宁夏沙湖几种主要荒漠植物成丛性分析

该文对宁夏沙湖地区几种主要荒漠植物成丛或聚集分布的空间特征进行了研究,提出应用成丛性表征植物丛聚水平,并以丛生植物的丛径或散生植物的聚集分布尺度范围衡量植物成丛性的发育程度。其中散生植物的聚集尺度以Riplay's K点格局法进行计算。结果表明,植物的丛聚水平与生境条件密切相关,强日照、干热风、空旷的立地、较高土壤含水率、强透水蓄水能力等生境条件会促进植物成丛性的发育,而蒸腾胁迫低、土壤供水能力较差的生境条件下植物成丛性发育较弱。荒漠植物通过成丛或聚集分布可以形成局部微生境,减少地上部分的水分胁迫,是植物在群落水平适应环境的重要途径。     

小波分析方法在心叶驼绒藜(Ceratoides ewersmanniana)空间格局尺度推绎研究中的应用

以古尔班通古特沙漠南缘莫索湾沙地选取相隔15km的两个200m×200m样地,以建群种心叶驼绒藜(Ceratoides ewersmanniana)及其生境地形为研究对象,应用小波分析定量研究了多尺度上空间格局的推绎以及空间异质性、空间格局依赖于尺度的变化关系。研究发现:小波分析尺度由1(5m)变化到4(20m)时,两个样地小尺度上的异质性和格局被合并到更大的尺度上,当小波分析的尺度大于等于5(25m)时,两个样地的格局变化平稳,对应地形(丘顶、丘坡、丘底)的基频稳定在110m左右,心叶驼绒藜的数量动态变化周期稳定在115～125m之间。结果表明:小波分析对信号整体特征的提取作用实现了小尺度上的信息到大尺度上的聚合。结合小波分析对信号突变点的检测,利用位置方差检验局部空间异质性程度,发现位置方差将大尺度上的格局分解到每个取样小样方,位置方差最大的地点对应的异质性也最强,实现了大尺度上的信息到小尺度上的分解。总结认为应用小波分析可以实现对空间格局的尺度推绎,具有对植被、环境的分布格局以及异质性有双重度量作用,由小波系数以及由其衍生的小波方差、位置方差来实现这种度量,图形表现直观,优越性明显。     

小波分析方法在心叶驼绒藜(Ceratoides ewersmanniana)空间格局尺度推绎研究中的应用

以古尔班通古特沙漠南缘莫索湾沙地选取相隔15km的两个200m×200m样地,以建群种心叶驼绒藜(Ceratoides ewersmanniana)及其生境地形为研究对象,应用小波分析定量研究了多尺度上空间格局的推绎以及空间异质性、空间格局依赖于尺度的变化关系。研究发现：小波分析尺度由1(5m)变化到4(20m)时,两个样地小尺度上的异质性和格局被合并到更大的尺度上,当小波分析的尺度大于等于5(25m)时,两个样地的格局变化平稳,对应地形（丘顶、丘坡、丘底）的基频稳定在110m左右,心叶驼绒藜的数量动态变化周期稳定在115～125m之间。结果表明：小波分析对信号整体特征的提取作用实现了小尺度上的信息到大尺度上的聚合。结合小波分析对信号突变点的检测,利用位置方差检验局部空间异质性程度,发现位置方差将大尺度上的格局分解到每个取样小样方,位置方差最大的地点对应的异质性也最强,实现了大尺度上的信息到小尺度上的分解。总结认为应用小波分析可以实现对空间格局的尺度推绎,具有对植被、环境的分布格局以及异质性有双重度量作用,由小波系数以及由其衍生的小波方差、位置方差来实现这种度量,图形表现直观,优越性明显。     

梭梭种群不同发育阶段的空间格局与关联性分析

运用点格局法中的Ripley'sK(r)函数的变形L(r)函数和g(r)函数,对古尔班通古特沙漠不同生境下不同发育阶段梭梭种群的空间格局及关联性进行了研究。结果表明:L(r)函数显示梭梭种群格局倾向于聚集分布,且集中分布在0-25m尺度范围内,而g(r)函数分析在小于3m的尺度上呈聚集分布,大于3m的尺度后波动较小,最大聚集尺度表现在0-10m范围内;梭梭在不同发育阶段过程中,L(r)和g(r)函数都显示由幼苗、幼树的聚集分布变为成年树的随机分布,甚至在某些尺度上变为均匀分布,同时幼苗幼树向成年树过渡过程中,梭梭的聚集强度呈逐渐减弱趋势。在关联性分析中,L(r)函数分析中正关联维持的尺度范围较g(r)函数大。L(r)函数分析幼苗与幼树、成年树在0-15m尺度内呈现正关联,g(r)函数在0-5m范围内表现为正关联,而幼树与成年树在0-10m尺度内多呈负关联,且两个大小级的形体大小差异越大,它们的正关联关系越弱,甚至表现为负关联或无关联。幼苗幼树的聚集分布和正关联是梭梭种子的传播和密度制约的一个平衡,对梭梭种群的生存和发展是有利的。另外,梭梭种群分布格局的强度在不同地形也存在差异,奎屯平地比五家渠的聚集强度和关联性大,缓坡差异较小,这说明地形对各种资源的再分配间接地影响了梭梭的格局。总体上看,同时应用L(r)和g(r)函数进行梭梭空间格局与关联性分析时结果不尽相同。L(r)函数的最大值可以反映典型的聚集尺度,而g(r)函数中出现的第1个最大值可以表示植株间典型距离。在小尺度下两种函数分析所得空间格局是一致的,而在大尺度上有较大差异。g(r)函数在小尺度范围内的分析结果更接近实际情况,有利于揭示出梭梭空间格局与生态过程有联系的"关键尺度",说明梭梭为了适应恶劣环境往往表现为聚集分布,这种聚集生长现象有利于个体的生存与繁衍。因此,联合使用L(r)函数和g(r)函数更有利于揭示植物个体间的关系。     

气候变化对6种荒漠植物分布的潜在影响

分析气候变化对植物分布的影响,对保护生物多样性具有重要意义。利用CART(分类和回归树)模型及A2和B2情景,分析了气候变化对短叶假木贼(Anabasis brevifolia)、裸果木(Gymnocarpos przewalskii)、梭梭(Haloxylon ammoden-dron)、膜果麻黄(Ephedra przewalskii)、驼绒藜(Ceratoides latens)和喀什膜果麻黄(Ephedra przewalskii var.kaschgarica)分布范围及空间格局的影响。结果表明:气候变化下,这些植物目前适宜分布范围减小;从新适宜及总适宜分布范围而言,短叶假木贼和梭梭从1991-2020年到2051-2080年时段增加,之后减小,其它植物从1991-2020年到2081-2100年时段减小;喀什膜果麻黄和驼绒藜适宜分布范围减小并破碎化,其它植物向目前适宜分布的西部、西北部(或青海西南部)、昆仑山、阿尔金山和祁连山区扩展;除驼绒藜和喀什膜果麻黄与年均气温变化具显著相关性外,其它植物分布范围与年均气温和降水量变化的相关性较弱(P0.05),除驼绒藜、喀什膜果麻黄和裸果木目前分布范围与年均气温和降水量变化的回归关系较强外,其它植物分布范围与年均气温和年降水量变化多元线性回归关系较弱。上述研究结果表明,气候变化下,这些植物空间分布格局改变,目前分布范围减少,新适宜及总适宜分布范围近期增加,随着气候变化程度的增强,又逐渐减小。     

昆仑山前山带植物群落调查及相似性初步研究

对塔克拉玛干沙漠南缘,昆仑山北坡前山带的荒漠植物群落进行调查.结果显示:(1)在调查区域内发现21种植物,参与建群种15种,其他6种为偶见种.21种植物分属于10科20属,其中菊科(Compositae)和藜科(Chenopodiaceae)植物13种;研究区5种植物群落的优势种分别为塔里木沙拐枣(Calligonum roborovskii)、琵琶柴(Reaumuria songarica)、河西苣(Hexinia polydichotoma)、蒿类植物(昆仑蒿Artemisia nanschanica+昆仑绢蒿Seriphidium korovinii)与驼绒藜(Ceratoides latens).(2)植物群落沿海拔高度变化地带性更替明显,低山砾质壤土母质上为塔里木沙拐枣和琵琶柴群落,集中分布范围分别为2 200～2 300 m和2 250～2 400 m,中部沙质土壤母质上为蒿类植物和河西苣群落,蒿类植物群落分布于海拔2 400～2 500 m,河西苣群落集中于2 500 m高大沙丘丘间低地;驼绒藜群落在砾质土壤和沙质土壤母质上均有分布,海拔范围在2 380～2 800 m.(3)群落结构简单,整体盖度小于10%,物种密度为4～13株(丛)/m2,灌木层优势种单一,密度很小(1.2株(丛)/m2),草本层冠幅水平低,盖度小(小于5%);群落间高度、盖度、密度存在不同程度差异,物种丰富度指数(dMA)和生物多样性指数(D、H′、Jsw、Jgi)差异并不明显,总体处于较低水平.(4)群落盖度、密度、高度和物种数随海拔高度变化趋势不同,生物多样性指数随着海拔高度增加呈增加趋势;群落相似性比较显示,低海拔地区植物群落间的相似性高于高海拔地区.     

柴达木盆地东部荒漠植物生态位特征

以柴达木盆地东部27个典型样地的植物群落为研究对象,通过生态位宽度和生态位重叠指数计算,分析该区13种优势植物在土壤含水量、容重、有机质、pH、全盐、全氮维上的生态位特征,以期为柴达木盆地植被恢复重建和荒漠系统生态保护提供理论参考。结果表明:①13种植物在6个土壤因子上平均生态位宽度从大到小依次是:驼绒藜、琵琶柴、芨芨草、芦苇、合头草、蒿叶猪毛菜、白刺、盐爪爪、小嵩草、麻黄、沙拐枣、柽柳和梭梭,其中,驼绒藜在土壤含水量、容重和有机质上占据最高值,琵琶柴在土壤pH、全盐、全氮维上占据最高值;②生态位宽度较大的物种在生态位重叠上并不占据最高重叠值,而是处于一个中游的位置;③驼绒藜和琵琶柴在生态位宽度和生态位重叠上均占相对高的位置,对群落的建群起重要作用;④78个种对在每一个土壤因子上的生态位重叠值0.3的占总对数的比例为76%,柴达木盆地东部植物总体生态位重叠偏低,竞争较小,群落处于一个相对稳定的状态。     

古尔班通古特沙漠固定沙丘上白梭梭和梭梭的空间分布及种间关联性

为了探讨沙漠中固沙灌木种群共存和演替机制, 本文基于古尔班通古特沙漠东南缘固定沙丘上白梭梭(Haloxylon persicum)和梭梭(H. ammodendron)种群的地理位置和生长发育阶段信息(幼株、营养株、生殖株和死株), 采用点格局分析方法(g(r)函数)及Monte-Carlo随机模拟检验和零模型选取的方法, 分析了固沙灌木白梭梭和梭梭种群不同生长发育阶段在0-20 m尺度内的空间分布格局及种间关联性。结果表明: (1)两个种群在研究尺度范围内呈聚集分布, 随着尺度的增大, 其聚集强度逐渐减弱; (2)两个种群整体上呈负关联关系, 尺度越大负关联关系越显著; (3)白梭梭种群生长发育阶段相差越大, 个体间正关联关系越显著; 梭梭种群生长发育阶段越接近, 个体间正关联关系越显著; (4)两个种群中龄级较大的个体(如营养株、生殖株和死株)会对对方种群中龄级较小的幼株产生一定的抑制作用; 同时, 随着两个种群中个体的成长, 双方受到的抑制作用逐渐减弱, 主要表现为正关联和无关联。总体而言, 古尔班通古特沙漠固定沙丘白梭梭和梭梭种群的分布格局整体上为聚集分布, 随龄级增加聚集性减弱, 受生境异质性和扩散限制的影响明显。种间关系多为负相关, 种内不同生长发育阶段之间均为正关联关系。     

气候变化对6种荒漠植物分布的潜在影响

分析气候变化对植物分布的影响,对保护生物多样性具有重要意义。利用CART（分类和回归树）模型及A2和B2情景,分析了气候变化对短叶假木贼（Anabasis brevifolia）、裸果木（Gymnocarpos przewalskii）、梭梭（Haloxylon ammoden-dron）、膜果麻黄（Ephedra przewalskii）、驼绒藜（Ceratoides latens）和喀什膜果麻黄（Ephedra przewalskii var.kaschgarica）分布范围及空间格局的影响。结果表明：气候变化下,这些植物目前适宜分布范围减小;从新适宜及总适宜分布范围而言,短叶假木贼和梭梭从1991-2020年到2051-2080年时段增加,之后减小,其它植物从1991-2020年到2081-2100年时段减小;喀什膜果麻黄和驼绒藜适宜分布范围减小并破碎化,其它植物向目前适宜分布的西部、西北部（或青海西南部）、昆仑山、阿尔金山和祁连山区扩展;除驼绒藜和喀什膜果麻黄与年均气温变化具显著相关性外,其它植物分布范围与年均气温和降水量变化的相关性较弱（P〉0.05）,除驼绒藜、喀什膜果麻黄和裸果木目前分布范围与年均气温和降水量变化的回归关系较强外,其它植物分布范围与年均气温和年降水量变化多元线性回归关系较弱。上述研究结果表明,气候变化下,这些植物空间分布格局改变,目前分布范围减少,新适宜及总适宜分布范围近期增加,随着气候变化程度的增强,又逐渐减小。     

基于零模型的宁夏荒漠草原优势种群点格局分析

植物种群空间分布格局是多种生态过程综合作用的结果。明确植物优势种群个体的空间分布格局与形成机制有助于认识种群生态适应对策与群落多样性维持机制。以宁夏荒漠草原优势种群蒙古冰草、短花针茅、牛枝子和牛心朴子为研究对象,采用完全空间随机零模型分析其种群空间分布格局特征,并通过异质泊松零模型与泊松聚块零模型探讨生境异质性、扩散限制等因子在其空间分布格局形成过程中的作用。结果显示:(1)完全空间随机零模型下,4个物种在4 m尺度范围内表现为聚集分布,随尺度增大,逐渐过渡到随机分布和均匀分布。(2)在排除生境异质性的异质泊松零模型下,蒙古冰草种群在整个研究尺度上表现为随机分布;牛枝子、短花针茅和牛心朴子种群仅分别在0—0.2、0.1—0.4 m与0—0.2 m尺度范围内发生偏离,表现为均匀分布与聚集分布,其他尺度均为随机分布。(3)在排除扩散限制的泊松聚块零模型下,所研究种群均表现为随机分布。综上,荒漠草原优势种群在小尺度范围内主要表现为聚集分布;生境异质性与扩散限制均是驱动其空间分布格局形成的重要因子,相对而言,小尺度空间范围内扩散限制的作用更为显著。     

Diet, residential origin, and pathology at Machu Picchu, Peru

Pathological conditions in human skeletal remains provide a wealth of information about archaeological populations, but many are limited in their interpretive significance by their nonspecific etiologies. This study analyzes three common pathological conditions known to manifest in infancy and childhood in the skeletal population from Machu Picchu, Peru (N = 74) with published carbon, nitrogen, oxygen, strontium, and lead isotopic data (Turner et al.: J Archaeol Sci 36 (2009) 317–332; Turner et al.: Chungara: Revista de Antropología Chilena 42 (2010) 515–524) to distinguish early‐life diet from residential origins as significantly associated with pathologies among the site's inhabitants. Analyses of variance indicate highly significant variation between enamel δ¹⁸O values, which serve as a rough proxy of local environment, and both cribra orbitalia (CO) and porotic hyperostosis (PH), generally understood to be markers of anemia. Results tentatively suggest that individuals manifesting these lesions may have lived closer to the arid coasts; however, no significant variation was found in parameters of diet (enamel δ¹³C_carbonate, dentin δ¹³C_collagen, dentin δ¹⁵N) by either CO or PH, suggesting that the primary factors causing anemia may have been more significantly related to residential origin rather than diet. Linear enamel hypoplasia (LEH) frequency significantly varied by both dietary and residential parameters, supporting models of LEH formation from a synergy of dietary and environmental factors. These results support previous research on the etiology of PH in the Andes; they also represent a useful approach to refining site‐specific interpretations of pathological conditions in archaeological populations, and exploring etiological variation between populations. Am J Phys Anthropol, 2012. © 2012 Wiley Periodicals, Inc.     

Relocated interglacial lacustrine sediments from an esker at Snickarekullen, S.W. Sweden

Lumps of diatom-rich, laminated sediments were discovered redeposited and interbedded in a Late Weichselian delta sequence in a small glaciofluvial esker at Snickarekullen, south-western Sweden. Radiocarbon dating of the sediments gave an infinite age (45 000 B.P.). The composition and sediment structure of the lumps were studied in epoxy-impregnated thin sections using SEM and EDS. Quantitative and qualitative diatom analyses of the sediments were carried out, as well as pollen and macrofossils analyses. The biostratigraphy is compared with that from Holsteinian interglacial sites in surrounding countries, the evidence for which is briefly reviewed. It is concluded that the sediments were deposited in the central part of a lake probably during different parts of the Holsteinian interglacial. The water body changed from a rather shallow lake with a high pH to a considerably deeper, oligotrophic lake with neutral to slightly acidic water during the sedimentation period. The local and regional vegetation developed from an open pine-birch forest into a much more closed vegetation of pine, spruce, larch, alder and hornbeam.     

Pollen and phytolith evidence for rice cultivation during the Neolithic at Longqiuzhuang, eastern Jianghuai, China

Phytolith and pollen analyses were carried out at the archaeological site at Longqiuzhuang in Gaoyou, Jiangsu, southern China. The results indicate that the key morphological phytolith types associated with cultivated rice (Oryza) are common in the Neolithic cultural layers at this site. The evidence strongly suggests that cultivated rice (mainlyO. japonica) was grown locally during the Neolithic. The archaeopalynological record provides information about the impact of human activity and, in particular, farming on the natural vegetation. The evergreen and deciduous broad-leaved forest was substantially altered, and herbaceous taxa, including ruderals, expanded. Based on the results from the phytolith and pollen analyses, two distinct phases of human activity have been recognized, namely (1) phase A (7000-6300 B.P., i.e. early Neolithic) a warm and humid period when arable farming, including rice cultivation, was pursued but the variation in the size of the carbonized rice grains was low, and (2) phase B (6300-5500 B.P., late Neolithic age), a period of relatively cold and/or arid climate when cultivated rice was of major importance and was morphologically similar to present-day rice. Environment, and in particular climate change in the late Neolithic, were important factors affecting the development of rice as a cultivated crop. It was mainly during this period that artificial selection favoured the emergence of forms similar to those of today.     

Odontometric determination of sex at Mound 72, Cahokia

The mortuary context of Mound 72 at the Cahokia site is one of the most unusual ever described in prehistoric North America. Previous skeletal analyses suggested that four large mass graves within the mound contained only female skeletons. However, these findings were complicated by extremely poor bone preservation that limited the number of skeletal observations that could be made. Furthermore, most skeletons were aged in the 15–25 year range, a time when sexually dimorphic bony traits may still be developing. In this study, dental remains were used to examine sex in the four presumably all‐female mass graves in Mound 72. Additional sources of information, including the original field/laboratory notes and new sexing data based on modern standards, were gathered to fully evaluate the dental estimates. Initially, discriminant function analysis was performed on odontometrics using the original Mound 72 sex assignment. Inconsistent results indicated that some of the skeletons may have been misclassified in the original analyses. To overcome this issue, discriminant function equations were generated using a large pooled skeletal sample from two sites in close temporal and geographic proximity to Cahokia. Application of the equations to Mound 72 revealed that each of the four mass burial groups contained individuals classified as male. These assignments were checked against the skeletal remains and the original field/laboratory notes. Discussion centers on how the results affect previous archaeological interpretations as well as the methodological considerations associated with this study. Am J Phys Anthropol 151:408–419, 2013.© 2013 Wiley Periodicals, Inc.     

Phytosociological studies at malham tarn moss and fen,Yorkshire, England

Summary During a field course the vegetation of the extensive mire complex on the west side of Malham Tarn was examined. 84 relevés were collected, with 210 taxa in total. This data set has been ‘structured’ by classical phytosociological techniques. It is suggested that it approaches the maximum size of data-set which can be handled in this way, especially if the data are not all collected by one person. Ordination of the quadrats was carried out but gave little insight into the data despite the use of non-centred as well as centred principal components analysis. Numerical classification of the quadrats using minimumvariance cluster analysis was shown to produce a structure interpretable in ecological terms. A classification of the taxa was carried out by the same method and a ‘rearranged’ table was drawn up using the results of the two classifications. A relocation technique was applied at an appropriate cluster level but little was felt to be gained from this. The use of ‘two-way’ minimum-variance cluster analysis for the rapid production of re-arranged tables is recommended for large data-sets. In addition the vegetational units recognised in the data are described and discussed. The authors wish to thank Miss D. R. Clowes, Mr. P. Gladders, Mr. A. R. Hall, Mr. R. N. Lentell, and Mr. J. E. Young for assistance in the collection of the data, and Mrs. M. E. Pettit and Mrs. S. Peglar for assistance in the data processing.     

Reporter gene expression at single-cell level characterized with real-time RT-PCR, chemiluminescence, fluorescence, and electrochemical imaging

mRNA from single cells was quantified using real-time RT-PCR after recording the address and reporter protein activity with chemiluminescence, fluorescence, and electrochemical techniques, using luciferase, green fluorescent protein, and secreted alkaline phosphatase. mRNA copy number ranging from below 103 to 10⁷ in single cells showed a lognormal distribution for both externally introduced reporter genes and internally expressed genes. The fluctuation in the gene expression decreased with the increase of the number of cells picked but did not decrease with the increase of mRNA copy number per cell. We found that the correlation coefficients for mRNA and protein expression in logarithmic plot at single-cell level were much lower than 1.00.     

Reconstruction of the vegetation at A.D. 915 at Ohse-yachi Mire, northern Japan, from pollen, present-day vegetation and tephra data

The Towada-a (To-a) Tephra from A.D. 915 allowed reconstruction of the local and regional vegetation at and near Ohse-yachi Mire from pollen samples taken just below the tephra. In earlier studies the tephra was dated from ¹⁴C data, stratigraphy at archaeological sites and a historical record. Twelve cores along two perpendicular transects yielded pollen from modern and pre-tephra samples. The modern pollen data were compared with the modern vegetation, and used to interpret the pollen data from A.D. 915. Ericaceae, Drosera, Sanguisorba, other Rosaceae, and Sphagnum were concluded to be local elements. Ohse-yachi Mire was a wet Sphagnum bog in A.D. 915, with Sphagnum dominating the central part of the mire. The present stand of scrub was not yet established, but there was a stand of Pinus pumila scrub. The bog subsequently became drier and changed to the present-day mixed Moliniopsis-Sphagnum bog.     

Biological and spatial structure of an early classic period cemetery at Charco Redondo,Oaxaca

This article presents an analysis of biological and spatial patterning of an Early Classic (A.D. 250–500) Chatino cemetery at the archaeological site of Charco Redondo, located in the lower Río Verde Valley, Oaxaca, Mexico. The Early Classic was a time of political instability positioned between two phases of state‐level centralization within the coastal valley. The communal cemetery at Charco Redondo adds significantly to the inventory of excavated graves from this time period and provides novel data on mortuary practices during a critical phase in the development of state level polities in the region. Cluster analysis of mortuary data is combined with intracemetery biodistance approaches to reconstruct how the Charco Redondo cemetery was organized with respect to biological relationships. Cluster analysis of mortuary data identified three groupings of burials. Multidimensional scaling of Euclidean distances and Gower coefficients based on 45 odontometric and 13 dental morphological variables suggests a strong relationship between grave characteristics and locations and phenotypic variation. In other words, the cemetery at Charco Redondo appears biologically kin‐structured. The communal nature of the cemetery conflicts with the assumed “household” burial model for this time period. We propose the observed combination of features represents a transitional practice in which aspects of community, kin, and individual identity were signaled simultaneously within the funerary environment during a time of political transition in the Valley. This article highlights the utility of intracemetery biodistance analyses for examining dimensions of kinship, “house,” and community throughout Mesoamerica where overarching models often mask regional variability. Am J Phys Anthropol 152:217–229, 2013. © 2013 Wiley Periodicals, Inc.     

Assessment of Soil Arsenic,Chromium, Mercury,and Lead at an Agricultural Landscape Scale

Knowledge of arsenic and heavy metal concentrations and distributions is essential in the design of environmental regulatory strategies. The present study was undertaken as a preliminary survey on soil contamination in a representative agricultural area of southwestern China. The objectives were: (1) to characterize the variability of As, Cr, Hg, and Pb; (2) to assess the effect of land use (vegetable land and paddy fields) on these elements; and (3) to identify their natural or artificial origins. Samples from 119 sites were collected and analyzed in 2006. Land use map units were delineated at a scale of 1:2000 from field survey. Analysis of variance, correlation analysis, factor analysis, and a geographic information system were adopted to investigate the spatial distributions and sources of the elements. The average concentrations of the elements were 6.26 mg As kg^?1, 52.90 mg Cr kg^?1, 0.066 mg Hg kg^?1, and 33.13 mg Pb kg^?1. Mean contents of Hg and Pb were markedly higher than their background levels indicating the risk of mercury and lead pollution (p < 0.05). Mean concentration of Pb was significantly higher in paddy fields than vegetable land (p < 0.05). The variability of Cr was associated with topography, while Hg was controlled by human activities and atmospheric deposition. The high heterogeneities of As and Pb were mainly ascribed to land use and the consequent agricultural management practices. The results of the study will assist planners and policymakers in developing effective policies to protect soils from long-term arsenic and heavy metal accumulation.     

Experimental charge density of sucrose at 20K: bond topological, atomic, and intermolecular quantitative properties

The charge density of sucrose was determined from a high-resolution X-ray data set measured at 20 K. The density distribution so obtained was analyzed quantitatively by application of Bader’s atoms in molecules (AIM) formalism, and a comparison was made with corresponding results from a B3LYP (6-311++G(3df,3pd)) calculation at the experimental geometry. Bond topological and atomic properties (volumes and charges) were derived and compared. The influence of hydrogen bonding on the experimental charge density was also studied qualitatively and quantitatively by means of topological properties. In terms of the hydrogen-bond energies, a grouping into strong, medium and very weak hydrogen bonds was made, the latter of which were involved in a bifurcated bond.