Primary productivity in the German Bight (1994–1996)

Within the KUSTOS program (Coastal Mass and Energy Fluxes-the Land-Sea Transition in the Southeastern North Sea) 28 to 36 German Bight stations were seasonally surveyed (summer 1994, spring 1995, winter 1995–1996) for light conditions, dissolved inorganic nutrient concentrations, chlorophylla (chla), and photosynthesis versus light intensity (P:E) parameters. Combining P:E curve characteristics with irradiance, attenuation, and chlorophyll data resulted in seasonal estimates of the spatial distribution of total primary production. These data were used for an annual estimate of the total primary production in the Bight. In winter 1996 the water throughout the German Bight was well mixed. Dissolved inorganic nutrient concentrations were relatively high (nitrogen [DIN], soluble reactive phosphorus [SRP], and silicate [Si]: 23, 1, and 10 μM, respectively). Chla levels generally were low (< 2 μg l⁻¹) with higher concentrations (4–16 μg l⁻¹) in North Frisian coastal waters. Phytoplankton was limited by light. Total primary production averaged 0.2 g C m⁻² d⁻¹. Two surveys in April and May 1995 captured the buildup of a strong seasonal thermo-cline accompained by the development of a typical spring diatom bloom. High nutrient levels in the mixed layer during the first survey (DIN, SRP, and Si: 46, 0.45, and 11 μM, respectively) decreased towards the second survey (DIN, SRP, and Si: 30.5, 0.12, and 1.5 μM, respectively) and average nutrient ratios shifted further towards highly imbalanced values (DIN:SRP: 136 in survey 1, 580 in survey 2; DIN:Si: 13.5 in survey 1, 96 in survey 2). Chla ranged from 2 to 16 μg l⁻¹ for the first survey and rose to 12–50 μg l⁻¹ in the second survey. Phytoplankton in nearshore areas continued to be light limited during the second survey, while data from the stratified regions in the open German Bight indicates SRP and Si limitation. Total primary production ranged from 4.0 to 6.3 g C m⁻² d⁻¹. During summer 1994 a strong thermal stratification was present in the German Bight proper and shallow coastal areas showed unusually warm (up to 22°C), mixed waters. Chla concentrations ranged from 2 to 18 μg l⁻¹. P:E characteristics were relatively high despite the low nutrient regime (DIN, SRP, and Si: 2, 0.2, and 1.5 μM, respectively), resulting in overall high total primary production values with an average of 7.7 g C m⁻² d⁻¹. Based on the seasonal primary production estimates of the described surveys a budget calculation yielded a total annual production of 430 g C m⁻² yr⁻¹ for the German Bight.     

Application of stacking and inversion techniques to three-dimensional wide-angle reflection and refraction seismic data of the Eastern Alps

We present new methods for the interpretation of 3-D seismic wide-angle reflection and refraction data with application to data acquired during the experiments CELEBRATION, 2000 and ALP 2002 in the area of the Eastern Alps and their transition to the surrounding tectonic provinces (Bohemian Massif, Carpathians, Pannonian domain, Dinarides). Data was acquired on a net of arbitrarily oriented seismic lines by simultaneous recording on all lines of seismic waves from the shots, which allows 2-D and 3-D interpretations. Much (80%) of the data set consists of crossline traces. Low signal to noise (S/N) ratio in the area of the young orogens decreases the quality of travel time picks. In these seismically heterogeneous areas it is difficult to assign clearly defined arrivals to the seismic phases, in particular on crossline record sections.
In order to enhance the S/N ratio, signal detection and stacking techniques have been applied to enhance the Pg -, Pn - and PmP phases. Further, inversion methods have been developed for the interpretation of WAR/R-data, based on automated 1-D inversion ( Pg ) and the application of the delay time concept ( Pn ). The results include a 3-D velocity model of the crust based on Pg waves, time and depth maps of the Moho and a Pn -velocity map. The models based on stacked data are robust and provide a larger coverage, than models based on travel time picks from single-fold (unstacked) traces, but have relatively low resolution, especially near the surface. They were used as the basis for constructing models with improved resolution by the inversion of picks from single-fold data. The results correlate well with geological structures and show new prominent features in the Eastern Alps area and their surrounds. The velocity distribution in the crust has strong lateral variations and the Moho in the investigation area appears to be fragmented into three parts.     

Die Tonminerale der Zechsteinformation

Ohne Zusammenfassung     

Determination Of The Surface Drag Coefficient

This study examines the dependence of the surface drag coefficienton stability, wind speed, mesoscale modulation of the turbulent flux and method of calculation of the drag coefficient. Data sets over grassland, sparse grass, heather and two forest sites are analyzed. For significantly unstable conditions, the drag coefficient does not depend systematically on z/L but decreases with wind speed for fixed intervals of z/L, where L is the Obukhov length. Even though the drag coefficient for weak wind conditions is sensitive to the exact method of calculation and choice of averaging time, the decrease of the drag coefficient with wind speed occurs for all of the calculation methods. A classification of flux calculation methods is constructed, which unifies the most common previous approaches.The roughness length corresponding to the usual Monin–Obukhovstability functions decreases with increasing wind speed. This dependence on wind speed cannot be eliminated by adjusting the stability functions. If physical, the decrease of the roughness length with increasing wind speed might be due to the decreasing role of viscous effectsand streamlining of the vegetation, although these effects cannot be isolated from existing atmospheric data.For weak winds, both the mean flow and the stress vector often meander significantly in response to mesoscale motions. The relationship between meandering of the stress and wind vectors is examined. For weak winds, the drag coefficient can be sensitive to the method of calculation, partly due to meandering of the stress vector.     

Monitoring Partitioning Tracer Testing and Surfactant Flooding by In-Line Gas Chromatography Techniques

An automated in-line analytical system has been developed to provide near real-time results for partitioning interwell tracer testing (PITT) and surfactant enhanced aquifer remediation (SEAR). The analytical methodology is based on gas chromatography (GC) with flame ionization detection and direct aqueous injection. The system was constructed from both commercially available and custom-manufactured components that are linked electronically to facilitate autonomous operation. For the field trials presented herein, the in-line GC method provided superior or comparable PITT and SEAR data compared to conventional sample collection followed by shipment and analysis at a commercial analytical laboratory. Analytical precolumns were shown to effectively safeguard the integrity of the analytical column, despite the consecutive analysis of more than 1000 samples per PITT or SEAR. Additionally, the use of the in-line GC resulted in an 85% and 74% reduction in analytical costs per PITT and SEAR, respectively.     

Eignen sich Fallen zur repräsentativen Erfassung aquatischer Meiofauna im hyporheischen Interstitial und im Grundwasser?

In the sediments of a southwestern German headwater, pumping and two types of unbaited traps were compared with respect to their suitability for the sampling of interstitial meiofauna. The aim of the study was to discover whether the type-2 trap, having been developed for universal use, could be utilised in the hyporheic zone, as well as in groundwater. Trap samples demonstrate both greater abundance and taxonomic richness than those samples obtained by pumping, though very few differences could be detected between the two types of trap. The taxonomic composition, however, was found to be very similar for all three sampling methods. Other researchers also observed a high similarity of stygofaunal communities between pumped groundwater and the water of the bores, which act as traps. This would imply that not only do trap samples as well or better reflect community structure of the surrounding sediment than does pumping, but also that the type-2 trap is, indeed, suitable for the sampling of meiofauna in both the hyporheic zone and in groundwater.     

Modelling of convective turbulence with a two-equation k-ɛ turbulence closure scheme

 In this study we aim at comparing turbulence parameters from field observations and model simulations under convective conditions. The comparison is focused on the depth dependence and temporal dynamics of viscous and diffusive dissipation rates ɛ and χ. The near-surface observations were obtained by using a quasi-free-rising profiler which measured small-scale shear and temperature fluctuations to within the vicinity of the water surface. Convective conditions during the experiment are characterized by low wind speeds (between 0 and 4 m s⁻¹) and a typical heat loss of about 150 Wm⁻². We applied a state-of-the-art two-equation k-ɛ turbulence model with an algebraic second-moment closure scheme. The qualitative agreement of the turbulence quantities resulting from observations and simulations is rather good. The temporal dynamics of the temperature field is simulated correctly, whereas in the spatial dynamics some deficiencies of the model due to its local character can be seen. It is concluded that such models realistically reproduce convective turbulence and therefore represent a reasonable compromise between complexity and simplicity, so that they can be used with acceptable costs in large-scale models. Received: 31 October 2001 / Accepted: 20 September 2002 Acknowledgements The whole project was intitiated by Peter Schlittenhardt, who strongly supported the development of the observational technique in uprising mode and encouraged us to undertake the experiment in Lake Maggiore; for which we will thank him most. Performing the measurement campaign was only possible with the help of several colleagues from the Marine Environment Unit at the Joint Research Centre. Thanks to all of them, but especially to Dirk van d. Linde, Ulisse Devisioni, Bjarke Rasmussen and Hartmut Prandke. The Istituto Italiano di Idrobiologia, Verbania Pallanza, provided the boat Livia for the installation and removal of the measurement system; thanks to the master Stefano Maurizio for his engagement. Ute Tschesche provided the data evaluation and presentation software and Judith Challis helped to polish our English. Part of the study was␣supported by the PROVESS project (MAS3-CT97-0159); thanks to our sponsors at the European Commission. We are further grateful to two anonymous referees for their constructive comments. Responsible Editor: Charitha Pattiaratchi     

Imaging of groundwater resources in glacial deposits using high-resolution reflection seismics, Sweden

Two high-resolution reflection seismic profiles were acquired in the Heby area of eastern Sweden over glacial deposits for the purpose of mapping groundwater resources. The majority of shot points were located in clay resulting in good quality data along most of the profiles. On stacked and migrated sections, the uppermost clay is about 20 m thick and is characterized by its subhorizontal reflectivity. Sand/gravel deposits below it contain more dipping interfaces and have a chaotic reflectivity pattern. Depth to bedrock is interpreted to be 90 and 65 m on the respective profiles and occurs in about a 100-m-wide trough on both profiles. Reflections from the tops of sandy gravel zones generally have higher amplitudes. Clear reflections from a thin silt layer (20 cm thick) at about 10-m depth are observed on one of the profiles. Elastic finite difference modeling and the observation of this reflection in shot gathers show that the reflection is not an artifact of the acquisition nor the processing. The modeling also shows that there is no marked low-velocity waveguide in the near surface, but that an effective low Q zone may be present. Comparison with refraction profiling on the other profile shows that there is better agreement between the reflection seismic results and penetration tests than the refraction results with these tests. Both profiles allow the thickness of the overlying clay layers to be determined, as well as the thickness of the underlying sand/gravel deposits. This is important for estimating the amount of groundwater resources in an area.