Drinking water production from surface water sources in the tropics: Brasília DF,Brazil

Drinking water production at three waterworks was evaluated with respect to variable weather conditions in the Brasília Distrito Federal. Results of the investigation revealed that seasonal variations in rainfall play an important role in influencing the quality of the surface water sources used for drinking water production in the district. In most surface sources, particles and apparent colour are likely to originate from erosion during rain events. This represents the primary challenge facing waterworks, notably when the raw water qualities of the sources to be treated at one facility differ by one order of magnitude, as well significantly varying from one season to the next. Treatment efficiencies in terms of turbidity, apparent colour and dissolved organic carbon (DOC) removal were evaluated. Drinking water quality was found to be significantly influenced by raw water quality at all considered treatment plants. With regard to DOC removal, treatment was most efficient in waterworks which treated raw water with high percentages of biopolymers and humics. Most dissolved organics were removed by coagulation. Finally, conclusions are drawn on how to better cope with challenges facing drinking water production in a tropical climate. The first of these recommendations is the introduction of online turbidity and dissolved organic matter monitoring in order to optimise the coagulation process for the removal of these two parameters. A combination of different coagulants could also be considered for this process. Additional more sophisticated improvements to process stability, such as determination of floc characteristics, introduction of artificial neural networks or the eventual upgrade of the treatment train using membrane filtration, are also suggested.     

Catabolic and anabolic energy for chemolithoautotrophs in deep-sea hydrothermal systems hosted in different rock types

Active deep-sea hydrothermal vents are hosted by a range of different rock types, including basalt, peridotite, and felsic rocks. The associated hydrothermal fluids exhibit substantial chemical variability, which is largely attributable to compositional differences among the underlying host rocks. Numerical models were used to evaluate the energetics of seven inorganic redox reactions (potential catabolisms of chemolithoautotrophs) and numerous biomolecule synthesis reactions (anabolism) in a representative sampling of these systems, where chemical gradients are established by mixing hydrothermal fluid with seawater. The wide ranging fluid compositions dictate demonstrable differences in Gibbs energies (ΔG_r) of these catabolic and anabolic reactions in three peridotite-hosted, six basalt-hosted, one troctolite-basalt hybrid, and two felsic rock-hosted systems. In peridotite-hosted systems at low to moderate temperatures (<∼45 °C) and high seawater:hydrothermal fluid (SW:HF) mixing ratios (>10), hydrogen oxidation yields the most catabolic energy, but the oxidation of methane, ferrous iron, and sulfide can also be moderately exergonic. At higher temperatures, and consequent SW:HF mixing ratios <10, anaerobic processes dominate the energy landscape; sulfate reduction and methanogenesis are more exergonic than any of the aerobic respiration reactions. By comparison, in the basalt-hosted and felsic rock-hosted systems, sulfide oxidation was the predominant catabolic energy source at all temperatures (and SW:HF ratios) considered. The energetics of catabolism at the troctolite-basalt hybrid system were intermediate to these extremes. Reaction energetics for anabolism in chemolithoautotrophs—represented here by the synthesis of amino acids, nucleotides, fatty acids, saccharides, and amines—were generally most favorable at moderate temperatures (22-32 °C) and corresponding SW:HF mixing ratios (∼15). In peridotite-hosted and the troctolite-basalt hybrid systems, ΔG_r for primary biomass synthesis yielded up to ∼900 J per g dry cell mass. The energetics of anabolism in basalt- and felsic rock-hosted systems were far less favorable. The results suggest that in peridotite-hosted (and troctolite-basalt hybrid) systems, compared with their basalt (and felsic rock) counterparts, microbial catabolic strategies—and consequently variations in microbial phylotypes—may be far more diverse and some biomass synthesis may yield energy rather than imposing a high energetic cost.     

Late Cambrian deformation in the Lesser Himalaya

The Tons Valley, situated in the central-easternmost part of the Himachal Lesser Himalaya, adjoining the Garhwal Himalaya, shows geological features suggestive of a strong pre-Tertiary deformational episode. The Paleoproterozoic Dharagad Group, overlain by the Mesoproterozoic Deoban and Neoproterozoic Simla groups rest as a thrust sheet over the Middle Cambrian Chilar Formation, which occurs as windows and also as tectonic slivers within the thrust sheet designated as the Dharagad Thrust Sheet (DTS). The mineral lineation, inclination of tectonic slivers and overturned beds suggest that the DTS was translated from the NE. The westernmost and southwesternmost leading edges of the DTS are exposed at Subathu and Morni WNW and WSW respectively of the Tons Valley. The position of the leading edges of the DTS vis-à-vis the windows in the Tons Valley suggest a minimum translation of about 50 km for the DTS. The Simla Group at Subathu and the Deoban at Morni, forming parts of the DTS, constitute basement for the Thanetian–Lutetian Subathu Formation of the Himalayan Foreland Basin (HFB). This stratigraphic relationship unambiguously demonstrates that the Simla and the Deoban Groups, forming leading edges of the allochthonous DTS, were already translated and emplaced at Subathu and Morni before the creation of the HFB in which the deposition commenced with the Subathu Formation in Thanetian. It implies that the DTS was translated from the NE to the present position at Subathu and Morni in pre-Thanetian time. There is no direct evidence to constrain the age of the thrusting.In view of regional regression in Late Cambrian, a distinct angular unconformity between the Cambrian and the overlying Ordovician, Early Paleozoic metamorphism and extensive development of Early Paleozoic granites and their rapid exhumation, a Late Cambrian age is suggested for the DTS thrusting. Not only the direction of movement of the DTS is same as that of the Tertiary thrust sheets but also Cambrian folds are co-axial with the Tertiary folds. This strange coincidence shows that similar kinematic field existed during two tectonic events. A ridge, like the present Central Crystalline Axis, was elevated between the Tethyan and Lesser Himalayan basins, which contributed zircons of the Early Cambrian age to both basins.     

<Emphasis Type="Italic">Scombroclupea occidentalis</Emphasis> sp. nov. (Clupeiformes,Teleostei) from the Cenomanian (Cretaceous) Plattenkalk deposits of NE Mexico

A new species of the clupeid genus Scombroclupea is described from the Upper Cretaceous (Cenomanian) Plattenkalk locality “Loma la Mula” in Coahuila, northeastern Mexico. The material provides new osteological data for the genus, which clarify its systematic position. The Mexican Scombroclupea points to an occurrence of the genus in the western Tethys and indicates a vicariant event between S. macrophthalma from Lebanon and Croatia and the new species described herein. The analysis of the functional morphology of Scombroclupea supports the reconstruction of an oscillatory locomotion mode in this genus.     

Quantifying the influence of channel sinuosity on the depositional mechanics of channelized turbidity currents: A laboratory study

Here we present results from a suite of laboratory experiments that highlight the influence of channel sinuosity on the depositional mechanics of channelized turbidity currents. We released turbidity currents into three channels in an experimental basin filled with water and monitored current properties and the evolution of topography via sedimentation. The three channels were similar in cross-sectional geometry but varied in sinuosity. Results from these experiments are used to constrain the run-up of channelized turbidity currents on the outer banks of moderate to high curvature channel bends. We find that a current is unlikely to remain contained within a channel when the kinetic energy of a flow exceeds the potential energy associated with an elevation gain equal to the channel relief; setting an effective upper limit for current velocity. Next we show that flow through bends induces a vertical mixing that redistributes suspended sediment back into the interiors of depositional turbidity currents. This mixing counteracts the natural tendency for suspended sediment concentration and grain size to stratify vertically, thereby reducing the rate at which sediment is lost from a current via deposition. Finally, the laboratory experiments suggest that turbidity currents might commonly separate from channel sidewalls along the inner banks of bends. In some cases, sedimentation rates and patterns within the resulting separation zones are sufficient to construct bar forms that are attached to the channel sidewalls and represent an important mechanism of submarine channel filling. These bar forms have inclined strata that might be mistaken for the deposits of point bars and internal levees, even though the formation mechanism and its implications to channel history are different.     

An Improved Gas Chromatographic Method for the Determination of C6–C12 Petroleum Hydrocarbons in Soil Water

In this work, investigations dealing with the determination of hydrocarbons in contaminated soil water are presented. The hydrocarbons under investigation range from low to high volatility compounds. A GC‐FID method was developed that due to its efficiency, routine suitability, relative rapidity, and low cost is suitable for the analysis of complex chemical mixtures of highly volatile hydrocarbons (with boiling points between 69 and 190°C). The standard used was a gasoline mixture with boiling points ranging from 100 to 190°C. For this standard, no supplementary preparation is needed and it is suitable for the whole range of hydrocarbons under investigation. The determination of the hydrocarbon content of the samples was performed applying univariate and multivariate statistical analysis to the experimental data. In the characterization of a contamination with highly volatile hydrocarbons of soil water originating from different depth layers from the chemistry location Leuna (Sachsen‐Anhalt, Germany), the advantages of a multivariate method are demonstrated in exemplary manner.     

Modelling the biogeochemistry of a tidal flat ecosystem with EcoTiM

The ecological tidal model simulates the cycling of carbon, nitrogen, phosphate, and silicate and describes the tidal, diurnal, and annual dynamics of the back barrier area of the island Spiekeroog in the German Bight. The region is characterized by strong tidal currents and extensive tidal flats. It is strongly influenced by the conditions in the southern part of the German Bight. This model study investigates the dependence of the model behavior on the boundary conditions and the forcing. The effect of short- and long-term sea level rise on nutrient and plankton dynamics is analyzed. As the model is set up as semi-Lagrangian with only a coarse approximation of the hydrodynamics, the seasonal and intratidal variability in the biogeochemical cycling can only be reproduced qualitatively. By varying the boundary conditions, the intrinsic dynamics of the back barrier area can be separated from boundary condition effects. This study shows that any agreement between model results and field data cannot be expected without correct boundary conditions. The seasonal variability is of major importance, while higher-frequency variability only plays a minor role.     

Unusual exsolution phenomena in omphacite and partial replacement of phengite by phlogopite + kyanite in an eclogite from the Erzgebirge

In the Erzgebirge Crystalline Complex, eclogites occur in three different high pressure (HP) units (1, 2 and 3) recording contrasting pressure (P)–temperature (T) conditions. Eclogites from HP-unit 1 experienced peak metamorphic conditions in the coesite stability field at about 33 kbar/850 °C. Commonly, these eclogites from HP-unit 1 are all very similar, with an eclogitic peak assemblage of omphacite–garnet–coesite–K-feldspar, rarely accompanied by kyanite, and omphacites systematically deviating from a stoichiometric composition. In contrast, an eclogite recently found near Blumenau, is mineralogically and geochemically different from the typical eclogites of HP-unit 1. This unusual eclogite reveals the eclogitic equilibrium assemblage omphacite–garnet–coesite–phengite–phlogopite–kyanite, and yields metamorphic peak conditions of 870 °C and >29 kbar. There is clear textural evidence of the formation of phlogopite and kyanite under partial consumption of phengite and garnet. Moreover, the omphacite is stoichiometric and contains abundant exsolution lamellae, the thickest of which were identified as quartz by the electron microprobe. The finer lamellae were studied by transmission electron microscopy (TEM). Oligoclase was identified as an exsolution phase. Other lamellae proved to consist of K-white mica, also interpreted as exsolution. Prior to exsolution, the omphacite composition must have been cation-deficient, as that of the other, common HP-unit 1 eclogites. These non-stoichiometric compositions are ascribed to partial substitution by the Ca-Eskola pyroxene component, which calculates to an average of 8 mol% for omphacite in HP-unit 1 eclogites. According to experiments, this substitution becomes significant at P > 30 kbar. Exsolution of K-white mica may indicate hydroxyl defects in the original omphacite, also favoured by high pressure. Oligoclase and K-white mica exsolution from Ca-Eskola-rich clinopyroxene has not previously been reported. The omphacite has a disordered C2/c structure; and in just one case very small (a few tens of nanometres) antiphase domains, resulting from the C2/c to P2/n transformation, are present. These features may indicate a brief thermal history and rapid tectonic processes. Received: 4 January 1999 / Accepted: 20 April 2000     

Identifying causes of ground-penetrating radar reflections using time-domain reflectometry and sedimentological analyses

Ground-penetrating radar (GPR) is a geophysical technique widely used to study the shallow subsurface and identify various sediment features that reflect electromagnetic waves. However, little is known about the exact cause of GPR reflections because few studies have coupled wave theory to petrophysical data. In this study, a 100- and 200-MHz GPR survey was conducted on aeolian deposits in a quarry. Time-domain reflectometry (TDR) was used to obtain detailed information on the product of relative permittivity (ɛ_r) and relative magnetic permeability (μ_r), which mainly controls the GPR contrast parameter in the subsurface. Combining TDR data and lacquer peels from the quarry wall allowed the identification of various relationships between sediment characteristics and ɛ_rμ_r. Synthetic radar traces, constructed using the TDR logs and sedimentological data from the lacquer peels, were compared with the actual GPR sections. Numerous peaks in ɛ_rμ_r, which are superimposed on a baseline value of 4 for dry sand, are caused by potential GPR reflectors. These increases in ɛ_rμ_r coincide with the presence of either organic material, having a higher water content and relative permittivity than the surrounding sediment, or iron oxide bands, enhancing relative magnetic permeability and causing water to stagnate on top of them. Sedimentary structures, as reflected in textural change, only result in possible GPR reflections when the volumetric water content exceeds 0·055. The synthetic radar traces provide an improved insight into the behaviour of radar waves and show that GPR results may be ambiguous because of multiples and interference.     

Lippmann Diagrams: Theory and Application to Carbonate Systems

Since 1980 when F. Lippmann's seminal paper appeared, ourunderstanding of solubility equilibria involving ionic solidsolutions has been advanced by theoretical considerations as wellas careful experimental studies designed to determine excess Gibbsfunctions. A unified theory of solid-solution aqueous-solutionequilibria as well as the thermodynamic background of thephenomenon of ``stoichiometric saturation' are reviewed.It is shown that Lippmann diagrams effectively summarize thethermodynamic basis of solid-solute aqueous-solution equilibria ofsparingly soluble metal carbonate systems. Clearly, the predictivepower of these diagrams may be limited due to kineticrestrictions. Only when dissolution and precipitation areessentially reversible, favourable conditions to synthesizehomogeneous solid phases can be derived from studies of equilibria.