An adjustment of benthic ecological quality assessment to effects of salinity     

Dirk Fleischer  Michael L. Zettler 《Marine pollution bulletin》2009,58(3):351-357

In the last decade a politically inspired marine protection movement arose in the European Union. This movement leads to an holistic strategy. Merging the Water Framework Directive (WFD) and the Marine Strategy Directive (MSD) along the European coastline demands sophisticated ecological classification procedures. The ‘Benthic Quality Index’ (BQI) is one of several indices created in view of the WFD. We used the dynamic species reference system ES_500.05 to test the capability of BQI to exclude primary environmental factors including the salinity gradient and depth (a proxy for the oxygen regime) from the ecological quality (EcoQ) assessment.A macrozoobenthos dataset of the southern Baltic Sea spreading over more than 20 years and over 100,000 km² was used for the EcoQ assessment. Quality assurance rules were applied to the record set and an analytical dataset of 936 sampling events with 20,451 abundance records was used in the analysis. We show that the natural salinity gradient has a severe impact on the BQI based EcoQ. We adapted the calculation procedure to reduce the salinity effects to a minimum.According to the adaptation 503 sensitivity/tolerance values for 87 species were computed. These values were calculated within seven salinity ranges from 0 to >30 PSU and two depth zones. These values can be used as a reference for further investigation in the Baltic and other areas with similar environmental conditions.  相似文献   

Resource availability and meiofauna in sediment of tropical seagrass beds: local versus global trends     

De Troch M  Van Gansbeke D  Vincx M 《Marine environmental research》2006,61(1):59-73

Characterisation of productivity-diversity relationships forms an essential step towards a better understanding of biodiversity. In terrestrial systems this is a topical subject and most studies reported a hump-shaped relationship. For marine systems, however, the number of studies dedicated to this is low despite the high interest in this productivity-diversity relationship. The present study reports on meiofauna density/diversity patterns in relation to resource availability as an indicator for the productivity of the ecosystem. Standardised meiofauna samples were collected in tropical seagrass beds from three localities (Kenya, Mexico, the Philippines) in order to contrast local patterns with a more global scale. Although these sites were physically comparable, a range of resource availabilities was found. These differences between localities were mainly due to different tidal regimes and related input of organic matter. At all sites a significant positive effect of resource increase on meiofauna densities was found. This positive effect was less clear for meiofauna diversity. Highest density and diversity levels were reported for the Kenyan site and this is probably linked to a high tidal range. Pooling all localities together resulted in a significant positive linear relationship between resource availability and meiofauna density/diversity. Caution should be taken when choosing resource indicators. Chlorophyll a concentrations, for example, resulted in a positive density-productivity relationship while organic carbon content, an indicator for more refractory material, showed a negative relationship. In all cases, no hump-shaped relationship could be found suggesting that each ecosystem and each group of organisms may show a particular productivity-diversity/density relationship.  相似文献   

Subsurface formation of oxidants on Mars and implications for the preservation of organic biosignatures     

Alfonso F. Davila  Alberto G. Fairn  Luis Gago-Duport  Carol Stoker  Ricardo Amils  Rosalba Bonaccorsi  Jhony Zavaleta  Darlene Lim  Dirk Schulze-Makuch  Christopher P. McKay 《Earth and Planetary Science Letters》2008,272(1-2):456-463

Hydrogen peroxide can form through the interaction of pyrite and anoxic water. The oxidation of pyrite results in the precipitation of sulfates and iron oxides, high redox potentials (~ 1000 mV) and acidic pH (3–4). The oxidative potential of the resultant solution may be responsible for the oxidation of organic compounds, as observed in the subsurface of the Rio Tinto Mars analog. On Mars subsurface migration of groundwater interacting with volcanogenic massive pyrite deposits would have mobilized acidic and oxidizing fluids through large portions of the crust, resulting in the widespread deposition of sulfates and iron oxides. This groundwater could have leached substantial volumes of aquifer material and crustal rocks, thereby erasing any organic compounds possibly down to depths of hundreds of meters. Therefore, the preservation of organic biosignatures must have been severely constrained in the portions of the ancient Martian crust that were exposed to aqueous processes, calling for a redefinition of the future targets in the search for biomolecular traces of life on Mars.  相似文献   

Interacting Loop Current variability and Mississippi River discharge over the past 400 kyr     

Dirk Nürnberg  Martin Ziegler  Cyrus Karas  Ralf Tiedemann  Matthew W. Schmidt 《Earth and Planetary Science Letters》2008,272(1-2):278-289

The Loop Current mediating the oceanic heat and salt flux from the Caribbean Sea into the Atlantic Ocean and its interference with the Mississippi River discharge are critical for both the regional climate in the Gulf of Mexico area and the water vapor transport towards high northern latitudes. We present a 400-kyr record of sea surface temperature and local surface salinity from the northeastern Gulf of Mexico (IMAGES core MD02-2575) approximated from combined planktonic foraminiferal δ¹⁸O and Mg/Ca, which reflects the temporal dynamics of the Loop Current and its relationship to both varying Mississippi discharge and evolution of the Western Hemisphere Warm pool. The reconstructed sea surface temperature and salinity reveal glacial/interglacial amplitudes that are significantly larger than in the Western Hemisphere Warm pool. Sea surface freshening is observed during the extreme cool periods of Marine Isotope Stages 2, 8, and 10, caused by the strengthened Mississippi discharge which spread widely across the Gulf favored by the less established Loop Current. Interglacial and interstadial sea-surface conditions, instead, point to a strengthened, northward flowing Loop Current in line with the northward position of the Intertropical Convergence Zone, allowing northeastern Gulf of Mexico surface hydrographic conditions to approach those of the Caribbean. At these times, the Mississippi discharge was low and deflected westward, promoted by the extended Loop Current. Previously described deglacial megadischarge events further to the west did not affect the northeastern Gulf of Mexico hydrography, implying that meltwater routing from the Laurentide Ice Sheet via the Mississippi River is unlikely to have affected Atlantic Meridional Overturning Circulation.  相似文献   

High-frequency and meso-scale winter sea-ice variability in the Southern Ocean in a high-resolution global ocean model     

Achim Stössel  Jin-Song von Storch  Dirk Notz  Helmuth Haak  Rüdiger Gerdes 《Ocean Dynamics》2018,68(3):347-361

This study is on high-frequency temporal variability (HFV) and meso-scale spatial variability (MSV) of winter sea-ice drift in the Southern Ocean simulated with a global high-resolution (0.1°) sea ice-ocean model. Hourly model output is used to distinguish MSV characteristics via patterns of mean kinetic energy (MKE) and turbulent kinetic energy (TKE) of ice drift, surface currents, and wind stress, and HFV characteristics via time series of raw variables and correlations. We find that (1) along the ice edge, the MSV of ice drift coincides with that of surface currents, in particular such due to ocean eddies; (2) along the coast, the MKE of ice drift is substantially larger than its TKE and coincides with the MKE of wind stress; (3) in the interior of the ice pack, the TKE of ice drift is larger than its MKE, mostly following the TKE pattern of wind stress; (4) the HFV of ice drift is dominated by weather events, and, in the absence of tidal currents, locally and to a much smaller degree by inertial oscillations; (5) along the ice edge, the curl of the ice drift is highly correlated with that of surface currents, mostly reflecting the impact of ocean eddies. Where ocean eddies occur and the ice is relatively thin, ice velocity is characterized by enhanced relative vorticity, largely matching that of surface currents. Along the ice edge, ocean eddies produce distinct ice filaments, the realism of which is largely confirmed by high-resolution satellite passive-microwave data.  相似文献   

Simultaneous joint migration inversion for high-resolution imaging/inversion of time-lapse seismic datasets     

Shan Qu  Dirk Jacob Verschuur 《Geophysical Prospecting》2020,68(4):1167-1188

The current time-lapse practice is to exactly repeat well-sampled acquisition geometries to mitigate acquisition effects on the time-lapse differences. In order to relax the rigid requirements on acquisition effects, we propose simultaneous joint migration inversion as an effective time-lapse tool for reservoir monitoring, which combines a joint time-lapse data processing strategy with the joint migration inversion method. Joint migration inversion is a full-wavefield inversion method that explains the measured reflection data using a parameterization in terms of reflectivity and propagation velocity. Both the inversion process inside the imaging/inversion scheme and the extra illumination provided by including multiples in joint migration inversion makes the obtained velocity and reflectivity operator largely independent of the utilized acquisition geometry and, thereby, relaxes the strong requirement of non-repeatability during the monitoring. Because simultaneous joint migration inversion inverts for all datasets simultaneously and utilizes various constraints on the estimated reflectivities and velocity, the obtained time-lapse differences have much higher accuracy compared to inverting each dataset separately. It allows the baseline and monitor parameters to communicate with each other dynamically during inversion via a user-defined spatial weighting operator. In order to get more localized time-lapse velocity differences, we further extend the regular simultaneous joint migration inversion to a robust high-resolution simultaneous joint migration inversion process using the time-lapse reflectivity difference as an extra constraint for the velocity estimation during inversion. This constraint makes a link between the reflectivity- and the velocity difference by exploiting the relationship between them. We demonstrate the feasibility of the proposed method with a highly realistic synthetic model based on the Grane field offshore Norway and a time-lapse field dataset from the Troll Field.  相似文献   

Quartz-Helium Method to Estimate Fluid Flow in Thick Aquitards,Gunnedah Basin,Australia     

Stanley D. Smith  Emeline Mathouchanh  Dirk Mallants 《Ground water》2019,57(1):153-165

The hydraulic integrity of aquitards is generally assumed and relies on a few core-scale permeability measurements, drill-stem tests, or textbook values. This approach is because hydraulic data across the full aquitard thickness is generally lacking. Proper assessment of aquitard integrity should be studied at the formation (spanning its entire thickness at a single point) or regional (formation properties at multiple locations throughout the basin) scale. One formation-scale approach uses environmental tracers and advection-dispersion modeling to constrain fluid flow rates. This study demonstrates the use of helium concentrations in quartz as a method of constraining the rate of fluid flow in a 520-m thick aquitard in the Gunnedah Basin, NSW, Australia. Quartz was separated from existing core samples in the Watermark and Porcupine Formations at depths from 750 to 1200 m. The helium was released from these samples by heating and select samples were impregnated with helium to determine the rate of helium diffusion through the quartz. One-dimensional advection-dispersion modeling of the helium profile accounting for diffusive helium exchange between quartz and pore water revealed, that (1) vertical fluid velocity has been on the order of 0.02 mm/year or less for tens to thousands of years, (2) helium is in equilibrium between quartz and pore water, and (3) the helium profile is transient indicating that helium concentrations in the underlying Maules Creek Formation has varied over geological time. Further modeling identified aquitard conditions (thickness and temperature) for which equilibrium exists, a precondition for deriving formation-scale permeability.  相似文献   

Production of Drinking Water from Highly Contaminated Surface Waters: Removal of Organic,Inorganic, and Microbial Contaminants Applying Mobile Membrane Filtration Units     

Thomas Heberer  Dirk Feldmann  Kirsten Reddersen  Hans‐Juergen Altmann  Thomas Zimmermann 《洁净——土壤、空气、水》2002,30(1):24-33

In military out of area missions of the Bundeswehr, it can be necessary to produce drinking water even from highly polluted surface waters containing a variety of organic, inorganic, and microbiological contaminants. Thus, mobile drinking water purification systems must be able to remove such contaminants as far as possible to meet the requirements of the German and European drinking water regulation/directive. Presently, two novel drinking water purification units applying membrane filtration undergo intensive long‐term trials carried out by the Bundeswehr. If these trials positively proof the functionality of these units and their ability to remove all possible contaminants they shall substitute so far available devices which use large amounts of chemicals and charcoal filtration for water purification.In the course of a research project, the functionality of the new devices and their efficacy to remove high amounts of algae, microbes, and organic and inorganic pollutants are additionally tested in “worst‐case” field studies. In September 2000, the first mobile drinking water purification unit was tested at the Teltowkanal in Berlin, Germany.This canal was chosen because it carries high burdens of municipal sewage effluents. The results from the fatigue test confirmed the ability of the water purification unit to reduce the concentrations of all contaminants meeting the maximum tolerance levels set by the German/European drinking water regulation.The pre‐filtration device was very effective in removing algae and solid particles to protect the membranes from clogging and to enable an almost maintenance‐free operation. Residues of pharmaceuticals and some other organic contaminants have almost totally been removed from the surface water where they were detected at individual concentrations up to the μg/L‐level.  相似文献   

Red-Pelaged Harbour Seals, in Humboldt County, California: why some Seals Rust     

Dirk R Neumann  Wolfgang W Schmahl 《Marine pollution bulletin》1999,38(12):273-1183

In this paper we present data on the occurrence of red-pelaged harbour seals, Phoca vitulina, at a haul-out in Humboldt County, California. Density of red seals ranged from 4% to 17.5% (n=21) and was comparable to that reported for San Francisco Bay, being the highest documented worldwide. The red colouration is the result of natural inorganic iron oxide/hydroxide pigments (limonite), which are present in small patches on the beach sand of the seals haul-out at the mouth of the Mad River. Thorough analysis of the river water and ocean water excluded these as possible sources for the iron oxide/hydroxide pigments. We found that the manmade reinforcement of the river bank adjacent to the haul-out consisted of greenshist boulders with a very high iron content. Weathering of these rocks produces red iron oxide/hydroxide particles which are then redeposited by rain or river action in small patches across the haul-out. Seals receive their red colouration through direct physical contact with these patches. SEM examination showed that these particles can adhere lastingly to the seals’ hair. Other studies provide reason for concern that this situation may detrimentally impact the seals’ health.  相似文献   

Exhumation, strain localization, and emplacement of granitoids along the western part of the Central Bohemian shear zone (Bohemian Massif)   总被引：1，自引：1，他引：0  

Dirk Scheuvens  Gernold Zulauf 《International Journal of Earth Sciences》2000,89(3):617-630

Emplacement of granitoid magmas and simultaneous exhumation of deeply buried rocks has been investigated along the western part of the Central Bohemian shear zone (CBSZ, Bohemian Massif). Combined structural, petrological and geochronological data of the steeply dipping shear zone suggest complex uplift and exhumation of deeply buried, high-temperature Moldanubian rocks, resulting in the juxtaposition against the supracrustal Teplá-Barrandian unit. Uplift of Moldanubian rocks from depths of probably more than 30 km was initiated after crustal stacking in Upper Devonian times. Syntectonic Lower Carboniferous emplacement of the Klatovy pluton into the pre-existing shear zone led to melt-controlled strain softening and localization. However, the major part of the total displacement of the CBSZ was accommodated within a late- to post-intrusive high-temperature shear zone in the uprising Moldanubian unit and a post-intrusive unexposed fault zone in the Klatovy pluton, respectively. During uplift of the Moldanubian rocks, strain was strongly partitioned into melt-bearing zones (Klatovy pluton, migmatites of the Moldanubian unit) resulting in a repeated shift of deformation in space and time.  相似文献