共查询到20条相似文献,搜索用时 31 毫秒
1.
David A. Jay Philip M. Orton Thomas Chisholm Douglas J. Wilson Annika M. V. Fain 《Estuaries and Coasts》2007,30(6):1106-1125
Estuarine turbidity maxima (ETM) retain suspended particulate matter (SPM) through advection, settling, aggregation, and nonlinearities
in bed processes, but the relative importance of these processes varies strongly between systems. Observations from two strongly
advective systems (the Columbia and Fraser Rivers) are used to investigate seasonal cycles of SPM retention and the effects
of very high flows. Results for the Fraser and Columbia plus literature values for 13 other estuaries illustrate the applicability
of scaling parameters and the response of ETM phenomena to a range of river flow (U
r
) levels and tidal forcing. The most efficient trapping (represented by Trapping EfficiencyE, the ratio of maximum ETM concentration to the source SPM concentration) occurs for low ratios of river flow to tidal current
amplitude (UT), represented by low values of the Supply number Sr.E in the Columbia is found to be maximal in a null zone where advection or tidal asymmetry (represented by Advection numberA) is weak(A ∼ 0). The ratio of aggregation to disaggregation (the Floc number Θ) is maximal on neap tides, while the ratio of erosion to
deposition (the Erosion number P) is maximal on spring tides. The ratio of settling velocity to vertical mixing (Rouse numberP) is relatively constant in the Columbia ETM(P ∼ 0.7), because particle settling velocity and turbulence levels adjust together. Assuming that this result applies broadly,
scaling variables and data are combined to express ETM properties in terms of the friction velocity (U*),U
r
, andU
T
, allowing a considerable simplification of the parameters used to describe ETM. 相似文献
2.
Annika M. V. Fain David A. Jay Doug J. Wilson Phil M. Orton Antonio M. Baptista 《Estuaries and Coasts》2001,24(5):770-786
We investigated seasonal and tidal-monthly, suspended particulate matter (SPM) dynamics in the Columbia River estuary from May to December 1997 using acoustic backscatter (ABS) and velocity data from four long-term Acoustic Doppler Profiler (ADP) moorings in or near the estuarine turbidity maximum (ETM). ABS profiles were calibrated and converted to total SPM profiles using pumped SPM samples and optical backscatter (OBS) data obtained during three seasonal cruises. Four characteristic settling velocity (W s) classes were defined from Owen Tube samples collected during the cruises. An inverse analysis, in the form of a non-negative least squares minimization, was used to determine the contribution of the four,W s-classes to each, total SPM profile. The outputs from the inverse analyses were 6–8 mo time-series ofW s-specific SPM concentration and transport profiles at each mooring. The profiles extended from the free surface to 1.8–2.7 m from the bed, with 0.25–0.50 m resolution. These time series, along with Owen Tube results and disaggregated size data, were used to investigate SPM dynamics. Three non-dimensional parameters were defined to investigate how river flow and tidal forcing affect particle trapping: Rouse numberP (balance between vertical mixing and settling) trapping efficiencyE (ratio of maximum SPM concentration in the estuary to fluvial source concentration), and advection numberA (ratio of height of maximum SPM concentration to friction velocity). The most effective particle trapping (maximum values ofE) occurs on low-flow neap tides. The location of the ETM and the maximal trapping migrated seasonally in a manner consistent with the increase in salinity intrusion length after the spring freshet. Maximum advection (high values ofA) occurred during highly stratified neap tides. 相似文献
3.
Determination of Coefficient of Radial Consolidation Using Steepest Tangent Fitting Method 总被引:1,自引:1,他引:0
J. S. Vinod A. Sridharan Buddhima Indraratna 《Geotechnical and Geological Engineering》2010,28(4):533-536
Barron (Trans ASCE 113:718–724, 1948) theoretical relationship between degree of consolidation (U
r
) and time factor (T
r
) is generally used to determine the coefficient of radial consolidation c
r
. Several researchers have proposed different laboratory techniques for obtaining the value of c
r
. However, the usual approach is to compare some salient features of the theoretical U
r
–T
r
relationship with the compression, δ and time, t based on the laboratory data. In this paper, rapid consolidation test procedure originally proposed by Su (J Soil Mech Found
Div Am Soc Civ Eng No. 95: Proc. Pap. 1729 (1–9), 1958) to determine the coefficient of vertical consolidation (c
v
) is extended to evaluate Barron’s coefficient of radial consolidation c
r
for the case of equal strain. The characteristic feature of the proposed method is the identification of the steepest tangent
from the δ–log t plot. The slope of steepest tangent is independent of the drain spacing ratio (n) with a value of 0.847. This approach is rapid, and it predicts more reliable values of c
r
as it is less influenced by the secondary compression. In addition, this method is more versatile and can be applied for
consolidation trends which do not always exhibit the typical S-shape. 相似文献
4.
R. Shynu V. Purnachandra Rao Pratima M. Kessarkar T. G. Rao 《Environmental Earth Sciences》2012,65(3):725-739
Studies on the suspended particulate matter (SPM) in the Mandovi estuary, western India indicate that during the monsoon and
pre-monsoon, the SPM increases, and the major and trace metals decrease from stations in the upstream to downstream of the
estuary. SPM is consistently low at all stations during the post-monsoon. Trace metals (Cu, Ni, Zn, Cr, and Pb) show strong
inter-relationships. They correlate well with Fe and Mn only during the monsoon. The concentrations of Cr, Cu, and Pb are
high during the post-monsoon. Enrichment factors and I
geo values of metals indicate that Mn shows significant to strong pollution in all seasons, while Cr, Ni, and Zn during monsoon,
and Cr during the post-monsoon show moderate pollution. SPM is controlled by the turbidity maximum, while major and trace
metals are governed seasonally by a combination of river discharge, resuspension, spillage of Fe–Mn particulates, and anthropogenic
contamination. Incursion of saline waters deep into the river channel during the dry season facilitates aggregation and settling
of particulate-borne pollutants close to the discharge area, thereby keeping the estuarine waters free from major contamination. 相似文献
5.
Brant W. Touchette Kirsten L. Rhodes Gracen A. Smith Mariana Poole 《Estuaries and Coasts》2009,32(5):917-925
Salt spray is one of many abiotic factors that can influence plant productivity and species composition in coastal ecosystems.
However, little is known about how marsh plants respond physiologically to the accumulation of sea aerosols on foliar tissues.
In this study, experimental microcosms maintained in controlled greenhouse conditions were used to evaluate how low- (1.7 mg
dm−2 day−1, weekly averages) and high- (8.6 mg dm−2 day−1) salt-spray loads would influence plant–water relations in Spartina alterniflora (Loisel.). While no differences in plant performance (e.g., changes in biomass and leaf area) were observed between the treatments
and control plants, a number of physiological modifications attributed to salt spray were observed. In general, salt-treated
plants underwent significant decreases in water potential (Ψ) and osmotic potential (Ψ
π) and increases in leaf conductance (g) and bulk modulus of elasticity (ε). It is likely that these physiological responses were used to generate lower Ψ while maintaining osmotic and water homeostasis. That is, by decreasing Ψ
π and increasing g and ε, more efficient water flow through the soil–plant–atmosphere continuum can be achieved, thus generating lower Ψ without promoting loss of turgor. 相似文献
6.
Pratima M. Kessarkar V. Purnachandra Rao R. Shynu Ishfaq Mir Ahmad Prakash Mehra G. S. Michael D. Sundar 《Journal of Earth System Science》2009,118(4):369-377
Systematic studies on the suspended particulate matter (SPM) measured on a seasonal cycle in the Mandovi Estuary, Goa indicate
that the average concentrations of SPM at the regular station are ∼20mg/l, 5mg/l, 19mg/l and 5mg/l for June–September, October–January,
February–April and May, respectively. SPM exhibits low-to-moderate correlation with rainfall indicating that SPM is also influenced
by other processes. Transect stations reveal that the SPM at sea-end stations of the estuary are at least two orders of magnitude
greater than those at the river-end during the monsoon. Estuarine turbidity maximum (ETM) of nearly similar magnitude occurs
at the same location in two periods, interrupted by a period with very low SPM concentrations. The ETM occurring in June–September
is associated with low salinities; its formation is attributed to the interactions between strong southwesterly winds (5.1–5.6ms−1) and wind-induced waves and tidal currents and, dominant easterly river flow at the mouth of the estuary. The ETM occurring
in February–April is associated with high salinity and is conspicuous. The strong NW and SW winds (3.2–3.7ms−1) and wind-driven waves and currents seem to have acted effectively at the mouth of the estuary in developing turbidity maximum.
The impact of sea breeze appears nearly same as that of trade winds and cannot be underestimated in sediment resuspension
and deposition 相似文献
7.
H. Chandra 《Journal of Earth System Science》1989,98(4):327-338
The effect of low-pass filtering on the various drift and anisotropy parameters obtained by full correlation analysis of spaced
receiver records is studied theoretically, assuming Gaussian correlation functions. A decrease in the characteristic velocityV
cis shown with increasing filtering, unlessV ≫ V
v, whenV
cincreases with filtering. The ratioV
c/V however shows an increase as the decrease in the true drift velocityV is steeper thanV
c. An increase in the size of the ground pattern with increasing filtering is also shown, while the axial ratio for anisotropic
patterns shows a decrease. The results are verified with experimental data recorded earlier at Tiruchirapalli. 相似文献
8.
Lars Chresten Lund-Hansen Thorbjørn Joest Andersen Morten Holtegaard Nielsen Morten Pejrup 《Estuaries and Coasts》2010,33(6):1442-1451
Optical constituents as suspended particulate matter (SPM), chlorophyll (Chl-a), colored dissolved organic matter (CDOM),
and grain sizes were obtained on a transect in the arctic fjord-type estuary Kangerlussuaq (66°) in August 2007 along with
optical properties. These comprised diffuse attenuation coefficient of downwelling PAR (K
d(PAR)), upwelling PAR (K
u(PAR)), particle beam attenuation coefficient (c
p), and irradiance reflectance R(−0, PAR). PAR is white light between 400 and 700 nm. The estuary receives melt water from the Greenland Inland Ice and stations
covered a transect from the very high turbid melt water outlet to clear marine waters. Results showed a strong spatial variation
with high values as for suspended matter concentrations, CDOM, diffuse attenuation coefficient K
d(PAR), particle beam attenuation coefficients (c
p), and reflectance R(−0, PAR) at the melt water outlet. Values of optical constituents and properties decreased with distance from the melt water
outlet to a more or less constant level in central and outer part of the estuary. There was a strong correlation between inorganic
suspended matter (SPMI) and diffuse attenuation coefficient K
d(PAR) (r
2 = 0.92) and also for particle beam attenuation coefficient (c
p; r
2 = 0.93). The obtained SPMI specific attenuation—K
d*(PAR) = 0.13 m2 g−1 SPMI—and the SPMI specific particle beam attenuation—c
p* = 0.72 m2 g−1—coefficients were about two times higher than average literature values. Irradiance reflectance R(−0, PAR) was comparatively high (0.09−0.20) and showed a high (r
2 = 0.80) correlation with K
u(PAR). Scattering dominated relative to absorption—b(PAR)/a(PAR) = 12.3. Results strongly indicated that the high values in
the optical properties were related to the very fine particle sizes (mean = 2–6 μm) of the suspended sediment. Data and results
are discussed and compared to similar studies from both temperate and tropical estuaries. 相似文献
9.
M. V. Kuznetsov Kh. F. Khaliullin A. I. Khaliullina V. G. Metlov L. V. Mossakovskaya 《Astronomy Reports》2011,55(11):989-999
We have derived the first photoelectric light curve of the eclipsing binary V974 Cyg from our own photoelectric observations.
Analysis of the light curve has yielded the system’s photometric elements (r
1 ≈ r
2 = 0.1192, e = 0.058, L
1 ≈ L
2 = 0.486, and L
3 = 0.028) and absolute parameters (M
1 ≈ M
2 = 2.2M
⊙, T
eff,1 ≈ T
eff,2 = 9500 K, a = 15.0R
⊙, distance d = 1.29 kpc, age log t = 8.0, t/tMS = 0.11). We have detected apsidal motion with the period U
obs
= (1140 ± 170) yrs, and the presence of a third body in the system. The orbital parameters derived for the third body are
P
3 = 26.5 yrs, e
3 = 0.78, and a
3 sin i
3 = 1.5 AU; and the lower limit for its mass is M
3 > 0.58M
⊙. The observed apsidal-motion rate is higher than is expected theoretically by a factor of 1.5. The axial rotation of the
system’s components is not yet synchronized with the orbital motion, probably because V974 Cyg is relatively young and detached. 相似文献
10.
Anna Wachnicka Evelyn Gaiser Laurel Collins Thomas Frankovich Joseph Boyer 《Estuaries and Coasts》2010,33(5):1080-1098
The composition and distribution of diatom algae inhabiting estuaries and coasts of the subtropical Americas are poorly documented,
especially relative to the central role diatoms play in coastal food webs and to their potential utility as sentinels of environmental
change in these threatened ecosystems. Here, we document the distribution of diatoms among the diverse habitat types and long
environmental gradients represented by the shallow topographic relief of the South Florida, USA, coastline. A total of 592
species were encountered from 38 freshwater, mangrove, and marine locations in the Everglades wetland and Florida Bay during
two seasonal collections, with the highest diversity occurring at sites of high salinity and low water column organic carbon
concentration (WTOC). Freshwater, mangrove, and estuarine assemblages were compositionally distinct, but seasonal differences
were only detected in mangrove and estuarine sites where solute concentration differed greatly between wet and dry seasons.
Epiphytic, planktonic, and sediment assemblages were compositionally similar, implying a high degree of mixing along the shallow,
tidal, and storm-prone coast. The relationships between diatom taxa and salinity, water total phosphorus (WTP), water total
nitrogen (WTN), and WTOC concentrations were determined and incorporated into weighted averaging partial least squares regression
models. Salinity was the most influential variable, resulting in a highly predictive model (r
apparent2 = 0.97, r
jackknife2 = 0.95) that can be used in the future to infer changes in coastal freshwater delivery or sea-level rise in South Florida
and compositionally similar environments. Models predicting WTN (r
apparent2 = 0.75, r
jackknife2 = 0.46), WTP (r
apparent2 = 0.75, r
jackknife2 = 0.49), and WTOC (r
apparent2 = 0.79, r
jackknife2 = 0.57) were also strong, suggesting that diatoms can provide reliable inferences of changes in solute delivery to the coastal
ecosystem. 相似文献
11.
Characteristics of winter mass balance of Glacier No.1 at the headwaters of the Urumqi River,Tianshan Mountains 总被引:1,自引:1,他引:0
This study analyzes the response of glacier to climate change during the past 49 years in Urumqi River source region, the
Tianshan Mountains of China. The temporal and spatial variations of winter mass balance (bn-w) at different time scales were
analyzed to identify their response to climate change during 1988–2006 (The observation of winter mass balance observation
began in 1988) on the Glacier No.1 at the headwaters of the Urumqi River, Tianshan Mountains, China. The winter accumulation
shows a significantly decreasing trend. The results show that the cumulative values on Glacier No.1 is 2,202 mm water equivalent
during 1988–2006 and the mean values is 116 mm a−1. Furthermore, the trend analysis of the winter mass balance indicates a rapid decrease since 1990, and the mean mass balance
is only 79 mm a−1 during 1997–2006. Winter mass balance correlates well negatively with the total evaporation from September to April (r = −0.68, α = 0.01), and positively with the total precipitation from September to April (r = 0.74, α = 0.01). However, winter mass balance shows a weak correlation with mean minimum air temperature during September
to April (r = −0.35), and runoff on September (r = −0.13). 相似文献
12.
Minimum energy geometries and electron density distributions, ϱ(r), for ∼40 polyatomic oxide molecules containing first and second row M-cations have been calculated at the Hartree-Fock level with a 6-311++G** basis set. The nature of the bonded interactions
in these molecules is examined in terms of the relative electronegativities, χ
M
, of the M-cations and the properties of the electron density distribution, ϱ(r
c
), evaluated at the bond critical points, r
c
, along each MO bond. As ϱ(r
c
) and the Laplacian of ϱ(r
c
) increase, χ
M
increases indicating an increase in the covalent character of the bonded interactions between M and O. The ratios of the curvatures of ϱ(r
c
) indicate that the NO bond is predominantly covalent, that the CO and SO bonds are of intermediate type and that the remaining
MO bonds are indicated to be predominantly ionic in character. A comparison of the critical point properties of ϱ(r
c
) and χ
M
indicates that the minimum energy MO bond length is an important determinate of the properties of ϱ(r
c
) and the character of the MO bonds.
On the other hand, values of the local energy density, H(r
c
), indicate that the LiO, BeO, NaO, MgO and AlO bonds are predominantly ionic and that the BO, CO, NO, SiO, PO and SO bonds
are predominantly covalent in character. The χ
M
-values provided by the properties of ϱ(r
c
) indicate that the covalent component of a bond increases with decreasing bond length, coordination number and increasing
bond strength. Each MO bond seems to represent a unique entity and to possess a distinct set of ϱ(r
c
) properties, the distinction being greater for the more electronegative cations.
The bonded radius of the oxide ion, r
b
(O), and the χ
M
-values determined from ϱ(r
c
) correlate with values determined from promolecule electron density distributions. In addition, r
b
(O) and χ
M
-values determined from experimental electron density distributions for crystals correlate with values determined from procrystal
electron density distributions. The number of critical points and bond paths are modeled rather faithfully by procrystal and
promolecule electron density distributions, despite the neglect of the binding forces in their constructions.
Received: October 15, 1996/Revised, accepted: February 10, 1997 相似文献
13.
Shahid Azam 《Geotechnical and Geological Engineering》2012,30(1):107-118
Knowledge of slurry settling is essential for geotechnical engineering applications such as coastal land reclamation and mine
waste disposal. In the presence of charged solids and ion-rich liquids, complex physicochemical interactions govern the behavior
of slurries. The main objective of this study was to develop a fundamental understanding of self-weight settling of laterite
ore slurries. To capture the influence of geology and the environment, samples were obtained from mining operations in different
parts of the globe. Based on laboratory testing, the investigated ores were found to be either oxide-rich with goethite, gibbsite,
meghamite and hematite making at least 90% of the material or clay-rich with chrysotile, cholritic intergrade, and siliceous
minerals accounting for more than 50% of the sample. The dominance of salt forming ions such as Na+, K+, Ca2+, Mg2+, Cl−, NO3
−, HCO3
− and SO4
2− in the pore waters indicated the influence of seawater on the waters used for slurry preparation. The oxide-rich ores in
low ionic waters resulted in flocculated fabrics whereas the clay-rich ores in high ionic waters led to cardhouse microstructures.
The aggregated fabrics with low tortuousity and fewer dead ends resulted in a high settling rate and amount (k
i
= 10−1 to 10−2 cm/s and SP = 62 to 49%) whereas the cardhouse morphologies with high tortuousity and lower pore connectivity exhibited a
slow and low settling (k
i
= 10−3 to 10−4 cm/s and SP = 37 to 17%). The initial hydraulic conductivity was found to be directly proportional to settling potential. 相似文献
14.
Selenium (Se), an animal toxicant and aquifer contaminant, occurs in coal mine environments of Wyoming. There is a paucity
of information on solution-phase Se speciation in mine soils. The objectives of this study were to compare Se extraction efficiencies
of various reagents and to characterize SeO2–
3 (selenite), SeO2–
4 (selenate) and organic Se components in these extracts. Forty coal mine soils were extracted using DI (deionized) water,
hot water (0.1% CaCl2), AB-DTPA, NaOH, and KH2PO4. Each solution was analyzed for total dissolved Se, and inorganic and organic Se fractions. Both inorganic and organic Se
fractions were detected in the soil extracts. The order of Se (total, inorganic, and organic) extraction efficiency for different
reagents was DI water < hot water < AB-DTPA < NaOH < KH2PO4. The inorganic–organic Se ratios in DI water, hot water, AB-DTPA, NaOH, and KH2PO4 extracts were 60 : 40, 26 : 74, 61 : 39, 87 : 13, and 52 : 48, respectively, indicating predominance of inorganic Se in all
but the hot water extract. Selenite was the dominant inorganic species in AB-DTPA and KH2PO4 extracts, while SeO2–
4 was the major Se species in the DI water, hot water, and NaOH extracts. Significant correlations (P<0.01) were observed among extractable inorganic Se [NaOH and KH2PO4 (r=0.95); hot water and AB-DTPA (r=0.89)], total soluble Se [DI water with hot water (r=0.98) and AB-DTPA (r=0.95)], and Se species [SeO2–
3 in AB-DTPA with SeO2–
4 in NaOH (r=0.94) and SeO2–
3 in KH2PO4 (r=0.88)]. These correlations are indicative of Se extraction efficiency, thermodynamically predicted chemical transformations
(such as oxidation of SeO2–
3 to SeO2–
4), and probable interconversions between the organic and inorganic Se fractions (r=0.70 in KH2PO4 extracts); as a whole the correlations can be used as statistical validations of possible geochemical processes.
Received: 21 August 1995 · Accepted: 16 October 1995 相似文献
15.
Vertical distribution patterns of organic geochemical constituents and the enzymes aminopeptidase and β-glucosidase provide
insights about the nature and reactivity of sediment organic matter in the sandy sediments of two shallow “South Texas” estuaries.
Sediment total organic carbon (TOC) δ13C values indicated that the organic matter (OM) was derived more from a mixture of seagrass and phytoplankton than from terrigenous
OM. Down-core amounts of TOC and total nitrogen (TN) were <0.2% of dry weight, respectively. Enzyme activities were highest
near surface and ranged from 25 to 1 μM/h for aminopeptidase as compared to 5 to 0.2 μM/h for glucosidase. In Aransas Bay,
aminopeptidase activity correlated with sediment TN content (r
s = 0.30) and β-glucosidase with TOC content (r
s = 0.27). In Copano Bay, aminopeptidase correlated with TOC, TN, and carbohydrate content (r
s = 0.89, 0.90, and 0.83, respectively). Variations of glucosidase activity also related positively to TOC, TN, and total carbohydrate
content (r
s = 0.68, 0.77, and 0.48, respectively). Overall, enzyme activities in these low OM, sandy sediments resembled those for other
benthic marine environments. 相似文献
16.
S. Feth G. V. Gibbs M. B. Boisen Jr. F. C. Hill 《Physics and Chemistry of Minerals》1998,25(3):234-241
Bond critical point properties calculated for the MN bonds in a number of geometry optimized nitride molecules containing first- and second-row M cations are compared with those calculated for a number of oxide molecules. As reported for the oxides, the value of the
electron density, ρ(r
c
), at the bond critical points, r
c
, increases with decreasing bond length while for the more electronegative cations, the local energy density, H(r
c
) decreases nonlinearly in value as the relative electronegativities of the M-cations, χ
M
, tend to increase. In the majority of cases, χM, |λ1|/λ3 and ∇2ρ(r
c
) increase with decreasing minimum energy bond lengths. The bond lengths adopted by the molecules are indicated to be an important
determinant of the critical point properties of the electron density distributions. The relative electronegativities derived
from the electron density distributions of the nitrides agree with those derived for the oxides and Pauling’s electronegativities
to within ∼5%, on average.
Received: 3 February 1997 / Revised, accepted: 11 July 1997 相似文献
17.
We consider groundwater steady flow in a heterogeneous porous formation of random and stationary log-conductivity Y = ln K, characterized by the mean 〈Y〉, and the two point correlation function C
Y
which in turn has finite, and different horizontal and vertical integral scales I and I
v
, respectively. The fluid velocity V, driven by a given head drop applied at the boundary, has constant mean value U ≡ (U, 0, 0). Approximate explicit analytical expressions for transverse velocity covariances are derived. The adopted methodology
follows the approach developed by Dagan and Cvetkovic (Spatial moments of kinetically sorbing plume in a heterogeneous aquifers,
Water Resour. Res. 29 (1993) 4053) to obtain a similar result for the longitudinal velocity covariance. Indeed, the approximate
covariances of transverse velocities are determined by requiring that they have the exact first order variances as well as
zero integral scale (G. Dagan, Flow and Transport in Porous Formations (Springer, 1989)) , and provide the exact asymptotic limits of the displacement covariance of the fluid particles obtained
by Russo (On the velocity covariance and transport modeling in heterogeneous anisotropic porous formations 1. Saturated flow,
Water Resour. Res., 31 (1995) 129). Comparisons with numerical results show that the proposed expressions compare quite well in the early time
regime, and for Ut/I >100. Since most of the applications, like assessing the effective mobility of contaminants or quantifying the potential
hazards of nuclear repositories, require predictions over higher times the proposed approximate expressions provide acceptable
results. The main advantage related to such expressions is that they allow obtaining closed analytical forms of spatial moments
pertaining to kinetically sorbing contaminant plumes avoiding the very heavy computational effort which is generally demanded.
For illustration purposes, we consider the movement of one contaminant species, and show how our approximate spatial moments
compare with the numerical simulations. 相似文献
18.
Zhiyuan Ma Juan Yu Yan Su Juan Xie Xubing Jia Yang Hu 《Environmental Earth Sciences》2010,59(5):995-1008
The thermal-waters resources in Weihe Basin of Shaanxi province, NW China are historically classified as middle- to low- temperature
thermal-waters in China. Recent exploitation of the deep thermal reservoir in the centre part of the basin (i.e. Xi’an and
Xianyang) had observed plentiful supply of thermal fluid with higher measured maximum temperature (120°C) and higher hydraulic
pressure (80.50 MPa) in the deeper (more than 4,000 m deep) sedimentary basin. A recent isotope study shows that deep geothermal
waters in the cities of Xi’an and Xianyang are characterized by an observable horizontal oxygen-18 (δ18O) shift and minor deuterium (2H) enrichment. The considerable oxygen shift is possibly due to the following four reasons: water–rock interaction at high
temperature, slow circulation rate of water, low water-to-rock ratio, and old age. On the end number of the δ18O shift, minor δ2H enrichment occur when there is higher concentrations of H2S, CH4, I and Br with lower rate of rSO4
2−/rCl− and r
Na+/r
Cl− suggesting relatively isolated geological environment. In a few thermal waters points,
r\textNa\text+ \text/r\textCl-r{\text{Na}}^{{\text{+}}} {\text{/}}r{\text{Cl}}^{-} < 0.85. This shows possible presence of formation waters. Combining the results from isotopic study and chemical analysis,
we can classify the types of geothermal waters into three groups, the shallow and fast circulating system, the semi-circulating
system and the deep and slow circulating system. 相似文献
19.
An integrated geological, geoelectrical and hydrochemical investigation of shallow groundwater occurrence in the Ibadan area,
southwestern Nigeria, is presented. The primary objective was to characterise the groundwater in a typical low-latitude environment
underlain by Precambrian crystalline basement complex rocks. The dominant rocks comprise suites of gneisses and quartzites.
Chemical analyses of the groundwater show that the mean concentration of the cations is in the order Na>Ca>Mg>K while that
for the anions is Cl>HCO3>NO3>SO4. Statistical analyses, using the product-moment coefficient of correlation, indicate positive correlations between the following
pairs of parameters: TDS and conductivity (r=0.96); Na++Mg2+ and Cl– (r=0.95); Na++K+ and Ca2+ (r=0.43); Na++K+ and HCO3
– (r=0.17); Ca2+ and Mg2+ (r=0.74); Ca2+ and HCO3
– (r=0.33); Ca2++Mg2+ and HCO3
– (r=0.31) and pH and HCO3
– (r=0.54). A very weak negative correlation was recorded between pH and Cl–, with r=–0.003. Five groundwater groups have been identified, namely, (1) the Na-Cl, Na-Ca-Cl, Na-Ca-(Mg)-Cl; (2) the Ca-(Mg)-Na-HCO3-Cl, Na-Ca-HCO3-Cl, and Ca-HCO3-Cl; (3) the Ca-(Mg)-Na-HCO3, Ca-Na-HCO3; (4) Ca-Na-Cl-(SO4)-HCO3 and (5) the Ca-(Mg)-Na-SO4-HCO3. The different groups reflect the diversity of bedrock types and consequently also of the products of weathering. Most of
the water sampled is unfit for drinking on account of the high NO3
– content. It can, however, be used for irrigation purposes as the sodium hazard is low while the salinity hazard ranges from
low to medium. Resistivity soundings indicate the presence of a thick weathering profile, which could be up to 60 m. Such
sites should be the target for any long-term and sustainable groundwater development in the area.
Received: 15 April 1998 · Accepted: 4 July 1998 相似文献
20.
H. Graetsch 《Physics and Chemistry of Minerals》2001,28(5):313-321
The crystal structure of intermediate incommensurate tridymite was refined at 150 °C from powder data. Upon cooling from
above 220 °C, the basic structure with space group symmetry C2221 is gradually distorted from orthorhombic to monoclinic symmetry. With decreasing temperature, the monoclinic angle γ smoothly
opens up to 90.3°, while a displacive modulation with temperature-dependent wavelength develops. The 3 + 1 dimensional superspace
group of the incommensurate phase is C1121(αβ0). The modulation mainly consists of two sinusoidal transverse displacement waves for the silicon atoms coupled to rotations
of the rigid SiO4/2 tetrahedra. The wave vector is r=0.1192(1)a* − 0.0043(1)b* at 150 °C. Below 150 °C tridymite discontinuously transforms to another orthorhombic phase and the modulation partially
locks in at the wave vector r
1=1/3a*. Simultaneously, an additional incommensurate modulation with r
2= 0.0395(1)b* − 0.3882(1)c* is formed. The two-dimensional modulation does not vary significantly with the temperature.
Received: 13 September 2000 / Accepted: 29 January 2001 相似文献