Water column data and porewater profiles are used to study the chemical evolution with time and with depth of a eutrophic lake. By using different approaches, diffusion fluxes for dissolved iron, manganese and phosphate are calculated and used to describe the processes occurring at the sediment-water interface as well as in the hypolimnion of the lake. These data are used in the elaboration of a qualitative model to describe the chemical behaviour of the sedimentary interface of an anoxic lake with emphasis on the Fe/P/S system. Acorona model is proposed to explain the evolution with time of the diffusion process by estimating the relative contribution of bottom and lateral sediment surfaces to the total fluxes of dissolved elements diffusing from the sediment to the overlying water. As the hypolimnion becomes more anoxic, it has been observed that lateral sediment surfaces (16 to 10 meters in depth) represents a larger supplier of diffusing dissolved components than the bottom sediment portion (bottom to 18 meters). 相似文献
Electrophoretic variation in proteins encoded by seven presumptive gene loci was analyzed in four populations of the stygobiont amphipodNiphargus rhenorhodanensis. The four populations occur in different habitats, including one in drainage canals, another from sediments of the Ain River, a tributary of the Rhône River, and the remaining two occur in a karstic massif (Dorvan, Ain, France) in the epikarstic and at the base level of the massif, respectively. Six of the seven loci were polymorphic within or among populations, with as many as three electromorphs segregating at the most variable loci. Significant deficiencies in the frequency of heterozygotes were common. Genetic divergence between the two populations of the Dorvan Massif and between the two of the Ain River (forest and sediment habitats) was large. This was highly unexpected, particularly in the case of the two hydrologically connected populations of the Dorvan Massif. It is suggested that either low migration rates or the presence of ecological barriers to gene flow may result in strong genetic differention among local populations ofNiphargus. 相似文献
There are three populations of fluid inclusions in quartz from the Sybille Monzosyenite: early CO2, secondary CO2, and rare secondary brines. The oldest consist of low density CO2 (0.70) inclusions that appear to be co-magmatic. The densities of these inclusions are consistent with the inferred crystallization conditions of the Sybille Monzosyenite, namely 3 kilobars and 950–1000° C. The other types of inclusions are secondary; they contain CO2 (0.50) and secondary brine inclusions that form trains radiating out from a decrepitated inclusion. The sites of these decrepitated inclusions are now marked by irregularly shaped fluid inclusions and solid inclusions of salt and carbonate. Rather than fluid inclusions, feldspar contain abundant solid inclusions. These consist of magmatic minerals, hedenbergite, hornblende, ilmenite, apatite, and graphite, intimately associated with K, Na chlorides. We interpret these relations as follows: The Sybille Monzosyenite formed from a magma that contained immiscible droplets of a halide-rich melt along with a CO2 vapor phase. The salt was trapped along with the other obvious magmatic minerals during growth of the feldspars. CO2 may have also been included in the feldspars but it probably leaked later during exsolution of the feldspars and was not preserved. Both the saline melt and the CO2 vapor were trapped in the quartz. The melt inclusions in the quartz later decrepitated, perhaps due to progressive exsolution of fluids, to produce the secondary H2O and CO2 inclusions. These observations indicate that the Sybille Monzosyenite, which is a markedly anhydrous rock, was actually vapor-saturated. Rather than being H2O, however, the vapor was CO2-rich and possibly related to an immiscible chloride-rich melt. 相似文献
Bally, R.J., 1988. Some specific problems of wetted loessial soils in civil engineering. Eng. Geol., 25: 303–324.
Loessial soils, wetted above the limit of collapsibility, remain in the category of difficult foundation grounds. Some case histories are presented herein: surpassing soil bearing capacity and non-stabilized settlements of buildings after initially dry loess wetting; slow but nondamped settlements or damped but great and, eventually, non-uniform settlements of structures erected on wet loess; supplementary settlements by water level lowering in loessial ground; great settlements of deep foundations passing through the collapsible loess to the underlaying wet but noncollapsible loess. Research on wetted loess performed in the laboratory (oedometer, triaxial) or in situ (full-scale experiments or real constructions) have emphasized the dependence of the soil structural resistance, deformability (compressibility and deformation under constant volume) and final resistance on both the moisture content or stress-state and on their history; the depth propagation of the active zone of surface loadings on wetted loess is different from that of the linear elastic theory; some suggestions to estimate the depth of the active zone are presented. The usual foundation systems on wetted loessial grounds, or in their vicinity, adopted in Romania include: loessial or gravel cushions; surface compaction (very efficient results of intensive dynamic compaction); foundation “stamping” or loessial ground “reinforcing”. It is recommendable to take into consideration: surveyed wetting under construction until maximum moisture content of the loessial ground; in situ columns of stabilized loess; the efficiency of geotextiles for filter-drainage and antierosional functions in loessial soils. 相似文献
A study is reported of air pollution episodes in the Broye valley, a rural area of Switzerland located to the north-east of the city of Lausanne, in which a number of industrial sources of SO2 are located. The study comprises numerical simulations of regional-scale meteorology, local plume behavior, as well as a wind tunnel investigation of the same region in order to ascertain the relative advantages and disadvantages of numerical and physical modeling.
In situ data are available for certain episodes which occured during a very cold period in the winter of 1985, allowing intercomparisons to be made between nature and models. Furthermore, a significant effort undertaken by cantonal authorities has led to the setting up of a detailed emission inventory, which includes industry, individual domestic heating and traffic. Such an inventory has proved invaluable in imposing source terms in the models. 相似文献
Field analyses of compressional faulting and folding in the Foothills of western Taiwan enable us to reconstruct paleostress trajectories over a large area and to establish the relative chronology of tectonic events. Two main compressional events have contributed to the present structure of the fold-thrust belt. Stratigraphic data show that these events are Plio-Pliocene in age. Older normal faulting indicates NNW-SSE extension across the Chinesse passive continental margin during the Neogene. The two main compressional events of the Taiwan collision correspond to similar fan-shaped distributions of maximum compressive stress trajectories, with a counterclockwise shift of 30°–50° between the two events. Using the relationship between recent stress trajectories and the direction of recent plate motion as a guide, we reconstruct the direction of plate convergence for the older event. We suspect that the relative motion Philippine Sea plate-Eurasia has rotated counterclockwise of at least 35°–45° in Taiwan during collision. This conclusion is in agreement with independent plate tectonic reconstructions. Several problems provide objectives to further tectonic and paleomagnetic studies, including the duration and diachronism of compressional events as well as possible clockwise rotation of northernmost Taiwan. 相似文献
Audiomagnetotelluric soundings were carried out on the volcanic island of Mayotte (Comores Archipelago). The field method and data are described and discussed. All the sounding cross sections show coherent curves with a high conductive layer between 100 and 200 m. depth. This layer is considered to be a fluctuating water table zone correlated to yearly climatic changes under tropical weathering processes. Dipping and sudden level variations are linked to tectonic volcanic features and are the visualization of a block faulting system of the primitive basaltic shield, a consequence of a distensive phase possibly connected with the collapse of the western flank of the volcano. Piano-key panels are the typical sub-surface style and the guide-line for any water prospection on the volcano and the activity of the island water transfer system. 相似文献