Combining Two Filter Paper-Based Analytical Methods to Monitor Temporal Variations in Fluvial Suspended Solid Properties

Many of the commonly used analytical techniques for assessing the properties of fluvial suspended solids are neither cost-effective nor time-efficient, making them prohibitive to long-term high-resolution monitoring.We propose a novel methodology utilising two types of spectroscopy which, when combined with automatic water samplers, can generate accurate, high-temporal resolution sediment property data, inexpensively and non-destructively, directly from sediment covered filter papers. A dual X-ray fluorescence spectroscopy (XRFS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) approach is developed to estimate concentrations for a range of elements (Al, Ca, Ce, Fe, K, Mg, Mn, Na, P, Si, Ti) and compounds (organic carbon, Aldithionate, Aloxalate, Fedithionate, and Feoxalate) within sediments trapped on quartz fibre filters at masses as low as 3 mg. Calibration models with small prediction errors are produced for a total of 16 elements and compounds for which the geochemical signal is demonstrated to be time stable enabling samples to be stored for several weeks prior to analysis. Spectral pre-processing methods are shown to enhance the reproducibility of results for some compounds, whilst corrections for sediment mass retention are derived, and the importance of filter paper selection and homogeneous sample preparation in minimising spectral interference are emphasized. The results presented here demonstrate the potential for a combined XRFS and DRIFTS analysis of sediment covered filter papers to be utilized under a range of in-stream hydrological conditions where there is an environmental requirement for high-resolution monitoring of suspended solid properties

Seawater carbonate chemistry and pteropod Limacina helicina antarctica shell dissolution during experiments, 2012

Anthropogenic ocean acidification is likely to have negative effects on marine calcifying organisms, such as shelled pteropods, by promoting dissolution of aragonite shells. Study of shell dissolution requires an accurate and sensitive method for assessing shell damage. Shell dissolution was induced through incubations in CO2 enriched seawater for between 4 and 14 days. We describe a procedure that allows the level of dissolution to be assessed and classified into three main types: Type I with partial dissolution of the prismatic layer; Type II with exposure of underlying crossed-lamellar layer, and Type III, where crossed-lamellar layer shows signs of dissolution. Levels of dissolution showed a good correspondence to the incubation conditions, with the most severe damage found in specimens held for 14 d in undersaturated condition (Ohm ~ 0.8). This methodology enables the response of small pelagic calcifiers to acidified conditions to be detected at an early stage, thus making pteropods a valuable bioindicator of future ocean acidification

Seawater carbonate chemistry and proportion of different dissolution levels in live juvenile Limacina helicina antarctica from the natural environment and ship-board incubations

The carbonate chemistry of the surface ocean is rapidly changing with ocean acidification, a result of human activities. In the upper layers of the Southern Ocean, aragonite-a metastable form of calcium carbonate with rapid dissolution kinetics-may become undersaturated by 2050. Aragonite undersaturation is likely to affect aragonite-shelled organisms, which can dominate surface water communities in polar regions. Here we present analyses of specimens of the pteropod Limacina helicina antarctica that were extracted live from the Southern Ocean early in 2008. We sampled from the top 200 m of the water column, where aragonite saturation levels were around 1, as upwelled deep water is mixed with surface water containing anthropogenic CO2. Comparing the shell structure with samples from aragonite-supersaturated regions elsewhere under a scanning electron microscope, we found severe levels of shell dissolution in the undersaturated region alone. According to laboratory incubations of intact samples with a range of aragonite saturation levels, eight days of incubation in aragonite saturation levels of 0.94-1.12 produces equivalent levels of dissolution. As deep-water upwelling and CO2 absorption by surface waters is likely to increase as a result of human activities, we conclude that upper ocean regions where aragonite-shelled organisms are affected by dissolution are likely to expand

Image et anthropologie

Que ce soit dans les sociétés dites traditionnelles ou au sein de notre propre tradition, on ne peut plus concevoir une ethnologie des objets sans la construction parallèle d'une esthétique. Inversement, aucune esthétique ne semble désormais possible sans que les questions posées par l'étude des images ne dépassent le modèle traditionnel de l'histoire de l'art pour devenir anthropologiques. Ce numéro provoque la rencontre de recherches qui, à partir de l'oeuvre d'Aby Warburg, grand pionnier d..