,开展了覆岩结构发育与微震能量演化研究,分析了覆岩变形与塑性破坏分布特征,提出了针对沟谷区下浅埋煤层导水裂隙防治措施,并应用于现场工程实践。结果表明:开采扰动下裂隙−渗流场模型呈“梯台”结构,并依次划分为初渗区域、稳渗区域、紊渗区域3个区域;将所研究矿井的工况数据代入模型结构,计算出各个渗透区域范围,并根据计算结果对矿井的稳渗区域采取注浆措施。工作面回采至沟谷区段,覆岩裂隙域形态呈现“拱形-梯形-复合梯形”的扩展演化特征,裂隙纵向发育高度达到163 m,并与沟谷区地表贯通。随工作面推进,地表裂隙依次经历“滑移-挤压-撕裂”过程;沟谷区域位移云图呈现出滞后开采“高位梯形”破断形态,在沟底处下沉位移最大,达3.47 m。针对开采导致的裂隙大范围扩展贯通,提出在地面进行采动裂缝注浆处理,在工作面上覆岩层进行注浆封堵,实现过沟谷区开采“井上−井下”联合防治,保证安全开采。该研究结果可为浅埋煤层的过沟谷区开采、采动裂隙防治及富水区“保水采煤”提供新的科学依据。

我国黄土高原地区地震动衰减关系研究的若干进展

地震动的衰减关系是指地震动随震级、距离和场地条件等变化的经验关系,近年来在我国亦被称为地震动预测方程,是估计地震动及其影响场的主要方法之一,在地震区划和重大工程场地地震安全性评价中被广泛应用。黄土是一种特殊土,在我国广泛分布。我国黄土高原地区地质构造复杂,新构造活动强烈,中强地震频发,地震动的衰减关系有其特殊性,总结我国黄土高原地区地震动衰减关系的研究成果对促进黄土高原地区抗震研究有重要意义。在简要介绍国内外地震动衰减关系研究的基础上,全面系统地总结我国学者在黄土高原地区的地震烈度衰减关系,基岩和土层场地地震动峰值加速度、峰值速度、峰值位移以及反应谱衰减关系方面的研究成果;评述和讨论在黄土覆盖地区地震动衰减研究领域存在的问题和今后的研究方向。文章的研究工作对从事黄土高原地区地震工程研究的科技人员有重要参考价值。

湿陷性黄土区输水隧洞盾构施工风险评估

为了提高针对湿陷性黄土区输水隧洞盾构法施工安全评估的可靠性,从人员管理、机械材料、施工技术、施工环境4个方面构建较为完善的施工安全风险评估指标体系;利用灰色-DEMATEL方法对中心度进行处理得到风险指标权重;以风险发生概率和风险损失程度两个维度为基础构建二维云评估模型,其中发生概率由主、客观方法相结合来确定,损失程度通过改进雷达图法从人员伤亡、经济损失、工期延误、功能缺陷和环境影响5个方面来综合确定。将该评估模型运用到引汉济渭工程X输水隧洞盾构法施工项目的安全评估中。结果表明:该项目施工风险评估等级为Ⅱ级,施工安全风险程度较小,评价结果符合工程实际,验证了该评估模型的可行性和有效性。研究成果可为湿陷性黄土区类似输水隧洞盾构法施工安全风险评估提供借鉴和参考。

宁夏黄土区稀疏带状山杏人工林土壤湿度动态与影响因素

【目的】以宁夏南部黄土丘陵区带状山杏人工林为例,揭示林带内与带间的不同深度处土壤湿度的时空变化及其关键环境影响因素,为半干旱区林草植被科学管理及雨水资源高效利用提供依据。【方法】2020—2022年,在宁夏彭阳县山杏人工林带内和带间各布设1套200 cm测深的智墒传感器,分层逐时监测土壤体积含水量和土壤温度变化,同时布设1台气象站连续监测近地面降水、气温、空气湿度等气象条件,采用相关分析探究土壤湿度对前1日土壤湿度、土壤温度和气象因子的响应规律。【结果】2020年和2021年为平水年,降水量分别为467.4和440.8 mm;2022年为枯水年,降水量为354.8 mm;土壤体积含水量平均值为平水年(2021年,17.0%)显著高于枯水年(2022年,14.3%)。土壤体积含水量随土层加深呈近线性增加,其斜率表现为林带间高于林带内,平水年高于枯水年。在0~120 cm土层的土壤体积含水量为林带内(15.3%)高于林带间(14.0%),但在120~200 cm土层为林带间(17.6%)高于林带内(16.8%)。在0~60 cm土层的土壤体积含水量变异系数为林带间(42.9%)高于林带内(37.8%),但在60~200 cm土层为林带内(23.2%)高于林带间(19.1%)。土壤湿度变化的季节格局为:相对稳定期(3—4月)、耗损期(5—8月)、恢复期(9—11月)和衰退期(12月—次年2月),最大值多出现在4月,最小值出现在8月(平水年)和12月(枯水年);土壤湿度变化的垂直空间格局为:速变层(0~50 cm)、活跃层(50~90 cm)、次活跃层(90~170 cm)、相对稳定层(170~200 cm)。相关分析发现,土壤湿度日变化相关性最强的环境因子为正相关的前1日土壤湿度和负相关的土壤温度,月变化相关性最强的环境因子为负相关的土壤温度。【结论】宁夏黄土区稀疏带状山杏人工林林带内和林带间土壤湿度在季节和剖面上均表现出较大波动,枯水年比平水年波动的层次更深。综合分析发现前1日土壤湿度、土壤温度、气象因子均是影响枯水年和平水年日及月尺度各剖面层次土壤湿度变化的要素。其中,前1日土壤湿度和土壤温度为主要影响因子;在0~120 cm土层内的土壤湿度为林带内高于林带间。本研究结果对宁夏半干旱黄土区水平沟整地后退化植被科学恢复及土壤水分高效利用有很好的指导意义。

黄土区煤矸石排矸场重金属污染风险分析及评价

为了探究黄土区煤矸石长期堆存产生的重金属污染问题,以宁夏王洼煤矿排矸场煤矸石和土壤为研究对象,分析排矸场煤矸石和土壤的理化特性,测定煤矸石和底层土壤的重金属总量和有效态含量,并通过潜在生态风险指数法评估煤矸石堆积过程中存在的生态风险,明确底层土壤中潜在危害性突出的重金属元素。结果表明:(1)煤矸石和底层土壤均呈碱性,煤矸石堆底层10cm和20cm深度的土壤全盐量大于1.5g/kg,呈轻度盐化水平,煤矸石的堆存对接触土壤层的盐分累积有一定的贡献。(2)煤矸石底层土壤中Cr、Cu、Pb、Ni、Zn、Cd、As和Hg这8种重金属元素总量平均值低于宁夏土壤背景值。煤矸石中除As元素外7种重金属总量均高于底层土壤、对照点黄土和宁夏土壤背景值,在底层土壤中Cr、Cu、Pb、Ni和Zn这5种元素有效态含量均高于对照点黄土。(3)基于底层土壤中8种重金属元素总量评价,单元素潜在生态风险指数(E_(r)^(i))均低于40,综合潜在生态风险指数(RI)为85.83<150,重金属元素生态风险等级均为Ⅰ级低生态危害水平。因此,宁夏王洼煤矿排矸场煤矸石的露天堆存对底层土壤重金属元素含量产生累积效应,但重金属生态风险等级为轻微水平,其中Hg和Cd元素是主要的生态风险贡献因子。研究结果可以为半干旱黄土丘陵区煤矿固体废物安全堆存和环境生态修复提供理论指导。