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1.
A three-dimensional two-phase flow model is coupled to a non-linear reactive transport model to study the efficacy of potassium permanganate treatment on dense, non-aqueous phase liquid (DNAPL) source removal in porous media. A linear relationship between the soil permeability (k) and concentration of manganese dioxide precipitate ([MnO2(s)]), k = ko + Srind [MnO2(s)], is utilized to simulate nodal permeability reductions due to precipitate formation. Using published experimental column studies, an Srind = −5.5 × 10−16 m2 L/mg was determined for trichloroethylene (TCE) DNAPL. This Srind was then applied to treatment simulations on three-dimensional TCE DNAPL source zones comprising either DNAPL at residual saturations, or DNAPL at pooled saturations.  相似文献   

2.
Bivalves, crabs, fishes, seawater, and sediment collected from the inner part of Tokyo Bay, Japan, were measured for 20 polybrominated diphenyl ether (PBDE) and 5 polychlorinated biphenyl (PCB) congeners. To determine the trophic levels of the organisms, carbon and nitrogen stable isotope ratios (δ13C and δ15N) were also measured. Bioconcentration factors of PBDE and PCB congeners increased as the octanol-water partition coefficient (Kow) rose to log Kow = 7, above which they decreased again. Biomagnification of PCBs and several PBDE congeners (BDE47, 99, 100, 153 and 154) up the trophic ladder was confirmed by a positive correlation between their concentrations and δ15N. Other PBDE congeners showed a negative or no correlation, suggesting their biotransformation through metabolism. The more hydrophobic congeners of both PBDEs (Br = 2-6) and PCBs (Cl = 6-9) were biomagnified more. It thus appears that PBDEs are less biomagnified than PCBs.  相似文献   

3.
Areliable sediment transport capacity function provides response against challenges of soil erosion prediction on the Loess Plateau of China. The popular sediment transport capacity functions are questionable on loess slopes because the experimental conditions from which they were derived, like bed materials, gentle slopes,and surface roughness, are different from soil erosion processes on the loess slopes. Due to the foregoing uncertainty, a suitable sediment transport capacity function was dev...  相似文献   

4.
Surface sediments and porewater from 12 sites within Xiamen offshore areas and organisms from a heavily contaminated site Yuandang Lagoon were sampled and analyzed for eight polybrominated diphenyl ethers (PBDEs) congeners (-28, -47, -99, -100, -153, -154, -183 and -209). The total concentrations of eight PBDEs (∑8PBDEs) and BDE-209 in sediments ranged from 0.27 to 76.54 ng/g with an average of 16.31 ng/g and from 0.10 to 70.11 ng/g with an average of 14.94 ng/g, respectively. Concentrations of ∑8PBDEs in porewater ranged from 2.5 to 34.1 ng/L, with a mean value of 15.3 ng/L. In this study, the partition coefficients (log ) of PBDE congeners (without -209) were significantly correlated with their octanol-water partition coefficients (log KOW) (r2 = 0.74, P < 0.01). ∑8PBDE concentrations ranged from 0.33 to 1.26 ng/g (lipid weight) in marine organisms, and PBDE congener patterns were significantly different between fish and clam, crab.  相似文献   

5.
We investigated the physical properties of beaches contaminated with plastic fragments. We compared sediment cores from Hawai‘i Island’s Kamilo Beach, notable for plastic accumulation, to cores from a nearby beach. Compared to the nearby beach, Kamilo sediments contained more plastics (up to 30.2% by weight), were coarser-grained, and were more permeable (t-test, p < 0.0001). 85% of the fragments were polyethylene, and 95% were concentrated in the top 15 cm of the cores. We constructed artificial cores of standardized grain size and varying plastic-to-sediment ratios. Adding plastic significantly increased the permeability (ANOVA, p = 0.002), which was partially attributed to the fragments increasing the mean grain size. Sediments with plastic warmed more slowly (16% maximum decrease in thermal diffusivity), and reached lower maximum temperatures (21% maximum increase in heat capacity). These changes have a variety of potential effects on beach organisms, including those with temperature-dependent sex-determination such as sea turtle eggs.  相似文献   

6.
Hudson River sediment microcosms from Piles Creek (PC), Piermont Marsh (PM), and Iona Island (II) were amended with ∼100 mM nitrate or sulfate to stimulate anaerobic bioremediation. Nitrate and sulfate decreased over two years of field incubation and the fraction of these losses due to diffusion to the water column was predicted using Fick’s law. Apparent diffusion (Dapp) values of 1-4 × 10−10 m2 s−1 predicted the majority of loss/gain from/to the sediments by 700 d, but not at all times. Effective diffusion (Deff) values predicted by the porosity function (Deff = Dmol ε4/3) were larger than those observed in the field, and field data indicates a cube power relationship: Deff = Dmol ε3. Dapp greatly increased in surficial layers at PM and PC in year two, suggesting that bioadvection caused by bioturbating organisms had occurred. The effects of bioturbation on transport to/from the sediments are modeled, and results can be applied to various sediment treatment scenarios such as capping.  相似文献   

7.
We have numerically modeled evolving fluid pressures and concentrations from a nine-year in situ osmosis experiment in the Pierre Shale, South Dakota. These data were obtained and recently interpreted by one of us (C.E.N.) as indicating a potentially significant role for chemical osmosis in media like the Pierre Shale. That analysis considered only the final pressure differentials among boreholes that were assumed to represent osmotic equilibrium. For this study, the system evolution was modeled using a recently developed transient model for membrane transport. The model simulates hydraulically and chemically driven fluid and solute transport. The results yield an estimate of the thickness of the water film between the clay platelets b of 40 Å, which corresponds to an osmotic efficiency σ of 0.21 for the ambient pore water salinity of 3.5 g/l TDS. These values largely confirm the results of the earlier equilibrium analysis. However, the new model analysis provides additional constraints suggesting that intrinsic permeability k = 1.4 × 10−19 m2, specific storage Ss = 1.7 × 10−5 m−1, and diffusion coefficient D* = 6 × 10−11 m2/s. The k value is larger than certain independent estimates which range from 10−21 to 10−20; it may indicate opening of microcracks during the experiments. The fact that the complex transient pressure and concentration behavior for the individual wells could be reproduced quite accurately, and the inferred parameter values appear to be realistic for the Pierre Shale, suggests that the new model is a useful tool for modeling transient coupled flows in groundwater systems.  相似文献   

8.
Polycyclic aromatic hydrocarbons (PAHs) were detected in water and sediment samples collected from three mariculture zones in China’s northern Yellow Sea. In these samples, total PAH concentrations ranged from 110.8 ng/L to 997.2 ng/L and 142.2 ng/g dry weight (dw) to 750.2 ng/g dw, respectively. The log KOC values of the various PAH compounds examined in this study increased with the log KOW values, which is consistent with the prediction regarding PAH behavior in the environment. However, these KOC values were lower than the predicted values as a result of the effects of organic matters, which were abundant in the mariculture water. The isomeric ratios of the PAHs in sediment indicated that the source of the PAHs in the mariculture zones were mainly pyrolytic. The TEQcarc values of PAHs ranged from 7 ng TEQ/g dw to 92 ng TEQ/g dw, and only a few samples met the safe criterion with respect to individual PAH concentrations.  相似文献   

9.
Long-term historical records of rainfall (P), runoff (Q) and other climatic factors were used to investigate hydrological variability and trends in the Volta River Basin over the period 1901-2002. Potential (Ep) and actual evaporation (E), rainfall variability index (δ), Budyko’s aridity index (IA), evaporation ratio (CE) and runoff ratio (CQ) were estimated from the available hydroclimatological records. Mann-Kendall trend analysis and non-parametric Sen’s slope estimates were performed on the respective time series variables to detect monotonic trend direction and magnitude of change over time.Rainfall variability index showed that 1968 was the wettest year (δ = +1.75) while 1983 was the driest (δ = −3.03), with the last three decades being drier than any other comparable period in the hydrological history of the Volta. An increase of 0.2 mm/yr2 (P < 0.05) was observed in Ep for the 1901-1969 sub-series while an increased of 1.8 mm/yr2 (P < 0.01) was recorded since 1970. Rainfall increased at the rate of 0.7 mm/yr2 or 49 mm/yr between 1901 and 1969, whereas a decrease of 0.2 mm/yr2 (6 mm/yr) was estimated for 1970-2002 sub-series. Runoff increased significantly at the rate of 0.8 mm/yr (23 mm/yr) since 1970. Runoff before dam construction was higher (87.5 mm/yr) and more varied (CV = 41.5%) than the post-dam period with value of 73.5 mm/yr (CV = 23.9%). A 10% relative decrease in P resulted in a 16% decrease in Q between 1936 and 1998. Since 1970, all the months showed increasing runoff trends with significant slopes (P < 0.05) in 9 out of the 12 months. Possible causes, such as climate change and land cover change, on the detected changes in hydroclimatology are briefly discussed.  相似文献   

10.
Estimating permeability from NMR well logs or mobile NMR core scanner data is an attractive method as the measurements can be performed directly in the formation or on fresh cores right after drilling. Furthermore, the method is fast and non-destructive. Compared to T 1 relaxation times, commonly measured T 2 distributions are influenced by external and internal magnetic field gradients. We performed two-dimensional T 1 and T 2 relaxation experiments on samples of Rhaetian sandstone, a rock with low porosity and small pore radii, using a mobile NMR core scanner which operates within a nearly homogeneous static magnetic field. Because small pore sizes are associated with high internal magnetic field gradients, standard methods from NMR logging in the oil industry cannot be applied for accurate permeability prediction. Therefore, a new model theory was developed, which describes the pore radius dependence of the surface relaxivity ρ 2 by both an analytical and a more practical empirical equation. Using corrected ρ 2 values, permeability can be predicted accurately from the logarithmic mean of the T 2 distribution and the physically based Kozeny-Carman equation. Additional core plug measurements of structural parameters such as porosity, permeability, specific inner surface area and pore radius distributions supported the NMR results.  相似文献   

11.
Heat transfer coefficients used in numerical simulations of volcanic eruptions are typically borrowed from industrial settings where the coefficients are well determined for non-permeable, machined (spherical) materials. Volcanic clasts, in contrast, are permeable and have irregular shapes. We performed a series of laboratory experiments to determine heat transfer coefficients for natural volcanic particles. We measured the surface and interior temperatures during cooling at wind speeds ranging from 0 to 10 m/s. We also measured the permeability and density of the particles. We find that the permeability of the particles has little effect on clast cooling. In the absence of any wind, heat loss occurs by free convection, and we find no relationship between the heat transfer coefficient and particle density. However, for non-zero Reynolds numbers (finite wind speed), the heat transfer coefficient decreases with increasing porosity. We obtain a correlation for the dimensionless heat loss, or Nusselt number, of the form Nu = 2 + aRe1/2Pr1/3 where a is a density dependent coefficient given by a = 0.00022ρ + 0.31, with ρ in kg/m3, and Re and Pr are the Reynolds number and Prandtl number, respectively. Compared with non-porous particles, heat transfer coefficients for natural pumice clasts are reduced by a factor of 2–3 for particles with similar Re. Numerical simulations show that this leads to an increase in depositional temperature by 50–90 °C.  相似文献   

12.
In the Jungwon area, South Korea, two contrasting types of deep thermal groundwater (around 20–33 °C) occur together in granite. Compared to shallow groundwater and surface water, thermal groundwaters have significantly lower δ18O and δD values (> 1‰ lower in δ18O) and negligible tritium content (mostly < 2 TU), suggesting a relatively high age of these waters (at least pre-thermonuclear period) and relatively long subsurface circulation. However, the hydrochemical evolution yielded two distinct water types. CO2-rich water (PCO2 = 0.1 to 2 atm) is characterized by lower pH (5.7–6.4) and higher TDS content (up to 3300 mg/L), whereas alkaline water (PCO2 = 10− 4.1–10− 4.6 atm) has higher pH (9.1–9.5) and lower TDS (< 254 mg/L). Carbon isotope data indicate that the CO2-rich water is influenced by a local supply of deep CO2 (potentially, magmatic), which enhanced dissolution of silicate minerals in surrounding rocks and resulted in elevated concentrations of Ca2+, Na+, Mg2+, K+, HCO3− and silica under lower pH conditions. In contrast, the evolution of the alkaline water was characterized by a lesser degree of water–rock (granite) interaction under the negligible inflow of CO2. The application of chemical thermometers indicates that the alkaline water represents partially equilibrated waters coming from a geothermal reservoir with a temperature of about 40 °C, while the immature characteristics of the CO2-rich water resulted from the input of CO2 in Na–HCO3 waters and subsequent rock leaching.  相似文献   

13.
Tidal current and elevation data were collected from five oceanographic moorings during October 2004 in Torres Strait, northern Australia, to assess the effects of large bedforms (i.e., sand banks) on the drag coefficient (CD) used for estimating bed shear stress in complex shallow shelf environments. Ten minute averages of tidal current speed and elevation data were collected for 18 days at an on-bank site (<7 m water depth) and an off-bank site (<10 m). These data were compared to data collected simultaneously from two shelf locations (<11 m) occupied to measure regional tidal behaviour. Overall CD estimates at the on- and off-bank sites attained 7.0±0.1×10−3 and 6.6±0.1×10−3, respectively. On-bank CD estimates also differed between the predominant east–west tidal streams, with easterly directed flows experiencing CD=7.8±0.18×10−3 and westerly directed flows CD=6.4±0.12×10−3. Statistically significant differences between the off-bank and on-bank sites are attributed to the large form drag exerted by the sand banks on the regional tidal currents, and statistically significant differences between the westward and eastward flows is ascribed to bedform asymmetry. Form drag from the large bedforms in Torres Strait comprises up to 65% of the total drag coefficient. When constructing sediment transport models, different CD estimates must therefore be applied to shelf regions containing steep bedforms compared to regions that do not. Our results extend the limited inventory of seabed drag coefficients for shallow shelf environments, and can be used to improve existing regional seabed mobilisation models, which have direct application to environmental management in Torres Strait.  相似文献   

14.
Emission rates of sulfur dioxide (SO2) were measured at Erebus volcano, Antarctica in December between 1992 and 2005. Since 1992 SO2 emissions rates are normally distributed with a mean of 61 ± 27 Mg d− 1 (0.7 ± 0.3 kg s− 1) (n = 8064). The emission rates vary over minutes, hours, days and years. Hourly and daily variations often show systematic and cyclic trends. Long-wavelength, large amplitude trends appear related to lava lake area and both are likely controlled by processes occurring at depth. Time series analysis of continuous sequences of measurements obtained over periods of several hours reveals periodicity in SO2 output ranging from 10 to 360 min, with a 10 min cycle being the most dominant. Closed and open-system degassing models are considered to explain observed variable degassing rates. Closed-system degassing is possible as rheological stiffening and stick/slip may occur within the system. However, the timescales represented in these models do not fit observations made on Erebus. Open-system degassing and convection fits the observations collected as the presented models were developed for a system similar to Erebus in terms of degassing, eruptive activity and process repose time. We show that with the observed emission rate (0.71 kg s− 1) and a crystal content of 30%, magma will cool 65 °C to match observed heat fluxes; this cooling is sufficient enough to drive convection.  相似文献   

15.
The Pontides are characterized by a series of Mesozoic-Cenozoic fold belts comprising a N-vergent foreland fold and thrust belt in the Western Pontides and a concave, upward-shaped fold belt in the Eastern Pontides. The curvature of the fold belt follows the Caucasus which may imply a phase of oroclinal bending. In order to test whether the fold curvature represents a phase of oroclinal bending, a paleomagnetic study has been carried out in the Eastern Pontides on late Cretaceous and middle Eocene volcanic and sedimentary rocks from 29 sites. Rock magnetic studies reveal medium-temperature components with an unblocking temperature of 400–580 °C, indicating pseudo-single domain titanomagnetite as the most abundant carrier of magnetic remanence in the middle Eocene rocks studied here. In the upper Cretaceous rocks, a high-temperature component with an unblocking range of 580–650 °C was isolated. Stepwise thermal and alternating field demagnetization isolated two components of remanent magnetization in middle Eocene rocks comprising a low unblocking temperature/coercivity component near the present field direction and a characteristic remanent magnetization (ChRM) component of Ds = 332.3°, Is = 49.9° (k = 33.3, α95 = 9.2°, N = 15 sites). A positive fold test at a 95% confidence level and a reversal test indicate a primary magnetization. Component analysis of the upper Cretaceous rocks identifies a stable ChRM Ds = 160.3°, Is = −45.0°, (k =  85.6, α95 = 6.0°, N =  8 sites) following removal of secondary remanence. Their ChRM direction passes fold and reversal tests at a 95% confidence level. Both the upper Cretaceous and middle Eocene paleomagnetic data from the Eastern Pontides and the Lesser Caucasus clearly demonstrate evidence of oroclinal bending that occurred contemporaneouslywith the convergence between Arabia and Eurasia in the Paleocene.  相似文献   

16.
Low tide rainfall may represent an important but little studied process affecting sediment fluxes on intertidal mudflats. In this study, we simulated rainfall events on an intertidal mudflat (median grain size=18.4 μm) of low slope (1 in 300) then quantified effects on sediment erodibility. Treatments consisted of a high (4.1 mm min−1 for 6 min) and low (0.36 mm min−1 for 60 min) rain intensity, chosen to match naturally occurring events and experiments were conducted seasonally (May and August) to encompass variations in ambient sediment stability. Changes in bed elevation due to rainfall were estimated using marked rods and sediment erodibility parameters (mass of sediment eroded at a flow velocity of 0.3 m s−1 (ME-30, g m−2) and critical erosion velocity (Ucrit, m s−1)) were determined in annular flumes (bed area=0.17 m2). Ambient/control sediment erodibility in May (ME-30=211 g m−2, Ucrit=0.18 m s−1) was higher than in August (ME-30=30 g m−2, Ucrit=0.26 m s−1) and was correlated with changes in biological activity. In May, surface sediment was influenced by high densities of the bioturbating snail Hydrobia ulvae (1736 ind. m−2) and low biomass of the sediment stabilising microphytobenthos (5.7 μg chlorophyll a cm−2). In contrast, in August H. ulvae densities were low (52 ind. m−2) and microphytobenthic biomass higher (9.2 μg chlorophyll a cm−2). The high rain treatment caused a decrease in bed elevation of between 1.5 mm (May) and 4.4 mm (August) and significantly reduced sediment organic content and microphytobenthic biomass. Rainfall increased sediment erodibility; compared to ambient sediments ME-30 increased by a factor of 1.4× in May and 8.8× in August and caused a 10–30% decline in Ucrit. The seasonal difference in treatment effect was due to the change in ambient sediment stability. The low rain treatment in August had no effect on bed elevation, microphytobenthic biomass or sediment erodibility. In May, the same treatment caused a reduction in bed elevation (0.5 mm) and microphytobenthic biomass but counter-intuitively, a decrease in sediment erodibility (ME-30 was reduced by 40%, Ucrit increased by 5%) compared to controls. We attribute this result to removal by rainfall of easily eroded surface flocs and biogenic roughness which resulted in an underlying sediment with a smoother surface and greater resistant to erosion. Results suggest that high intensity rain events may destabilise intertidal sediments making them more susceptible to erosion by returning tidal currents and that the sediment eroded during such events may represent a considerable fraction (up to 25%) of the seasonal variation in shore elevation. The impact of natural rain events are likely to vary considerably due to variations in droplet size, intensity and duration and the interaction with ambient sediment stability.  相似文献   

17.
The Schlumberger Doll Research (SDR) model and cross plot of porosity versus permeability cannot be directly used in tight gas sands. In this study, the HFU approach is introduced to classify rocks, and determine the involved parameters in the SDR model. Based on the difference of FZI, 87 core samples, drilled from tight gas sandstones reservoirs of E basin in northwest China and applied for laboratory NMR measurements, were classified into three types, and the involved parameters in the SDR model are calibrated separately. Meanwhile, relationships of porosity versus permeability are also established. The statistical model is used to calculate consecutive FZI from conventional logs. Field examples illustrate that the calibrated SDR models are applicable in permeability estimation; models established from routine core analyzed results are effective in reservoirs with permeability lower than 0.3 mD, while the unified SDR model is only valid in reservoirs with permeability ranges from 0.1 to 0.3 mD.  相似文献   

18.
In this study are discussed new SEM-EDS analyses performed on glass shards from five cores collected in the Central Adriatic Sea and two cores recovered from the South Adriatic Sea. A total of 26 tephra layers have been characterized and compared with the geochemical features of terrestrial deposits and other tephra archives in the area (South Adriatic Sea and Lago Grande di Monticchio, Vulture volcano). The compositions are compatible with either a Campanian or a Roman provenance. The cores, located on the Central Adriatic inner and outer shelf, recorded tephra referred to explosive events described in the literature: AP3 (sub-Plinian activity of the Somma-Vesuvius, 2710 ± 60 14C years BP); Avellino eruption (Somma–Vesuvius, 3548 ± 129 14C years BP); Agnano Monte Spina (Phlegrean Fields, 4100 ± 400 years BP); Mercato eruption (Somma–Vesuvius, 8010 ± 35 14C years BP; Agnano Pomici Principali eruption (Phlegrean Fields, 10,320 ± 50 14C years BP); Neapolitan Yellow Tuff (Phlegrean Fields, 12,100 ± 170 14C years BP). Some of these layers were also observed in the South Adriatic core IN68-9 in addition to younger (AP2, sub-Plinian eruption, Somma–Vesuvius, 3225 ± 140 14C years BP), and older layers (Pomici di Base eruption, Somma–Vesuvius, 18,300 ± 150 14C years BP). Significant is the tephra record of core RF95-7 that, for the first time in the Adriatic Sea, reports the occurrence of tephra layers older than 60 ka: the well known Mediterranean tephra layers X2 (ca. 70 ka), W1 (ca. 140 ka) and V2 (Roman origin, ca. 170 ka) as well as other tephra layers attributed, on the basis of geochemistry and biostratigraphy, to explosive eruptions occurred at Vico (138 ± 2 and 151 ± 3 ka BP) and Ischia (147–140 ka BP).  相似文献   

19.
The sequence of large Vulcanian explosions occurring at the andesitic Popocatépetl volcano, Mexico during November 1998 to April 1999 was studied. The size of 26 largest explosions was estimated from broadband seismic records at the distance of 4 km from the crater. The sequence began with the largest explosion (E = 2.6 × 1012 J) occurring on 25 November at 08:05, and following largest daily explosions were characterized by gradual decrease in the energy. The energy of 20 large (E ≥ 1011 J) explosions was distributed as Student's t-distribution with a geometrical mean Log E = 11.81 (J).  相似文献   

20.
The ‘Chicken Creek’ artificial catchment area, Welzow-South, E Germany, created to study processes and structures of initial ecosystem development, discharges into a small experimental lake (A=3805 m2, V=3992 m3, zmax=2.4 m). This lake was man-made in 2005 and filled by natural surface runoff until January 2006. In summer 2006 and 2008, the actual development of sediments and the evolution of the phosphorus (P) cycle were studied. 19.7% of the original lake volume was filled by sediment within the first 3 years. A fine-grained sediment representing silt (6.3-63 μm) accumulated at high accretion rates at the deepest point (200 mm a−1, 0-24 mm week−1) due to massive erosion in the catchment. The sediment is low in organic matter (2.5-5.2%) and total P (TP, 0.31-0.97 mg g−1). Low amounts of P associated with degradable organic matter and surplus of metal hydroxides (Fe:P∼40, Al:P∼20) favor an efficient P binding and low dissolved P concentrations in pore water (1-107 μg l−1). Hence, the mineral sediment quality and the low rates of P release (0.06 mg m−2 d−1) revealed that a lake at an initial stage of development has essentially no sedimentary P cycle compared to eutrophic shallow lakes. However, the increasing emersed and submersed macrophyte growth will control further lake succession by intensifying the internal nutrient cycling. The macrophytes drive the evolution of a sedimentary P cycle by mobilizing and translocating P, by accumulating carbon and thus by stimulating microbial and redox processes.  相似文献   

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