Is a regional flood signal reproducible from lake sediments?

The evolution of flood activity with global warming remains uncertain. To better assess flood–climate relationships, lake sediments are increasingly being investigated because they could provide regional flood histories long enough to cover past climate changes. However, site‐specific sedimentary processes may bias flood reconstructions. The aim of this article is to investigate these effects through the reconstruction of two distinct flood records from independent, neighbouring sedimentary basins of the same lake (Lake Allos in the Mediterranean French Alps), i.e. under the same climate conditions. Understanding of sedimentary processes is crucial in order to adapt the sampling strategy and the flood‐intensity proxy to each sedimentary system and, thereby, reconstruct a complete and reliable flood history. Thanks to this detailed approach, the main trends of the regional flood variability can be reproduced; i.e. periods of high flood‐frequency, ranges of flood‐frequency values and timing of the most intense events. In detail, some differences appeared associated to the various stream capacities to erode and transport flood sediments to the lake system, implying variable sensitivity of sedimentary systems in recording floods. Comparing regional flood records based on independent sedimentary systems from similar environments could thus be a complementary approach to assessing past flood intensity. Such an approach could open particularly interesting perspectives because reconstructing the long‐term evolution of flood intensity is a key challenge in the geosciences.     

Cytotoxic and genotoxic evaluation and chemical characterization of sewage treated using activated sludge and a floating emergent-macrophyte filter in a municipal wastewater treatment plant: a case study in Southern Brazil

This study was conducted to evaluate the chemical parameters and the cytotoxic and genotoxic potential of raw domestic sewage and effluents from treatment with activated sludge and a floating emergent-macrophyte filter from a domestic wastewater treatment plant in the city of Novo Hamburgo, Rio Grande do Sul, Brazil. The physicochemical analysis revealed that both treatment systems achieved the legal emission pattern for biochemical oxygen demand, chemical oxygen demand, and suspended solids, but ammoniacal nitrogen and E. coli values were above the limits in the macrophyte treatment effluent. Phosphorous values were above the maximum permitted for both treatments. The results obtained from the Allium cepa test and the micronuclei test in fish did not demonstrate any significant differences in both cytotoxicity (mitotic index) and genotoxicity (chromosome aberration and micronucleus) endpoints between the negative control group and the exposed groups. However, the comet assay in fish revealed a DNA damage increase in animals exposed to the 30 % concentration of the macrophyte effluent and two concentrations of the activated sludge treatment effluent (10 and 75 %), which suggests that these two treatment systems may increase wastewater genotoxicity.     

Low impact surface hardness testing (Equotip) on porous surfaces – advances in methodology with implications for rock weathering and stone deterioration research

The Equotip surface hardness tester is becoming a popular method for rock and stone weathering research. In order to improve the reliability of Equotip for on‐site application this study tested four porous limestones under laboratory conditions. The range of stone porosity was chosen to represent likely porosities found in weathered limestones in the field. We consider several key issues: (i) its suitability for soft and porous stones; (ii) the type of probe required for specific on‐site applications; (iii) appropriate (non‐parametrical) statistical methods for Equotip data; (iv) sufficient sampling size. This study shows that the Equotip is suitable for soft and porous rock and stone. From the two tested probes the DL probe has some advantages over the D probe as it correlates slightly better with open porosity and allows for more controlled sampling in recessed areas and rough or curved areas. We show that appropriate sampling sizes and robust non‐parametric methods for subsequent data evaluation can produce meaningful measures of rock surface hardness derived from the Equotip. The novel Hybrid dynamic hardness, a combination of two measuring procedures [single impact method (SIM) and repeated impact method (RIM)], has been adapted and is based on median values to provide a more robust data evaluation. For the tested stones in this study we propose a sample size of 45 readings (for a confidence level of 95%). This approach can certainly be transferred to stone and rock with similar porosities and hardness. Our approach also allows for consistent comparisons to be made across a wide variety of studies in the fields of rock weathering and stone deterioration research. Copyright © 2016 John Wiley & Sons, Ltd.     

Experimental boron isotope fractionation between tourmaline and fluid: confirmation from in situ analyses by secondary ion mass spectrometry and from Rayleigh fractionation modelling

Tourmaline synthesised in an experiment with low boron excess was analysed in situ by secondary ion mass spectrometry. It revealed significant B isotope zonation with ¹¹B/¹⁰B ratios increasing in the growth direction of the crystals. Trend, magnitude and absolute values strongly support results from high-B-excess isotope fractionation experiments. Furthermore, the closed system B-isotopic evolution of the experimental fluid was modelled by Rayleigh fractionation. The model results are in excellent agreement with the measured B-isotope composition of the run-product fluid. Consequently, low-element-excess experiments are proposed as an ideal approach to determine fluid-solid isotope fractionation factors for systems that are characterised by Rayleigh fractionation.     

Experimental study of a biotite-bearing granitic system under water-saturated and water-undersaturated conditions

Phase relationships in haplogranitic melts containing ferromagnesian minerals were investigated in the temperature range 760–850°C, atP _total=2 kbar, =0.25 1.00, and at NNO buffer conditions. The compositions of coexisting biotite, orthopyroxene, magnetite and granitic melt were determined by electron microprobe. Biotite was the only Fe–Mg mineral in the starting material. It disappeared in water-undersaturated melts at temperatures above 830°C and in melts saturated with water above 810°C. Magnetite was present in all runs. Orthopyroxene became stable between 780 and 800°C. The Mg/(Mg+Fe) ratios of biotite (0,63–0,72) and orthopyroxene (0,63–0,71) are similar in water-saturated and undersaturated melts at comparable temperatures and increase slightly with increasing temperature. The solubility of Mg in haplogranitic melts is very low (0,07–0,24 wt% MgO). It increases slightly with temperature and is independent of the prevailing water activity. The solubility of Fe is low (0,91–1,37 wt% FeO); it also increases with increasing temperature, and it is higher in water-saturated than in water-undersaturated melts.     

Field-aligned currents above an auroral arc

Simultaneous observations of precipitating electrons and protons in the energy range from 15 eV to 35 keV and magnetic field variations were made onboard a sounding rocket payload launched from the Andoya Rocket Range. The electric current density deduced from the electron precipitation observed during the passage over an auroral arc was comparable to that determined from the magnetic field variations. In addition, a downward current was observed by its magnetic field signature at the northern edge of the arc which was, however, not accompanied by significant particle fluxes in the energy range under consideration. It will be assumed that this current was carried by thermal electrons of ionospheric origin.     

Experimentally determined partitioning of Rb between richterites and aqueous (Na, K)-chloride solutions

The distribution of Rb-Na and Rb-K between richterite and a 2-molal aqueous (Na, K, Rb)-chloride solution has been investigated with hydrothermal experiments at 800^∘C and 200 MPa. Experiments were performed as syntheses in which amphiboles grew in the presence of an excess fluid containing the exchangeable cations Na⁺-Rb⁺ or Na⁺-K⁺-Rb⁺. The obtained amphiboles were large enough (up to 20 m in width) for reliable EMP analysis. They were chemically homogeneous and HRTEM investigations showed that they were structurally well ordered. The Rb, Na, K, Ca and Mg concentrations in coexisting fluids were measured by ICP-AES. According to the possible incorporation of Na, K and Rb on the A-site, solid solutions in the ternary Na(NaCa) Mg₅[Si₈O₂₂/(OH)₂] (richterite)-K(NaCa)Mg₅[Si₈O₂₂/(OH)₂] (K-richterite)-Rb(NaCa)Mg₅[Si₈O₂₂/(OH)₂] (Rb-richterite) were expected. However, Rb-rich richterites always had significant amounts of A-site vacancy concentrations (X _□ ^amph=□ ^A /(Rb^A+K^A +Na^A+□^A) of up to 0.42 in the K-free (Na,Rb)-richterites and of up to 0.67 in the (Na, K, Rb)-richterites which corresponds to the same content of tremolite+cummingtonite-component. Amphiboles containing practically only Rb besides vacancies and no Na and/or K on the A-site were also synthesized, however. The Rb-Na and Rb-K exchange coefficients between fluid and richterites are similar. Rubidium always fractionated strongly into the fluid phase. For low Rb-concentrations in richterite (X _Rb ^amph<0.1) a linear correlation between X _Rb ^fluid and X _Rb ^amph exists. In this concentration range, the derived exchange coefficients K _D(Rb−K) ^amph−fluid and K _D(Rb−Na) ^amph−fluid were 0.08 ± 0.04 and 0.04 ± 0.02, respectively. These low exchange coefficients show that significant amounts of Rb in amphiboles require a Rb-rich fluid phase. The results indicate that K-Rb fractionation between alkali amphiboles and fluids is significantly different from K-Rb fractionation between alkali feldspar/ phlogopite and fluid, with K_Ds of about 0.5 and 1.2, respectively. Formation of richterites will drastically alter the K/Rb-ratios of fluids or melts. These results may have important implications for the genetical interpretation of various geological settings, e.g., MARID-type rocks. Received: 6 October 1997 / Accepted: 7 July 1998     

Soho Observations of the Connection Between Line Profile Parameters in Active and Quiet Regions and the Net Red Shift in Euv Emission Lines

We present high spatial and spectral resolution observations of one active and one quiet-Sun region, obtained with CDS and SUMER on SOHO. The connections between the line profile parameters are studied and a systematic wavelength shift towards the red with increasing peak line intensity (line broadening) is detected. The large scatter in the data calls for another approach. We apply conditional probability analysis to a series of EUV emission lines and find significant correlations between line profile parameters. For a given interval in wavelength shift we find that: (1) line profiles with large intensities (line widths) and red shifts above the average constitute an increasing fraction of the profiles as the relative wavelength shift increases, (2) line profiles with large intensities (line widths) and blue shifts compared to the average, on the other hand, constitute a decreasing fraction of the profiles as the relative wavelength shift increases. These results extend the findings of an earlier quiet-Sun study from one to several emission lines and expand the validity to include the active region. Interestingly, the active region observations show correlations between peak line intensity and wavelength shift in the coronal lines.The tendency for red-shifted profiles to be more intense than blue-shifted profiles will shift line profiles derived by integrating along the slit towards the red. From the present observations we are not able to determine the fraction of the net red shift that emerges from this correlation. We suggest that the same mechanism is responsible both for the correlation between the line profile parameters and for the differential red shift between the transition region and chromospheric emission lines.