Inverse kinetic isotope fractionation during bacterial nitrite oxidation   总被引：4，自引：0，他引：4  

Karen L. Casciotti 《Geochimica et cosmochimica acta》2009,73(7):2061-2076

Natural abundance stable isotopes in nitrate (), nitrite (), and nitrous oxide (N₂O) have been used to better understand the cycling of nitrogen in marine and terrestrial environments. However, in order to extract the greatest information from the distributions of these isotopic species, the kinetic isotope effects for each of the relevant microbial reactions are needed. To date, kinetic isotope effects for nitrite oxidation and anaerobic ammonium oxidation (anammox) have not been reported. In this study, the nitrogen isotope effect was measured for microbial nitrite oxidation to nitrate. Nitrite oxidation is the second step in the nitrification process, and it plays a key role in the regeneration of nitrate in the ocean. Surprisingly, nitrite oxidation occurred with an inverse kinetic isotope effect, such that the residual nitrite became progressively depleted in ¹⁵N as the reaction proceeded. Three potential explanations for this apparent inverse kinetic isotope effect were explored: (1) isotope exchange equilibrium between nitrite and nitrous acid prior to reaction, (2) reaction reversibility at the enzyme level, and (3) true inverse kinetic fractionation. Comparison of experimental data to ab initio calculations and theoretical predictions leads to the conclusion that the fractionation is most likely inverse at the enzyme level. Inverse kinetic isotope effects are rare, but the experimental observations reported here agree with kinetic isotope theory for this simple N-O bond-forming reaction. Nitrite oxidation is therefore fundamentally different from all other microbial processes in which N isotope fractionation has been studied. The unique kinetic isotope effect for nitrite oxidation should help to better identify its role in the cycling of nitrite in ocean suboxic zones, and other environments in which nitrite accumulates.  相似文献   

Isolation,biodegradation ability and molecular detection of hydrocarbon degrading bacteria in petroleum samples from a Brazilian offshore basin     

Suzan Pantaroto de Vasconcellos  Elaine Crespim  Georgiana Feitosa da Cruz  Diego Barbosa Senatore  Karen Christina Marques Simioni  Eugênio Vaz dos Santos Neto  Anita Jocelyne Marsaioli  Valéria Maia de Oliveira 《Organic Geochemistry》2009,40(5):574-588

The detection of microorganisms with potential for biodeterioration and biodegradation in petroleum fields is of great relevance, since these organisms may be related to a decrease in petroleum quality in the reservoirs or damage in the production facilities. In this sense, petroleum formation water and oil samples were collected from the Campos Basin, Brazil, with the aim of isolating microorganisms and evaluating their ability to degrade distinct classes of hydrocarbon biomarkers (9,10-dihydrophenanthrene, phytane, nonadecanoic acid and 5α-cholestane). Twenty eight bacterial isolates were recovered and identified by sequencing their 16S rRNA genes. Biodegradation assays revealed that bacterial metabolism of hydrocarbons occurred through reactions based on oxidation, carbon–carbon bond cleavage and generation of new bonds or by the physical incorporation of hydrocarbons into microbial cell walls. Based on the biodegradation results, selective PCR-based systems were developed for direct detection in petroleum samples of bacterial groups of interest, namely Bacillus spp., Micrococcus spp., Achromobacter xylosoxidans, Dietzia spp. and Bacillus pumilus. Primer sets targeting 16S rRNA genes were designed and their specificity was confirmed in silico (i.e. computational analysis) and in PCR reactions using DNA from reference strains as positive and negative controls. Total DNA from oil was purified and the amplification tests revealed the presence of the target bacteria in the samples, unraveling a significant potential for petroleum deterioration in the reservoirs sampled, once proper conditions are present for hydrocarbon degradation. The application of molecular methods for rapid detection of specific microorganisms in environmental samples would be valuable as a supporting tool for the evaluation of oil quality in production reservoirs.  相似文献   

Climate-smart agriculture: perspectives and framings     

Alvin Chandra  Karen E. McNamara  Paul Dargusch 《Climate Policy》2018,18(4):526-541

This paper offers a systematic analysis of the concepts and contexts that frame the climate-smart agriculture (CSA) discourse in the academic and policy literature. Documents (n?=?113) related to CSA and published in peer-reviewed journals, books, working papers, and scientific reports from 2004 to 2016 were reviewed. Three key trends emerged from the analysis: studies are biased towards global policy agendas; research focuses on scientific and technical issues; and the integration of mitigation, adaptation, and food security (the three pillars of CSA) is becoming a popular scholarly solution. Findings suggest that CSA is a fairly new concept used to describe a range of adaptation and mitigation practices without a specific set of criteria. Although CSA is often framed around the three pillars, the underlying issues constructing the discourse differ at global, developing, and developed country scales. Although there is increasing research on developing countries, particularly in relation to how CSA can transform smallholder agriculture, there is a paucity of research documenting the experiences from developed countries. The findings suggest that research on CSA needs to move beyond solely focussing on scientific approaches and only in certain geographical contexts. If CSA is to be applicable for farmers across the globe, then cross-disciplinary research that is underpinned by broad socio-economic and political contexts is essential to understand how differences in narratives might affect implementation on-the-ground in both developing and developed countries.

POLICY RELEVANCE

Although policy makers are increasingly supportive of the climate-smart agriculture (CSA) approach, the rhetoric has largely been developed on the basis of scientific and technical arguments. The political implications of varying perspectives have resulted in a growing divide between how developing and developed countries frame solutions to the impacts of climate change on agriculture under the 2015 Paris Agreement. Different framings are part of the explanation for why the scope of CSA is being rethought, with the scientific community redirecting attention to seeking a separate work programme under the United Nations Framework Convention on Climate Change (UNFCCC). The current policy framing of CSA will give no new policy direction unless it grounds itself in the smallholder farmer and civil society contexts.  相似文献   

Learning from CDM SD tool experience for Article 6.4 of the Paris Agreement     

Karen Holm Olsen  Christof Arens  Florian Mersmann 《Climate Policy》2018,18(4):383-395

The Paris Agreement (PA) emphasizes the intrinsic relationship between climate change and sustainable development (SD) and welcomes the 2030 agenda for the global Sustainable Development Goals (SDGs). Yet, there is a lack of assessment approaches to ensure that climate and development goals are achieved in an integrated fashion and trade-offs avoided. Article 6.4 of the PA introduces a new Sustainable Mitigation Mechanism (SMM) with the dual aim to contribute to the mitigation of greenhouse gas emissions and foster SD. The Kyoto Protocol’s Clean Development Mechanism (CDM) has a similar objective and in 2014, the CDM SD tool was launched by the Executive Board of the CDM to highlight the SD benefits of CDM activities. This article analyses the usefulness of the CDM SD tool for stakeholders and compares the SD tool’s SD reporting requirements against other flexible mechanisms and multilateral standards to provide recommendations for improvement. A key conclusion is that the Paris Agreement’s SMM has a stronger political mandate than the CDM to measure that SD impacts are ‘real, measurable and long-term’. Recommendations for an improved CDM SD tool are a relevant starting point to develop rules, modalities, and procedures for SD assessment in Article 6.4 as well as for other cooperative mitigation approaches.

POLICY RELEVANCE

Research findings are relevant for developing the rulebook of modalities and procedures for Article 6.4 of the Paris Agreement, which introduces a new mechanism for mitigation of greenhouse gas emissions and sustainable development. Lessons learnt from the CDM SD tool and recommendations for enhanced SD assessment are discussed in context of Article 6 cooperative approaches, and make a timely contribution to inform negotiations on the rulebook agreed by the Conference of the Parties serving as the Meeting of the Parties to the Paris Agreement.  相似文献   

脓毒症患者中横纹肌溶解综合征与预后关系的研究     

XiMing Chen  Ling Zhang  HaiLi Sun  ShuYan Li  SiJing Chang  QingFeng Zhang  BingLin Zhang  Tuo Chen  GuangXiu Liu  Paul Dyson 《寒旱区科学》2017,9(5):503-510

目的 探讨脓毒症患者中横纹肌溶解综合征（RM）与病情严重程度及预后的关系。方法 采用前瞻性研究方法,入选2014年10月~2015年9月重庆医科大学附属第一医院中心ICU连续收治的脓毒症患者151例作为研究对象。检测入ICU当天的血清肌酸激酶（CK）,以CK≥1000U/L作为RM的诊断标准,比较发生RM的患者与未发生RM患者的感染标志物、危重症评分、器官功能障碍和28天病死率等。结果 151例脓毒症患者中37例（24.5%）发生RM。RM组的PCT水平、APACHEⅡ评分和SOFA评分较非RM组高（P<0.05）。RM组ICU期间肝脏功能障碍、循环障碍、肾脏功能障碍的发生率、人均器官障碍数、血肌酐峰值水平、接受连续肾脏替代治疗（CRRT）患者的比例和28天病死率较非RM组高（P<0.05）,而呼吸功能障碍、凝血功能障碍和神经系统障碍的发生率比较,差异无统计学意义（P>0.05）。CK对预测脓毒症患者28天死亡风险具有统计学意义,ROC曲线下面积（AUC）为0.694（P<0.05）,低于APACHEⅡ评分（0.841）和SOFA评分（0.805）（P<0.05）。结论 脓毒症患者中RM的发生率高,发生RM的患者的病情更危重,其ICU期间肝脏功能障碍、循环障碍、肾脏功能障碍的发生率和28天病死率均显著增加,CK可以作为预测脓毒症患者28天病死率的参考指标。  相似文献   

Does Magnetic Flux Submerge at Flux Cancelation Sites?     

Harvey  Karen L.  Jones  Harrison P.  Schrijver  Carolus J.  Penn  Matthew J. 《Solar physics》1999,190(1-2):35-44

Simultaneous measurements of the magnetic fields in the photosphere and chromosphere were used to investigate if magnetic flux is submerging at sites between adjacent opposite polarity magnetic network elements in which the flux is observed to decrease or `cancel'. These data were compared with chromospheric and coronal intensity images to establish the timing of the emission structures associated with these magnetic structures as a function of height. We found that most of the cancelation sites show either that the bipole is observed longer in the photosphere than in the chromosphere and corona (44%) or that the timing difference of the disappearance of the bipole between these levels of the atmosphere is unresolved. The magnetic axis lengths of the structures associated with the cancelation sites are on average slightly smaller in the chromosphere than the photosphere. These observations suggest that magnetic flux is retracting below the surface for most, if not all, of the cancelation sites studied.  相似文献   

Coming to Terms with “Integrated Coastal Management”: Problems of Meaning and Method in a New Arena of Resource Regulation     

Karen Nichols 《The Professional geographer》1999,51(3):388-399

This paper traces the emergence of coastal management in the late twentieth century and assesses the social and spatial implications of the new Integrated Coastal Management (ICM) philosophy that guides national regulatory programs worldwide. A review of the epistemology of ICM reveals its link to the United Nations marine regulatory regime (the Law of the Sea) and the sustainable development paradigm embraced at the 1992 United Nations Conference on Environment and Development. I suggest that the resulting regulatory regime facilitates the opening of coastal zones worldwide to aggressive state and global capital investment. By promoting the overhaul of existing social and spatial organization in coastal zones and by asserting the primacy of resource access for modern economic interests, ICM may introduce more rather than less social conflict and ecological degradation. To illustrate this dynamic, I examine the case of coral reef management in general, and in the context of the Sri Lankan ICM program.  相似文献   

Chronology of late Holocene climatic events in the northern North Atlantic based on AMS 14C dates and tephra markers from the volcano Hekla,Iceland     

Jn Eiríksson  Karen Luise Knudsen  Haflidi Haflidason  Jan Heinemeier 《第四纪科学杂志》2000,15(6):573-580

A combination of AMS¹⁴C dating and tephrochronology has been used to date late Holocene oceanographic events in a 335 cm marine record, covering about 4600 cal. yr with sedimentation rates exceeding 80 cm 1000 yr⁻¹. The core site is located 50 km offshore on the northern Icelandic shelf. Tephra markers from Iceland serve to correlate the marine and terrestrial records. Especially notable is the presence of three geochemically correlated tephra markers from the Icelandic volcano Hekla (Hekla 4, Hekla 3 and Hekla 1104). Benthic and planktonic foraminiferal abundance and distribution as well as the petrography of the sand fraction of the muddy shelf sediments are used as palaeoceanographic proxies. The foraminiferal assemblages reflect a general cooling trend during the last 4600 yr. A marked drop in sea‐surface temperatures is registered at about 3000 cal. yr BP, corresponding to the level of the Hekla 3 tephra. There is faunal indication of temperature amelioration during the Medieval Warm Period and a cooling again during the Little Ice Age. Periods of ice rafting events are indicated by ice rafted debris (IRD) concentrations, e.g. at around 3000 cal. yr BP and during the Little Ice Age. The former event occurred just prior to the deposition of the Hekla 3 tephra marker, the largest Holocene Hekla eruption. A correlation with terrestrial climatic events in Iceland is presented. A standard marine reservoir correction of 400 ¹⁴C yr appears to be reasonable, at least during periods with high influence of water masses from the Irminger Current on the northern Icelandic shelf. An increase to ca. 530 ¹⁴C yr may have occurred, however, when water masses derived from the East Greenland Current were dominant in the area. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

Gravel sediment routing from widespread,low- intensity landscape disturbance,Current River Basin,Missouri     

Robert B. Jacobson  Karen Bobbitt Gran 《地球表面变化过程与地形》1999,24(10):897-917

During the last 160 years, land-use changes in the Ozarks have had the potential to cause widespread, low-intensity delivery of excess amounts of gravel-sized sediment to stream channels. Previous studies have indicated that this excess gravel bedload is moving in wave-like forms through Ozarks drainage basins. The longitudinal, areal distribution of gravel bars along 160 km of the Current River, Missouri, was evaluated to determine the relative effects of valley-scale controls, tributary basin characteristics, and lagged sediment transport in creating areas of gravel accumulations. The longitudinal distribution of gravel-bar area shows a broad scale wave-like form with increases in gravel-bar area weakly associated with tributary junctions. Secondary peaks of gravel area with 1·8–4·1 km spacing (disturbance reaches) are superimposed on the broad form. Variations in valley width explain some, but not all, of the short-spacing variation in gravel-bar area. Among variables describing tributary drainage basin morphometry, present-day land use and geologic characteristics, only drainage area and road density relate even weakly to gravel-bar areal inventories. A simple, channel network-based sediment routing model shows that many of the features of the observed longitudinal gravel distribution can be replicated by uniform transport of sediment from widespread disturbances through a channel network. These results indicate that lagged sediment transport may have a dominant effect on the synoptic spatial distribution of gravel in Ozarks streams; present-day land uses are only weakly associated with present-day gravel inventories; and valley-scale characteristics have secondary controls on gravel accumulations in disturbance reaches. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Uncertainty in recurrence rates of large magnitude events due to short historic catalogs   总被引：2，自引：0，他引：2  

Tariq Mohammed  Gail M. Atkinson  Karen Assatourians 《Journal of Seismology》2014,18(3):565-573

Seismic hazard analysis requires knowledge of the recurrence rates of large magnitude earthquakes that drive the hazard at low probabilities of interest for seismic design. Earthquake recurrence is usually determined through studies of the historic earthquake catalogue for a given region. Reliable historic catalogues generally span time periods of 100–200 years in North America, while large magnitude events (M?≥?7) have recurrence rates on the order of hundreds or thousands of years in many areas, resulting in large uncertainty in recurrence rates for large events. Using Monte Carlo techniques and assuming typical recurrence parameters, we simulate earthquake catalogues that span long periods of time. We then split these catalogues into smaller catalogues spanning 100–200 years that mimic the length of historic catalogues. For each of these simulated “historic” catalogues, a recurrence rate for large magnitude events is determined. By comparing recurrence rates from one historic-length catalogue to another, we quantify the uncertainty associated with determining recurrence rates from short historic catalogues. The use of simulations to explore the uncertainty (rather than analytical solutions) allows us flexibility to consider issues such as the relative contributions of aleatory versus epistemic uncertainty, and the influence of fitting method, as well as lending insight into extreme-event statistics. The uncertainty in recurrence rates of large (M?>?7) events is about a factor of two in regions of high seismicity, due to the shortness of historic catalogues. This uncertainty increases greatly with decreasing seismic activity. Uncertainty is dependent on the length of the catalogue as well as the fitting method used (least squares vs. maximum likelihood). Examination of 90th percentile recurrence rates reveals that epistemic uncertainty in the true parameters may cause recurrence rates determined from historic catalogues to be uncertain by a factor greater than 50.  相似文献