首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 453 毫秒
1.
Over the last 25 years, considerable changes have been observed in the littoral vegetation of 11 lakes within the Sejny Lake District. In eight lakes (Dowcień, Jurkowo, Kunis, Miałkie, Pilwie, Płaskie, Wiłkokuk, Zelwa) where Chara species dominated, their communities declined or disappeared completely. In four of these lakes (Dowcień, Jurkowo, Kunis and Miałkie), charophytes were replaced by communities of the class Potametea (mainly Nupharo-Nymphaeetum albae and Ceratophylletum demersi). In three other lakes (Pilwie, Płaskie and Wiłkokuk), the area covered by charophyte communities decreased. In Lake Zelwa, Charetum rudis and Charetum jubatae disappeared while Charetum tomentosae and Charetum fragilis expanded. A total area of charophyte communities remained approximately the same. A considerable increase in the water total hardness and concentration was noted in each of the eight lakes. In most of them increased levels of dissolved organic matter (measured as COD-KMnO4) and pH were detected as well. However, the increase in the concentration was smaller in Lakes Wiłkokuk and Zelwa in which only slight changes in the vegetation were observed. In the above two lakes, the concentration of dissolved organic matter decreased and low water colour values are now noted. In three lakes (Długie, Dmitrowo and Gajlik), the charophyte communities tended to expand under the condition of moderate or high (Lake Długie) concentration, while dissolved organic matter concentrations were low. These lakes are also characterized by low values of colour. Charophyte communities may persist in lakes for a long period of time even when there is a moderate increase in concentration until the colour of water distinctly increases (>20 mg Pt L−1).  相似文献   

2.
Non-Darcian flow towards a well which fully penetrates a confined single vertical fracture is presented in this paper on the basis of the Izbash equation. We have obtained semi-analytical solutions for non-Darcian flow by using the Boltzmann transform and developed the non-Darcian flow well functions for cases with and without the effect of wellbore storage. The results show that the non-Darcian flow type curves are more or less deviated from the Darcian flow type curve. The non-linear effect is mainly attributable to the turbulent factor, v, a dimensionless parameter related to the pumping rate, the fracture aperture, the fracture thickness, and two constants k′ and n used in the Izbash power-law. The non-linear effect appears to be less sensitive to the power-law index, n. When excluding wellbore storage, the well function at early times is proportional to v−1/(n−1)u−n/(n−1), where u is a dimensionless term inversely proportional to time; whereas the well function at late times is approximated as , where A0(n) is a finite term depending on n. When considering wellbore storage, drawdowns inside the well with different v values approach the same asymptotic value at small times, and the effect of wellbore storage is only found at the early stage of pumping.  相似文献   

3.
In situ X-ray diffraction measurements on a calcium aluminosilicate (CAS) phase have been carried out using a laser-heated diamond anvil cell up to a pressure of 44 GPa, employing a synchrotron radiation source. CAS is the major mineral formed from sediments subducted into the Earth's mantle. The sample was heated using a YAG laser after each pressure increment to relax the deviatoric stress in the sample. X-ray diffraction measurements were carried out at T = 300 K using an angle-dispersive technique. The pressure was calculated using an internal platinum metal pressure calibrant. The Birch–Murnaghan equation of state for the CAS phase obtained from the experimental unit cell parameters showed a density of ρ0 = 3.888 g/cm3 and a bulk modulus of K0 = 229 ± 9 GPa for K′0 = 4.7 ± 0.7. When the first pressure derivative of the bulk modulus was fixed at K′0 = 4, then the value of K0 = 239 ± 2 GPa. From the experimental compressibility, the density of the CAS phase was observed to be lower than the density of co-existing Al-bearing stishovite, calcium perovskite, calcium ferrite-type phases, and (Fe,Al)-bearing Mg-perovskite in subducted sediments in the lower mantle. Therefore, the density of subducted sediments in the lower mantle decreases with increasing mineral proportion of the CAS phase.  相似文献   

4.
This study investigates the seismic demands due to the catastrophic 1999 Mw=7.4 Kocaeli and the Mw=7.1 Duzce earthquakes. The inelastic response spectra for the Kocaeli and Duzce earthquakes are investigated for systems with known strength and ductility. An analytical fiber element model is developed for a typical reinforced concrete building in Turkey. The interstory drifts are calculated from nonlinear dynamic analysis using 26 recorded strong-motion data from the 1999 Kocaeli and the Duzce earthquakes. In the dynamic analysis, the structural members are modeled by employing distributed plasticity fiber elements and both geometrical as well as material nonlinearities are taken into account. This study shows that the ductility and interstory drift demands due to the Kocaeli and the Duzce earthquakes were very severe (well above the code prescribed values) even for moderately inelastic structures. It is apparent from the results that the forward directivity effect is the most influential factor on the interstory drift demand. Both the distance to the fault rupture and the site conditions affect seismic demands, but the site conditions and the local topography are more influential than the distance from the fault rupture. This study shows that substantial damage should be expected in a future earthquake at all districts of Istanbul, but especially at Avcilar, Cekmece, Fatih, Bakirkoy and the Zeytinburnu districts. It is also shown that base isolation may substantially improve the performance of a structure in the inelastic domain and base isolated structures may be designed for lower minimum lateral strengths and higher strength reduction factors.  相似文献   

5.
《Journal of Hydrology》2001,240(3-4):206-224
A new model of the early evolution of limestone karst aquifers in the dimensions of length and depth is presented. In its initial state the aquifer consists of a rock massive with evenly spaced fractures of about 50 μm aperture widths with an hydraulic conductivity of 10−7 ms−1. In addition to this a coarser network of prominent fractures with aperture widths of several 100 μm is also present. Boundary conditions of constant recharge 450 mm/year, or constant head from the input of allogenic streams are imposed. First the position of the water table in the aquifer is calculated, then dissolutional widening during a time step in all the fractures below the water table is found by use of the well-known nonlinear dissolution kinetics of limestone. This is iterated and the position of the water table as well as the fracture widths are found as a function of time. In the case of constant recharge to a karst plateau, the water table in any case drops to base level and conduits there propagate from the spring headwards. If constant head conditions are valid the position of the water table remains almost stable and conduits propagate along the water table from the input towards the spring. There is competition between conduit evolution along prominent fractures and along tight fissures close to the water table. In any case under constant head conditions one of these pathways wins, and early karst evolution is terminated by a breakthrough event with an explosive increase of the flow through the aquifer until constant head conditions break down. Depending on the boundary conditions of constant head or constant recharge or a combination of both it is possible to describe models of cave genesis, which have been derived from field evidence, such as the water table models of Swinnerton and Rhoades as well as the four-state model by Ford and Ewers (Can. J. Earth Sci., 15 (1978) 1783).  相似文献   

6.
The singular evolutive extended Kalman (SEEK) filter has been proposed recently by Pham et al. (1997) for data assimilation into numerical oceanic models. This filter has been applied in different realistic ocean frameworks and has provided satisfactory results ( Pham et al., 1997; Verron et al., 1998). However, the SEEK filter remains expensive in real operational assimilation. To reduce cost and obtain a better representativity, we introduce the idea ‘local correction basis'. Such basis however cannot be made to evolve according to the model without destroying its locality property. Therefore we shall keep this basis fixed and we augment it by a few global basis vectors which evolve. The resulting semi-evolutive partially local filter is much less costly to implement than the SEEK filter and yet can yield better results. In the first application, validation twin experiments are conducted in a realistic setting of the OPA model over the tropical Pacific Ocean.  相似文献   

7.
On the use of microtremor recordings in seismic microzonation   总被引：4，自引：0，他引：4  
Experimental methods involving microtremor recordings are useful for determining site effects in regions of moderate seismic activity where ground motion records are few, and in urban or industrial contexts where the noise level is high. The aim of this study is to establish a microzonation by using the Nogoshi–Nakamura method,[1, 2] a simple experimental technique based on microtremor recordings. Since the physical phenomena underlying the method are only partially understood, the spectral responses obtained cannot be used alone. We, therefore, complete our experimental results by comparing them with the solutions of a one-dimensional numerical simulation (SHAKE91).[3, 4] The experimental programme was carried out on a plain near the Rhone Delta (South of France). H/V spectral ratios were calculated at 137 noise measurement points. In addition, we were able to compute the numerical transfer functions from soil columns defined by geotechnical characteristics inside the studied region. A comparison of the results obtained by the experimental and numerical methods showed that the fundamental frequencies are in good agreement, but that the amplitudes obtained by the two techniques are sometimes different. The analysis of H/V spectral ratios enabled us to establish maps to characterize the region: a resonance frequency map and maps of amplification levels as a function of frequency range, leading to a seismic microzonation for the whole of the region.  相似文献   

8.
Values of bulk modulus (K), shear modulus (G) and mechanical quality factor (Q) have been determined for polycrystalline samples across the CaTiO3 (CST0)–SrTiO3 (CST100) solid solution by resonant ultrasound spectroscopy. Because of similarities with low frequency elastic and anelastic anomalies due to twin wall motion reported in previous studies, a working hypothesis is developed in which dissipation processes are interpreted in terms of twin wall displacements. At high temperatures in CST50 the stability field of the I4/mcm structure is marked by the disappearance of all resonance peaks (superattenuation). This is attributed to anelastic domain wall sliding. At room temperature the I4/mcm phase of CST70 and CST80 has values of G which are lower than those of cubic or orthorhombic phases, and a concomitant drop in Q is interpreted as implying that the domain wall pinning process reported elsewhere to occur below 400–450 K is only partial. A similar drop in G and Q was found in CST95 below the transition at 238 K. The I4/mcm ↔ Pbcm transition in CST70 at 230 K is marked by an abrupt increase in Q, suggesting that mobile twins in crystals with the I4/mcm structure become effectively immobile in antiferroelectric crystals with the Pbcm structure. The I4/mcm ↔ Pnma transition in CST50 is marked by a similarly abrupt increase in Q, consistent with twin walls becoming effectively immobile also in crystals with the Pnma structure. A fall in Q below 800 K in CST0, however, could imply that a degree of twin wall mobility might develop in Pnma crystals if the tetragonal spontaneous strain departs significantly from zero. The remarkable attenuation behaviour of crystals with the I4/mcm structure at the relatively low stress conditions which apply during resonances of a parallelepiped with edge dimensions of 2–4 mm, is consistent with the view that a characteristic signature for tetragonal CaSiO3 in the Earth's lower mantle should be a marked attenuation of seismic waves.  相似文献   

9.
The estimation of the fundamental period of soil profiles has been the subject of numerous studies. An extensive evaluation of several procedures by Dobry et al. [1] concluded that both the Simplified Version of the Rayleigh Procedure [1] and the Successive Use of Two-Layer Solution by Madera [2] give errors of less than 10% for all of the 76 representative soil profiles considered in the evaluation. The simplified Rayleigh procedure is iterative and requires an initial estimate of the mode shape. The Madera procedure is based on the solution of a two-layer system, usually obtained from charts. In this paper the solution charts are replaced by approximate relations for implementation on a spreadsheet. Since the Madera procedure calculates only the fundamental period, mode shapes need to be calculated by other means. The Madera procedure is extended to calculate mode shapes and modal participation factors of layered soil profiles. Unlike the simplified Rayleigh procedure [1], the proposed solution incorporates the different densities of the layers and gives direct results without iterations. The proposed solution can be considered a simpler alternative to the Rayleigh method for shear beams or soil columns.  相似文献   

10.
Metallothionein (MT) from mammals is a low molecular weight (about 6–7 KD), and cystein-rich (20 cystein per molecular) protein (Vallee, 1991). So MT has the strong binding ability of metal such as Cd, Hg and Pd. Wild-typed cyanobacteria have their own metallothionein-like proteins, which are of low cysteine content and have weak ability to bind heavy metal. Therefore, it is imperative to transfer the MT-I gene from mammal into cyanobacteria cell for the absorption and accumulation of heavy metals in aqueous system including marine and lake ( Misra and Gedamu, 1989). We inserted the MT-I cDNA gene after the strong promoter PpsbA or Psmt into the intermediary vector pRL-439, and then pRL-MT was ligated with shuttle vector pKT-210 (a shuttle vector pDC-08 was used at an earlier time) to construct the shuttle expression vector pKT-MT. (The MT-I mutant -KKS- also was selected as aim gene.) Then the constructed vector was introduced into cyanobacterium Anabaena sp. PCC7120, Synechocystis sp. PCC6803 and Synechococcus sp. PCC7942 with triparental conjunctive transfer (Bryant, 1994). The expression efficiency is about 1%. We also used homologous recombination vector pTZ18-8 to introduce MT-I cDNA into chromosomes in cyanobacteria and got higher expression efficiency. Metal tolerance tests show that the transgenic cyanobacteria acquire metal resistance up to 60 μmol/g CdCl2 and expression efficiency up to 1045 μg MT/g fresh cells according to the data of ELISA.  相似文献   

11.
This paper provides a comprehensive overview of the merits and limitations of using an economics based approach to assess and implement initiatives for coastal habitat rehabilitation and creation. A review of the literature indicates that habitat rehabilitation/creation costs vary widely between and within ecosystems. For coral reefs, costs range from US$ 10,000 to 6.5 million/hectare (ha);1 for mangroves US$ 3000–510,000/ha; for seagrasses US$ 9000–680,000/ha and for saltmarshes US$ 2000–160,000/ha. A review of the economic benefits derived from various coastal habitats based on a ‘Total Economic Value’ approach (i.e. accounting for direct and indirect uses, and ‘non-uses’) reveals that many thousands of US$ per hectare could ultimately accrue from their rehabilitation/creation. The paper concludes that despite its limitations, the ‘benefit-cost analysis’ framework can play an important role both in assessing the justification of coastal habitat rehabilitation/creation initiatives, and by helping to improve the overall effectiveness of such initiatives.  相似文献   

12.
Spatial variation of earthquake ground motion is an important phenomenon that cannot be ignored in the design and safety of strategic structures. Several models have been developed to describe this variation using statistical, mathematical or physical approaches. The latter approach is not specific to an event. A recent contribution, which uses such an approach and called complete stochastic deamplification approach (CSDA), was developed [1]. The aim of this paper is to analyze the spatial variation of earthquake motion induced by the propagation of body waves using the CSDA. Coherency functions are evaluated for the cases of SH–SV–P waves propagating through stratified soil. Results obtained show that the variation of the coherency function is not the same for vertical and horizontal components and that the motion is more coherent at depth than at the free surface. In fact, we found that the rate of decrease with frequency and distance is not the same if P–SV waves propagate through stratified soil.  相似文献   

13.
Probabilistic seismic hazard maps for the Japanese islands   总被引：1，自引：0，他引：1  
Probabilistic seismic hazard maps are constructed by utilising a new methodology called the parametric-historic method, since it combines the best features of the ‘deductive’ ([2]) and ‘historic’ ( [4]) procedures.

The technique has been developed specifically for the estimation of seismic hazard at individual sites without the subjective judgment involved in the definition of seismic source zones, when specific active faults have not been mapped or identified, and when the causes of seismicity are not well understood. The combination of historical and instrumental data is permitted. The historical part of the catalogue contains only the strongest events, whereas the complete part can be divided into several subcatalogues, each assumed complete above a specified threshold of magnitude. Uncertainty in the determination of magnitude has also been taken into account. The maximum credible magnitude, mmax, is of paramount importance in this approach.

The seismic hazard maps are based on a long-term earthquake history (599–1997) compiled of the catalogues of Utsu (Utsu T. Catalog of large earthquakes in the region of Japan from 1885 through 1980. Bull Earthq Res Inst, Univ Tokyo, 1982;57:401–63), Usami (Usami T. Materials for comprehensive list of destructive earthquakes in Japan. Tokyo: Tokyo Press, 1996) and JMA for the Japanese islands. The analysis is based on subregions at a grid size of 0.05° along the Japanese islands, for each of which peak ground accelerations and spectral accelerations for natural frequencies of 1, 3, 5 and 10 Hz, are predicted and mapped to occur at a 10% probability in 50 years.  相似文献   


14.
The one-dimensional pressure head profile above a fixed water-table was studied for different steady infiltration rates. As shown in previous studies, when the infiltration rate (qin) is less than the soil saturated hydraulic conductivity (Ks), this profile can be divided into two parts: (1) from the water-table surface (z0) to an elevation zγ, the pressure head varies from 0 to a value hγ such as K(hγ)=−qin; (2) above the elevation zγ the pressure head is constant and equal to hγ. Above the water-table the zone where the pressure head is variable has been called ‘transition zone’. Its height is shown to be highly variable and to depend on soil properties as well as on the infiltration rate. This transition zone is not the ‘capillary fringe’ as defined by Gillham (Gillham R.W., 1984. The capillary fringe and its effect on water-table response. J. Hydrol. 67, 307–324). Numerical experiments performed with HYDRUS-2D® for the case of a water-table drained by parallel ditches have shown that the height of the transition zone is similar in the one-dimensional profile and in the two-dimensional system as long as the local slope of the water-table is small. This result is important since in a two-dimensional system, the transition zone is the place where all the horizontal component of the unsaturated flow occurs. The ratio of the horizontal component of the unsaturated flow vs the total horizontal flow in both the unsaturated and saturated zones has been computed. For a given soil, this ratio decreases as the infiltration rate increases; for a given infiltration rate, the soil with the thinnest transition zone transfers the largest amount of water above the water-table.  相似文献   

15.
A total of 51 potential pathogenic vibrios were isolated from moribund silver sea bream (Sparus sarba) collected from fish farms in Hong Kong. Using the API 20E system and the scheme of Alsina and Blanch (1994), 7 species were identified from all isolates. These species were Vibrio alginolyticus (24 strains), Vibrio vulnificus (12 strains), Vibrio parahaemolyticus (7 strains), Vibrio logei (4 strains), Vibrio pelagius II (2 strains), Vibrio fluvialis (1 strain) and Vibrio meditterranei (1 strain). The three dominant species (V. alginolyticus, V. vulnificus and V. parahaemolyticus) were confirmed to be virulent to sea bream by experimental challenge.

All isolates were screened for plasmid DNA by agarose gel electrophoresis and tested for susceptibility to 16 antibiotics by the agar dilution method. Of the 51 isolates examined, all strains were sensitive to ceftriaxone, streptomycin, nalidixic acid and rifampicin, and almost all were sensitive to ceftazidime, netilimicin, chloramphenicol and sulfamethoxazole. Most isolates were resistant to ampicillin (60.8%), cefuroxime (66.7%), amikacin (55%), kanamycin (58.8%) and trimethoprim (76.5%). Fifteen of the 51 isolates harboured 1–4 plasmids, with sizes ranging from 9 to 123 kb. Both the plasmids and the associated antibiotic resistance (ampicillin, cefuroxime and trimethoprim) of 9 isolates could be transferred to a recipient by single-step conjugation. However, the frequencies were very low, ranging from 10−11 to 10−9. The present results indicate that resistance to these antibiotics is chromosomal.  相似文献   


16.
The biotic composition, structure, and function of aquatic, wetland, and riparian ecosystem depend largely on the hydrological regime (Poff, N.L., Ward, J.V., 1990. Implications of streamflow variability and predictability for lotic community structure: a regional analysis of streamflow patterns. Can. J. Fisheries Aquat. Sci. 46, 1805–1818; Richter, B.D., Baumgartner, J.V., Wiginton, R., Braun, D.P., 1997 How much water does a river need? Freshwater Biol. 37, 231–249). Available flow data for many rivers in the world can be used to validate these ecological theories. There is a demand for studies that use hydrological indices to establish criteria, which serve to group together regime types at a local level. Once this has been done, these hydrologically similar groups can be used to identify communities of living organisms that are linked to specific aspects of the river's behaviour.

An approach to characterise flow regimes in the river network of the Tagus basin in Spain is presented. The river Tagus (río Tajo) is one of the seven major rivers of the Iberian peninsula. All hydrological data were acquired from the measurements made in the Tagus basin, at 25 gauging stations. Twelve variables were derived for each gauged site to describe variability and predictability of average streamflow conditions, and to describe the frequency, timing and intensity of high flow and low flow extremes.

A hierarchical clustering routine was used to identify similar groups of rivers as defined in terms of similar characteristics of their streamflow regime. The variables were also examined with simple correlations to determine if multicollinearity occurred, in order to reject redundant parameters or to identify similar behaviour trends between pairs of parameters. Some parameters have shown a tendency to increase or decrease along the east–west axis, suggesting that some of the studied characteristics may have a geographical cause.

Cluster analysis, with the values of the 12 parameters, reveals two main groups, each of which splits into two main subdivisions. One of these subgroups contains six rivers with similar characteristics, can be considered to be ‘classic regular rivers’, the stations in this first subgroup are mostly situated geographically close to each other. At the other end, we have found a subgroup, with a high variation of flows over the year and high flood flows; these rivers are highly irregular rivers with great changes. This regular–irregular gradient found between the groups is similar to that observed by others authors (Poff, N.L., Allan J.D., 1995. Functional organization of stream fish assemblages in relation to hydrological variability. Ecology 76, 606–627), and strong associations have been documented with compositions of populations and probably reflect differences in other similar important environmental factors.  相似文献   


17.
Mafic and ultramafic intrusions in East Greenland adjacent to the offshore Greenland–Iceland ridge were emplaced 5–9 My after continental breakup at 55 Ma [1]. Rare earth element (REE) concentrations determined by secondary ion mass spectrometry are reported for cumulus clinopyroxene from these intrusions, and the data are used to estimate REE abundance in equilibrium melts using available partitioning data. Estimated equilibrium melts from intrusions have strongly fractionated REE patterns with Nd/Dy(N) in the range 2 to 5.6 and Yb/Dy(N) 0.55 to 0.92, similar to values for coeval basalts. These melts have markedly higher Nd/Dy(N) than earlier breakup related flood basalts. The moderately low Yb/Dy(N) for the post-breakup volcanism is indicative of residual garnet in the source, while their high Nd/Dy(N) ratios can best be explained by aggregating low degree melts from a light-REE-enriched garnet- and spinel-bearing mantle source. We also report He, Sr, and Nd isotopic data for the intrusions. The highest 3He/4He ratios (>10 R/Ra) are found in the samples whose REE data reflect the largest proportion of melts from a garnet-bearing source, and having Sr and Nd isotopic compositions identical with the radiogenic Sr and unradiogenic Nd isotope end of the Iceland compositional field. There is no indication of a MORB-type mantle in the source of the intrusions. We postulate that post-breakup volcanism along the East Greenland coastline reflects the increasing proximity of the mantle plume to the East Greenland continental margin. The low degree of melting at high mean pressure inferred for the parental melts for the intrusions may reflect re-thickening of the lithosphere, which in turn was caused by the vigorous volcanism during breakup, with accompanying depletion of upper mantle and underplating of the crust at the continental margin.  相似文献   

18.
Anomalous transient electric signals (ATESs) in the ultra low frequency (ULF) band have been often observed during magnetotelluric (MT) investigations [Nature 319 (1986) 310; Phys. Earth Planet. Int. 114 (1999) 141; Geophys. J. Int. 142 (2000) 948], but their origin was unknown until now. They have the same characteristics as the so-called seismic electric signals (SES) claimed to be earthquake precursors by the VAN group (e.g. [Tectonophysics 110 (1984) 73] and later works by this group). Our analysis suggests that the so-called SES could be of anthropic origin. Following the devastating 7 September 1999 Athens earthquake, the VAN group claimed that a SES had been recorded at LAM station (Lamia, central Greece) some days prior to the main shock and that a second SES, which might correspond to an impending even larger earthquake, had been observed after the main shock. In the 2 years after the Athens main shock, no subsequent large earthquakes have occurred near Athens. We conducted a campaign of measurement in the Lamia region in May and June 2001. The results show that ATESs, which look like SES, have several different sources: pump-stations for ground-water, high power electric lines, and factories located to the SE of Lamia city. The ATESs can be generated by two electrochemical mechanisms of metallic electrode polarization: the “galvanic cell” and the “ac electrolytic cell” which are studied by simulated field experiments and discussed in detail in Appendix A. These two mechanisms can occur over a wide range of length scales in the field. Any isolation failure in buried metallic conductors, such as electrical and telecommunication networks, oil, water and gas pipes, railways, high power electric lines, factories and so on, can produce a galvanic cell or an ac electrolytic cell, or both, which could generate, under some circumstances, an “overvoltage”, the ATES. Finally, the absence of a magnetic signal has been observed during ATES and does not constitute a firm criterion for SES [Acta Geophys. Pol. 44 (1996b) 301]. Thus, great care must be taken when claiming the existence of electric precursors of seismic or volcanic events.  相似文献   

19.
Water chemical data from the Botucatu Sandstone aquifer in the São Paulo State part of the Paraná Basin, Brazil, was evaluated using geochemical methods and two statistical analyses: cluster analysis and factor analysis. The results were used to develop a conceptual geochemical model, in which three geochemical regions were identified, and their chemical behavior was modeled. The characteristic chemicals, changing from the recharge area to the center of the basin, are: SiO2—(HCO3− and Ca2+)—(Na+, CO32−, and SO42−). The distribution of the chemicals is interpreted as controlled by different water–rock interaction processes in the different regions. In the recharge area, dissolution of alkali–feldspar minerals in the sandstone is the main reaction observed; in the mid-section of the basin, calcite dissolution results in high calcium and bicarbonate concentration; in the center of the basin, leakage from underlying layers becomes the governing factor.  相似文献   

20.
Water-budget components and the vertical conductance were determined for Lowry (Sand Hill) Lake in north-central Florida, USA. In this type of lake, which interacts with both the surface-water and groundwater systems, the inflow components are precipitation, surface-water inflow, groundwater inflow, and direct runoff (i.e. overland flow), and the outflow components are evaporation, groundwater outflow, and surface-water outflow. In a lake and groundwater system that is typical of many karst lakes in Florida, a large part of the groundwater outflow occurs by means of vertical leakage through an underlying confining unit to a deeper, highly transmissive aquifer called the upper Floridan aquifer. The water-budget component that represents vertical leakage to the upper Floridan aquifer was calculated as a residual using the water-budget equation. For the 13 month period from August 1994 to August 1995, relative to the surface area of the lake, rainfall at Lowry Lake was 1.55 m yr−1, surficial aquifer inflow was 0.79 m yr−1, surface-water inflow was 1.92 m yr−1, and direct runoff was 0.01 m yr−1. Lake evaporation was 1.11 m yr−1, and surface-water outflow was 1.61 m yr−1. The lake stage increased 0.07 m yr−1, and the vertical leakage to the upper Floridan aquifer was 1.48 m yr−1. Surficial aquifer outflow from the lake was negligible. At Lowry Lake, vertical leakage is a major component of the water budget, comprising about 35% of the outflow during the study period. The vertical conductance (KV/b), a coefficient that represents the average of the vertical conductances of the hydrogeologic units between the bottom of a lake and the top of the upper Floridan aquifer, was determined to be 2.51 × 10−4 day−1 for Lowry Lake.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号