Trace metals in porewater of surface sediments and their bioavailability in Jiaozhou Bay,Qingdao, China     

Siyuan Ye  Edward A. Laws  Xigui Ding  Hongming Yuan  Guangming Zhao  Jin Wang 《Environmental Earth Sciences》2011,64(6):1641-1646

Samples of porewater and the edible tissue of mottled clams, Ruditapes variegatus, were collected simultaneously at each of 12 stations from Jiaozhou Bay near Qingdao, China, in June of 2003. Chemical analysis focused on trace metals and major elements. Porewater concentrations of Cd, Cr, Pb, and Zn were distributed in a bimodal fashion among the 12 stations, with mean concentrations at six of the stations being 8–32 times mean values at the other six stations. The concentrations of the same metals in clams were remarkably similar among stations, the coefficients of variation being only 12–37%. Calculations performed with the computer program PHREEQC indicated that Pb and Cr in porewater were present only in the +2 and +3 states, respectively, and because dissolved Cd and Zn exist only in the +2 state, the bimodal distribution of these four metals likely reflects secondary effects associated with their scavenging by Fe and/or Mn under oxidizing conditions and subsequent dissolution in the reducing environment of the porewaters. Consistent with this hypothesis is the fact that the distribution of high and low metal concentrations was closely correlated with the granularity of the sediment, with lower metal concentrations associated with relatively coarse sediment. Comparison of published biological concentration factors with the ratios of metal concentrations in the clams to porewater metal concentrations indicated that the porewaters were not the primary sources of the metals in the clams. Mixing processes in the bay likely account for the rather uniform concentrations of metals in clam tissue.  相似文献   

Mapping coastal erosion at the Nile Delta western promontory using Landsat imagery     

Mohamed E. Hereher 《Environmental Earth Sciences》2011,64(4):1117-1125

A set of six Landsat satellite images with 5–9 years apart was used in a post-classification analysis to map changes occurred at Rosetta promontory between 1973 and 2008 due to coastal erosion. Spectral information were extracted from two multi-spectral scanner (MSS) images (1973 and 1978), three thematic mapper (TM) images (1984, 1990, and 1999), and one enhanced thematic mapper plus (ETM+) image (2008). To estimate the quantity of land loss in terms of coastal erosion, a supervised classification scheme was applied to each image to highlight only two classes: seawater and land. The area of each class was then estimated from the number of pixels pertaining to this class in every image. In addition, the shoreline position was digitized to address retreat/advance pattern throughout the study period. Results showed that Rosetta promontory had lost 12.29 km² of land between 1973 and 2008 and the shoreline withdrew southward about 3.5 km due to coastal erosion. Most land loss and shoreline retreat occurred between 1973 and 1978 (0.55 km²/year and 132 m/year, respectively). Coastal protection structures were constructed successively at the promontory. These structures have considerably contributed to reduce coastal erosion; however, they promoted downdrift erosion.  相似文献   

Geochemistry of granites and metasediments of the urban area of Vila Real (northern Portugal) and correlative radon risk   总被引：2，自引：2，他引：0  

M. E. P. Gomes  L. J. P. F. Neves  F. Coelho  A. Carvalho  M. Sousa  A. J. S. C. Pereira 《Environmental Earth Sciences》2011,64(2):497-502

Radon concentration was evaluated in dwellings of the urban area of Vila Real (Northern Portugal). The area is mainly composed of Hercynian granites and Cambrian metasediments, and CR-39 passive detectors (n = 112) were used for the purpose. The results obtained in winter conditions suggest that the most productive geological unit is the Hercynian granite G1 (geometric mean of 364 Bq/m³), while Cambrian metasediments of the Douro Group show the lowest average indoor radon concentration (236 Bq/m³). The geological, geochemical and radiological data obtained suggest that the most effective control on the radon concentrations of the area is related with the uranium content of the rocks; indeed, the highest contents were observed in granite G1 (21 ppm) and the lowest in the metasediments (3 ppm). This is also confirmed by the results obtained for groundwater, where granites present the highest concentrations of dissolved radon (up to 938 Bq/l), uranium (5–18 ppb) and gross α activities (0.47–0.92 Bq/l). No important radiometric anomalies were found in relation with geological structures such as faults, veins and contacts, but a moderate increase of the uranium content can occur locally in such structures. Petrographic observations and SEM studies show that uranium is mainly contained within the rock in heavy accessory minerals (apatite, zircon, monazite, xenotime), which reduces radon emanation. Notwithstanding, due to the high U contents granites show a significant potential to induce indoor radon concentrations in dwellings in excess of the recommended value of 400 Bq/m³. Overall, we can conclude that the region of Vila Real presents a moderate to high radon risk in dwellings and groundwater.  相似文献   

Geomorphological and sedimentological comparison of fluvial terraces and karst caves in Zhangjiajie,northwest Hunan,China: an archive of sandstone landform development     

Guifang Yang  Xujiao Zhang  Mingzhong Tian  Yamin Ping  Anze Chen  Zhiliang Ge  Zhiyun Ni  Zhen Yang 《Environmental Earth Sciences》2011,64(3):671-683

The Zhangjiajie Sandstone Peak Forest Geopark (Zhangjiajie World Geopark) of northwest Hunan, China hosts a well-preserved sequence of fluvial terraces and karst caves. In this contribution, a comparative study of fluvial terraces with karst caves along the middle-lower Suoxi River in Zhangjiajie World Geopark is presented to improve the understanding of the development of striking sandstone landscape in the upper Suoxi River. By integrating geomorphological, sedimentological, and geochronological techniques, the possible correlation between fluvial terraces and karst caves, as well as their climatic and tectonic implications is investigated. The available electron spin resonance and thermo-luminescence numerical ages coupled with morphostratigraphic analysis indicate that aggradation of fluvial terrace levels occurred at ca. 347 ± 34 ka (T₄), 104.45 ± 8.88 to 117.62 ± 9.99 ka (T₃), 60.95 ± 5.18 ka (T₂), and Holocene (T₁), followed by the stream incision. Fluvial terrace levels (T₄ to T₁) correlate morphologically with the karst cave levels (L₁ to L₄), yet the proposed chronology for the fluvial terrace levels is a bit later than the chronological data obtained from karst caves. In northwest Hunan, where a unique sandstone peak forest landscape was extensively developed, the fluvial terrace sequences as well as the cave systems are the important archives for studying the evolution of the sandstone landscape. The beginning of the sandstone landscape development must be earlier than the aggradation of the fluvial terrace T₄, allowing this unique landscape to occur in the Middle Pleistocene.  相似文献   

Pore-scale removal mechanisms of residual light non-aqueous phase liquids in porous media     

Helian Li  Jiajun Chen  Jian Yang 《Environmental Earth Sciences》2011,64(8):2223-2228

Glass-etched micromodel and visualization technology were used to research the removal mechanisms of residual light non-aqueous phase liquids (LNAPLs) droplets at pore scale. In this research, n-hexadecane was selected as the LNAPL model substance. During the injection of de-ionized water into the pore channel, residual n-hexadecane droplet was removed quickly at first, then gradually became slow and finally remained nearly invariable; the droplet size after a definite time depends on its initial value. The relationship between total volume of residual n-hexadecane and time can be described by a logarithmic equation: V = V ₀ − 0.0152lnt + 0.0360 (0 < t < 9,420, R ² = 0.9621). Based on percolation theory, the relationship between fluid percolation velocity in pores and time was determined through the analysis of residual n-hexadecane droplet size and the flowing characteristics of injected fluid. Gaussian model was used to fit the cumulated dissolved n-hexadecane, the correlation coefficient R ² = 0.97269. The removal process of n-hexadecane in network model experiment is similar to that of the sand column flushing experiment, which indicates that the mass transfer micro-mechanism of network model experiment could be used to interpret the results of column flushing experiment.  相似文献   

Groundwater flow system in Bengal Delta,Bangladesh revealed by environmental isotopes     

Ratan K. Majumder  M. A. Halim  B. B. Saha  Reo Ikawa  Toshio Nakamura  Makoto Kagabu  Jun Shimada 《Environmental Earth Sciences》2011,64(5):1343-1352

A total number of 328 groundwater samples are analysed to evaluate the groundwater flow systems in Bengal Delta aquifers, Bangladesh using environmental isotope (²H, ¹⁸O, ¹³C, ³H, and ¹⁴C) techniques. A well-defined Local Meteoric Water Line (LMWL) δ²H = 7.7 δ¹⁸O + 10.7 ‰ is constructed applying linear correlation analyses to the monthly weighted rainfall isotopic compositions (δ¹⁸O and δ²H). The δ¹⁸O and δ²H concentrations of all groundwater samples in the study area are plotted more or less over the LMWL, which provides compelling evidence that all groundwaters are derived from rainfall and floodwater with a minor localized evaporation effects for the shallow groundwaters. Tritium concentration is observed in 40 samples out of 41 with values varying between 0.3 and 5.0 TU, which represents an evidence of young water recharge to the shallow and intermediate aquifers. A decreasing trend of ¹⁴C activity is associated with the heavier δ¹³C values, which indicates the presence of geochemical reactions affecting the ¹⁴C concentration along the groundwater flow system. Both vertical and lateral decrease of ¹⁴C activity toward down gradient show the presence of regional groundwater flow commencing from the unconfined aquifers, which discharges along the coastal regions. Finally, shallow, intermediate, and deep groundwater flow dynamics has revealed in the Bengal Delta aquifers, Bangladesh.  相似文献   

GIS-based impact assessment of land-use changes on groundwater quality: study from a rapidly urbanizing region of South India   总被引：4，自引：0，他引：4  

Haris H. Khan  Arina Khan  Shakeel Ahmed  Jerome Perrin 《Environmental Earth Sciences》2011,63(6):1289-1302

This study attempts to assess the influence of changing land-use patterns on the groundwater quality of the hard rock aquifer system in the Maheshwaram watershed, near Hyderabad, India. The study area is a rapidly urbanizing region with land development progressing at a fast pace. To study the impact of this rapid urbanization and overall land-use transition, a groundwater quality index (GQI) was prepared within a geographical information system (GIS). The GQI integrates the different water quality parameters to give a final index value that can be used for spatio-temporal comparisons. The land-use transitions were closely monitored from 2003 to 2008 using multispectral satellite images. The land-use pattern has changed drastically with an increase in the built-up area at the expense of other land uses. The analysis reveals a rapid deterioration of groundwater quality related mainly to the increase in built-up land with unsewered sanitation and poultry farms. Seasonal variability of the groundwater quality was also assessed. Mean GQI decreased from 84.16 to 83.26 over a period of 5 years from 2003 to 2008, while seasonal variability of water quality increased. GQI and Seasonal Variability of water quality were integrated in GIS to yield a groundwater sustainability map, in terms of water quality. Zones of sustainable and unsustainable groundwater use were demarcated for better decision making related to municipal land allotment in this rapidly urbanizing region.  相似文献   

Effects of monsoonal rainfall on waste dump stability and respective geo-environmental issues: a case study   总被引：1，自引：1，他引：0  

Mohan Yellishetty  William J. Darlington 《Environmental Earth Sciences》2011,63(6):1169-1177

The stability of mine waste dumps is of critical importance and an issue, the mining industry of Goa, India is continually facing. The State of Goa receives high rainfall of around 3,000 mm annually. This heavy monsoonal rainfall is often believed to be the cause of dump slope instability. In light of several dump collapses encountered in the State and their damaging effects on both mine operations and local geo-environmental conditions, this paper examines their stability considering various geotechnical factors and the downstream environmental effects of a slope failure. The mechanical properties of dump waste material are reported at different compaction levels. The effect of these properties and changes in pore-water pressure are specifically examined using limit equilibrium analysis. An empirical formula is developed relating dump height, material mechanical parameters and pore-water pressure to the factor of safety of the slope. It was found that the level of compaction experienced by the material had a significant effect on the factor of safety.  相似文献   

A Leaky-Conduit Model of Transient Flow in Karstic Aquifers   总被引：1，自引：0，他引：1  

David E. Loper  Eric Chicken 《Mathematical Geosciences》2011,43(8):995-1009

Karst Flow Model (KFM) simulates transient flow in an unconfined karstic aquifer having a well-developed conduit system. KFM treats the springshed as a two-dimensional porous matrix containing a triangulated irregular network of leaky conduits. The number and location of conduits can be specified arbitrarily, perhaps using field information as a guide, or generated automatically. Conduit networks can be tree-like or braided. Rainwater that has infiltrated down from the surface leaks into the conduits from the adjacent porous matrix at a rate dictated by Darcy’s law, then flows turbulently to the spring via the conduits. KFM is calibrated using the known steady state; geometry and recharge determine the steady fluxes in the conduits, and the head distribution determines conduit gradients and sizes. Spring flow can vary with time due to spatially and temporally variable recharge and due to prescribed variations in the elevation of the spring. KFM is illustrated by four examples run on a test aquifer consisting of 27 nodes, 42 elements, and 26 conduits. Three examples (drought, uniform rainstorm, storm-water input to one element) are simulations, while the fourth uses data from a spring-basin flooding event. The qualitative fit between the predicted and observed spring discharge in the fourth example provides support of the hypothesis that the dynamic behavior of a karst conduit system is an emergent property of a self-organized system, largely independent of the locations and properties of individual conduits.  相似文献   

Comparison of Two Methods Used to Model Shape Parameters of Pareto Distributions     

Chenglin Liu  Ronald R. Charpentier  Jin Su 《Mathematical Geosciences》2011,43(7):847-859

Two methods are compared for estimating the shape parameters of Pareto field-size (or pool-size) distributions for petroleum resource assessment. Both methods assume mature exploration in which most of the larger fields have been discovered. Both methods use the sizes of larger discovered fields to estimate the numbers and sizes of smaller fields: (1) the tail-truncated method uses a plot of field size versus size rank, and (2) the log–geometric method uses data binned in field-size classes and the ratios of adjacent bin counts. Simulation experiments were conducted using discovered oil and gas pool-size distributions from four petroleum systems in Alberta, Canada and using Pareto distributions generated by Monte Carlo simulation. The estimates of the shape parameters of the Pareto distributions, calculated by both the tail-truncated and log–geometric methods, generally stabilize where discovered pool numbers are greater than 100. However, with fewer than 100 discoveries, these estimates can vary greatly with each new discovery. The estimated shape parameters of the tail-truncated method are more stable and larger than those of the log–geometric method where the number of discovered pools is more than 100. Both methods, however, tend to underestimate the shape parameter. Monte Carlo simulation was also used to create sequences of discovered pool sizes by sampling from a Pareto distribution with a discovery process model using a defined exploration efficiency (in order to show how biased the sampling was in favor of larger fields being discovered first). A higher (more biased) exploration efficiency gives better estimates of the Pareto shape parameters.  相似文献