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1.
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   

2.
We estimated the net annual air–sea exchange of carbon dioxide (CO2) using monitoring data from the East Gotland Sea, Bornholm Sea, and Kattegat for the 1993–2009 period. Wind speed and the sea surface partial pressure of CO2 (pCO2w), calculated from pH, total alkalinity, temperature, and salinity, were used for the flux calculations. We demonstrate that regions in the central Baltic Sea and the Kattegat alternate between being sinks (−) and sources (+) of CO2 within the −4.2 to +5.2 mol m−2 yr−1 range. On average, for the 1994–2008 period, the East Gotland Sea was a source of CO2 (1.64 mol m−2 yr−1), the Bornholm Sea was a source (2.34 mol m−2 yr−1), and the Kattegat was a sink (−1.16 mol m−2 yr−1). Large inter-annual and regional variations in the air–sea balance were observed. We used two parameterizations for the gas transfer velocity (k) and the choice varied the air–sea exchange by a factor of two. Inter-annual variations in pCO2w between summers were controlled by the maximum concentration of phosphate in winter. Inter-annual variations in the CO2 flux and gas transfer velocity were larger between winters than between summers. This indicates that the inter-annual variability in the total flux was controlled by winter conditions. The large differences between the central Baltic Sea and Kattegat were considered to depend partly on the differences in the mixed layer depth.  相似文献   

3.
The attenuation characteristics of Indian lithosphere and its comparison with different tectonic settings in the world are determined from the observations of the Q for Lg(QLg)-, and S(QS)-waves in the 1-30 Hz frequency range. The scattering is approximated with a Gaussian distribution of spherical scatterers. To approximate single scattering, we use Dainty's [Geophy. Res. Lett. 8 (11) (1981) 1126] model that attenuation is given by 1/Q(ω) = 1/Qi + g(ω)v/ω, where Qi is intrinsic Q due to anelastic attenuation, v is shear wave velocity, ω is angular frequency, g = ∫n(a)σ da is the total scattering coefficient for S-to-S scattering, n(a) da is the number of scattering spheres of radius a per unit volume, and σ is the scattering cross-section for the sphere. We find that if n(a) is described by a simple two parameter (a0 and c) Gaussian of amplitude c and standard deviation and mean a0, the attenuation data for different regions of the world are well approximated over the frequency band of seismic observations. Our major findings are: (1) the maximum effect of scattering on attenuation occurs at 0.84 Hz or a wavelength of 4.16 km; (2) the values of g are frequency dependent. Values of g are of the order of 10−3 km−1 at 1-30 Hz, varying from 0.0031 to 0.01 and 0.001 to 0.0083 km−1 for tectonically active and stable regions, respectively; (3) regions of active tectonics and seismicity generally have lower Qi values (1000) than that in stable regions (2000); and (4) regions of high Qi value exhibit low intensity of scattering.  相似文献   

4.
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5.
The power of total coliforms (TC), faecal coliforms (FC) and Enterococci to predict the presence of Salmonella in seawater was investigated. Indicator cut-off values with the most satisfactory combination of sensitivity and specificity in predicting Salmonella presence were 1000 CFU 100 ml−1 TC, 200 CFU 100 ml−1 FC, 500 CFU 100 ml−1 Enterococci. When TC or FC were used for Salmonella prediction in logistic regression, then the addition of another indicator did not have a statistically significant effect. When Enterococci were used for prediction, then the addition of either of the two other indicators led to a statistically significant improvement (P = 0.001 for TC, P = 0.003 for FC). These results suggest that using either TC or FC alone provided an adequate indicator of Salmonella presence, but a statistically significant improvement is possible over using Enterococci alone. Concerning Enterococci, European Union limits for excellent coastal water quality (100 CFU 100 ml−1) and United States Environmental Protection Agency criteria for marine bathing waters (35 CFU 100 ml−1) have the same value in predicting Salmonella absence (92.5%).  相似文献   

6.
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   

7.
The southern Yellow Sea (SYS), located to the north of the East China Sea (ECS), was considered part of the ECS when Tsunogai et al. (1999) proposed the “continental shelf pump” (CSP) hypothesis. However, the original CSP carbon dioxide (CO2) uptake flux (2.9 mol C m−2 yr−1) appears to have been overestimated, primarily due to the differences between the SYS and the ECS in terms of their CO2 system. In this paper, we estimated air-sea CO2 fluxes in the SYS using the surface water partial pressure of CO2 (pCO2) measured in winter, spring, and summer, as well as that estimated in fall via the relationship of pCO2 with salinity, temperature, and chlorophyll a. The results indicate that overall, the entire investigated area was a net source of atmospheric CO2 during summer, winter, and fall, whereas it was a net sink during spring. Spatially, the nearshore area was almost a permanent CO2 source, while the central SYS shifted from being a CO2 sink in spring to a source in the other seasons of the year. Overall, the SYS is a net source of atmospheric CO2 on an annual scale, releasing ∼7.38 Tg C (1 Tg=1012 g) to the atmosphere annually. Thus, the updated CO2 uptake flux in the combined SYS and ECS is reduced to ∼0.86 mol C m−2 yr−1. If this value is extrapolated globally following Tsunogai et al. (1999), the global continental shelf would be a sink of ∼0.29 Pg C yr−1, instead of 1 Pg C yr−1 (1 Pg=1015 g).The SYS as a net annual source of atmospheric CO2 is in sharp contrast to most mid- and high-latitude continental shelves, which are CO2 sinks. We argue that unlike the ECS and the North Sea where carbon on the shelf could be exported to the open ocean, the SYS lacks the physical conditions required by the CSP to transport carbon off the shelf effectively. The global validity of the CSP theory is thus questionable.  相似文献   

8.
A population of Theodoxus fluviatilis L in the littoral zone of Lake Esrom was investigated from November 1977 to February 1979. The population was sampled every month in the winter period and twice during the rest of the year. Biomass was estimated as ash-free dry weight (AFDW) of the organic matter both of the soft parts of the animal and the shell itself. The relation between AFDW (c) and shell length (l) was log c=2.9509×log (l)−1.7120. The population comprised more than 1 year-class, which could be separated by shell length, by a narrow band on the shells and the growth of algae on the shell. The life cycle lasted years. The oldest animals had a shell length of 7.0-7.5 mm. A few individuals who were estimated to be years had a shell length up to 8.6 mm. Population density varied between 575 and 2115 individuals m−2 on the stony substratum. The average was 1160 individuals m−2. Mortality was low during the summer period. In winter many animals died due to the effect of ice and stormy weather on the stony substratum. Growth of the animals was estimated from the shell length. Maximum growth was observed from May to August with no growth during the winter. Egg capsules were found on the stones all year round. New capsules were found from late May to the middle of November. Most freshly laid capsules were observed in May-June and August-September. Capsules from the late summer hatched in spring and capsules laid in the spring hatched in August-September. The average annual net production for the whole population was estimated by three methods. The Allen curve method gave 1.895 AFDW m−2, the growth-increment method gave 1.784 mg AFDW m−2 and the Hynes method 2.284 mg AFDW m−2. Corresponding estimated P/B ratios were 1.29, 1.30 and 1.57. Annual net-production of the four investigated year-classes was 16 mg AFDW m−2 year−1 for 1975, 224 mg AFDW m−2 year−1 for 1976, 1.258 mg AFDW m−2 year−1 for 1977 and 287 mg AFDW m−2 year−1 for 1978. P/B ratios for the three oldest year-classes were, respectively, 0.32, 0.50 and 1.67. A comparison with other investigations on gastropod life cycles, reproduction and P/B ratios is made and differences discussed. Variations are correlated to temperature, and food quality and quantity.  相似文献   

9.
Huang L  Ma T  Li D  Liang FL  Liu RL  Li GQ 《Marine pollution bulletin》2008,56(10):1714-1718
A novel bacterium T7-2 was isolated from the oil-polluted sea-bed mud of Bohai Sea, northern China, which can degrade diesel oil at 15 °C. This bacterium was identified as a strain of Rhodococcus erythropolis according to its 16S rDNA gene. In order to enhance degradation efficiency, a five-level, three-factor central composite design was employed to optimize the nutrition supplied to artificial seawater. The results indicate that a supplement of 2.53 g (NH4)2SO4 L−1, 2.75 g Na2HPO4 L−1 and 0.01 g yeast extract L−1 to artificial seawater increases the degradation rate from 12.61% to 75% within 7 d.  相似文献   

10.
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11.
Semi-diurnal and fortnightly surveys were carried out to quantify the effects of wind- and navigation-induced high-energy events on bed sediments above intertidal mudflats. The mudflats are located in the upper fluvial part (Oissel mudflat) and at the mouth (Vasière Nord mudflat) of the macrotidal Seine estuary. Instantaneous flow velocities and mudflat bed elevation were measured at a high frequency and high resolution with an acoustic doppler velocimeter (ADV) and an ALTUS altimeter, respectively. Suspended particulate matter concentrations were estimated by calibrating the ADV acoustic backscattered intensity with bed sediments collected at the study sites. Turbulent bed shear stress values were estimated by the turbulent kinetic energy method, using velocity variances filtered from the wave contribution. Wave shear stress and maximum wave–current shear stress values were calculated with the wave–current interaction (WCI) model, which is based on the bed roughness length, wave orbital velocities and the wave period (TS). In the fluvial part of the estuary, boat passages occurred unevenly during the surveys and were characterized by long waves (TS>50 s) induced by the drawdown effect and by short boat-waves (TS<10 s). Boat waves generated large bottom shear stress values of 0.5 N m−2 for 2–5 min periods and, in burst of several seconds, larger bottom shear stress values up to 1 N m−2. At the mouth of the estuary, west south-west wind events generated short waves (TS<10 s) of HS values ranging from 0.1 to 0.3 m. In shallow-water environment (water depth <1.5 m), these waves produced bottom shear stress values between 1 and 2 N m−2. Wave–current shear stress values are one order of magnitude larger than the current-induced shear stress and indicate that navigation and wind are the dominant hydrodynamic forcing parameters above the two mudflats. Bed elevation and SPM concentration time series showed that these high energy events induced erosion processes of up to several centimetres. Critical erosion shear stress (τce) values were determined from the SPM concentration and bed elevation measurements. Rough τce values were found above 0.2 N m−2 for the Oissel mudflat and about 1 N m−2 for the Vasière Nord mudflat.  相似文献   

12.
The annual and life-cycle mercury bioaccumulation pattern in selected tissues of the economically relevant Elasmobranchii species Scyliorhinus canicula was studied, and the risks associated with its consumption evaluated.Preferential mercury bioaccumulation occurred in muscle tissue, and followed the order muscle > heart > liver > gills > pancreas. Total mercury in muscle tissue ranged from 0.13 mg kg−1 (wwt) in 1+ year old males to 0.8 mg kg−1 (wwt) in 8+ year old mature females, with no significant differences found between genders, and no clear lifespan bioaccumulation pattern observed, except for mature females. Organic mercury in the muscle ranged from 0.05 mg kg−1 (wwt) to 0.52 mg kg−1 (wwt), corresponding to an average of 70% of total mercury content. In mature females, a significant correlation (R = 0.99, P = 0.01) was found between size and organic mercury fraction, suggesting reproduction as an important factor controlling organic mercury bioaccumulation in the spotted dogfish.  相似文献   

13.
Two-dimensional numerical simulations of two-phase (DNAPL-water) flow in spatially correlated random fields demonstrate the influence of nonwetting phase (NWP) relative permeability–saturation (kr,N–SW) relationships correlated to porous media intrinsic permeability (k). Both the volume of porous media invaded by the NWP and the length of time during which the NWP is migrating are under predicted if kr,N–k correlation is not accounted for in the model formulation. Not accounting for the kr,N–k correlation resulted in under predicting the volume of porous media invaded by up to approximately 10%, which is likely not significant for many practical applications. However, not accounting for the kr,N–k correlation resulted in under predicting field scale migration times by up to a factor of 4, which is likely significant in that the migration times are on the order of years to several decades for the DNAPL (1,2-DCE) considered in this study. The under prediction of migration times was greater for lower permeability aquifers.  相似文献   

14.
Diverse linear and nonlinear statistical parameters of rainfall under aggregation in time and the kind of temporal memory are investigated. Data sets from the Andes of Colombia at different resolutions (15 min and 1-h), and record lengths (21 months and 8-40 years) are used. A mixture of two timescales is found in the autocorrelation and autoinformation functions, with short-term memory holding for time lags less than 15-30 min, and long-term memory onwards. Consistently, rainfall variance exhibits different temporal scaling regimes separated at 15-30 min and 24 h. Tests for the Hurst effect evidence the frailty of the R/S approach in discerning the kind of memory in high resolution rainfall, whereas rigorous statistical tests for short-memory processes do reject the existence of the Hurst effect.Rainfall information entropy grows as a power law of aggregation time, S(T) ∼ Tβ with 〈β〉 = 0.51, up to a timescale, TMaxEnt (70-202 h), at which entropy saturates, with β = 0 onwards. Maximum entropy is reached through a dynamic Generalized Pareto distribution, consistently with the maximum information-entropy principle for heavy-tailed random variables, and with its asymptotically infinitely divisible property. The dynamics towards the limit distribution is quantified. Tsallis q-entropies also exhibit power laws with T, such that Sq(T) ∼ Tβ(q), with β(q) ? 0 for q ? 0, and β(q) ? 0.5 for q ? 1. No clear patterns are found in the geographic distribution within and among the statistical parameters studied, confirming the strong variability of tropical Andean rainfall.  相似文献   

15.
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16.
The concentrations and sea-to-air fluxes of dissolved methane (CH4) were investigated in the North Yellow Sea during August 2006, January, April and October 2007. Dissolved CH4 concentrations showed obvious seasonal variation, with maximum values occurring in summer and lowest values occurring in winter. The saturations of dissolved CH4 in surface waters ranged from 78.7% to 1679.7% with an average of 252.4%. The estimated atmospheric CH4 fluxes using the Liss and Merlivat (LM86), and Wanninkhof formulae (W92) were (4.2±4.7), (11.6±10.3), (8.5±12.7) and (0.2±1.0), and (6.9±7.3), (14.6±22.3), (13.8±14.3) and (0.4±1.7) μmol·(m2 d)−1, respectively, for spring, summer, autumn and winter. Based on the average annual atmospheric CH4 flux and the area of the North Yellow Sea, the annual CH4 emission was estimated to be (2.4×10−2–4.2×10−2) Tg a−1, which suggests that the North Yellow Sea was a net source of atmospheric CH4.  相似文献   

17.
The State of São Paulo is the most developed area in Brazil and was impacted by persistent organic pollutants for several decades. This study investigated organochlorines in five species of small cetaceans (Pontoporia blainvillei, Stenella frontalis, Sotalia guianensis, Tursiops truncatus and Steno bredanensis) found dead along the coast of São Paulo between 1997 and 2003. DDTs (15.9 μg g−1 lipid; mean for all pooled individuals) and PCBs (8.08 μg g−1) exhibited the highest concentrations in the animals, reflecting large amounts formerly used in Brazil. Lower levels of mirex (0.149 μg g−1), HCB (0.051 μg g−1), CHLs (0.008 μg g−1) and HCHs (0.007 μg g−1) were detected in all species. Residual pattern of DDTs in dolphins suggests that o,p′-DDT is more recalcitrant than p,p′-DDT in the body of the animals and/or the environment. In contrast to p,p′-DDT, residues of o,p′-DDT seem to be preferentially converted into o,p′-DDD rather than o,p′-DDE.  相似文献   

18.
The distribution and photoreactivity of chromophoric dissolved organic matter (CDOM) in the northern Gulf of Mexico along the Louisiana coastal shelf were examined during three cruises in summer 2007, fall 2007, and summer 2008. The influence of the Mississippi River plume was clearly evident as CDOM levels (defined as a305) and dissolved organic carbon (DOC) concentrations were well-correlated with salinity during all cruises. Elevated CDOM and CDOM:DOC ratios of surface samples collected offshore of Atchafalaya Bay and the Breton-Chandeleur Sound complex indicated emanations of organic-rich waters from coastal wetlands are also an important source to nearshore shelf waters. Generally, CDOM and DOC levels were highest in surface waters and decreased with depth, but during summer 2007 and summer 2008, CDOM levels in near-bottom samples were occasionally higher than at mid-depths without concomitant increases in DOC. CDOM photobleaching was measured during 24 irradiations using a SunTest XLS+ solar simulator with photobleaching rate coefficients (k305) ranging from 0.011 to 0.32 h−1. For fall 2007 and summer 2008, higher k305 values were generally observed in samples with higher initial CDOM levels. However, samples collected during summer 2007 did not exhibit a similar pattern nor were there differences in photobleaching rates between surface and bottom samples. Spectral slope coefficients (S275-295 or S350-400) and DOC levels were largely unchanged after 24 h irradiations. Modeled CDOM photobleaching for northern Gulf of Mexico mid-shelf waters predicts that during the summer when solar irradiance is high and the water column becomes stratified, nearly 90% of the CDOM in the upper 1 m may be lost to photobleaching, with losses up to 20% possible even at 10 m depth.  相似文献   

19.
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20.
Estimates of clearance rates (CR) of Cerastoderma edule (300 ind. m−2) as a function of free-stream current velocity (U) (from 5 to 40 cm s−1) were compared between a small annular (60 l) and a large racetrack (8850 l) flume with different hydrodynamic conditions. Results showed that the flumes differ considerably in their hydrodynamic characteristics. The relationship between CR and U is different in the two flume tanks, however there appears to be a straightforward unimodal trend between CR and shear velocity (U*). It was found that the cockles themselves influence the benthic boundary layer (BBL) characteristics, by causing steeper velocity gradients and increasing the mixing over the cockle bed compared to bare sediment. This provides new evidence on how endobenthic organisms can affect the BBL. However, the influence of CR on U* could not be quantified because these parameters have interactive effects that cannot be dissociated.  相似文献   

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