Nitrous oxide fluxes in three experimental boreal forest reservoirs

Global atmospheric concentrations of nitrous oxide (N2O), a powerful greenhouse gas, continue to increase. While many sources and sinks have been identified, there is little known about how existing and newly constructed reservoirs, such as those created for hydroelectric production, impact current atmospheric N2O concentrations. We hypothesized that N2O fluxes to the atmosphere would increase because enhanced nutrient availability and increased soil respiration following the flooding of soils during reservoir creation would favor denitrification. Furthermore, we hypothesized that emissions would be linked to the amount of organic carbon contained in the flooded landscape. These hypotheses were tested by creating three experimental reservoirs over boreal upland subcatchments that ranged in the amount of organic carbon stored in soils and vegetation. Diffusive surface N2O fluxes within each reservoir were estimated using surface water concentrations of N2O and the thin boundary layer method. Surface fluxes ranged from -1.0 to -3.5 microg N2O m(-2) d(-1), and water column N2O concentrations indicated that contrary to expectations, the reservoirs were acting as slight sinks for atmospheric N2O. This net consumption of N2O was likely related to an excess of labile carbon and low concentrations of oxygen (O2) and nitrate (NO3-) in the flooded soils. Therefore, it is postulated that reservoir creation by flooding boreal soils will likely have little or no net effect of adding additional N2O to the current greenhouse gas (GHG) atmospheric burden, at least over the short term.     

Modelling the influence of single acid and mixture on bacterial growth

Depending on environmental factors, the prediction of bacterial growth is made difficult by the complexity of foodstuff. Although the influence of temperature, pH, and water activity are usually taken into account, models have to be completed with the influence of acid mixture. Nine strains of Listeria spp., four Salmonella spp., one Staphylococcus aureus, one Escherichia coli, and Listeria innocua ATCC 33090 were used for this study to extend model proposed by [Le Marc, Y., Huchet, V., Bourgeois, C., Guyonnet, J., Mafart, P., Thuault, D., 2002. Modelling the growth kinetics of Listeria as a function of temperature, pH and organic acid concentration. International Journal of Food Microbiology 73, 219–237]. Derived from data of [Houtsma, P.C., Kusters, B.J., De Wit, J.C., Rombouts, F.M., Zwietering, M.H., 1994. Modelling growth rates of Listeria innocua as a function of lactate concentration. International Journal of Food Microbiology 24, 113–123] and our own data, the extended model described accurately different effects of addition of acid salts in the medium (decrease of water activity and pH, variation of undissociated weak acid form, and variation of synergetic effect between environmental factors). This previous model was implemented to describe the observed variability of behaviour of the different studied strains. reflected the general behaviour of species (sensitiveness to low or high undissociated acid concentration), and MIC_U reflected the various resistances of strains. From this simple model, a new model was built for describing the effects of concentrations of several mixed acids on bacterial growth rates. Simulations of growth were carried out from three acids mixtures by inputting parameter estimates previously obtained. Despite a very variable effect of investigated acids on growth, the new model yielded fair predictions.     

Terpene profiles in Cantal and Saint‐Nectaire‐type cheese made from raw or pasteurised milk

Terpene profiles in cheese can be considered a ‘terroir’ fingerprint as the information contained in it should enable the pastures on which the animals were fed to be recognised. Yet a certain elasticity of the signature must be taken into account when determining authentication strategies, since products acknowledged as containing a common signature may have undergone certain procedures, such as cheese making and milk pasteurisation, that could have potentially altered their terpene profiles. In this study, Cantal and Saint‐Nectaire‐type cheeses were made from both raw and pasteurised milk from the same herd of dairy cows that had been grazed on natural grassland. Cheeses from raw and pasteurised milk were made from the same milking on the same days. Cantal and Saint‐Nectaire‐type cheeses were made on 4 different days, alternatively over four weeks. The terpenes in the cheese fat were analysed by dynamic headspace/gas chromatography/mass spectrometry. A great diversity of monoterpenes, sesquiterpenes and oxygen‐containing derivatives were identified. The major terpenes identified in most cheeses were β‐caryophyllene, α‐ and β‐pinene and limonene. Milk pasteurisation did not induce changes in the terpene profile of the cheese. Significant differences (p < 0.001) were observed between Cantal and Saint‐Nectaire cheeses: α‐pinene, β‐myrcene and β‐phellandrene were, respectively, three, five and five times more abundant in Cantal cheese, while tricyclene, α‐phellandrene and geraniol were found exclusively in Cantal cheese. In contrast, unidentified sesquiterpenes with retention indices (KI) = 1342 and 1511, α‐cubebene, longifolene and γ‐elemene were more abundant or exclusively found in Saint‐Nectaire cheese. A significant relationship with the date of milking (p < 0.01) was observed for α‐pinene and tricyclene in Cantal, for β‐myrcene, δ‐3‐carene, p‐cymene and α‐terpinene in Saint‐Nectaire cheese. Copyright © 2005 Society of Chemical Industry     

Differences in mercury bioaccumulation between polar bears (Ursus maritimus) from the Canadian high- and sub-Arctic

Polar bears (Ursus maritimus) are being impacted by climate change and increased exposure to pollutants throughout their northern circumpolar range. In this study, we quantified concentrations of total mercury (THg) in the hair of polar bears from Canadian high- (southern Beaufort Sea, SBS) and sub- (western Hudson Bay, WHB) Arctic populations. Concentrations of THg in polar bears from the SBS population (14.8 ± 6.6 μg g(-1)) were significantly higher than in polar bears from WHB (4.1 ± 1.0 μg g(-1)). On the basis of δ(15)N signatures in hair, in conjunction with published δ(15)N signatures in particulate organic matter and sediments, we estimated that the pelagic and benthic food webs in the SBS are ～ 4.7 and ～ 4.0 trophic levels long, whereas in WHB they are only ～ 3.6 and ～ 3.3 trophic levels long. Furthermore, the more depleted δ(13)C ratios in hair from SBS polar bears relative to those from WHB suggests that SBS polar bears feed on food webs that are relatively more pelagic (and longer), whereas polar bears from WHB feed on those that are relatively more benthic (and shorter). Food web length and structure accounted for ～ 67% of the variation we found in THg concentrations among all polar bears across both populations. The regional difference in polar bear hair THg concentrations was also likely due to regional differences in water-column concentrations of methyl Hg (the toxic form of Hg that biomagnifies through food webs) available for bioaccumulation at the base of the food webs. For example, concentrations of methylated Hg at mid-depths in the marine water column of the northern Canadian Arctic Archipelago were 79.8 ± 37.3 pg L(-1), whereas, in HB, they averaged only 38.3 ± 16.6 pg L(-1). We conclude that a longer food web and higher pelagic concentrations of methylated Hg available to initiate bioaccumulation in the BS resulted in higher concentrations of THg in polar bears from the SBS region compared to those inhabiting the western coast of HB.     

Methylmercury and total mercury in plant litter decomposing in upland forests and flooded landscapes

The overall objectives of this study were to examine the effects of flooding on the decomposition and mercury (Hg) content of tissues from plants common to boreal upland forests at the Experimental Lakes Area in northwestern Ontario. We used litterbags to study changes in total Hg (THg), methyl Hg (MeHg), carbon (C), and nitrogen (N) in 12 different plant tissues (birch, alder, blueberry, and Labrador tea leaves, bunchberry plants, jack pine needles, Sphagnum spp., Polytrichum spp., and Pleurozium spp. bryophytes, lichen, and fresh and extensively decomposed wood) placed on unflooded boreal forest soils and in experimentally created reservoirs over an approximately 800 day period. Rates of decomposition (as indicated by differences in the percentage of C and N mass left in the tissues over time) were slower in plant tissues placed on unflooded soils compared to the same tissues that were inundated in reservoirs. Depending on tissue type and initial THg concentrations, decomposing litter on both unflooded and flooded soils was either a source or a sink for THg. Tissues where initial THg concentrations were greater than 30 ng g(-1) represented a source of THg to the surrounding environment, whereas tissues that had initial concentrations of less than 30 ng g(-1) gained THg mass. Initial rates of change in THg were more rapid in plant tissues placed in reservoirs compared to the same plant tissue placed on unflooded soils, but there were no differences in final THg masses after approximately 800 days. Plant tissues placed in reservoirs exhibited large increases in MeHg mass, whereas MeHg mass decreased in the same plants placed on unflooded soils. This is the first study examining THg and MeHg cycling in decomposing plants in upland boreal forests and reservoirs.     

Bioavailability of a bilberry anthocyanin extract and its impact on plasma antioxidant capacity in rats

Anthocyanins are secondary metabolites from the flavonoid family, frequently found in fruits and vegetables. They have been shown to possess beneficial health effects and various in vitro assays have highlighted their powerful antioxidant capacity. However, little is known about their metabolism after digestion and their antioxidant potency in vivo. The aim of this work was to evaluate anthocyanin bioavailability and to determine the impact of an anthocyanin‐rich diet on plasma antioxidant status in rats. Animals were fed for 8 days with a vitamin E‐deficient diet supplemented with a bilberry (Vaccinium myrtillus L.) anthocyanin extract providing daily 1.43 mmol anthocyanins kg^?1 body weight. An anthocyanin‐enriched diet significantly enhanced the plasma antioxidant capacity compared with a control diet (P < 0.0001). Moreover, anthocyanins were recovered in urine in the intact glycosidic forms in addition to unknown metabolites. Urinary excretion of bilberry anthocyanins and their metabolites was 0.71 ± 0.08 µmol per 24 h (ie 0.22% of the ingested dose). Anthocyanins and their corresponding aglycones were detected in caecal contents. After a single oral administration of the bilberry extract, native anthocyanins quickly (30 min) appeared in plasma. Hence, in spite of a low bioavailability, bilberry anthocyanin extract consumption has a positive effect on plasma antioxidant capacity. Copyright © 2005 Society of Chemical Industry     

Influence of petroleum on the failure pattern of saturated pre-cracked and intact sandstone

Bulletin of Engineering Geology and the Environment - Failures of the surrounding rock mass have been identified as the most serious threat to the stability of underground water-sealed petroleum...