The Horqin Sandy Grassland is one of the most seriously desertified areas in China's agro-pastoral ecotone due to its fragile ecology, combined with improper and unsustainable land management. We inves... 相似文献
A large amount of deep oil has been discovered in the Tazhong Uplift, Tarim Basin whereas the oil source is still controversial. An integrated geochemical approach was utilized to unravel the characteristics, origin and alteration of the deep oils. This study showed that the Lower Cambrian oil from well ZS1C (1x) was featured by small or trace amounts of biomarkers, unusually high concentration of dibenzothiophenes (DBTs), high δ34S of DBTs and high δ13C value of n-alkanes. These suggest a close genetic relationship with the Cambrian source rocks and TSR alteration. On the contrary, the Middle Cambrian oils from well ZS1 (2a) were characterized by low δ13C of n-alkanes and relatively high δ34S of individual sulfur compounds and a general “V” shape of steranes, indicating a good genetic affinity with the Middle–Upper Ordovician source rocks. The middle Cambrian salt rock separating the oils was suggested to be one of the factors responsible for the differentiation. It was suggested that most of the deep oils in the Tazhong Uplift were mixed source based on biomarkers and carbon isotope, which contain TSR altered oil in varied degree. The percentage of the oils contributed by the Cambrian–Lower Ordovician was in the range of 19–100% (average 57%) controlled by several geological and geochemical events. Significant variations in the δ34S values for individual compounds in the oils were observed suggesting a combination of different extent of TSR and thermal maturation alterations. The unusually high DBTs concentrations in the Tazhong-4 oilfield suggested as a result of mixing with the ZS1C oil (1x) and Lower Ordovician oils based on δ34S values of DBT. This study will enhance our understanding of both deep and shallow oil sources in the Tazhong Uplift and clarify the formation mechanisms of the unusually high DBTs oils in the region. 相似文献
Private sector actors are playing an increasingly significant role in the definition and governance of ‘sustainable’ agri-food practices. Yet, to date little attention has been paid by social scientists to how greenhouse gas (GHG) emissions are addressed as part of private agri-food governance arrangements. This paper examines how private actors within agri-food supply chains respond to emerging pressure for measures to reduce GHG emissions from agriculture. Drawing upon the Anglo-Foucauldian governmentality literature, we introduce the notion of the corporate carbon economy to conceptualise the practical techniques that enable private agri-food actors to make GHG emissions thinkable and governable in the context of existing market, regulatory, and supply chain pressures. Using a case study of the Australian dairy industry, we argue that private agri-food actors utilise a range of techniques that enable them to respond to existing government environmental regulations, balance current market pressures with future supply chain requirements, and demonstrate improved eco-efficiency along food supply chains. These techniques – which include environmental self-assessment instruments, tools for measuring GHG emissions, and sustainability reporting – have little direct relevance to the ‘international climate regime’ of carbon trading, and carbon markets more broadly, yet individually and in combination they are crucial in enacting an alternative regime of GHG governance. In concluding, we contend that the growing use of sustainability metrics by international food companies is likely to have the most powerful implications for GHG governance in the agri-food sector, with potentially far-reaching consequences for how future action on climate change is rendered thinkable and practicable. 相似文献
Chemolithotrophic homoacetogenic bacteria apparently express a characteristic stable carbon isotope fractionation and may contribute significantly to acetate production in anoxic environments. However, fractionation factors (ε) in bacterial cultures have rarely been determined and the effect of substrate availability has not been assessed. We therefore studied the kinetic carbon isotope effect in cultures of Thermoanaerobacter kivui grown at 55 °C. The fractionation factor in HCO3− buffered medium was ca. 15‰ more negative than that in PO43− buffered medium. To test whether the difference was caused by the initial substrate ratio of H2 and total inorganic carbon (TIC; 0.5 in HCO3− vs. 4.0 in PO43− buffered medium), T. kivui was grown in either [3-(N-morpholino) propanesulfonic acid, MOPS] buffered or PO43− buffered media with different HCO3− concentration. Indeed, the fractionation factor became more negative with increasing HCO3− concentration and decreasing H2/TIC ratio. While pH had only a small effect, the fractionation was generally more negative in MOPS buffered than in phosphate buffered media, indicating that the buffer system also affected fractionation. Collectively, the results show that substrate availability and other environmental factors affect the magnitude of isotope fractionation during acetate production by chemolithotrophic homoacetogenesis. 相似文献
The past several decades have witnessed a significant expansion of mining activities in the Athabasca oil sands region, raising concerns about their impact on the surrounding boreal forest ecosystem. To better understand the extent to which distal sites are impacted by oil sands-derived airborne contaminants, we examine sources of polycyclic aromatic hydrocarbons (PAHs) in surface sediments and dated sediment cores from Saskatchewan lakes situated ∼100–220 km east–northeast of the main area of bitumen mining activities. The concentrations and fluxes of both parent and alkylated PAHs are low and show considerable variability over the past 70–100 years. Small yet discernible increases in PAH concentrations and fluxes occurred over the past 30 years, a trend which coincides with the rapid growth in bitumen production. However, several lines of evidence point to wildfires as the principal source of PAHs to these lakes: (1) the significant co-variations in most cores between retene (1-methyl-7-isopropyl phenanthrene) and other groups of parent and alkylated PAHs, (2) the similarity in compound specific δ13C signatures of the parent PAHs phenanthrene and pyrene in recently deposited surficial sediments and those corresponding to time intervals considerably pre-dating the large scale development of the oil sands and (3) the discernible up-core increases in the proportion of refractory carbon (i.e., char) in Rock-Eval 6 data. The collective evidence points to softwood combustion from boreal forest fires as the principal source of retene in sediments and the general increase in forest fire activity in this region over the past several decades as the source of refractory carbon. Mining activities associated with the Athabasca oil sands are thus not considered a major source of PAHs to these lakes. 相似文献
In mine soil, quantification of soil organic carbon (OC) derived recently from biomass decomposition is complicated by the presence of fossil (geogenic) C derived from coal, oil shale, or similar material in the overburden. The only reliable method for such measurement is 14C analysis (i.e. radiocarbon dating) using instrumentation such as accelerator mass spectrometry, which is too expensive for routine laboratory analysis. We tested two previously used and two new methods for recent C quantification and compared them with 14C AMS radiocarbon dating as a reference using a set of soil samples (n = 14) from Sokolov, Czech Republic: (i) 13C isotope ratio composition, (ii) cross polarization magic angle spinning 13C nuclear magnetic resonance (CPMAS 13C NMR) spectroscopy, (iii) near infrared spectroscopy (NIRS) coupled with partial least squares regression and (iv) Rock–Eval pyrolysis. Conventional methods for OC determination (dry combustion, wet dichromate oxidation, loss-on-ignition) were also compared to quantify any bias connected with their use. All the methods provided acceptable recent carbon estimates in the presence of mostly aliphatic fossil C from kerogen. However, the most accurate predictions were obtained with two approaches using Rock–Eval pyrolysis parameters as predictors, namely (i) S2 curve components and (ii) oxygen index (OI). The S2 curve approach is based on the lower thermal stability of recent vs. fossil organic matter. The OI approach corresponded well with 13C NMR spectra, which showed that samples rich in recent C were richer in carboxyl C and O-alkyl C. These two methods showed the greatest potential as routine methods for recent C quantification. 相似文献
A procedure for determining a wide range of chalcophile and siderophile elements in typical crustal rocks using standard addition and ICP‐SFMS (inductively coupled plasma sector field mass spectrometry) is presented. New results for Ga, Ge, Mo, Ag, Cd, In, Sn, Sb, W, Tl and Bi abundances in USGS whole‐rock reference materials AGV‐2, BHVO‐1, BIR‐1, G‐2, GSP‐1 and W‐2 are reported using this analytical procedure. Intermediate precision of means based on multiple dissolved aliquots of each USGS reference material was 10% RSD or better for Ga, Ge, In and Sn in all, and similarly good for Ag, Cd, Sb, Tl and Bi in most reference materials. Poorer intermediate precision of Mo and W measurements in several reference materials is probably due to higher analytical blanks on these elements and powder heterogeneity due to a sulfide‐related nugget effect in the specific case of Mo in GSP‐1. Results for all elements fell within the range of available published data with the exception of Ag, which yielded systematically higher concentrations than found in the literature for five of the six reference materials, likely reflecting interference from unresolved polyatomic species. 相似文献
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