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21.
Stefan Jansen Eva Walpersdorf Ursula Werner Markus Billerbeck Michael E Böttcher Dirk de Beer 《Ocean Dynamics》2009,59(2):317-332
In this article, we describe the dynamics of pH, O2 and H2S in the top 5–10 cm of an intertidal flat consisting of permeable sand. These dynamics were measured at the low water line
and higher up the flat and during several seasons. Together with pore water nutrient data, the dynamics confirm that two types
of transport act as driving forces for the cycling of elements (Billerbeck et al. 2006b): Fast surface dynamics of pore water chemistry occur only during inundation. Thus, they must be driven by hydraulics (tidal
and wave action) and are highly dependent on weather conditions. This was demonstrated clearly by quick variation in oxygen
penetration depth: Seeps are active at low tide only, indicating that the pore water flow in them is driven by a pressure
head developing at low tide. The seeps are fed by slow transport of pore water over long distances in the deeper sediment.
In the seeps, high concentrations of degradation products such as nutrients and sulphide were found, showing them to be the
outlets of deep-seated degradation processes. The degradation products appear toxic for bioturbating/bioirrigating organisms,
as a consequence of which, these were absent in the wider seep areas. These two mechanisms driving advection determine oxygen
dynamics in these flats, whereas bioirrigation plays a minor role. The deep circulation causes a characteristic distribution
of strongly reduced pore water near the low water line and rather more oxidised sediments in the centre of the flats. The
two combined transport phenomena determine the fluxes of solutes and gases from the sediment to the surface water and in this
way create specific niches for various types of microorganisms. 相似文献
22.
The texture diffractometer SV7-b which is operated at the Forschungszentrum Jülich as a user and service instrument has been improved with respect to the efficiency of the position-sensitive detector system and to the variety of wavelengths available. Instrumental aspects of data collection and different methods of data processing for pole figure evaluation are discussed. Recent examples of texture investigations on geological materials are presented for quartz, hematite, hematite-quartz, orthopyroxen-quartz and anorthosite rocks. 相似文献
23.
M. J. Zandvliet J. F. M. Van Doren O. H. Bosgra J. D. Jansen P. M. J. Van den Hof 《Computational Geosciences》2008,12(4):605-622
Over the past few years, more and more systems and control concepts have been applied in reservoir engineering, such as optimal
control, Kalman filtering, and model reduction. The success of these applications is determined by the controllability, observability,
and identifiability properties of the reservoir at hand. The first contribution of this paper is to analyze and interpret
the controllability and observability of single-phase flow reservoir models and to investigate how these are affected by well
locations, heterogeneity, and fluid properties. The second contribution of this paper is to show how to compute an upper bound
on the number of identifiable parameters when history matching production data and to present a new method to regularize the
history matching problem using a reservoir’s controllability and observability properties. 相似文献
24.
John Jansen Bassem Haddad Wayne Fassbender Patrick Jurcek 《Ground Water Monitoring & Remediation》1992,12(4):103-109
A frequency domain electromagnetic induction sounding survey (FDEM) was conducted on a landfill in northern Illinois to determine the depth of fill, locate areas of drum disposal, and locate areas of heavy metal sludge disposal. Sketchy information obtained from interviews of the site personnel identified specific exploration targets and areas of concern. The results of the geophysical survey verified much of the reported disposal history and identified areas suspected to contain hazardous waste.
Based on the results of the survey, the thickness of fill was estimated and two areas with highly conductive fill were located. These areas could represent leachate pockets or sludge disposal areas. An area in which the fill appears to be thicker than expected was identified. This area is thought to represent industrial sludge disposal in trenches excavated into the existing fill and underlying soils. An area with several linear in-phase, quadrature, and conductivity highs was detected. A subsequent magnetometer survey detected linear magnetic anomalies that are believed to be caused by parallel trenches filled with steel drums. This area is believed to be a previously unreported hazardous waste drum disposal cell excavated into the native soil.
As of this writing, the results of this survey have not been verified by traditional intrusive methods. When these investigations begin, we expect that information provided by the FDEM survey will reduce project costs by directing subsequent investigations, thereby reducing the number of borings and test pits required to characterize the site. While there is an unavoidable margin of error and uncertainty in remote sensing methods, the subsurface coverage provided by this geophysical survey could not have been reproduced by traditional methods without substantial expense. This paper presents the results of the survey and discusses application of the FDEM method on landfills. 相似文献
Based on the results of the survey, the thickness of fill was estimated and two areas with highly conductive fill were located. These areas could represent leachate pockets or sludge disposal areas. An area in which the fill appears to be thicker than expected was identified. This area is thought to represent industrial sludge disposal in trenches excavated into the existing fill and underlying soils. An area with several linear in-phase, quadrature, and conductivity highs was detected. A subsequent magnetometer survey detected linear magnetic anomalies that are believed to be caused by parallel trenches filled with steel drums. This area is believed to be a previously unreported hazardous waste drum disposal cell excavated into the native soil.
As of this writing, the results of this survey have not been verified by traditional intrusive methods. When these investigations begin, we expect that information provided by the FDEM survey will reduce project costs by directing subsequent investigations, thereby reducing the number of borings and test pits required to characterize the site. While there is an unavoidable margin of error and uncertainty in remote sensing methods, the subsurface coverage provided by this geophysical survey could not have been reproduced by traditional methods without substantial expense. This paper presents the results of the survey and discusses application of the FDEM method on landfills. 相似文献
25.
For ejections in the galactic centre (the galactic centre lobe, the galactic centre jet, and the low-energy jet), which were discovered recently, the efficiency of two low plasma- electron re-acceleration processes (Alfvén resonance heating and dissipation by magnetic non-equilibrium) considered recently by one of us (T.M.K.) are discussed and order of magnitude calculations for the dissipated power are given. 相似文献
26.
Predicting riverine dissolved silica fluxes to coastal zones from a hyperactive region and analysis of their first-order controls 总被引:2,自引:1,他引:1
Jens Hartmann Nils Jansen Hans H. Dürr Akira Harashima Kenji Okubo Stephan Kempe 《International Journal of Earth Sciences》2010,99(1):207-230
Silicate weathering and resulting transport of dissolved matter influence the global carbon cycle in two ways. First by the
uptake of atmospheric/soil CO2 and second by providing the oceanic ecosystems via the fluvial systems with the nutrient dissolved silica (DSi). Previous
work suggests that regions dominated by volcanics are hyperactive or even “hot spots” concerning DSi-mobilization. Here, we
present a new approach for predicting DSi-fluxes to coastal zones, emphasizing “first-order” controlling factors (lithology,
runoff, relief, land cover and temperature). This approach is applied to the Japanese Archipelago, a region characterized
by a high percentage of volcanics (29.1% of surface area). The presented DSi-flux model is based on data of 516 catchments,
covering approximately 56.7% of the area of the Japanese Archipelago. The spatial distribution of lithology—one of the most
important first order controls—is taken from a new high resolution map of Japan. Results show that the Japanese Archipelago
is a hyperactive region with a DSi-yield 6.6 times higher than the world average of 3.3 t SiO2 km−2 a−1, but with large regional variations. Approximately 10% of its area exceeds 10 times the world average DSi-yield. Slope constitutes
another important controlling factor on DSi-fluxes besides lithology and runoff, and can exceed the influence of runoff on
DSi-yields. Even though the monitored area on the Japanese Archipelago stretches from about 31° to 46°N, temperature is not
identified as a significant first-order model variable. This may be due to the fact that slope, runoff and lithology are correlated
with temperature due to regional settings of the Archipelago, and temperature information is substituted to a certain extent
by these factors. Land cover data also do not improve the prediction model. This may partly be attributed to misinterpreted
land cover information from satellite images. Implications of results for Earth System and global carbon cycle modeling are
discussed. 相似文献
27.
Francis X. O’Beirn Peter B. Heffernan Randal L. Walker Michelle L. Jansen 《Estuaries and Coasts》1996,19(3):651-658
Young-of-the-year (YOY) oysters (Crassostrea virginica) in the Gulf of Mexico mature sexually and spawn in their first year. This study determined whether YOY oysters in the southeastern United States also mature and spawn in their first year. In 1991 and 1993, 300 YOY oysters were marked in May and 20–30 were sampled in subsequent months along with 20 adult controls. Two sites were chosen in 1991 (House Creek and Skidaway River) and one in 1993 (Skidaway River). At House Creek, YOY oysters were mature and spawned in September. YOY oysters at Skidaway spawned in October. Adult oysters did not appear to spawn in 1991. In 1993, the adult oysters spawned in August and September whereas, the YOY oysters spawned heavily in October. Oyster recruitment in coastal Georgia extends through October. The potential contribution of YOY oysters to this late season set is substantial, given that the YOY oysters are relatively large (≈4 cm) and are found in greater numbers than the adults. Oysters are capable of having two, if not more, generations within one year, prior to exposure of disease-causing organisms. Also, this particular reproductive strategy would increase the oysters suitability as a test subject in population genetic studies. 相似文献
28.
Summary Array data processing techniques, which are based upon signal similarity between the stations, offer important tools in seismic signal analysis.P waves recorded in the Fennoscandian network in general exhibit the signal resemblance required for applying array processing methods. The largest station separation in this network is about 1800 km, and the site structures range from sedimentary rocks in Denmark to the homogeneous crust of the Baltic shield. Inother words, we can consider the Fennoscandian station network as a super-large aperture seismic array (SLASA). An analysis of the background noise shows that application of even very simple processing techniques results in very effective noise suppression.A general adaptation of array processing techniques to ordinary seismograph stations is considered possible. Such methods will greatly improve our ability to extract reliable information from ordinary seismograms. Although theC-D (compression-dilatation) readings are usually correct, they often do not refer to the very first signal onset. Records of nuclear explosions from stations all over the world exhibit a high degree of signal similarity. 相似文献
29.
Summary An efficient tool in seismic signal analysis is offered by the array data processing techniques which are based upon similarity of pulse shapes between stations. Records at the six Swedish stations in general exhibit the signal resemblance required by the array methods. By applying a simple processing technique, the signal-to-noise ratio is increased by a factor of about 2, and the accuracy ofP-wave readings is improved. High similarity is found not only between the same phase (P, pP) at different stations, but also between different phases (P, pP) at the same or different stations. Altogether, records of eleven earthquakes were investigated in detail. The Swedish station network can be considered as a super-large aperture seismic array (SLASA), despite some differences in instrumental equipment. A general adaptation of array techniques to SLASA systems is discussed. Such methods will greatly improve the seismological information which can be extracted from ordinary station records, provided the stations are located on geologically homogeneous ground. 相似文献
30.
We present a numerical model to quantify calcite dissolution in the guts of deposit feeding invertebrates. Deposit feeder guts were modeled as constantly stirred reactors (CSTRs) following terminology from digestion theory. Saturation state and dissolution of calcium carbonate were calculated from changes in total dissolved carbon dioxide and alkalinity resulting from sediment passage through the digestive tract, while accounting for dissolution of calcite and respiration of organic carbon. Typical dissolution rates for a gut volume of 1 ml ranged between 0.5-4 mg calcite d−1. Sensitivity analysis revealed gut pH, sediment organic matter (OM) content and OM reactivity to be the critical parameters determining calcite dissolution rate. Carbonate dissolution rate was inversely related to gut pH. However, calcite dissolution was found to be possible even at alkaline gut pH due to respiration by intestinal microbes. The kinetics of calcite dissolution had only marginal influence on daily calcite dissolution rates: Varying the calcite dissolution rate constant κ by six orders of magnitude affected calcite dissolution rates by less than a factor of 10. Calcite dissolution rates were calculated for 4 different hydrographic regimes that differed in their content of sedimentary calcite and OM and furthermore in their OM reactivity. Highest dissolution rates were calculated for the shallow water setting, where relatively high OM content facilitated high microbial respiration rates depressing gut pH. However, dissolution rates for the deep sea setting were only slightly lower, due to greatly elevated ingestion rates resulting from low OM content. As a consequence of much higher faunal abundances, shallow-water benthos is likely to contribute the vast majority of gut-mediated carbonate dissolution. Nevertheless, the fraction of sedimentary calcite that dissolves during one gut passage is probably too small to be observable by simple gravimetric analysis. This may explain the notable scarcity of evidence for gut-mediated carbonate dissolution in the literature to date. Assuming depth-dependent calcite dissolution rates and deposit feeder abundances, we estimate gut-mediated carbonate dissolution to contribute approximately 5% of the annual global sedimentary carbonate dissolution rate, which corresponds to an average calcite dissolution rate of approximately 0.5 mg m−2 d−1 for the entire ocean floor. 相似文献