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排序方式: 共有211条查询结果,搜索用时 140 毫秒
31.
Justus E. E. van Beusekom Sabine Diel-Christiansen 《International Journal of Earth Sciences》2009,98(2):269-280
Phytoplankton plays a dominant role in shelf biogeochemistry by producing the major part of organic matter. Part of the organic
matter will reach the sediment where diagenetic processes like denitrification, apatite formation or burial will remove nutrients
from the biogeochemical cycle. In this article current knowledge on the decadal plankton variability in the North Sea is summarized
and possible implications of these changes for the biogeochemistry of the North Sea are discussed. Most of the observed interdecadal
dynamics seem to be linked to large-scale oceanographic and atmospheric processes. Prominent changes in the North Sea ecosystem
have taken place around 1979 and 1988. In general, the phytoplankton color (CPRS indicator of phytoplankton biomass) reached
minimum values during the end of the 1970s and has increased especially since the mid 1980s. Changes with a similar timing
have been identified in many time series from the North Sea through the entire ecosystem and are sometimes referred to as
regime shifts. It is suggested that the impact of global change on the local biogeochemistry is largely driven by the phyto-
and zooplankton dynamics during spring and early summer. At that time the extent of zooplankton–phytoplankton interaction
either allows that a large part of the new production is settling to the sediment, or that a significant part of the new production
including the fixed nutrients is kept within the pelagic system. The origin of the extent of the phytoplankton–zooplankton
interaction in spring is probably set in the previous autumn and winter. In coastal areas, both large-scale atmospheric and
oceanographic changes as well as anthropogenic factors influence the long-term dynamics. Due to eutrophication, local primary
production nowadays still is up to five times higher than during pre-industrial conditions, despite a decreasing trend. Recently,
introduced species have strengthened the filter feeder component of coastal ecosystems. Especially in shallow coastal seas
like the Wadden Sea, this will enhance particle retention, shift organic matter degradation to the benthic compartment and
enhance nutrient removal from the biogeochemical cycle by denitrification or apatite formation. 相似文献
32.
Filiz Bilgili Hans-Jürgen Götze Roman Pašteka Sabine Schmidt Ron Hackney 《International Journal of Earth Sciences》2009,98(3):571-583
An unsolved problem of regional importance for both the evolution and structure of the Northwest German Basin is the existence
or non-existence of the so-called Bramsche Massif. Explaining the nature of this massif and the cause of a related strong,
positive Bouguer anomaly (Bramsche Anomaly) is critical. In the study described here, we tested an existing “intrusion model”
against a newer “inversion model” in the southern Northwest German Basin. In the intrusion model, the strongly-positive Bouguer
anomaly represents the gravity effect of an intrusion at depths between 6 and 10 km. More recent interpretations invoke tectonic
inversion rather than intrusion to explain increased burial and the low level of hydrocarbon maturity found in boreholes.
We tested these different interpretations by constructing 3D forward density models to 15 km depth. The intrusion model was
updated and adjusted to incorporate recent data and we also modelled pre-Zechstein structures using different scenarios. The
final model has a very good fit between measured and modelled gravity fields. Based on currently available seismic and structural
models, as well as borehole density measurements, we show that the positive Bouguer anomaly cannot be modeled without a high-density,
intrusive-like body at depth. However, further in-sight into the crustal structures of the Bramsche region requires more detailed
investigations.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
33.
Sabine Caré Richard Crane Paolo S. Calabrò Antoine Ghauch Emile Temgoua Chicgoua Noubactep 《洁净——土壤、空气、水》2013,41(3):275-282
Over the past 30 years the literature has burgeoned with in situ approaches for groundwater remediation. Of the methods currently available, the use of metallic iron (Fe0) in permeable reactive barrier (PRB) systems is one of the most commonly applied. Despite such interest, an increasing amount of experimental and field observations have reported inconsistent Fe0 barrier operation compared to contemporary theory. In the current work, a critical review of the physical chemistry of aqueous Fe0 corrosion in porous media is presented. Subsequent implications for the design of Fe0 filtration systems are modeled. The results suggest that: (i) for the pH range of natural waters (>4.5), the high volumetric expansion of Fe0 during oxidation and precipitation dictates that Fe0 should be mixed with a non‐expansive material; (ii) naturally occurring solute precipitates have a negligible impact on permeability loss compared to Fe0 expansive corrosion; and (iii) the proliferation of H2 metabolizing bacteria may contribute to alleviate permeability loss. As a consequence, it is suggested that more emphasis must be placed on future work with regard to considering the Fe0 PRB system as a physical (size‐exclusion) water filter device. 相似文献
34.
S. Bauer H. Class M. Ebert V. Feeser H. G?tze A. Holzheid O. Kolditz Sabine Rosenbaum W. Rabbel D. Sch?fer A. Dahmke 《Environmental Earth Sciences》2012,67(2):351-367
Capture and geological sequestration of CO2 from large industrial sources is considered a measure for reducing anthropogenic emissions of CO2 and thus mitigating climate change. One of the main storage options proposed are deep saline formations, as they provide the largest potential storage capacities among the geologic options. A thorough assessment of this type of storage site therefore is required. The CO2-MoPa project aims at contributing to the dimensioning of CO2 storage projects and to evaluating monitoring methods for CO2 injection by an integrated approach. For this, virtual, but realistic test sites are designed geometrically and fully parameterized. Numerical process models are developed and then used to simulate the effects of a CO2 injection into the virtual test sites. Because the parameterization of the virtual sites is known completely, investigation as well as monitoring methods can be closely examined and evaluated by comparing the virtual monitoring result with the simulation. To this end, the monitoring or investigation method is also simulated, and the (virtual) measurements are recorded and evaluated like real data. Application to a synthetic site typical for the north German basin showed that pressure response has to be evaluated taking into account the layered structure of the storage system. Microgravimetric measurements are found to be promising for detecting the CO2 phase distribution. A combination of seismic and geoelectric measurements can be used to constrain the CO2 phase distribution for the anticline system used in the synthetic site. 相似文献
35.
Sabine Geiß Nicole Lettmann Aurélien Rey Herbert Lepper Birgit Körner Silvio Mais Theodor Prey Bettina Hilger Moana Engelke Stephan Lebertz Claudine Chatellier George Sawal Dirk Löffler Tom Schillings 《洁净——土壤、空气、水》2011,39(6):537-542
A first preliminary interlaboratory trial was planned to prepare ISO/DIS 12010: Water quality – determination of short chain polychlorinated alkanes (SCCP) in water – method using GC/MS and electron capture negative ionisation (ECNI). The task was to determine the sum of short chain polychlorinated n‐alkanes with carbon chain lengths of C10–C13 and a chlorine content between 49 and 67% in water by GC‐ECNI‐MS and quantification by multiple linear regression described in ISO/DIS 12010 as the compulsory method. Distributed samples were obtained from a real water extract spiked with a target concentration of 0.4 µg/mL sum of SCCP, i.e. the environmental quality target level according to the Water Framework Directive. The interlaboratory trial included the calibration, a column chromatographic clean up, a concentration step and an integration of chromatographic unresolved humps as well as the quantification with multiple linear regression. Reproducibility standard deviations between 21.5 and 22.9% were achieved by 17 participating laboratories from four countries. The method outlined no significant difference of the results between the standard solution and a real water matrix extract. On the basis of this succeeded preliminary interlaboratory trial the final interlaboratory trial for validation of ISO 12010 was prepared in autumn 2010. 相似文献
36.
Female and male individuals of the same species often differ with respect to their susceptibility to toxicant stress. In the present study, sea urchins (Psammechinus miliaris) of both sexes were exposed to high (150 μg L?1) and environmentally relevant (5 μg L?1) concentrations of phenanthrene over 10 days. While food intake was significantly decreased following exposure to 150 μg L?1 phenanthrene, histological indices (lipofuscin accumulation, fibrosis, oocyte atresia), energetic status (energy charge, sum adenylates, AMP/ATP ratio) as well as ascorbate levels in the gonads showed either little or no effect upon phenanthrene exposure. However, most parameters (vitamin C, energy charge, sum adenylates, AMP/ATP ratio, ATP and ADP concentrations, lipofuscin content, fibrosis) significantly differed between male and female animals. This study illustrates the difficulties to identify toxic injury in reproductive tissue as it may be superimposed by gametogenesis and spawning of gametes. 相似文献
37.
Patrick Drupp Eric Heinen De Carlo Fred T. Mackenzie Paul Bienfang Christopher L. Sabine 《Aquatic Geochemistry》2011,17(4-5):473-498
The marine shelf areas in subtropical and tropical regions represent only 35% of the total shelf areas globally, but receive a disproportionately large amount of water (65%) and sediment (58%) discharges that enter such environments. Small rivers and/or streams that drain the mountainous areas in these climatic zones deliver the majority of the sediment and nutrient inputs to these narrow shelf environments; such inputs often occur as discrete, episodic introductions associated with storm events. To gain insight into the linked biogeochemical behavior of subtropical/tropical mountainous watershed-coastal ocean ecosystems, this work describes the use of a buoy system to monitor autonomously water quality responses to land-derived nutrient inputs and physical forcing associated with local storm events in the coastal ocean of southern Kaneohe Bay, Oahu, Hawaii, USA. The data represent 2.5 years of near-real time observations at a fixed station, collected concurrently with spatially distributed synoptic sampling over larger sections of Kaneohe Bay. Storm events cause most of the fluvial nutrient, particulate, and dissolved organic carbon inputs to Kaneohe Bay. Nutrient loadings from direct rainfall and/or terrestrial runoff produce an immediate increase in the N:P ratio of bay waters up to values of 48 and drive phytoplankton biomass growth. Rapid uptake of such nutrient subsidies by phytoplankton causes rapid declines of N levels, return to N-limited conditions, and subsequent decline of phytoplankton biomass over timescales ranging from a few days to several weeks, depending on conditions and proximity to the sources of runoff. The enhanced productivity may promote the drawing down of pCO2 and lowering of surface water column carbonate saturation states, and in some events, a temporary shift from N to P limitation. The productivity-driven CO2 drawdown may temporarily lead to air-to-sea transfer of atmospheric CO2 in a system that is on an annual basis a source of CO2 to the atmosphere due to calcification and perhaps heterotrophy. Storms may also strongly affect proximal coastal zone pCO2 and hence carbonate saturation state due to river runoff flushing out high pCO2 soil and ground waters. Mixing of the CO2-charged water with seawater causes a salting out effect that releases CO2 to the atmosphere. Many subtropical and tropical systems throughout the Pacific region are similar to Kaneohe Bay, and our work provides an important indication of the variability and range of CO2 dynamics that are likely to exist elsewhere. Such variability must be taken into account in any analysis of the direction and magnitude of the air?Csea CO2 exchange for the integrated coastal ocean, proximal and distal. It cannot be overemphasized that this research illustrates several examples of how high frequency sampling by a moored autonomous system can provide details about ecosystem responses to stochastic atmospheric forcing that are commonly missed by traditional synoptic observational approaches. Finally, the work exemplifies the utility of combining synoptic sampling and real-time autonomous observations to elucidate the biogeochemical and physical responses of coastal subtropical/tropical coral reef ecosystems to climatic perturbations. 相似文献
38.
39.
A detailed compilation of distal tephrostratigraphy comprising the last 20,000 yrs is given for the Central Mediterranean region. A total of 47 distinct ash layers identified in the maar lake sediments of Lago Grande di Monticchio (Basilicata, Southern Italy) are compared with proximal and distal terrestrial-marine tephra deposits in the circum-central Mediterranean region. The results of these studies provide valuable information for reconstructing the Late Pleistocene and the Holocene dispersal of pyroclastic deposits from south Italian explosive volcanoes, in particular Somma-Vesuvius, the Campi Flegrei caldera, Ischia Island and Mount Etna. Prominent tephras are discussed with respect to their reliability as dating and correlation tools in sedimentary records. Ashes from Plinian eruptions of Somma-Vesuvius (i.e. Avellino, Mercato, Greenish, Pomici di Base), for instance, are well-defined by their distribution patterns and their unique composition. The widespread Y-1 tephra from Mount Etna, on the other hand, derived most likely from two distinct Plinian events with changing wind conditions, and therefore becomes a less reliable stratigraphic marker. Statistical–numerical calculations are presented in order to discriminate between Holocene tephras from the Campi Flegrei caldera (i.e. Astroni 1–3, Agnano Monte Spina, Averno 1, Lagno Amendolare), since these ashes are characterized by an almost indistinguishable chemical fingerprint. As a highlight, numerous Campanian eruptions of proposed low-intensity have been identified in the distal site of Monticchio suggesting a revision of existing tephra dispersal maps and re-calculation of eruptive conditions. In summary, the tephra record of Monticchio is one of the key successions for linking both, terrestrial records from Central-southern Italy and marine sequences from the Tyrrhenian, Adriatic and Ionian Seas. 相似文献
40.
Sabine Hanisch Martin Wessels Frank Niessen Antje Schwalb 《Journal of Paleolimnology》2009,41(3):393-406
This study used organic matter in oligotrophic Lake Constance (southern Germany) to reconstruct lake environment and to disentangle
the multiple factors, such as climate change and human impacts, which influence sedimentation in large lakes. A sediment core
from Upper Lake Constance, which represents 16,000 years of Late Glacial and Holocene lake history, was analysed for organic
biomarkers, hydrogen index and elements calcium, strontium, and magnesium. Magnetic susceptibility was measured to establish
a high-resolution stratigraphic framework for the core and to obtain further information about changes with respect to relative
allochthonous versus autochthonous sedimentation. Dinosterol—a biomarker for dinoflagellates—and calcium have low concentrations
in Younger Dryas sediments and consistently high concentrations between 10,500 and 7,000 cal. years BP. These variations are
attributed to changes in lake productivity, but are not reflected in the proportion of total organic carbon within the sediment.
During the Younger Dryas and between 6,000 and 2,800 cal. years BP, concentrations and accumulation rates of land-plant-derived
C29-steroids (β-sitosterol, stigmastanol and stigmasterol), in combination with a relatively low HI, indicate periods of enhanced
terrigenous input to the lake. For the Younger Dryas, higher runoff can be attributed to a cold climate, leading to decreased
vegetation cover and increased erosion. After 6,000 cal. years BP, high terrestrial input may be explained by enhanced precipitation.
Biomarker and HI results, in combination with archaeological studies, raise the question as to whether lakeshore settlements
affected sedimentation in Upper Lake Constance between 6,000 and 2,800 cal. years BP. 相似文献