Effect of Soil Fabric on Transport of a LNAPL through Unsaturated Fine-Grained Soils: A Centrifugal Model Study

Centrifugal model tests were performed to study the impact of the fabric of a fine-grained soil on transport of a light non-aqueous phase liquid (LNAPL). An image processing technique was developed to extract contaminant transport and fate data from the centrifugal model. Two unconsolidated sites with different moisture contents and a saturated site consolidated due to self-weight were simulated using the centrifuge. The LNAPL migrated in the vertical direction as a narrow plume and formed a free product pool above the saturated zone in unsaturated and unconsolidated soils. However, the LNAPL migrated in the horizontal direction before moving in the vertical direction as a broad plume in the consolidated site. The test results showed that the final width of the plume in the unsaturated zone of the consolidated site was nearly two times as large as that for the unconsolidated sites. In addition, the rate of leak from the underground storage tanks (USTs) on consolidated soils was substantially higher when compared with those on the unconsolidated state. The comparison of LNAPL saturation profiles at the centerline of the centrifugal models during leakage showed that, depending on the soil fabric at a given time and depth, the LNAPL phase would be different; i.e., mobile or immobile (residual) in the same soil type. The test results provided additional insight into contribution of soil fabric on transport and fate of contaminants. The soil fabric controls the geological and hydro-geological properties of fine-grained soils and hence the contamination plume.     

Effects of plant size on photosynthesis and water relations in the desert shrub Prosopis glandulosa (Fabaceae)

The Jornada del Muerto basin of the Chihuahuan Desert of southern New Mexico, USA, has undergone a marked transition of plant communities. Shrubs such as mesquite (Prosopis glandulosa) have greatly increased or now dominate in areas that were previously dominated by perennial grasses. The replacement of grasses by shrubs requires an establishment phase where small shrubs must compete directly with similar-sized grass plants. This is followed by a phase in which large, established shrubs sequester nutrients and water within their biomass and alter soil resources directly under their canopy, creating “islands” of fertility. We hypothesized that these two phases were associated with shrubs having different physiological response capacities related to their age or size and the resource structure of the environment. As a corollary, we hypothesized that responses of small shrubs would be more tightly coupled to variation in soil moisture availability compared to large shrubs. To test these hypotheses, we studied gas exchange and water relations of small (establishing) and large (established) shrubs growing in the Jornada del Muerto as a function of varying soil moisture during the season. The small shrubs had greater net assimilation, stomatal conductance, transpiration, and xylem water potential than large shrubs following high summer rainfall in July, and highest seasonal soil moisture at 0.3 m. High rates of carbon assimilation and water use would be an advantage for small shrubs competing with grasses when shallow soil moisture was plentiful. Large shrubs had greater net assimilation and water-use efficiency, and lower xylem water potential than small shrubs following a dry period in September, when soil moisture at 0.3 m was lowest. Low xylem water potentials and high water-use efficiency would allow large shrubs to continue acquiring and conserving water as soil moisture is depleted. Although the study provides evidence of differences in physiological responses of different-sized shrubs, there was not support for the hypothesis that small shrubs are more closely coupled to variation in soil moisture availability than large shrubs. Small shrubs may actually be less coupled to soil moisture than large shrubs, and thus avoid conditions when continued transpiration could not be matched by equivalent water uptake.     

Distribution of Microbial Physiologic Types in an Aquifer Contaminated by Crude Oil

Abstract We conducted a plume-scale study of the microbial ecology in the anaerobic portion of an aquifer contaminated by crude-oil compounds. The data provide insight into the patterns of ecological succession, microbial nutrient demands, and the relative importance of free-living versus attached microbial populations. The most probable number (MPN) method was used to characterize the spatial distribution of six physiologic types: aerobes, denitrifiers, iron-reducers, heterotrophic fermenters, sulfate-reducers, and methanogens. Both free-living and attached numbers were determined over a broad cross-section of the aquifer extending horizontally from the source of the plume at a nonaqueous oil body to 66 m downgradient, and vertically from above the water table to the base of the plume below the water table. Point samples from widely spaced locations were combined with three closely spaced vertical profiles to create a map of physiologic zones for a cross-section of the plume. Although some estimates suggest that less than 1% of the subsurface microbial population can be grown in laboratory cultures, the MPN results presented here provide a comprehensive qualitative picture of the microbial ecology at the plume scale. Areas in the plume that are evolving from iron-reducing to methanogenic conditions are clearly delineated and generally occupy 25–50% of the plume thickness. Lower microbial numbers below the water table compared to the unsaturated zone suggest that nutrient limitations may be important in limiting growth in the saturated zone. Finally, the data indicate that an average of 15% of the total population is suspended. Received: 28 October 1998; Accepted: 26 February 1999     

Indoor Air Inhalation Risk Assessment for Volatiles Emanating from Light Nonaqueous Phase Liquids

The indoor air inhalation pathway for volatile contaminants in soil and groundwater has received much attention recently. The risk of exposure may be higher when volatile organic compounds (VOCs) reside as constituents of a free product plume below residential or commercial structures than when dissolved in groundwater or adsorbed on soil. A methodology was developed for assessing the potential for vapor phase migration—and associated risk of indoor air inhalation—of volatile constituents from a light nonaqueous phase liquid (LNAPL) plume on top of the water table. The potential risk from inhalation of VOCs in indoor air emanating from a subsurface Jet Fuel 4 (JP-4) plume by hypothetical residential receptors was assessed at a site. Chemicals of concern (COCs) were identified and evaluated using data from the composition of JP-4 mixtures and published chemical, physical, and toxicological data. The method estimates the equilibrium vapor concentrations of JP-4 constituents using Raoult's Law for partial vapor pressure of mixtures based on assumptions about the mixture composition of JP-4. The maximum allowable vapor concentration at the source (immediately above the LNAPL) corresponding to an indoor air target concentration based on acceptable risk levels are calculated using the Johnson and Ettinger model. The model calculates the attenuation factor caused by the migration of the vapor phase VOCs through the soil column above the JP-4 plume and through subsurface foundation slabs. Finally, the maximum allowable soil gas concentrations above the LNAPL for individual constituents were calculated using this methodology and compared to the calculated equilibrium vapor concentrations of each COC to assess the likelihood of potential risk from the indoor air inhalation pathway.     

Detection of Brucella antigens by dot immunoassay using specific antibodies labelled with colloid gold particles]

Dot immunoassay was developed to improve the quality of laboratory diagnosis of brucellosis. Particles of colloid gold were used as a marker of specific antibodies. The method was used for detecting Brucella antigens in artificially contaminated environmental objects (soil and water) and in biological material (milk, blood serum, and visceral homogenates of animals). The sensitivity of the test system was 19.5.10(3)-62.5.10(4) CFU/ml. Specificity of the assay was tested with 10 heterologous antigenically closely related bacterial species. The proposed test system is simple, economic, highly sensitive and specific, and requires no expensive equipment and reagents.     

Effect of Watering and Soil Moisture on Mercury Emissions from Soils

This paper presents data from experiments that measured Mercury (Hg) flux as a function of water addition and subsequent soil drying, and maintenance of soil water content over time utilizing small dynamic gas exchange chambers and large mesocosms. When soil surfaces were dry and water was added at an amount less than that necessary to saturate the soil an immediate large (relative to dry soil flux) release of Hg occurred. Diel Hg emissions from soils, unenriched (0.02 μg g⁻¹) and enriched (3 μg g⁻¹) in Hg and wet below saturation, were significantly elevated above that occurring from dry soils (2–5 times depending on soil water content) for weeks to months. Enhancement of emissions from wet soils in direct sunlight were greater than that from soils shaded or in the dark suggesting that a synergism exists between soil moisture and light. When soils were watered to saturation Hg emissions were suppressed or remained the same depending on the degree of saturation. It is hypothesized that the addition of soil water in amounts less than that necessary to saturate the soil surface results in an immediate release of elemental Hg from soil surface as the more polar water molecule out competes Hg for binding sites. As the water moves into the soil, Hg adsorbed to soil particles is desorbed into soil gas and dissolved in the soil water. The process of evaporation facilitates movement of Hg as mass flow to the soil surface where it is made available for subsequent release. The latter is hypothesized to be an important process by which Hg is recharged at the soil–air interface.     

Environmental effects on CO2 efflux from riparian tundra in the northern foothills of the Brooks Range,Alaska, USA

Summary Carbon dioxide efflux and soil microenvironmental factors were measured diurnally in Carex aquatilus-and Eriophorum angustifolium-dominated riparian tundra communities to determine the relative importance of soil environmental factors controlling ecosystem carbon dioxide exchange with the atmosphere. Measurements were made weekly between 18 June and 24 July 1990. Diurnal patterns in carbon dioxide efflux were best explained by changes in soil temperature, while seasonal changes in efflux were correlated with changes in depth to water table, depth to frozen soil and soil moisture. Carbon dioxide efflux rates were lowest early in the growing season when high water tables and low soil temperatures limited microbial and root activity. Individual rainfall events that raised the water table were found to strongly reduce carbon dioxide efflux. As the growing season progressed, rainfall was low and depth to water table and soil temperatures increased. In response, carbon dioxide efflux increased strongly, attaining rates late in the season of approximately 10 g CO₂ m^–2 day^–1. These rates are as high as maxima recorded for other arctic sites. A mathematical model is developed which demonstrates that soil temperature and depth to water table may be used as efficient predictors of ecosystem CO₂ efflux in this habitat. In parallel with the field measurements of CO₂ efflux, microbial respiration was studied in the laboratory as a function of temperature and water content. Estimates of microbial respiration per square meter under field conditions were made by adjusting for potential respiring soil volume as water table changed and using measured soil temperatures. The results indicate that the effect of these factors on microbial respiration may explain a large part of the diurnal and seasonal variation observed in CO₂ efflux. As in coastal tundra sites, environmental changes that alter water table depth in riparian tundra communities will have large effects on ecosystem CO₂ efflux and carbon balance.     

影像设备电路板测试与故障诊断之系统实现

大型医学影像设备是医院中的贵重设备,其中不少进口设备的维护修理的技术难度较高,医院每年花费在医学影像设备上的维护修理费是非常之大。本文从建立国内的维修力量着眼,研讨医学影像设备维修方法。     

Intense but variable autotrophic activity in a rapidly flushed shallow‐water hydrothermal plume (Kueishantao Islet,Taiwan)

Shallow‐water hydrothermal plumes concomitantly host both photosynthetic and chemoautotrophic organisms in a single biotope. Yet, rate measurements to quantify the contributions of different autotrophic activity types are scarce. Herein, we measured the light and dark dissolved inorganic carbon (DIC) uptake rates in the plume water of the Kueishantao hydrothermal field using the ¹³C‐labeling approach. Seventy percent of the plume‐water samples had chemoautotrophy as the dominant mode of carbon fixation, with the dark DIC uptake rates (up to 18.6 mg C/m³/h) within the range of the primary production in productive inner‐shelf waters. When considered alongside the geochemical and microbiological observations, the rate data reveal the distribution of different trophic activities in the hydrothermal plume. The autotrophic activity at the initial phase of plume dispersal is low. This is explained by the short response time the chemoautotrophs have to the stimulation from vent‐fluid discharge, and the harmful effects of hydrothermal substances on phytoplankton. As plume dispersal and mixing continue, chemoautotrophic activities begin to rise and peak in waters that have low‐to‐moderate Si(OH)₄ content. Toward the plume margin, chemoautotrophy declines to background levels, whereas photosynthesis by phytoplankton regains importance. Our results also provide preliminary indication to the loci of enhanced heterotrophy in the plume. Results of artificial mixing experiments suggest that previously formed plume water is the primary source of microbial inoculum for new plume water. This self‐inoculation mechanism, in combination with the intense DIC uptake, helps to sustain a distinct planktonic autotrophic community in this rapidly flushed hydrothermal plume.     

Correlation among soil test values and elemental composition of chrysanthemums

Summary Chrysanthemum morifolium Ramat. plants were grown in a soil mix fertilized daily with a balanced solution containing N, P, K, Ca, and Mg at 4 rates which were 0.5, 1, 2, and 4 times. At the end of 4 weeks of vegetative growth, the above-ground portions of the plants were analyzed for elemental content, and the soil mix was analyzed by 3 soil testing procedures. The N, P, and K contents of chrysanthemum were positively correlated with the reported values of these nutrients in the soil as determined by the Spurway, Penn State, and Intensity-Balance soil tests. Magnesium, as in the Penn State and Intensity-Balance soil tests, was negatively correlated with plant Mg content; however, Ca was not significantly correlated with plant Ca in the Penn State test and negatively correlated in the Intensity-Balance test. The magnitude of the correlation coefficients between nutrient content of the plants, and the soil test value of the nutrient by all three soil tests were similar indicating that all three soil tests can be used.Paper No. 5686 in the Journal Series of the Pennsylvania Agricultural Experiment Station.     

Digitise This! A Quick and Easy Remote Sensing Method to Monitor the Daily Extent of Dredge Plumes

Technological advancements in remote sensing and GIS have improved natural resource managers’ abilities to monitor large-scale disturbances. In a time where many processes are heading towards automation, this study has regressed to simple techniques to bridge a gap found in the advancement of technology. The near-daily monitoring of dredge plume extent is common practice using Moderate Resolution Imaging Spectroradiometer (MODIS) imagery and associated algorithms to predict the total suspended solids (TSS) concentration in the surface waters originating from floods and dredge plumes. Unfortunately, these methods cannot determine the difference between dredge plume and benthic features in shallow, clear water. This case study at Barrow Island, Western Australia, uses hand digitising to demonstrate the ability of human interpretation to determine this difference with a level of confidence and compares the method to contemporary TSS methods. Hand digitising was quick, cheap and required very little training of staff to complete. Results of ANOSIM R statistics show remote sensing derived TSS provided similar spatial results if they were thresholded to at least 3 mg L⁻¹. However, remote sensing derived TSS consistently provided false-positive readings of shallow benthic features as Plume with a threshold up to TSS of 6 mg L⁻¹, and began providing false-negatives (excluding actual plume) at a threshold as low as 4 mg L⁻¹. Semi-automated processes that estimate plume concentration and distinguish between plumes and shallow benthic features without the arbitrary nature of human interpretation would be preferred as a plume monitoring method. However, at this stage, the hand digitising method is very useful and is more accurate at determining plume boundaries over shallow benthic features and is accessible to all levels of management with basic training.     

Integrating field survey and orthophoto information to monitor coastal habitats — A pilot study to develop methods and resolve key issues

Implementation of mapping and monitoring is necessary to supply sufficient information to guide an effective management of species, habitats and landscapes. Coastal ecosystems can be difficult to monitor effectively in the field due to spatially discontinuous and unpredictable processes such as encroachment, erosion and succession, while coverage of large extents is very expensive. Remote sensing-based monitoring provides an alternative, but satellite image data is often too expensive or too coarse in spatial resolution to detect fine-scale habitat structures. Using Danish coastal habitats as a case, a method is presented for monitoring habitat types and fine-scale structures, based on integration of field-acquired habitat characteristics with the habitat information interpreted from sub-meter RGB/NIR aerial imagery and digital elevation model data. Initial pilot studies show good correspondence between field-observed structure elements and structures delineated through object-based image analysis, while initial classifications results suggest possibilities of discriminating between different types of shrubs, herb communities and non-vegetated structures.     

Evaluation and application of aquatic toxicity tests: use of the Microtox test for the prediction of toxicity based upon concentrations of contaminants in soil

The quality control for the reuse of cleaned soil from a contaminated site consisted in the determination of the main contaminants by analytical chemical methods such as GC and HPLC. Since it is not possible to analyze for all contaminants a toxicity test should be used to detect large concentrations of not routinely analyzed chemicals. The aim of the study was to develop a system for toxicity testing, which should be able to predict the toxicity of soil samples based on the concentration of chemicals in the soil and to detect toxic chemicals not analyzed by the routinely conducted soil analysis.Based upon the relative sensitivity to various contaminants as well as practical aspects such as test duration and costs the Microtox® test was favoured over the bioassays with Daphnia magna and Scenedesmus subspicatus. The Microtox® test was used to measure the toxicity of various pesticides and their major metabolites. The toxicity data of the pure compounds were used to predict the toxicity (EC₅₀ and % inhibition of the bioluminescence reaction) of defined mixtures of chemicals in water by applying two different mathematical appriaches which are based on the additivity of the effects of the single chemicals. The predicted values were compared with the experimental data and showed good agreement.In order to be able to predict the toxicity of soil samples using the Microtox® test the soil/water partition coefficient (K _d) was measured for the main contaminants. The toxicity of soil samples was predicted by calculating the concentration of the contaminants in the leachate by using the corresponding concentration in the soil and applying the K _d values determined. From the calculated composition of the leachate the expected toxicity was estimated. This value was compared with the toxicity experimentally determined in the Microtox® test.     

Decomposition of cellulose in soils

1. Cellulose decomposition in forest and orchard soils was investigated by studying the breakdown of boiled and washed cellophane in the soils and in vitro. Decomposition occurred from quick to slow in the order: orchard on clay soil, forest on clay soil, forest on sandy loam, and in the latter in the order: calcareous mull, acid mull and mor. 2. In the different forest soils which were investigated the rate of decomposition was parallel to their water capacity. It slowed down considerably when the water content of the soil decreased, especially after the wilting point was reached. 3. Of the fungi isolated from these soils, those from orchard soil — 5% to 50%Fusarium spp. — were among the fastest decomposers of cellulose. This agrees with, and may explain the high rate of decomposition in orchard soil. 4. Decomposition in pure culture is quicker than in soil. As filtersterilized soil extract checked the decomposition in pure culture, but heat-sterilized soil extract did not, an extractable but heat-sensitive substance may be one retarding factor.     

淹水-控温模式下砷污染水稻土溶液中砷形态的变化

以水稻种植区的砷污染土壤为研究对象,采用高效液相色谱(HPLC)-电感耦合等离子体质谱(ICP-MS)联用分析测试系统,研究了不同培养温度(5、27和50 ℃)对灭菌和不灭菌的土壤淹水后其溶液中砷赋存形态变化的影响.结果表明： 在土壤溶液中检测到的砷形态只有无机三价砷(As^Ⅲ)、无机五价砷(As^V)和有机的二甲基砷(DMA^V),未检测到单甲基砷(MMA^V)的存在;在不同控温条件下随淹水时间的延长,As^Ⅲ逐渐转变为砷的主要赋存形态,平均比例约为64%;As^V次之,约占35%,DMA^V的含量相对最低,约占1%;土壤灭菌与否对土壤溶液中五价砷的水平没有明显影响,但明显影响了五价砷的还原和促进了无机三价砷的甲基化,并且灭菌的促进效果随着淹水及培养时间的延长而逐渐降低;50 ℃、淹水23 d时,灭菌土壤溶液中DMA^V浓度最高,为23.7 ng·mL^-1,这说明灭菌土壤中残留的某些嗜热微生物成为优势菌群并促进了土壤溶液中砷的甲基化.结合水稻生长的实际环境条件对该研究结果进行分析,培养温度27 ℃淹水23 d后不灭菌的自然土壤溶液中砷浓度处于较低水平,因此在砷污染的水稻种植区建议采用短周期干湿交替的水分管理模式,在保障产量的情况下可尽量降低土壤溶液中砷的水平.     

黄河三角洲植被指数与地形要素的多尺度分析

结合地理信息系统和遥感技术, 研究了黄河三角洲植被指数NDVI与一系列地形要素间的尺度依赖关系, 从而检验在较大尺度上滨海生态系统植被分布格局是否存在水分再分配的调控作用。结果表明: 1)NDVI值在4种主要群落类型间差异显著, 这种显著差异是由滨海盐生植物的生境特点决定的; 2)地表高程在所有的10个粒度尺度上均与NDVI相关关系显著, 这种显著关系在小尺度上与地下水埋深有关, 而在大尺度上可能参与水分再分配过程; 3)在750 m粒度尺度附近存在水分再分配的调控作用, 在该尺度附近地形湿润度指数(TWI)和坡度与NDVI相关达到极显著, 而且其Moran’sI指数突然增大。黄河三角洲的植被地形关系表现为不同尺度上对土壤水分和盐分的调控, 在小尺度上地形因素通过土壤表面蒸发过程影响土壤水分与盐分, 而在大尺度上地形因素主要通过地表径流对土壤水分与盐分进行再分配。     

岷江上游森林土壤大孔隙特征及其对水分出流速率的影响

大孔隙是森林土壤中常见的现象 ,对土壤壤中流的产生有重要的影响。但由于大孔隙研究方法的不成熟 ,各种方法得到的大孔隙半径范围并不一致。一般认为田间持水量和饱和含水量之间的土壤孔隙为大孔隙 ,利用水分穿透曲线和 Poiseuille方程研究了岷江上游不同植被下土壤的大孔隙状况 ,这种方法一方面与传统的研究方法相衔接 ,另一方面所得到的大孔隙与土壤水分运动有关 ,反映了土壤大孔隙的研究目的 ,因而是一种相对合理的研究方法。岷江上游几种主要植被下土壤大孔隙半径主要集中于 0 .3～ 2 .4 mm之间 ,平均在 0 .4 8～ 1.17mm之间 ,均值为 0 .84 mm,均方差为 0 .2 2 6 ;且随着剖面的发育表现出上部土层多 ,下部土层少的特点。同时 ,半径在 2 .4～ 1.4 m m之间的特大孔隙较少 ,<1.0 m m的小孔隙较多。大孔隙的平均半径对于水分出流速率有重要的影响 ,特别是半径 >1.4 mm的孔隙数量影响最大 ,虽然其数量仅占大孔隙数量的 5 %以下 ,但决定了稳定出流速率 70 %的变异。大孔隙所占过水断面的最高比例为 2 1.2 2 % ,最低为 2 .6 % ;在大孔隙所占过水断面的比例小于 2 0 %的条件下 ,稳定出流速率随大孔隙的增多而增大     

Leaf and root growth dynamics in Eucalyptus globulus seedlings grown in drying soil

Summary Seedlings of Eucalyptus globulus growing in soil columns were subjected to a 24 day soil drying treatment. Water and solute potentials of both young expanding and fully expanded leaves declined under reduced soil water availability, while slightly higher turgor was sustained by the fully expanded leaves. Although leaf area of unwatered seedlings was smaller, the corresponding leaf dry weight was quite similar to that of well-watered seedlings. Soon after rewatering, leaf area of plants experiencing water shortage was comparable to that of well-watered plants. It seems that a difference in wall properties between juvenile and mature leaves allows for an effective pattern of water use by eucalypt plants growing in drying soil. Some stomatal opening is sustained and therefore, presumably, some carbon may be fixed, keeping the carbon balance of the whole plant positive, and allowing a continuous cell division despite the limited water supply. The highest root density of both well-watered and unwatered plants was found in the upper soil layers. However, root growth of unwatered seedlings was gradually increased in the deeper soil layers, where thicker root apices and higher soil water depletion rates per unit root length were recorded. As a consequence, root absorbing surface area was as large in unwatered plants as in well-watered plants.     

Fate and Transport of 2,4,6-Trinitrotoluene in Loams at a Former Explosives Factory

Natural attenuation processes affecting 2,4,6-trinitrotoluene (TNT) were determined within loams for two study areas at the former Explosives Factory Maribyrnong, Australia. TNT fate and transport was investigated through spectrophotometric/High Performance Liquid Chromatography (HPLC) analyses of soil and groundwater, adsorption and microcosm testwork. A five tonne crystalline TNT source zone delineated within near surface soils at the base of a TNT process waste lagoon was found to be supplying aqueous TNT loading (7 ppm) to subsurface soils and groundwater. The resultant plume was localized within the loam aquitard due to a combination of natural attenuation processes and hydrogeological constraints, including low hydraulic conductivity and upward hydraulic gradients. Freundlich described sorptive partitioning was the main TNT sink (K_F = 29 mL/g), while transformation rates were moderate (1.01 × 10^-4 h^-1) under the aerobic conditions. Increasing 2-amino-4,6-dinitrotoluene predominance over 4-amino-2,6-dinitrotoluene was discovered with depth (in situ) and time (microcosms). Simplified dissolution rate calculations indicate that without mitigation of the TNT source, contaminant persistence within the vadose zone may approach 2000 years, while ATRANS20 simulations demonstrate that the TNT plume propagates very slowly along the flow path within the aquitard.