Temporal and Spatial Variations of Inorganic Nitrogen Levels in Surface and Groundwater Around Hanoi,Vietnam

Abstract

Pollution of surface and groundwater by inorganic nitrogen (N) was assessed in farm villages of northern Vietnam. The pH and ammonium‐N and nitrate‐N concentrations were monitored at three communes near Ha Noi in the Red River Delta in March and September 2003, following monitoring in October 2002. In each monitoring time, ammonium‐N concentrations exceeded the Vietnamese water standards applicable to surface and groundwater, whereas the nitrate‐N concentrations were relatively low and below the corresponding standards. Neither spatial nor temporal variation was found in the ammonium‐N and nitrate‐N concentrations of the surface water. A temporal increase in the ammonium‐N concentration was statistically confirmed in the groundwater. Intensively applied fertilizer‐N and disposed animal/human wastes were thought to be sources of ammonium‐N. Ammonium‐N originating from those sources was seen to accumulate steadily in the groundwater through percolation from the surface water and surrounding land. A spatial variation of the nitrate‐N concentration was observed in the groundwater. The nitrate‐N concentration in the groundwater was particularly low in communes located in lowland areas with alluvial soils. The suppression of nitrification or promotion of denitrification was considered to be responsible for the low nitrate‐N concentration. A spatial variation was also found in the groundwater pH. Therefore, variation of the pH may be linked to variation of the nitrate‐N concentration in the groundwater.     

Spatial and temporal variations in resistance of loess-derived soils to ephemeral gully erosion

Planners would like a simple means of describing spatial and temporal variations in soil erodibility accurately. We have done a series of concentrated flow detachment experiments to investigate the feasibility. Four different soil horizons, typical of loess‐derived soils in Belgium, were sampled seven times during one year, so that a representative range of initial soil moisture contents was obtained. Undisturbed soil samples were subjected to five different combinations of slope gradient and concentrated flow discharge. Results showed that for a given soil horizon, variations in detachment rate could be related well to temporal variations in initial soil moisture content. For a given initial soil moisture content the ploughed topsoil horizon (A_p) and the underlying clay‐enriched horizon (B_t) had only one fifth of the erodibility of the loess horizon whether decalcified (C₁) or still calcareous (C₂). Combining knowledge on spatial distribution of soil profiles and initial soil moisture content allowed us to explain observed spatial and temporal variations in resistance to ephemeral gully erosion for soils in loess. Also, differences in ephemeral gully morphology (cross‐sections) could be explained from differences in initial soil moisture content and soil horizon. In the short term these results have important implications for spatial and temporal variations in erosion, while in the medium or long term information on spatial distribution of soil profiles is crucial when predicting the volumes and patterns of (ephemeral gully) erosion. Finally, the importance of combining the effect of water and tillage erosion with respect to soil profile evolution and consequent erosion risk is stressed.     

Analytical Studies on Lead Pollution in Roadside Soil Samples of Raipur and Bhilai,Chhattisgarh State,India

Abstract

Although lead in gasoline represents only 2.2% of total global lead use, this fuel remains by far the single largest source of this heavy metal in urban areas. In developing countries like India approximately 90% of all lead emissions into the atmosphere are due to the use of leaded gasoline. In many countries in Southeast Asia, unleaded gasoline is scarce, and the maximum allowed lead content might reach or exceed 0.8 ppm per liter. Emissions from the metallurgical operations and the waste incineration are also responsible for the rising levels of lead in the environment. Battery recycling, lead‐glazed pottery, and lead pigments industries are other sources of lead in the environment. In the present work, lead pollution in soil samples from Raipur (capital city) and Bhilai, Chhattisgarh State, India, has been investigated. The lead concentration in the surface soil of Raipur and Bhilai was found in the range of 7.2–84.0 and 9.5–79.7 ppm, respectively. The seasonal and temporal variations in the concentration of metal, its distribution pattern, and trend are discussed as well as the mobility, deposition, and sources of lead in the area. The enrichment factor of lead in the urban soil was found to be very high, depending on the nature of sources.     

Inverse models to analyze the spatiotemporal variations of chemical weathering fluxes in a granito-gneissic watershed: Mule Hole, South India

Water-rock reactions are driven by the influx of water, which are out of equilibrium with the mineral assemblage in the rock. Here a mass balance approach is adopted to quantify these reactions. Based on field experiments carried out in a granito-gneissic small experimental watershed (SEW), Mule Hole SEW (~ 4.5 km²), quartz, oligoclase, sericite, epidote and chlorite are identified as the basic primary minerals while kaolinite, goethite and smectite are identified as the secondary minerals. Observed groundwater chemistry is used to determine the weathering rates, in terms of ‘Mass Transfer Coefficients’ (MTCs), of both primary and secondary minerals.Weathering rates for primary and secondary minerals are quantified in two steps. In the first step, top red soil is analyzed considering precipitation chemistry as initial phase and water chemistry of seepage flow as final phase. In the second step, minerals present in the saprolite layer are analyzed considering groundwater chemistry as the output phase. Weathering rates thus obtained are converted into weathering fluxes (Q_weathering) using the recharge quantity.Spatial variability in the mineralogy observed among the thirteen wells of Mule Hole SEW is observed to be reflected in the MTC results and thus in the weathering fluxes. Weathering rates of the minerals in this silicate system varied from few 10 μmol/L (in case of biotite) to 1000 s of micromoles per liter (calcite). Similarly, fluxes of biotite are observed to be least (7 ± 5 mol/ha/yr) while those of calcite are highest (1265 ± 791 mol/ha/yr). Further, the fluxes determined annually for all the minerals are observed to be within the bandwidth of the standard deviation of these fluxes. Variations in these annual fluxes are indicating the variations in the precipitation. Hence, the standard deviation indicated the temporal variations in the fluxes, which might be due to the variations in the annual rainfall. Thus, the methodology adopted defines an inverse way of determining weathering fluxes, which mainly contribute to the groundwater concentration.     

A field lysimeter study to evaluate herbicide transport in a wyoming irrigated pasture

Abstract

A field study was conducted to assess the fate and mobility of two commonly used herbicides, dicamba (3,6‐dichloro‐2‐methoxybenzoic acid), and picloram (4‐amino‐3,5,6, trichloro‐2 pyridinecarboxylic acid), in an irrigated pasture. The herbicides were applied at two application rates to four plots (two replicates) that contained soil‐water collectors. Herbicide concentrations as a function of depth and application rate were evaluated statistically to determine if replicate data could be combined. Results indicated dicamba concentration variations were low, suggesting the mean value of the replicate plots could be compared; however, picloram concentration variations were high, and the replicate plot data could not be combined. Half‐time values for herbicide disappearance (time required for herbicide concentration to diminish from its maximum to half maximum levels), calculated from the arithmetic mean of the logistic equations, were found to be useful in describing herbicide transport. Half‐time values were dependent upon application rate, collector depth, pesticide type, and plot location. Dicamba applied at the low application rate was detected at 15 and 30 cm depths only, and was not detected throughout the entire study period (467 days) at deeper depths. Significant differences occurred between plots receiving the high dicamba application rate, which was attributed to permeability differences that affected herbicide migration in the soil profile. Picloram half‐time values were also affected by soil organic carbon, which increased picloram adsorption. In general, differences in herbicide concentrations were observed within plots receiving the high picloram application rates, which was primarily attributed to spatial differences in hydraulic conductivity. Herbicide disappearance was most rapid at the shallow depth (e.g., 15 cm) within plots receiving lower herbicide application rates.     

土壤-地下水中微塑料迁移的影响因素及机制研究进展

微塑料在环境中广泛分布,世界范围内的农业土壤及地下水中都已发现微塑料污染,生态环境和人体健康受到严重威胁。研究土壤-地下水中微塑料迁移的影响因素及机制,对于准确评价其分布归趋及环境风险具有重要意义。该研究通过文献调研,对土壤-地下水环境中微塑料的来源、团聚及迁移研究进行梳理、归纳和总结,系统阐明了土壤-地下水中微塑料迁移的影响因素,剖析了影响微塑料迁移的机制,并对未来研究进行展望。土壤中微塑料的来源可分为原位型微塑料和外源输入型微塑料2种,地下水中的微塑料一般源自于土壤中微塑料的垂直迁移及地表-地下水微塑料交换。水体中微塑料的团聚受多种水环境因素的影响,其团聚程度与迁移能力密切相关,是迁移行为的基础和前提。土壤-地下水中影响微塑料迁移的因素可分为化学、物理、生物3类。水化学条件、介质成分、水流条件、介质物理条件、植物生长发育、小型动物及微生物的生命活动均会影响土壤-地下水中微塑料的迁移行为,且影响机制各不相同。目前,土壤-地下水中微塑料的迁移研究处于起步阶段,在进一步的研究中,野外尺度微塑料迁移、多元化微塑料迁移、微塑料特性对其迁移行为影响、微塑料迁移过程中的转化等研究值得重点关注。     

鲁西北黄河冲积平原盐渍化灌区地下水动态变化

区域土壤盐渍化状况研究是进行区域地下水资源合理开发和盐碱化土壤防治的依据。以山东省德州市齐河县为研究区,采用ENVI,GIS和统计学方法,分析研究区土壤盐渍化状况及地下水埋深的时空变化规律。研究表明：(1)研究区全境均有不同程度盐渍土分布,在整体空间分布上,盐渍化呈现出由东向西,由南向北,逐步减轻的趋势。(2)该区地下水位较高,埋深最浅的晏城镇(2005年年均埋深仅为0.76m),埋深最深的仁里集镇西高村(观测点2005年年均埋深达到了5.12m)。齐河县2000,2005和2009年3a地下水位埋深分布格局相似,埋深年际变化总体波动较小。分析该区丰水年(2005年)、枯水年(2009年)年内地下水位变化发现灌溉后地下水位普遍升高。(3)研究区在2000-2009年10a间地下水位空间变异明显,距离黄河越近,埋深越浅。黄河通过影响研究区的灌溉模式和地下水位埋深间接影响着当地次生盐渍化的发生。     

不同土地利用方式对贵州岩溶土壤微量重金属元素含量的影响

利用地统计学的方法,对贵州水城岩溶盆地复合土地利用方式下土壤微量重金属元素含量的时空变异进行了研究。结果表明:贵州水城盆地岩溶土壤微量重金属元素含量的变化与不同的土地利用方式时空上的变异有很好的一致性。盆地中工业区往往成为土壤微量重金属元素迁移富集的高值中心,而受人类活动影响较小的自然林区则基本保持了原始状况成为低值中心。因此合理进行土地利用对保护土壤和岩溶地下水免受污染具有重要的意义。     

Temporal variation in topsoil water repellency in two recently burnt eucalypt stands in north-central Portugal

The aim of this study is to improve our knowledge of the temporal and spatial variations of soil water repellency following wildfire, in particular for the eucalypt stands that now dominate the landscape of north-central Portugal.     

黄河三角洲地区浅层地下水与耕层土壤积盐空间分异规律定量分析

为研究黄河三角洲地区地下水作用条件下耕层土壤的积盐规律,运用GIS和地统计学的原理与方法,结合地下水埋深的空间分布以及临界埋深的划分标准对研究区域进行分区,并从空间尺度对各分区地下水矿化度与耕层土壤积盐规律进行了定量分析。结果表明：地下水埋深、矿化度和耕层土壤盐分均属于中等变异强度,在东西方向和南北方向上均具有2阶的趋势效应;受结构性因素和随机性因素的共同作用,地下水埋深呈中等的空间自相关性,地下水矿化度与耕层土壤盐分呈弱空间自相关性;耕层土壤盐分与地下水矿化度的空间分布具有一定的相关性,与地下水埋深呈负相关性。对空间尺度上的地下水矿化度与耕层土壤盐分定量分析结果表明,耕层土壤积盐与地下水矿化度呈极显著的相关关系,而地下水埋深增加使其相关性减弱,采用分区研究法使地下水矿化度对耕层土壤积盐规律分析更加客观准确。该结果对研究黄河三角洲地区土壤盐渍化的发生机理以及预测与评估该地区土壤盐渍化的发生发展具有重要意义。     

Spatial variability of groundwater solute concentrations at the water table under arable land and coniferous forest. Part 1: Methods for quantifying spatial variability (geostatistics,time series analysis,Fourier transform smoothing)

The solute load from soil into the groundwater plays an important role in considerations about the causes of groundwater pollution. Solute concentrations in the uppermost groundwater can be used to characterize the solute input into the groundwater in a particular area. Such interpretation, however, depends on a knowledge of the spatial variability and patterns of these concentrations. Geostatistical methods (semivariance and autocorrelation), spectral and cospectral analysis, and Fourier transform smoothing of data were used to quantify spatial relationships of the solute concentrations determined along 30 m transects. Electrical conductivity and calcium concentration data of the uppermost groundwater in a sandy soil under arable land were used for testing the procedures mentioned above. The range of the semi-variogram was found to be 6 m. Spectral analysis and Fourier transform smoothing yielded a periodical variation of 12 m length for this data.     

近30 a玛纳斯县北部土壤有机碳储量变化

研究玛纳斯县北部土壤有机碳时空变异特征,可以为当地土壤肥力管理提供理论依据。本文采用地统计学和GIS相结合的方法,研究了玛纳斯县北部地区1980-2011年间土壤有机碳的时空变异特征。研究结果表明:研究区32a来1m深土体土壤有机碳密度和储量呈现增加的趋势,分别较1980年二次土壤普查时增加1.81kg/m2和7.7×106kg;2011年0～20、>20～60和>60～100cm土壤有机碳质量分数平均值为5.74、4.44和2.17g/kg;0～20cm和>20～60cm土壤有机碳含量符合正态分布特征,相应土壤有机碳变异函数理论模型分别符合指数和球状模型;0～20cm土壤有机碳和>20～60cm土壤有机碳均具有中等程度的空间变异性,土壤有机碳的空间分布受土壤母质、地形等结构因素和耕作、施肥等随机因素的共同影响并呈现出南部和东北部高,中部地区偏低的分布特征;>60～100cm土壤有机碳呈现出南部高北部低的空间分布特征。本文获取了玛纳斯县北部地区土壤有机碳时空变异特征,该结果对研究区域土壤肥力管理具有重要意义。     

Information extraction and dynamic evaluation of soil salinization with a remote sensing method in a typical county on the Huang-Huai-Hai Plain of China

Monitoring the dynamics of soil salinization is of great importance for agricultural production. This study selected Yucheng County, a typical county on the Huang-Huai-Hai Plain (HHHP) of China, as the study area and evaluated the spatial and temporal variation of soil salinization. Three methods, consisting of principal component analysis (PCA) transformation, tasseled cap (TC) transformation, and optimal band combination (OBC), were used to extract information from an early Landsat multispectral scanner (MSS) image from 1984, and their advantages were compared. In addition, OBC was used on a thematic mapper (TM) image from 2009. An iteratively self-organizing data analysis algorithm was used together with prior knowledge of likely classifications to interpret the MSS and TM images for data classification. Finally, a transfer matrix method was used to assess the spatial and temporal variability of soil salinization and analyze the driving factors of soil salinization. Compared to PCA transformation and OBC, TC transformation was a more effective method for extracting soil salinization information from the MSS sensor. The results indicate that a soil area of approximately 298 km² was affected by salinity in 1984 in Yucheng County, of which 5.40%, 11.96%, and 12.75% were classified as being subject to slight, moderate, and severe salinization, respectively. In 2009, the saline area was reduced to only 146 km², of which 10.70% and 3.75% were characterized by slight to moderate salinization and no severe salinization, respectively. The saline land decreased at an average rate of 6 km² per year. This decrease was probably a result of lower groundwater depth, increased organic fertilizer or crop straw in soil, changed land use type, and increased vegetation coverage.     

三江平原人类活动的水文效应

分析了三江平原人类活动对地表径流过程、土壤水、地下水以及地表水质的影响。对人类活动水文影响的尺度和趋势进行了预测分析,指出人类活动水文影响的时空尺度将日益扩大,径流过程人为化、区域水系网状化、湿地景观破碎化及地表水质恶化等问题将越来越严峻。     

Remediation Actions by a Risk Assessment Approach: A Case Study of Mercury Contamination

The risk assessment procedure for identifying the remediation actions which may be adopted at a mercury contaminated site, when the plants are upgraded in the future, is proposed. The potentially active exposure/migration pathways in the future arrangement of the area will be due to Hg contaminated subsoil as a primary source (vapor inhalation and groundwater leaching) and to groundwater as a possible secondary source (transport to the point of compliance). The data of mercury concentration in the soil were acquired through environmental monitoring campaigns, and were processed to establish the three-dimensional distribution of contamination in subsoil, to locate sources and to define their geometrical and chemical characteristics. Speciation tests of mercury in the soil indicated that the most abundant species present were poorly leachable under the site-specific environmental conditions, confirming the coefficient distribution value obtained by the leaching tests. Analytical and numerical fate and transport modeling tools were used to locate digging zones in the contaminated subsoil, so as to reduce the possible groundwater contaminant loading and to avoid the down-gradient exceeding the concentration limit according to regulations. Remediation actions additional to civil works were required, which consists of soil digging within one contamination source, for about 22,200 m³ of soil. In order to evaluate the Hazard Index (HI) for human receptors due to Hg vapor inhalation, the air concentration of volatile mercury at the exposure point was estimated, based on direct measurements carried out at the site. Simulation gave HI values below 1 for all tested scenarios, suggesting that public health is protected without any additional actions to the already scheduled plant upgrading and digging for groundwater protection.     

盐渍化灌区土壤水盐时空变异特征分析及地下水埋深对盐分的影响

针对盐渍化灌区土壤盐渍化问题,以河套灌区下游乌拉特灌域为研究区,通过野外实测与室内试验分析结合,采用统计学方法地质统计学原理分析表层土壤(0-20,20-40 cm)及深层土壤(40-100 cm)含水率与盐分(EC值)时空分布和变异规律,以及探求地下水埋深对土壤盐分的影响。结果表明:(1)除6月0-20 cm(9.779%)外,表层土壤含水率变异系数均在12.384%~19.667%,属于中等变异性,深层土壤含水率变异系数较小,在3.513%~9.757%,属于弱变异性;表层土壤盐分(EC值)变异系数在100.845%~129.279%,属于强变异性,深层土壤盐分变异系数均在83.685%~98.853%,属于中等变异性;随着土壤深度的增加,含水率和盐分的变异性都相对减弱。(2)不同时期土壤含水率和盐分在一定范围内具有空间结构特征,均可用高斯模型模拟,各层土壤含水率空间相关度在0.038%~20.408%,各层土壤盐分空间相关度在0.043%~8.374%,均小于25%,说明具有强烈的空间相关性,可以认为主要是受结构性因素的影响,其自相关引起的空间变异性较强。(3)试验区土壤盐分主要集中在北侧盐荒地,由于蒸发强烈,包气带毛细水上升,把深层土壤以及地下水中的可溶性盐类带到土壤表层,致使盐分升高,属于典型的盐分表聚型土壤,需及时防治与治理,同时土壤盐分受地下水埋深的影响较大,随着地下水埋深减小而增大,荒地地下水埋深与土壤盐分满足线性关系,耕地地下水埋深与土壤盐分满足指数关系。荒地0-20 cm土壤盐分含量随地下水埋深变化趋势较大,20-40,40-100 cm土壤盐分含量随地下水埋深变化趋势较小,耕地地下水埋深在1~1.6 m时,土壤盐分含量随着地下水埋深变化趋势较大,当地下水埋深大于1.6 m时,土壤盐分含量随着地下水埋深变化趋势较小。研究结果为河套灌区下游盐渍化土壤的防治与改良提供了重要的理论基础和参考依据。     

An examination of temporal/spatial variations in landfill-generated methane gas

The experimental findings of a data-intensive in situ landfill monitoring study are described. Particular attention is given to the methodology employed in collecting the data, analyses of the spatial/ temporal variability of the gas percentages, by volume and the extent to which the variability in collected results is explained by variations in exogenous independent variables. Measurable gas flow rates from the soil could not be detected through the probe system employed in the field study.     

对土壤侵蚀研究的几点思考

土壤侵蚀是现代地理环境条件下改变地貌景观的主要过程,也是引起土壤质量退化、沙漠化与石漠化的核心因素,与土壤、生态、水文等多个地表过程密切相关。虽然土壤侵蚀研究需要气候、地质、地貌、土壤、水文、生态等相关学科的基本知识,分析土壤侵蚀发生、发展过程的动力机制,但需要明确界定土壤侵蚀研究的时空尺度。土壤侵蚀与水土保持之间相互联系、相互促进。土壤侵蚀研究的时间尺度以次降雨、月、年为主,研究主题为次降雨侵蚀过程、土壤侵蚀季节变化与年际变化,时间尺度不宜超过100年。土壤侵蚀研究的空间尺度以小流域为主,基于土壤侵蚀垂直分带性,可以进一步分为样点、坡面、沟坡与小流域。在不同空间尺度上,研究内容与研究方法差异明显。土壤侵蚀过程包括土壤分离、泥沙输移和泥沙沉积,各个过程的主控因素存在差异,研究成果积累差异明显,研究重点会随着时空尺度的变化而有所不同。在土壤侵蚀过程研究中,应充分理解分离控制和输移控制及其时空转换阈值。虽然土壤侵蚀研究已经取得了大量成果,但在细沟网络结构及其时空变化、泥沙沉积过程、沟蚀形成与演变动力机制、重力侵蚀发育过程动力学机理、小流域土壤侵蚀过程模型等诸多方面,亟待加强研究。     

奇台县绿洲农田土壤盐渍化逆向演替过程

在奇台县绿洲中部平原区和绿洲沙漠交错带选择不同耕种时间的农田,分析其剖面土壤可溶性总盐、pH值、有机质含量随耕种时间的变化。研究表明:奇台县绿洲地下水位已低于影响地表盐渍化的水位临界值(5 m),地下水矿化度低于3 g/L,研究区整体处于有利于土壤盐渍化逆向演替的环境。随着地下水位的不断下降以及耕种时间的延长,农田土壤含盐量逐渐减少,土壤有机质逐渐增加,土壤盐渍化逆向演替过程已经发生。土壤盐渍化的逆向演替过程具有时空特征,可以划分为初级、中级、高级3个阶段。由绿洲下部向上部,土壤盐渍化逆向演替阶段逐渐向高级过渡。     

流域土壤侵蚀测量系统研究

流域内降雨-径流-土壤侵蚀过程中不同时空点处流量、流速、泥沙含量的获取是土壤侵蚀机理研究中的难点,它们的实时、准确测量将为侵蚀模拟-预报模型的建立与检验提供必要的数据支持。针对这一问题,提出一套测量流域土壤侵蚀动态变化过程变量的自动化测量系统。该系统由四部分构成:量水堰和水位传感器实现径流流量的测量;薄层水流流速测量系统测量坡面流及其流域内沟道中水流速度;径流含沙量测量系统测量径流中的泥沙含量;数据采集控制以及存储系统,实现试验设计点处侵蚀量的动态变化过程测量及数据存储。这一系统的构建及应用必将推动侵蚀过程测量向着更自动化和可操作化方向发展。