Field observations on the production of rainbow trout(Oncorhynchus mykiss) under high concentrations of water-borne iron

Effluents from brown coal mines are frequently rich in iron, the water being red-brown in colour and turbid. For several years a fish farm in the Lusatia (Brandenburg, Germany) has used such mine effluents for rearing rainbow trout. The total iron content of this water varies between 5 and 10 mg/l with pH ranging from 6.7 to 7.4. Water turbidity is high with a transparency of 10 to 40 cm at the most due to the substantial ferric hydroxide concentrations. Until 1989 trout have been reared in net cages within concrete settling basins destined for settling the ferric hydroxide mud. The cages were stocked with fingerlings in autumn, reaching portion size in the spring of the following year. Specific growth rate was 0.98% per day, comparable to that of trout in another farm unpolluted by iron but stocked at higher densities. The results show that fingerling rainbow trout may live in water containing more than 5 mg/l total iron but in the absence of Fe²⁺. These concentrations of water-borne iron seem to have only a limited detrimental effect on fish growth and feed conversion and do not prevent trout culture in principle.     

Ecology, shell morphology, anatomy and sperm ultrastructure of the caenogastropod Pyrgula annulata, with a discussion of the relationship between the ‘Pyrgulidae’ and Caspian and Baikalian Rissooideans

The composition of the Pyrgulidae and its relationships to other member families of the caenogastropod superfamily Rissooidea are examined after a consideration of new anatomical (including gross anatomy, sperm ultrastructure), conchological (including protoconch features), ecological, biogeographical and palaeontological data and a re-evaluation of existing literature. Pyrgulidae can be distinguished from hydrobiids unequivocally only with the aid of the radula. Sperm ultrastructural features suggest a very close relationship between the Pyrgulidae, the Hydrobiidae and the Bithyniidae (in fact no family-diagnostic sperm characters can be found to separate these three taxa). Based upon neontological and fossil evidence it is likely that pyrgulids represent a Miocene offshoot from a paratethyal hydrobiid lineage. Pyrgulids may also represent the stock from which the baicaliids arose, in which case the Pyrgulidae must be considered a paraphyletic group. The huge biogeographic gap between the Caspian Sea and Lake Baikal is to some extent bridged by the finding of a Neogene pyrgulid from the Altai Mountains. An alternative scenario for the origin of baicaliids is presented.     

On results of the surface wave analyses in poroelastic media by means of the Simple Mixture Model and the Biot model

This note is devoted to an overview of the results on the number, velocity and attenuation of surface waves in two-component saturated poroelastic media. The author's numerical results which have been obtained using the Simple Mixture Model are compared to some results of other authors who carried out either an analysis by means of the classical Biot model for poroelastic media or experiments. It is shown that the Simple Mixture Model is a simplification of the Biot model. Due to its simpler form the Simple Mixture Model is more suitable for a complex analysis which depends on several parameters. Thus, the Simple Mixture Model is the only model for which, simultaneously, either the dependence on the frequency, ω, and the dependence on the bulk permeability, π (boundary porous medium/vacuum) or the dependence on the frequency, ω, and the dependence on the surface permeability, α (boundary porous medium/fluid) has been considered.     

Permeability and degassing of dome lavas undergoing rapid decompression: An experimental determination

The gas permeability of volcanic rocks may influence various eruptive processes. The transition from a quiescent degassing dome to rock failure (fragmentation) may, for example, be controlled by the rocks permeability, in as much as it affects the speed by which a gas overpressure in vesicles is reduced in response to decompression. Using a modified shock-tube-based fragmentation bomb (Alidibirov and Dingwell 1996a,b; Spieler et al. 2003a), we have measured unsteady-state permeability at a high initial pressure differential. Following sudden decompression above the rock cylinder, pressurized gas flows through the sample. Two pressure transducers record the pressure signals above and below the sample. A transient 1D filtration code has been developed to calculate permeability using the experimental decay curve of the lower pressure transducer. Additionally an analytical steady-state method to achieve permeability is presented as an alternative to swiftly predict the sample permeability in a sufficiently precise manner. Over 100 permeability measurements have been performed on samples covering a wide range of porosity. The results show a general positive relationship between porosity and permeability with a high data scatter. Our preferred interpretation of the results is a combination of two different, but overlapping effects. We propose that at low porosities, gas escape occurs predominantly through microcracks or elongated micropores and therefore could be described by simplified forms of Kozeny–Carman relations (Carman 1956) and fracture flow models. At higher porosities, the influence of vesicles becomes progressively stronger as they form an increasingly connected network. Therefore, a model based on the percolation theory of fully penetrable spheres is used, as a first approximation, to describe the permeability-porosity trend. In the data acquired to date it is evident, that in addition to the porosity control, the samples bubble size, shape and distribution strongly influence the permeability. This leads to a range of permeability values up to 2.5 orders of magnitude at a given porosity.     

Upper bound analysis of tunnel face stability in layered soils

The working face of tunnel constructions has to be kept stable during tunneling to prevent large soil deformations or fatal failure. In layered soils with lower cohesion, failures happen more often and more abrupt than in cohesive soils. Therefore, the maintenance of a proper support pressure at the tunnel working face is of high importance. In this paper, an upper bound analysis is introduced to investigate the minimum support pressure for the face stability in layered soils. A three-dimensional kinematically admissible mechanism for the upper bound analysis is improved to model potential failure within different soil layers. An analytical solution for the support pressure assessment is achieved. The influence of the crossing and cover soil on the face stability is analyzed, respectively. This solution provides an analytical estimation of the minimum support pressure for the face stability. It may be used as a reference for projects under similar conditions.     

Tracing effects of decalcification on solute sources in a shallow groundwater aquifer, NW Germany

δ⁸⁷Sr values and Ca/Sr ratios were employed to quantify solute inputs from atmospheric and lithogenic sources to a catchment in NW Germany. The aquifer consists primarily of unconsolidated Pleistocene eolian and fluviatile deposits predominated by >90% quartz sand. Accessory minerals include feldspar, glauconite, and mica, as well as disperse calcium carbonate in deeper levels. Decalcification of near-surface sediment induces groundwater pH values up to 4.4 that lead to enhanced silicate weathering. Consequently, low mineralized Ca–Na–Cl- and Ca–Cl-groundwater types are common in shallow depths, while in deeper located calcareous sediment Ca–HCO₃-type groundwater prevails. δ⁸⁷Sr values and Ca/Sr ratios of the dissolved pool range from 7.3 to −2.6 and 88 to 493, respectively. Positive δ⁸⁷Sr values and low Ca/Sr ratios indicate enhanced feldspar dissolution in shallow depths of less than 20 m below soil surface (BSS), while equilibrium with calcite governs negative δ⁸⁷Sr values and elevated Ca/Sr ratios in deep groundwater (>30 m BSS). Both positive and negative δ⁸⁷Sr values are evolved in intermediate depths (20–30 m BSS). For groundwater that is undersaturated with respect to calcite, atmospheric supplies range from 4% to 20%, while feldspar-weathering accounts for 8–26% and calcium carbonate for 62–90% of dissolved Sr²⁺. In contrast, more than 95% of Sr²⁺ is derived by calcium carbonate and less than 5% by feldspar dissolution in Ca–HCO₃-type groundwater. The surprisingly high content of carbonate-derived Sr²⁺ in groundwater of the decalcified portion of the aquifer may account for considerable contributions from Ca-containing fertilizers. Complementary tritium analyses show that equilibrium with calcite is restricted to old groundwater sources.     

Spatio‐temporal variability of zooplankton biomass and environmental control in the Northern Benguela Upwelling System: field investigations and model simulation

Spatial and temporal distribution patterns of zooplankton are highly variable in the Northern Benguela Upwelling System. We studied the distribution of zooplankton (size class ≥ 0.33 mm) and used field data from four cruises that took place between March 2008 and February 2011, as well as simulation results of a regional ecosystem model. Remotely sensed sea surface temperatures (SST) and surface chlorophyll concentrations were analysed to investigate environmental influences on zooplankton biomass. The Intense Benguela Upwelling Index showed a distinct seasonal signal throughout the years and the highest upwelling peaks in August/September. Even though surface chlorophyll concentrations were very variable throughout the year, the highest concentrations were always detected in September, following the upwelling of nutrient‐rich water. In field catches, zooplankton biomass concentration in the upper 200 m was highest above the outer shelf and shelf‐break in December 2010 and February 2011, i.e. 6 months after the upwelling peaks. In contrast, zooplankton biomass simulated by the model in the surface water was highest in September. In March/April, biomass maxima were typically measured in the field at intermediate water depths, but the vertical distribution was also affected by extensive oxygen minimum zones. The ecosystem model reproduced this vertical pattern. Although general trends were similar, simulation data of zooplankton standing stocks overestimated the field data by a factor of 3. In upwelling systems, food webs are generally considered to be short and dominated by large cells. However, our field data indicate more small‐sized zooplankton organisms above the shelf than offshore.     

Fabrication and test of sol–gel based planar oxygen optodes for use in aquatic sediments

We describe the fabrication of organically modified sol–gel (ORMOSIL) planar optodes for mapping the two-dimensional oxygen distribution in sediments. All sensor foils were based on the use of ruthenium(II)-tris-(4,7-diphenyl-1,10-phenantrolin)-perchlorate, which is a fluorescent dye quenched dynamically by oxygen. Sensors made with different sol–gel immobilisation matrices, different concentrations of precursors and indicator dye, as well as different types of scattering particles co-immobilised in the sensor foil were investigated systematically. Optimal sensor performance was obtained with dye concentrations of 2–10 mmol/kg in an immobilisation matrix made of diphenyldiethoxy-silan and phenyltriethoxy-silan precursors with addition of organically coated TiO₂ particles. The sensors exhibited a good mechanical stability and a high sensitivity from 0% to 100% oxygen, which remained constant over at least 36 days. The planar optodes were used with a fluorescent lifetime imaging system for direct mapping of the spatio-temporal variation in oxygen distribution within marine sediment inhabited by the polychaete Hediste diversicolor. The measurements demonstrated the spatio-temporal heterogeneity of the oxygen distribution in bioturbated sediments due to burrow structures and non-constant irrigation activity of the polychaete, which is difficult to resolve with microsensors or with traditional biogeochemical techniques.     

Documenting channel features associated with gas hydrates in the Krishna–Godavari Basin,offshore India

During the India National Gas Hydrate Program (NGHP) Expedition 01 in 2006 significant sand and gas hydrate were recovered at Site NGHP-01-15 within the Krishna–Godavari Basin, East Coast off India. At the drill site NGHP-01-15, a 5–8 m thick interval was found that is characterized by higher sand content than anywhere else at the site and within the KG Basin. Gas hydrate concentrations were determined to be 20–40% of the pore volume using wire-line electrical resistivity data as well as core-derived pore-fluid freshening trends. The gas hydrate-bearing interval was linked to a prominent seismic reflection observed in the 3D seismic data. This reflection event, mapped for about 1 km² south of the drill site, is bound by a fault at its northern limit that may act as migration conduit for free gas to enter the gas hydrate stability zone (GHSZ) and subsequently charge the sand-rich layer. On 3D and additional regional 2D seismic data a prominent channel system was imaged mainly by using the seismic instantaneous amplitude attribute. The channel can be clearly identified by changes in the seismic character of the channel fill (sand-rich) and pronounced levees (less sand content than in the fill, but higher than in surrounding mud-dominated sediments). The entire channel sequence (channel fill and levees) has been subsequently covered and back-filled with a more mud-prone sediment sequence. Where the levees intersect the base of the GHSZ, their reflection strengths are significantly increased to 5- to 6-times the surrounding reflection amplitudes. Using the 3D seismic data these high-amplitude reflection edges where linked to the gas hydrate-bearing layer at Site NGHP-01-15. Further south along the channel the same reflection elements representing the levees do not show similarly large reflection amplitudes. However, the channel system is still characterized by several high-amplitude reflection events (a few hundred meters wide and up to ~ 1 km in extent) interpreted as gas hydrate-bearing sand intervals along the length of the channel.     

Factors that influence the accumulation of copper and cadmium by transplanted eastern oysters (Crassostrea virginica) in the Patuxent River, Maryland

To investigate the continued accumulation of copper and cadmium by oysters in the Patuxent River, MD, which have been at high levels since at least the mid 1960s, hatchery-raised Eastern oysters were transplanted into trays at four sites in the upper estuary. At each site two groups of oysters were used to determine growth and mortality, and another group was sampled for meat condition, metal concentration and body burden. Copper in oysters in the discharge of a coal-fired power plant was significantly greater than at all other sites, but maximum concentration of 310 micrograms g-1 was well below the maximum of 1880 micrograms g-1 detected in 1982. Cadmium levels were also significantly greater in the discharge than at the other sites, but probably because of higher discharge temperatures. Trace metal loadings, the local salinity gradient and the higher temperatures caused by power plant operation all appear to contribute to metal accumulation by oysters in the upper Patuxent estuary.