Tracer Methods Research Articles

Evaluating the effect of liming on N2O fluxes from denitrification in an Andosol using the acetylene inhibition and 15N isotope tracer methods

We assessed the effect of liming on (1) N2O production by denitrification under aerobic conditions using the 15N tracer method (experiment 1); and (2) the reduction of N2O to N2 under anaerobic conditions using the acetylene inhibition method (experiment 2). A Mollic Andosol with three lime treatments (unlimed soil, 4 and 20 mg CaCO3 kg−1) was incubated at 15 and 25 °C for 22 days at 50% and then 80% WFPS with or without 200 mg N kg−1 added as 15N enriched KNO3 in experiment 1. In experiment 2, the limed and unlimed soils were incubated under completely anaerobic conditions for 44 h (with or without 100 mg N kg−1 as KNO3). In experiment 1, limed treatments increased N2O fluxes at 50% WFPS but decreased these fluxes at 80% WFPS. At 25 °C, cumulative N2O and 15N2O emissions in the high lime treatment were the lowest (with at least 30% less 15N2O and total N2O than the unlimed soil). Under anaerobic conditions, the high lime treatment showed at least 50% less N2O than the unlimed treatment at both temperatures with or without KNO3 addition but showed enhanced N2 production. Our results suggest that the positive effect of liming on the mitigation of N2O evolution from soil was influenced by soil temperature and moisture conditions.

Editorial introductions

Editorial introductions

Constraints on primary and secondary particulate carbon sources using chemical tracer and 14C methods during CalNex-Bakersfield

The present study investigates primary and secondary sources of organic carbon for Bakersfield, CA, USA as part of the 2010 CalNex study. The method used here involves integrated sampling that is designed to allow for detailed and specific chemical analysis of particulate matter (PM) in the Bakersfield airshed. To achieve this objective, filter samples were taken during thirty-four 23-hr periods between 19 May and 26 June 2010 and analyzed for organic tracers by gas chromatography – mass spectrometry (GC-MS). Contributions to organic carbon (OC) were determined by two organic tracer-based techniques: primary OC by chemical mass balance and secondary OC by a mass fraction method. Radiocarbon (14C) measurements of the total organic carbon were also made to determine the split between the modern and fossil carbon and thereby constrain unknown sources of OC not accounted for by either tracer-based attribution technique.From the analysis, OC contributions from four primary sources and four secondary sources were determined, which comprised three sources of modern carbon and five sources of fossil carbon. The major primary sources of OC were from vegetative detritus (9.8%), diesel (2.3%), gasoline (<1.0%), and lubricating oil impacted motor vehicle exhaust (30%); measured secondary sources resulted from isoprene (1.5%), α-pinene (<1.0%), toluene (<1.0%), and naphthalene (<1.0%, as an upper limit) contributions. The average observed organic carbon (OC) was 6.42 ± 2.33 μgC m−3. The 14C derived apportionment indicated that modern and fossil components were nearly equivalent on average; however, the fossil contribution ranged from 32 to 66% over the five week campaign. With the fossil primary and secondary sources aggregated, only 25% of the fossil organic carbon could not be attributed. Whereas, nearly 80% of the modern carbon could not be attributed to primary and secondary sources accessible to this analysis, which included tracers of biomass burning, vegetative detritus and secondary biogenic carbon. The results of the current study contributes source-based evaluation of the carbonaceous aerosol at CalNex Bakersfield.

Slow Lithium Transport in Metal Oxides on the Nanoscale

Abstract This article reports on Li self-diffusion in lithium containing metal oxide compounds. Case studies on LiNbO3, Li3NbO4, LiTaO3, LiAlO2, and LiGaO2 are presented. The focus is on slow diffusion processes on the nanometer scale investigated by macroscopic tracer methods (secondary ion mass spectrometry, neutron reflectometry) and microscopic methods (nuclear magnetic resonance spectroscopy, conductivity spectroscopy) in comparison. Special focus is on the influence of structural disorder on diffusion.

Time-resolved analysis of particle emissions from residential biomass combustion – Emissions of refractory black carbon, PAHs and organic tracers

Time-resolved particle emissions from a conventional wood stove were investigated with aerosol mass spectrometry to provide links between combustion conditions, emission factors, mixing state of refractory black carbon and implications for organic tracer methods. The addition of a new batch of fuel results in low temperature pyrolysis as the fuel heats up, resulting in strong, short-lived, variable emission peaks of organic aerosol-containing markers of anhydrous sugars, such as levoglucosan (fragment at m/z 60). Flaming combustion results in emissions dominated by refractory black carbon co-emitted with minor fractions of organic aerosol and markers of anhydrous sugars. Full cycle emissions are an external mixture of larger organic aerosol-dominated and smaller thinly coated refractory black carbon particles. A very high burn rate results in increased full cycle mass emission factors of 66, 2.7, 2.8 and 1.3 for particulate polycyclic aromatic hydrocarbons, refractory black carbon, total organic aerosol and m/z 60, respectively, compared to nominal burn rate. Polycyclic aromatic hydrocarbons are primarily associated with refractory black carbon-containing particles. We hypothesize that at very high burn rates, the central parts of the combustion zone become air starved, leading to a locally reduced combustion temperature that reduces the conversion rates from polycyclic aromatic hydrocarbons to refractory black carbon. This facilitates a strong increase of polycyclic aromatic hydrocarbons emissions. At nominal burn rates, full cycle emissions based on m/z 60 correlate well with organic aerosol, refractory black carbon and particulate matter. However, at higher burn rates, m/z 60 does not correlate with increased emissions of polycyclic aromatic hydrocarbons, refractory black carbon and organic aerosol in the flaming phase. The new knowledge can be used to advance source apportionment studies, reduce emissions of genotoxic compounds and model the climate impacts of refractory black carbon, such as absorption enhancement by lensing.

Multi-tracer investigation of river and groundwater interactions: a case study in Nalenggele River basin, northwest China

Environmental tracers (such as major ions, stable and radiogenic isotopes, and heat) monitored in natural waters provide valuable information for understanding the processes of river–groundwater interactions in arid areas. An integrated framework is presented for interpreting multi-tracer data (major ions, stable isotopes (2H, 18O), the radioactive isotope 222Rn, and heat) for delineating the river–groundwater interactions in Nalenggele River basin, northwest China. Qualitative and quantitative analyses were undertaken to estimate the bidirectional water exchange associated with small-scale interactions between groundwater and surface water. Along the river stretch, groundwater and river water exchange readily. From the high mountain zone to the alluvial fan, groundwater discharge to the river is detected by tracer methods and end-member mixing models, but the river has also been identified as a losing river using discharge measurements, i.e. discharge is bidirectional. On the delta-front of the alluvial fan and in the alluvial plain, in the downstream area, the characteristics of total dissolved solids values, 222Rn concentrations and δ18O values in the surface water, and patterns derived from a heat-tracing method, indicate that groundwater discharges into the river. With the environmental tracers, the processes of river–groundwater interaction have been identified in detail for better understanding of overall hydrogeological processes and of the impacts on water allocation policies.

Assessment of Aliphatic Hydrocarbons in Sediments of Shatt Al-Arab River, Southern Iraq, North East Arabian Gulf

Shatt Al-Arab River is one of the important rivers for water supply, industry and irrigation in Basrah City, south of Iraq. It's also supply drinking water to users in the region. Despite the significance of this river, there is a lack of previous studies dealing with petroleum pollution especially for geochemical studies of organic matter in the river sediments using molecular tracer methods. Therefore, the identification and quantification of petroleum hydrocarbons in this river at the elemental and molecular levels will be of the utmost interest. Sediments were analyzed in nine Shatt Al-Arab River stations. Texture was silty clay or silty sand. TOC and TN ranged from 0.39-0.90 and 0.02-0.16%. OM varied from 17.43-34.36 µg g-1 dw, representing 0.27-0.87% of TOC. AHs ranged from 3.19-10.27 µg g-1 dw and constituted 16.07-29.88% of OM. Total n-alkanes concentrations ranged from 0.08-42.58 µg g-1 dw with carbon numbers from C11-C34 were identified. N-alkanes content was relatively moderate compared to sites contaminated with oil worldwide. Dominance of even carbon number n-alkanes (C11-C20) with CPI and LMW/HMW values close to unity, indicated to oil-related n-alkanes. This was verified by the values of U/R (1.27-2.45), pri/phy (0.82-1.00), C17/pri (0.70-1.94) and C18/phy (0.95-1.56) ratios and the presence of UCM. Biogenic contributions were detected within the n-alkanes distribution of C17-C31 and CPI and LMW/HMW values of <1 that mainly related to terrestrial plants, phytoplankton, algae and bacteria sources, confirmed by TAR (0.79-2.15) and C31/C19 ratio (0.28-1.62) values. However, the contribution from biogenic hydrocarbons is overshadowed by petroleum origin n-alkanes. This was obvious by the presence of UCM. PCA showed concordant results with n-alkanes ratios indicating mixed n-alkanes sources in sediments. Hopanes and steranes in sediments displayed similar signatures that were characteristic of mature organic matter contribution from oil contaminations.

Deconstructing white matter connectivity of human amygdala nuclei with thalamus and cortex subdivisions in vivo.

Structural alterations in long‐range amygdala connections are proposed to crucially underlie several neuropsychiatric disorders. While progress has been made in elucidating the function of these connections, our understanding of their structure in humans remains sparse and non‐systematic. Harnessing diffusion‐weighted imaging and probabilistic tractography in humans, we investigate connections between two main amygdala nucleus groups, thalamic nuclei, and cortex. We first parcellated amygdala into deep (basolateral) and superficial (centrocortical) nucleus groups, and thalamus into six subregions, using previously established protocols based on connectivity. Cortex was parcellated based on T1‐weighted images. We found substantial amygdala connections to thalamus, with different patterns for the two amygdala nuclei. Crucially, we describe direct subcortical connections between amygdala and paraventricular thalamus. Different from rodents but similar to non‐human primates, these are more pronounced for basolateral than centrocortical amygdala. Substantial white‐matter connectivity between amygdala and visual pulvinar is also more pronounced for basolateral amygdala. Furthermore, we establish detailed connectivity profiles for basolateral and centrocortical amygdala to cortical regions. These exhibit cascadic connections with sensory cortices as suggested previously based on tracer methods in non‐human animals. We propose that the quantitative connectivity profiles provided here may guide future work on normal and pathological function of human amygdala. Hum Brain Mapp 38:3927–3940, 2017. © 2017 Wiley Periodicals, Inc.

Chloride and bromide sources in water: Quantitative model use and uncertainty

Dissolved chloride is a commonly used geochemical tracer in hydrological studies. Assumptions underlying many chloride-based tracer methods do not hold where processes such as halide-bearing mineral dissolution, fluid mixing, or diffusion modify dissolved Cl− concentrations. Failure to identify, quantify, or correct such processes can introduce significant uncertainty to chloride-based tracer calculations. Mass balance or isotopic techniques offer a means to address this uncertainty, however, concurrent evaporation or transpiration can complicate corrections.In this study Cl/Br ratios are used to derive equations that can be used to correct a solution’s total dissolved Cl− and Br− concentration for inputs from mineral dissolution and/or binary mixing. We demonstrate the equations’ applicability to waters modified by evapotranspiration. The equations can be used to quickly determine the maximum proportion of dissolved Cl− and Br− from each end-member, providing no halide-bearing minerals have precipitated and the Cl/Br ratio of each end member is known. This allows rapid evaluation of halite dissolution or binary mixing contributions to total dissolved Cl− and Br−.Equation sensitivity to heterogeneity and analytical uncertainty is demonstrated through bench-top experiments simulating halite dissolution and variable degrees of evapotranspiration, as commonly occur in arid environments. The predictions agree with the experimental results to within 6% and typically much less, with the sensitivity of the predicted results varying as a function of end-member compositions and analytical uncertainty. Finally, we present a case-study illustrating how the equations presented here can be used to quantify Cl− and Br− sources and sinks in surface water and groundwater and how the equations can be applied to constrain uncertainty in chloride-based tracer calculations.

Dislocation-pipe diffusion in nitride superlattices observed in direct atomic resolution

Device failure from diffusion short circuits in microelectronic components occurs via thermally induced migration of atoms along high-diffusivity paths: dislocations, grain boundaries, and free surfaces. Even well-annealed single-grain metallic films contain dislocation densities of about 1014 m−2; hence dislocation-pipe diffusion (DPD) becomes a major contribution at working temperatures. While its theoretical concept was established already in the 1950s and its contribution is commonly measured using indirect tracer, spectroscopy, or electrical methods, no direct observation of DPD at the atomic level has been reported. We present atomically-resolved electron microscopy images of the onset and progression of diffusion along threading dislocations in sequentially annealed nitride metal/semiconductor superlattices, and show that this type of diffusion can be independent of concentration gradients in the system but governed by the reduction of strain fields in the lattice.

Chemical and photophysiological impact of terrestrially‐derived dissolved organic matter on nitrate uptake in the coastal western Arctic

AbstractThe Arctic is warming at a rate nearly twice the global average, leading to thawing permafrost, increased coastal erosion, and enhanced delivery of riverine terrestrially‐derived dissolved organic matter (tDOM) to coastal waters. This humic‐rich tDOM has the ability to attenuate light required for photosynthesis and stimulate heterotrophic growth by supplying a source of labile organic carbon. Due to tDOM's high carbon to nitrogen (C : N) ratio, additional nitrogen is required for microorganisms to utilize this excess carbon for growth, thus exacerbating competition between autotrophs and heterotrophs for limiting nutrients and potentially reducing primary production. The effect of Arctic tDOM additions on nitrate uptake by two microplankton size fractions in the coastal Chukchi Sea was quantified using 15N tracer methods. To assess the biogeochemical vs. spectral impacts of tDOM, the uptake incubations were amended with either tDOM or light attenuating films that mimic light absorption by the tDOM. Nitrate uptake and primary production rates in the larger, predominantly phytoplankton, size fraction generally decreased with increasing tDOM additions. The change in light attenuation alone accounted for a ∼ 50% reduction in nitrate uptake. Responses in the smaller size fraction varied seasonally with tDOM additions stimulating uptake in spring and suppressing it in summer. The largest variation in summer nitrate uptake can be explained by the shared effect of biogeochemistry and light attenuation. Therefore, large increases in tDOM delivery currently occurring and predicted to increase in the coastal Arctic, could reduce primary production, broadly impact nitrogen and carbon cycling, and affect higher trophic levels.

Evaluation of multiple tracer methods to estimate low groundwater flow velocities

Four different tracer methods were used to estimate groundwater flow velocity at a multiple-well site in the saturated alluvium south of Yucca Mountain, Nevada: (1) two single-well tracer tests with different rest or “shut-in” periods, (2) a cross-hole tracer test with an extended flow interruption, (3) a comparison of two tracer decay curves in an injection borehole with and without pumping of a downgradient well, and (4) a natural-gradient tracer test. Such tracer methods are potentially very useful for estimating groundwater velocities when hydraulic gradients are flat (and hence uncertain) and also when water level and hydraulic conductivity data are sparse, both of which were the case at this test location. The purpose of the study was to evaluate the first three methods for their ability to provide reasonable estimates of relatively low groundwater flow velocities in such low-hydraulic-gradient environments. The natural-gradient method is generally considered to be the most robust and direct method, so it was used to provide a “ground truth” velocity estimate. However, this method usually requires several wells, so it is often not practical in systems with large depths to groundwater and correspondingly high well installation costs. The fact that a successful natural gradient test was conducted at the test location offered a unique opportunity to compare the flow velocity estimates obtained by the more easily deployed and lower risk methods with the ground-truth natural-gradient method. The groundwater flow velocity estimates from the four methods agreed very well with each other, suggesting that the first three methods all provided reasonably good estimates of groundwater flow velocity at the site. The advantages and disadvantages of the different methods, as well as some of the uncertainties associated with them are discussed.

Methodology of determining effective porosity and longitudinal dispersivity of aquifer and the application to field tracer injection test in Southern Hanoi, Vietnam

Groundwater field pumping out and tracer injection test had been carried out at Nghiem Xuyen commune, Thuong Tin district, Hanoi where salinized and fresh groundwater boundary exist in the Pleistocene aquifer. The test was executed with pumping out rate of 9l/sec and tracer injection rate of 0.7l/sec of water with the salt concentration of 5g/l. The interpretation and analysis of the groundwater solute transport parameters by the field pumping out and tracer injection test is a rather complicated and delicate task due to the variability of the temporal boundary conditions. The test results have shown that although the tracer injection time is rather long (up to 60 hours), the tracer breakthrough curve of the tracer concentration of the pumped out water has its very specific characteristic shape, however with some variation due to the test invisible variability of conditions. The results of the parameter identification based on the method of least squares have given effective porosity of 0.32 and longitudinal dispersivity of 2.5m (which give the hydrodynamic dispersion of from D=250m2/day right outside the pumping well screen to D=18m2/day right outside the injection well screen). The minimal sum of squares of the differences between the observed and model normalized tracer concentration is 0.00119, which is corresponding to the average absolute difference between observed and model normalized concentrations of 0.0355 (while 1 is the worse and 0 is the best). The results have also shown that the maximal tracer concentration right outside the pumping out well screen is 6.1 times greater than the tracer concentration of the pumped out water. The distortion flow coefficient αW (the ratio between the flow rate through the injection well section without its presence) and the groundwater flow into the tracer injection well is from 18.66 (at the early testing time) to 10.76 (at the later testing time).References Bear J. and Verruijt A., 1987. Modeling groundwater flow and pollution, D. Reidel Publishing Company, Dordrecht, Holand, 414pp. Brouyère S. 2008. Modeling tracer injection and well-aquifer interactions: a new mathematical and numerical approach. Water Resour. Res, 39(3), 1070-1075. Drost, W., D. Klotz, A. Koch, H. Moser, F. Neumaier, and W. Rauert, 1968. Point dilution methods of investigating ground water flow by means of radioisotopes. Water Resour. Res., 4(1), 125-146. Fetter C.W., 2001. Applied Hydrogeology. Prentice Hall Inc. New Jersey 07458, 598pp. Hall, S.H., 1996. Practical single-well tracer methods for aquifer testing, In: Tenth National Outdoor Action Conference and Exposition, National Groundwater Association, Colombus, Ohio, USA, 11pp. Huyakorn P.S., and Pinder G. F., 1983. Computational Methods in Subsurface Flow. Academic Press, New York, 473pp. Nguyen Van Hoang, 2016. Modeling of pollutant transport in water environment. Vietnam Academy of Science and Technology Publishers, 201pp. Nguyen Van Hoang (project head) (2014-2017). Science and Technology Proposal: Study on the finite element modeling software for simulation of groundwater flow and solute transport by groundwater-application to aquifer in Central plain of Vietnam" codded ĐT.NCCB-ĐHƯD.2012-G/04 supported by NAFOSTED-MOST. Nguyen Van Hoang, Dinh Van Thuan, Nguyen Duc Roi, Le Duc Luong, 2012. Study on the impact of the Tri An reservoir on its downstream groundwater level regime. Vietnam Journal of Earth Sciences, 34(4), 465-476. Nguyen Van Hoang, Pham Lan Hoa, Le Thanh Tung, 2014. Study on the accuracy of the numerical modeling of the groundwater movement due to spatial and temporal discretization. Vietnam Journal of Earth Sciences, 36(4), 424-431. Nguyen Van Hoang and Nguyen Duc Roi, 2015. Finite element method in estimation of lag time of rainfall recharge to Holocene groundwater aquifer in Hung Yen province. Vietnam Journal of Earth Sciences, 37(4), 355-362. Nguyen Van Hoang, Nguyen Thanh Cong, Pham Lan Hoa, Le Thanh Tung, 2016. Study on the characteristics of salinity transport in 2D cross-section unconfined aquifer. Vietnam Journal of Earth Sciences, 38(1), 66-78. Novakowski, K.S., 1992. An evaluation of boundary conditions for one-dimensional solute transport, 1, Mathematical development. Water Resour. Res., 28(9), 2399-2410. Polubarinova-Kotrina P. IA., 1977. Theory of Groundwater. Moscow Science Publishers. 664pp. Tong Thanh Tung, 2015. Specialized report: Interpretation and analysis of aquifer parameters for pumping test at group-well test CHN5 in Nghiem Xuyen-Thuong Tin-Hanoi. Project "Groundwater protection in large cities (city: Hanoi)". Vietnam National Center for Water Resources Planning and Investigation-MoNRE, 16pp. Trieu Duc Huy (Project head), 2015. Science and Technology Proposal: Groundwater protection in large cities (city: Hanoi) approved by MoNRE Minister in Decision 1557/QD-BTNMT dated 30th Aug. 2013. Vietnam National Center for Water Resources Planning and Investigation-MoNRE. Vitaly A. Zlotnik and John David Logan, 1996. Boundary Conditions for Convergent Radial Tracer Tests and Effect of Well Bore Mixing Volume. Papers in the Earth and Atmospheric Sciences, 159pp. Zienkiewicz O. C. and Morgan K., 1983. Finite Elements and Approximation. Academic Press, 328p.

A simple and inexpensive technique for assessing contamination during drilling operations

AbstractSubsurface exploration relies on drilling. Normally drilling requires a drilling fluid that will infiltrate into the drill core. Drilling fluid contains non‐indigenous materials and microbes from the surface, so its presence renders a sample unsuitable for microbiological and many other analyses. Because infiltration cannot be avoided, it is of paramount importance to assess the degree of contamination to identify uncontaminated samples for geomicrobiological investigations. To do this, usually a tracer is mixed into the drilling fluid. In past drilling operations a variety of tracers have been used, each has specific strengths and weaknesses. For microspheres the main problem was the high price, which limited their use to spot checks or drilling operations that require only small amounts of drilling fluid. Here, we present a modified microsphere tracer approach that uses an aqueous fluorescent pigment dispersion with a similar concentration of fluorescent particles as previously used microsphere tracers. However, it costs four orders of magnitude less, allowing for a more liberal use even in large operations. Its applicability for deep drilling campaigns was successfully tested during two drilling campaigns of the International Continental Drilling Program (ICDP) at Lake Towuti, Sulawesi, Indonesia, and Lake Chalco, Mexico. Quantification of the tracer requires only a fluorescence microscope or a flow cytometer. The latter allowing for high‐resolution data to be obtained directly on‐site within minutes and with minimal effort, decreasing sample processing times substantially relative to traditional tracer methods. This approach offers an inexpensive, rapid, but powerful alternative technique for contamination assessment during drilling campaigns.

Mg2+-Based Method for the Pertuso Spring Discharge Evaluation

This paper deals with the Environmental Monitoring Plan concerning the catchment work project of the Pertuso karst spring, which is going to be exploited to supply an important drinking water network in the south part of Roma district. The Pertuso Spring, located in the Upper Valley of the Aniene River, is the main outlet of a large karst aquifer, which is one of the most important water resources in the southeast part of Latium Region, Central Italy, used for drinking, agriculture, and hydroelectric supplies. The environmental monitoring activities provided data about one spring and two cross-sections of the Aniene River, from July 2014 to May 2016. A combined approach based on discharge measurements and hydrogeochemical analysis has been used to study flow paths and groundwater–surface water interaction in the study area. Tracer methods are particularly suitable in hydrogeological studies to assess transit times and flow properties in karst aquifers. The analysis of solute contents in the sampling points brought forth the identification of the Mg2+ ion as a conservative tracer in this specific system and, consequently, to the development of a conceptual model based on chemical mass balance for the Pertuso Spring discharge evaluation.

Acidification Enhances Hybrid N2O Production Associated with Aquatic Ammonia-Oxidizing Microorganisms.

Ammonia-oxidizing microorganisms are an important source of the greenhouse gas nitrous oxide (N2O) in aquatic environments. Identifying the impact of pH on N2O production by ammonia oxidizers is key to understanding how aquatic greenhouse gas fluxes will respond to naturally occurring pH changes, as well as acidification driven by anthropogenic CO2. We assessed N2O production rates and formation mechanisms by communities of ammonia-oxidizing bacteria (AOB) and archaea (AOA) in a lake and a marine environment, using incubation-based nitrogen (N) stable isotope tracer methods with 15N-labeled ammonium (15) and nitrite (15), and also measurements of the natural abundance N and O isotopic composition of dissolved N2O. N2O production during incubations of water from the shallow hypolimnion of Lake Lugano (Switzerland) was significantly higher when the pH was reduced from 7.54 (untreated pH) to 7.20 (reduced pH), while ammonia oxidation rates were similar between treatments. In all incubations, added was the source of most of the N incorporated into N2O, suggesting that the main N2O production pathway involved hydroxylamine (NH2OH) and/or produced by ammonia oxidation during the incubation period. A small but significant amount of N derived from exogenous/added 15 was also incorporated into N2O, but only during the reduced-pH incubations. Mass spectra of this N2O revealed that and 15 each contributed N equally to N2O by a “hybrid-N2O” mechanism consistent with a reaction between NH2OH and , or compounds derived from these two molecules. Nitrifier denitrification was not an important source of N2O. Isotopomeric N2O analyses in Lake Lugano were consistent with incubation results, as 15N enrichment of the internal N vs. external N atoms produced site preferences (25.0–34.4‰) consistent with NH2OH-dependent hybrid-N2O production. Hybrid-N2O formation was also observed during incubations of seawater from coastal Namibia with 15 and . However, the site preference of dissolved N2O here was low (4.9‰), indicating that another mechanism, not captured during the incubations, was important. Multiplex sequencing of 16S rRNA revealed distinct ammonia oxidizer communities: AOB dominated numerically in Lake Lugano, and AOA dominated in the seawater. Potential for hybrid N2O formation exists among both communities, and at least in AOB-dominated environments, acidification may accelerate this mechanism.

氮素类型和剂量对寒温带针叶林土壤N2O排放的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 氮素类型和剂量对寒温带针叶林土壤N2O排放的影响 DOI: 10.5846/stxb201508041639 作者: 作者单位: 中国科学院地理科学与资源研究所,中国科学院大学资源与环境学院,中国科学院地理科学与资源研究所,中国科学院地理科学与资源研究所,中国科学院大学资源与环境学院,中国科学院地理科学与资源研究所,中国科学院地理科学与资源研究所,中国科学院大学资源与环境学院,中国科学院大学资源与环境学院 作者简介: 通讯作者: 中图分类号: Q142 基金项目: 国家自然科学基金项目（41471212，31470558，31290221，31130009，31290222）；国家重点基础研究发展计划项目（2012CB417103）；中国科学院地理科学与资源研究所“秉维”优秀青年人才基金项目（2011RC202）；中国科学院战略性先导科技专项（XDA05050600） The effects of types and doses of nitrogen addition on soil N2O flux in a cold-temperate coniferous forest, northern China Author: Affiliation: Key Laboratory of Ecosystem Network Observation and Modeling,Institute of Geographical Sciences and Natural Resources Research,Chinese Academy of Sciences,College of Resources and Environment,University of Chinese Academy of Sciences,Key Laboratory of Ecosystem Network Observation and Modeling,Institute of Geographical Sciences and Natural Resources Research,Chinese Academy of Sciences,Key Laboratory of Ecosystem Network Observation and Modeling,Institute of Geographical Sciences and Natural Resources Research,Chinese Academy of Sciences,College of Resources and Environment,University of Chinese Academy of Sciences,Key Laboratory of Ecosystem Network Observation and Modeling,Institute of Geographical Sciences and Natural Resources Research,Chinese Academy of Sciences,Key Laboratory of Ecosystem Network Observation and Modeling,Institute of Geographical Sciences and Natural Resources Research,Chinese Academy of Sciences,College of Resources and Environment,University of Chinese Academy of Sciences,College of Resources and Environment,University of Chinese Academy of Sciences Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:大气氮沉降输入会增加森林生态系统氮素有效性，进而改变土壤N2O产生与排放，然而有关不同氮素离子（氧化态NO3--N与还原态NH4+-N）沉降对土壤N2O排放的影响知之甚少。以大兴安岭寒温带针叶林为研究对象，构建了3种类型（NH4Cl、KNO3、NH4NO3）和4个施氮水平（0、10、20、40 kg N hm-2 a-1）的增氮控制试验，利用流动化学分析仪和静态箱-气相色谱法4次/月测定凋落物层和矿质层土壤无机氮含量、土壤-大气界面N2O净交换通量以及相关环境因子，分析施氮类型和剂量对土壤氮素有效性、土壤N2O通量的影响，探讨氮素富集条件下土壤N2O通量的环境驱动机制。结果表明：施氮类型和剂量均显著影响土壤无机氮含量，土壤NH4+-N的积累效应显著高于NO3--N。施氮一致增加寒温带针叶林土壤N2O排放，NH4NO3促进效应最为明显，增幅为442%-677%，高于全球平均水平（134%）。土壤N2O通量与土壤温度、凋落物层NH4+-N含量正相关，且随着施氮水平增加而增加。结果表明大气氮沉降短期内不会导致寒温带针叶林土壤NO3--N大量流失，但会显著促进土壤N2O的排放。此外，外源性NH4+和NO3-输入对土壤N2O排放的促进作用具有协同效应，在未来森林生态系统氮循环和氮平衡研究中应该区分对待。 Abstract:Increasing atmospheric nitrogen (N) deposition would change soil N availability, and thereby changes N2O production and emission from N-limiting forest soils. However, it is still unclear about the contrasting effects of different N ion (i.e., oxidized NO3--N and reduced NH4+-N) deposition on soil N2O emission in boreal forests. In the present study, a cold-temperate coniferous forest in the Great Khingan region was selected for conducting the manipulative N addition experiment, including three forms of N fertilizers (NH4Cl, KNO3, and NH4NO3) and four rates of N addition (0, 10, 20, and 40 kg N hm-2 a-1). Soil-atmospheric N2O exchanging fluxes were measured four times per month using static chamber-gas chromatography. Simultaneously, soil temperature, moisture, and inorganic N contents were measured to explore how the main factors affect soil N2O emission. The results showed that the types and doses of N addition significantly changed soil inorganic N contents, and the accumulation of soil NH4+-N was significantly higher than that of soil NO3--N due to N addition. N addition increased N2O emission from the boreal forest soil, and the NH4NO3 addition treatments promoted high soil N2O fluxes, with an increase of 442% to 667%, which was higher than the global average (134%). There were positive correlations between soil N2O fluxes and soil temperature, and between soil N2O fluxes and soil NH4+-N contents in the litter layer. Soil N2O fluxes were driven by soil temperature, followed by soil NH4+-N contents in the litter layer. These findings suggest that atmospheric N deposition cannot lead to a significant soil NO3--N leaching and loss in boreal forests over the short term, but it can significantly promote soil N2O emission. Furthermore, exogenous NH4+ and NO3- inputs into boreal forests have synergic effects on soil N2O emission, which should be distinguished in N cycle and balance in terrestrial ecosystems using 15N tracer methods in the future. 参考文献 相似文献 引证文献

Laboratory Insights into Water-rock-CO2 Interactions Controlling the Isotopic Composition of CO2 Leaking from Storage Sites

A series of batch laboratory experiments were conducted involving synthetic saline waters, crushed core and CO2 to study the effect of these reactions on potentially leaking CO2. The purpose of these experiments was to study the evolution of carbon isotope values of dissolved inorganic carbon (DIC) after CO2 injection under simulated reservoir conditions. Observed increases in bicarbonate alkalinity can be attributed to the dissolution of calcite in carbonic acid brine. Furthermore, the isotopic analysis results suggest that the equilibrium carbon isotope values of DIC are controlled largely by added CO2 and system temperature, and not by calcite dissolution. The measured isotopic value of the CO2 in the headspace of each reaction cylinder remained unchanged. Hence, leakage detection with carbon isotope tracer methods appears feasible as long as the injected CO2 is isotopically distinct from baseline carbon compounds (preferably > 10 ‰ difference in δ13C).

Sentinel node navigation in gastric cancer: new horizons for personalized minimally invasive surgical oncology?

Complete (R0) resection and regional lymph nodes (LNs) dissection represent undoubtedly the basic surgical tools for patients with gastric cancer. It is reported that the LN metastasis rate in patients with early gastric cancer (EGC) is approximately 15-20%. Therefore, the innovative clinical application of sentinel node navigation surgery (SNNS) for EGC might be able to prevent unnecessary LN dissection as well as to reduce significantly the volume of gastric resection. Recent evidence suggests that double tracer methods appear superior compared to single tracer techniques. However, the researchers' interest is now focused on the identification of new LN detection methods utilizing sophisticated technology such as infrared ray endoscopy, fluorescence imaging and near-infrared technology. Despite its notable limitations, hematoxylin-eosin is still considered the mainstay staining for assessing the metastatic status of LNs. In this review, we summarize the current evidences and we provide the latest scientific information assessing safety, efficacy and potential limitations of the innovative sentinel node (SN) navigation technique for gastric cancer. We try also to provide a "view" towards a future potential application of personalized minimally invasive surgery in gastric cancer field.

Synoptic estimates of diffuse groundwater seepage to a spring-fed karst river at high spatial resolution using an automated radon measurement technique

Groundwater (GW) seepage can provide a major source of water, solutes, and contaminants to rivers, but identifying magnitudes, directions and locations of seepage is complicated by its diffuse and heterogeneous distributions. However, such information is necessary to develop programs and policies for protecting ecosystems and managing water resources. Here, we assess GW seepage to the Ichetucknee River, a spring-fed, low gradient, gaining stream in north-central Florida, through automated longitudinal surveys of radon (222Rn) activities at three different flow conditions. A 222Rn mass balance model, which integrates groundwater and spring water end member 222Rn activities and longitudinal 222Rn distributions in river water, shows that diffuse groundwater seepage represents about 16% of the total river baseflow, consistent with previous results obtained from ion (Ca2+, Cl−, SRP and Fe) mass balances and dye tracer methods. During high river stage, the contribution from seepage increases to 18–23% of the river flow. The spatial distribution of GW seepage is more variable in the upper 2.2-km reach of the river than the lower 2.8-km reach, regardless of river flow conditions. The upper reach has a narrower flood plain than the lower reach, which limits evapotranspiration and increases hydraulic gradients toward the river following storm events. Seepage in the lower reach is also limited by hydrologic damming by the receiving river, which inundates the floodplain during high flow conditions, and reduces the hydraulic head gradient. These results demonstrate the variable nature of seepage to a gaining river in both time and space and indicate that multiple synoptic analyses of GW seepage are required to assess seepage rates, determine time-averaged solute fluxes, and develop optimal management policies for riverine ecosystems.