Yves Gélinas

Preservation of organic matter in sediments promoted by iron

The biogeochemical cycles of iron and organic carbon are strongly interlinked. In oceanic waters, organic ligands have been shown to control the concentration of dissolved iron. In soils, solid iron phases shelter and preserve organic carbon, but the role of iron in the preservation of organic matter in sediments has not been clearly established. Here we use an iron reduction method previously applied to soils to determine the amount of organic carbon associated with reactive iron phases in sediments of various mineralogies collected from a wide range of depositional environments. Our findings suggest that 21.5 ± 8.6 per cent of the organic carbon in sediments is directly bound to reactive iron phases. We further estimate that a global mass of (19–45) × 1015 grams of organic carbon is preserved in surface marine sediments as a result of its association with iron. We propose that these associations between organic carbon and iron, which are formed primarily through co-precipitation and/or direct chelation, promote the preservation of organic carbon in sediments. Because reactive iron phases are metastable over geological timescales, we suggest that they serve as an efficient ‘rusty sink’ for organic carbon, acting as a key factor in the long-term storage of organic carbon and thus contributing to the global cycles of carbon, oxygen and sulphur.

Comparative analysis of black carbon in soils

Black carbon (BC), produced by incomplete combustion of fossil fuels and vegetation, occurs ubiquitously in soils and sediments. BC exists as a continuum from partly charred material to highly graphitized soot particles, with no general agreement on clear-cut boundaries of definition or analysis. In a comparative analysis, we measured BC forms in eight soil samples by six established methods. All methods involved removal of the non-BC components from the sample by thermal or chemical means or a combination of both. The remaining carbon, operationally defined as BC, was quantified via mass balance, elemental composition or by exploiting benzenecarboxylic acids as molecular markers or applying 13C MAS NMR (magic angle spinning nuclear magnetic resonance) spectroscopy. BC concentrations measured for individual samples vary over 2 orders of magnitude (up to a factor of 571). One possible explanation for this wide range of results is that the individual BC methods rely on operational definitions with clear-cut but different boundaries and developed for specific scientific questions, whereas BC represents a continuum of materials with widely contrasting physicochemical properties. Thus the methods are inherently designed to analytically determine different parts of the continuum, and it is crucial to know how measurements made by different techniques relate to each other. It is clear from this preliminary comparative analysis that a collection of BC reference materials should be established as soon as possible 1 ) to ensure long-term intralaboratory and interlaboratory data quality and 2) to facilitate comparative analyses between different analytical techniques and scientific approaches

Mechanisms of the Depot Specificity of Peroxisome Proliferator–Activated Receptor γ Action on Adipose Tissue Metabolism

In this study, we aimed to establish the mechanisms whereby peroxisome proliferator–activated receptor γ (PPARγ) agonism brings about redistribution of fat toward subcutaneous depots and away from visceral fat. In rats treated with the full PPARγ agonist COOH (30 mg · kg−1 · day−1) for 3 weeks, subcutaneous fat mass was doubled and that of visceral fat was reduced by 30% relative to untreated rats. Uptake of triglyceride-derived nonesterified fatty acids was greatly increased in subcutaneous fat (14-fold) and less so in visceral fat (4-fold), with a concomitant increase, restricted to subcutaneous fat only, in mRNA levels of the uptake-, retention-, and esterification-promoting enzymes lipoprotein lipase, aP2, and diacylglycerol acyltransferase 1. Basal lipolysis and fatty acid recycling were stimulated by COOH in both subcutaneous fat and visceral fat, with no frank quantitative depot specificity. The agonist increased mRNA levels of enzymes of fatty acid oxidation and thermogenesis much more strongly in visceral fat than in subcutaneous fat, concomitantly with a stronger elevation in O2 consumption in the former than in the latter. Mitochondrial biogenesis was stimulated equally in both depots. These findings demonstrate that PPARγ agonism redistributes fat by stimulating the lipid uptake and esterification potential in subcutaneous fat, which more than compensates for increased O2 consumption; conversely, lipid uptake is minimally altered and energy expenditure is greatly increased in visceral fat, with consequent reduction in fat accumulation.

Microbial‐mineral floc associated with nascent hydrothermal activity on CoAxial Segment, Juan de Fuca Ridge

Following a June 1993 seafloor eruption at CoAxial Segment, Juan de Fuca Ridge, extensive accumulation of microbial-mineral floc was observed in association with abundant diffuse venting on new lava flows, and around less extensive new venting on older basalts. Microscopic and SEM examination revealed a diverse assemblage of microbial forms contained within a poorly organized organo-mineral matrix. Samples more closely resembled microbial floc described from other hydrothermal areas than the layered bacterial mats observed after the eruption at 9°N on the East Pacific Rise. Iron and silica were the major compositional elements in all samples, with the latter likely important in preserving microbial remains. Organic carbon content was on the order of 3–4%. Enzyme assays indicated the presence of autotrophic CO2 fixation and potential for sulfide oxidation. Floc covered 7–14% of the seafloor on the hydrothermally active part of the new lava flow. We discuss the possibility that the CoAxial floc originated as ejecta from the sub-seafloor hydrothermal system rather than from in situ production around vent openings.

Methane Baseline Concentrations and Sources in Shallow Aquifers from the Shale Gas-Prone Region of the St. Lawrence Lowlands (Quebec, Canada)

Hydraulic fracturing is becoming an important technique worldwide to recover hydrocarbons from unconventional sources such as shale gas. In Quebec (Canada), the Utica Shale has been identified as having unconventional gas production potential. However, there has been a moratorium on shale gas exploration since 2010. The work reported here was aimed at defining baseline concentrations of methane in shallow aquifers of the St. Lawrence Lowlands and its sources using δ(13)C methane signatures. Since this study was performed prior to large-scale fracturing activities, it provides background data prior to the eventual exploitation of shale gas through hydraulic fracturing. Groundwater was sampled from private (n = 81), municipal (n = 34), and observation (n = 15) wells between August 2012 and May 2013. Methane was detected in 80% of the wells with an average concentration of 3.8 ± 8.8 mg/L, and a range of <0.0006 to 45.9 mg/L. Methane concentrations were linked to groundwater chemistry and distance to the major faults in the studied area. The methane δ(1)(3)C signature of 19 samples was > -50‰, indicating a potential thermogenic source. Localized areas of high methane concentrations from predominantly biogenic sources were found throughout the study area. In several samples, mixing, migration, and oxidation processes likely affected the chemical and isotopic composition of the gases, making it difficult to pinpoint their origin. Energy companies should respect a safe distance from major natural faults in the bedrock when planning the localization of hydraulic fracturation activities to minimize the risk of contaminating the surrounding groundwater since natural faults are likely to be a preferential migration pathway for methane.

Well water survey in two districts of Conakry (Republic of Guinea), and comparison with the piped city water

Analyses of water from wide-diameter open wells were carried out in two districts of Conakry (Republic of Guinea) during the dry season of 1994 (April-May) to evaluate its bacteriological and physico-chemical quality and to compare well water to the piped city water. Widespread well water contamination for nitrate and fecal bacteria was found throughout both districts. The other common water-quality parameters, as well as total organic carbon and halogens, oils and greases of general use, and 34 inorganic elements were within the standard norms for safe drinking water. Chromium and, to a lesser extent, lead and mercury could become a threat to health if the situation worsens. Although thorough hydrogeological studies are needed to determine contaminant pathways, insufficient well maintenance appears to be the main factor contributing to the bacteriological contamination, while the nitrate contamination seems more closely linked to infiltration of organic contaminants from the soil surface. Piped city water was found to comply with WHO norms for drinking water and its use should be strongly encouraged to reduce the incidence of water-borne diseases.

Larval nutrition affects life history traits in a capital breeding moth.

SUMMARY Fitness depends not only on resource uptake but also on the allocation of these resources to various life history functions. This study explores the life-history consequences of larval diet in terms not only of larval performance but also of adult body composition and reproductive traits in the forest tent caterpillar (Malacosoma disstria Hübner). Caterpillars were reared on their preferred tree host, trembling aspen (Populus tremuloides), or on one of three artificial foods: high protein:low carbohydrate, equal protein-to-carbohydrate ratio or low protein:high carbohydrate. Survivorship, larval development rate and adult body size were lowest on the carbohydrate-biased diet and similar on the protein-biased and equal-ratio diets. Fecundity increased with body size but did not otherwise differ between diets. Moths reared on the carbohydrate-biased diet allocated a lower proportion of their mass to the ovaries and more to somatic growth whereas those on equal-ratio and protein-biased diets allocated more to reproductive tissue and less to somatic tissue. These differences in allocation to reproduction arose from differences in the size of eggs, an index of offspring quality. No differences were found in lipid and protein content of female ovaries, accessory glands or somatic tissue, or of the whole body of male moths. The findings show that physiological processes regulate the composition of the different components of the adult body. Diet effects occur as differences in overall body size and in relative allocation to these components. Although lepidopterans can, to a large extent, compensate post-ingestively for nutritionally deficient diets, investment in reproduction vs somatic growth depends on the nutrients available.

History of the atmospheric deposition of major and trace elements in the industrialized St. Lawrence Valley, Quebec, Canada.

The history of the atmospheric deposition of major and trace elements over southwestern Quebec, Canada, was reconstructed using multielemental analysis of lacustrine sediments sampled in a small and undisturbed lake located on top of a mountain in the heart of the industrialized St. Lawrence Valley. Acid leachable and residual elements were extracted from a 37-cm long core (1-cm resolution) using clean techniques and analyzed by inductively coupled plasma mass spectrometry. Organic matter and sulfur concentrations were high and played a major role in the low postdepositional diagenetic remobilization of many trace elements. Sulfur, manganese, iron, arsenic, molybdenum and barium displayed a high mobility making it exceedingly difficult to infer unambiguously time-dependent changes in atmospheric deposition for these elements. Atmospheric deposition rates for the less mobile elements (e.g., potassium, vanadium, chromium, cobalt, nickel, copper, zinc, rubidium, cadmium, tin, antimony, mercury, thallium, lead, and bismuth) increased regularly between 1942 and 1960–1975 in the Lake Hertel area and then stabilized for most of these elements, with the exception of nickel, copper, zinc and tin. Lead deposition rate was reduced by about 25% between 1982 and 1995, and a slight decreasing trend was also found for cobalt, mercury, and thallium during the same period. Present-day atmospheric deposition of metals directly on the lake surface represents a small percentage of the sedimentary deposition rates at this location. Deposition followed by surface runoff and outwash of terrestrial organic and inorganic matter most likely is the driving mechanism leading to the non-diagenetic enrichment of metals in Lake Hertel sediments.

Multi-element analysis of biological tissues by inductively coupled plasma mass spectrometry

Abstract A general method for the quasi-simultaneous determination of most of the elements present in biological tissues by inductively coupled plasma mass spectrometry is described. Its validity was assessed by the multi-element analysis of NBS SRM 1577a Bovine Liver and its sensitivity was established by spiking digested samples of fish muscle tissue with known amounts of elements (0.125, 0.250, 0.500, 1.00 and 10.00 ng ml −1 ). Spike recoveries of 0.124±0.002 ng ml −1 (five repeated determinations for each element in the multi-elemental determination mode) were obtained for eleven elements (Ag, Co, Cr, Li, Mn, Mo, Sb, Sr, Tl, V and Y), 0.241 ±0.008 ng ml −1 for eight elements (As, Ba, Cd, Hg, Pb, Sn, Zr and U), 0.487±0.015 ng ml −1 for seven elements (B, Cu, Ni, Rb, Se, Ti and W), 0.97±0.06 ng ml −1 for Al and Zn and 9.53±0.76 ng ml −1 for Bi, Fe, Sc, Si and I.

Coupling a High-Temperature Catalytic Oxidation Total Organic Carbon Analyzer to an Isotope Ratio Mass Spectrometer To Measure Natural-Abundance δ13C-Dissolved Organic Carbon in Marine and Freshwater Samples

The stable isotope composition of dissolved organic carbon (delta(13)C-DOC) provides powerful information toward understanding carbon sources and cycling, but analytical limitations have precluded its routine measurement in natural samples. Recent interfacing of wet oxidation-based dissolved organic carbon analyzers and isotope ratio mass spectrometers has simplified the measurement of delta(13)C-DOC in freshwaters, but the analysis of salty estuarine/marine samples still proves difficult. Here we describe the coupling of the more widespread high-temperature catalytic oxidation-based total organic carbon analyzer to an isotope ratio mass spectrometer (HTC-IRMS) through cryogenic trapping of analyte gases exiting the HTC analyzer for routine analysis of delta(13)C-DOC in aquatic and marine samples. Targeted elimination of major sources of background CO2 originating from the HTC analyzer allows for the routine measurement of samples over the natural range of DOC concentrations (from 40 microM to over 2000 microM), and salinities (<0.1-36 g/kg). Because consensus reference natural samples for delta(13)C-DOC do not exist, method validation was carried out with water-soluble stable isotope standards as well as previously measured natural samples (IAEA sucrose, Suwannee River Fulvic Acids, Deep Sargasso Sea consensus reference material, and St. Lawrence River water) and result in excellent delta(13)C-DOC accuracy (+/-0.2 per thousand) and precision (+/-0.3 per thousand).