Hydrogen isotope exchange kinetics between H₂O and H₄SiO₄ from ab initio calculations     

M.A. Felipe  J.D. Kubicki 《Geochimica et cosmochimica acta》2003,67(7):1259-1276

Hydrogen isotope exchange between water and orthosilicic acid (H₄SiO₄) was modeled using B3LYP calculations and classical transition-state theory. Configurations of 1, 2, 3 and 7 water molecules and H₄SiO₄ were used to investigate energetically viable reaction pathways. An upper-bound of 71 kJ/mol was assumed for the zero-point energy corrected barrier (ZPECB) because this is the experimentally determined activation energy for Si-O bond breaking (Rimstidt and Barnes, 1980) and ZPECB is expected to be close to this value. Long range solvation forces were accounted for using the integral equation formalism polarized continuum model (IEFPCM; Cancès et al., 1997). Primary and secondary isotope effects were computed by exchanging hydrogen atoms with deuterium. Results show that reaction mechanisms involving 3 and 7 water molecules have ZPECB of 34 to 38 kJ/mol, whereas those involving 1 and 2 water molecules have ZPECB in excess of the set upper-bound. The lower range of ZPECB with 3 or 7 water molecules is reasonable to explain rapid hydrogen isotope exchange with silicates. Rate constant calculations accounting for tunneling, anharmonicity and scaling factors indicate that the reaction is fast and equilibrium can be assumed under most geologic conditions.  相似文献   

Assessment and Measurement Issues Related to Soil Carbon Sequestration in Land-Use, Land-Use Change, and Forestry (LULUCF) Projects under the Kyoto Protocol   总被引：9，自引：0，他引：9  

Felipe García-Oliva  Omar R. Masera 《Climatic change》2004,65(3):347-364

Mitigating the potential large negative impacts of a change in the earth's climate will require strong and definite actions in the different economic sectors, particularly within agriculture and forestry. Specifically, soils deserve a close examination due to their large carbon mitigation potential. The Kyoto protocol establishes the possibility for crediting greenhouse gas emission reductions from forestry and agriculture activities. In most circumstances, particularly those regarding developing countries, greenhouse gas mitigation activities will be carried out through projects. These projects will have to meet a series of criteria, for the carbon benefits to be measurable, transparent, verifiable and certified. These criteria include: establishing credible baselines (without-project or reference scenario), additionality, permanence, quantifying and reducing potential leakage of greenhouse gases across project borders, coping with natural or human induced risks, accurately measuring changes in carbon stocks using carbon accounting techniques, and – in the case of the Clean DevelopmentMechanism – resulting in sustainable development benefits. In this paper we describe the methods and approaches that have been developed to cope with the different criteria and discuss their implications for carbon sequestration in soils. Soil carbon represents the largest carbon pool of terrestrial ecosystems, and has been estimated to have one of the largest potentials to sequester carbon worldwide. However, getting credits from soil carbon sequestration through project activities presents several challenges: the need to monitor small incremental changes in soil carbon content relative to large carbon pools, long-time periods to accrue the full carbon benefits, high local variability of soil carbon content, and relatively costly soil carbon measurement procedures. Also, the responses of soil C stocks to forestry and agriculture activities are complex and need careful attention. Specifically, the time dynamics of soil C responses to land use changes, the diversity of soil types, soil-plant interactions, and the availability of accurate soil C inventories, should be considered to successfully implement LULUCF projects.  相似文献   

Submarine groundwater discharge: A large, previously unrecognized source of dissolved iron to the South Atlantic Ocean   总被引：4，自引：5，他引：4  

Herbert L. Windom  Willard S. Moore  L. Felipe H. Niencheski  Richard A. Jahnke   《Marine Chemistry》2006,102(3-4):252-266

This paper reports the initial results of a study of groundwater and coastal waters of southern Brazil adjacent to a 240 km barrier spit separating the Patos Lagoon, the largest coastal lagoon in South America, from the South Atlantic Ocean. The objective of this research is to assess the chemical alteration of freshwater and freshwater–seawater mixtures advecting through coastal permeable sands, and the influence of the submarine discharge of these fluids (SGD) on the chemistry of coastal waters. Here we focus on dissolved iron in this system and use radium isotopic tracers to quantify SGD and cross-shelf fluxes. Iron concentrations in groundwaters vary between 0.6 and 180 μM. The influence of the submarine discharge of these fluids into the surf zone produces dissolved Fe concentrations as high as several micromolar in coastal surface waters. The offshore gradient of dissolved Fe, coupled with results for Ra isotopes, is used to quantify the SGD flux of dissolved Fe from this coastline. We estimate the SGD flux to be 2 × 10⁶ mol day^− 1 and the cross-shelf flux to be 3.2 × 10⁵ mol day^− 1. This latter flux is equal to about 10% of the soluble atmospheric Fe flux to the entire South Atlantic Ocean. We speculate on the importance of this previously unrecognized iron input to regional ocean production and on the potential significance of this source to understanding variations in glacial–interglacial ocean production.  相似文献   

Diversity of the 2014 Iquique’s foreshocks and aftershocks: clues about the complex rupture process of a Mw 8.1 earthquake     

Sergio León-Ríos  Sergio Ruiz  Andrei Maksymowicz  Felipe Leyton  Amaya Fuenzalida  Raúl Madariaga 《Journal of Seismology》2016,20(4):1059-1073

We study the foreshocks and aftershocks of the 1 April 2014 Iquique earthquake of Mw 8.1. Most of these events were recorded by a large digital seismic network that included the Northern Chile permanent network and up to 26 temporary broadband digital stations. We relocated and computed moment tensors for 151 events of magnitude Mw?≥?4.5. Most of the foreshocks and aftershocks of the Iquique earthquake are distributed to the southwest of the rupture zone. These events are located in a band of about 50 km from the trench, an area where few earthquakes occur elsewhere in Chile. Another important group of aftershocks is located above the plate interface, similar to those observed during the foreshock sequence. The depths of these events were constrained by regional moment tensor (RMT) solutions obtained using the records of the dense broad band network. The majority of the foreshocks and aftershocks were associated to the interplate contact, with dip and strike angles in good agreement with the characteristics of horst and graben structures (>2000 m offset) typical of the oceanic Nazca Plate at the trench and in the outer rise region. We propose that the spatial distribution of foreshocks and aftershocks, and its seismological characteristics were strongly controlled by the rheological and tectonics conditions of the extreme erosive margin of Northern Chile.  相似文献   

Time-Based Network Analysis Before and After the M_w  8.3 Illapel Earthquake 2015 Chile     

Denisse Pastén  Felipe Torres  Benjamín Toledo  Víctor Muñoz  José Rogan  Juan Alejandro Valdivia 《Pure and Applied Geophysics》2016,173(7):2267-2275

  相似文献   

Organic carbon accumulation in oligotrophic coastal lakes in southern Brazil during the last century     

Bueno  Carolina  Sanders  Christian J.  Niencheski  Felipe Hax  Andrade  Carlos  Burnett  William  Santos  Isaac R. 《Journal of Paleolimnology》2021,66(1):71-82

Journal of Paleolimnology - We report organic carbon (OC) accumulation rates in three freshwater ecosystems in southern Brazil, along the largest shallow coastal lagoon ecosystem in the world, the...  相似文献   

Modeling the Uncertainty in the Layout of Geological Units by Implicit Boundary Simulation Accounting for a Preexisting Interpretive Geological Model     

Ferrer  Renato  Emery  Xavier  Maleki  Mohammad  Navarro  Felipe 《Natural Resources Research》2021,30(6):4123-4145

Natural Resources Research - An implicit simulation algorithm that uses signed distance functions is proposed to represent subsurface geological configuration while accounting for two sources of...  相似文献   

Spillover effect offsets the conservation effort in the Amazon   总被引：1，自引：0，他引：1  

Yue Dou  Ramon Felipe Bicudo da Silva  Hongbo Yang  Jianguo Liu 《地理学报(英文版)》2018,28(11):1715-1732

Diverse conservation efforts have been expanding around the globe, even under the stress of increasing agricultural production. A striking example is the supply-chain agreements put upon the Amazon forest which had reduced deforestation by 80% from the early 2000s (27,772 km²) to 2015 (6207 km²). However, evaluation of these conservation efforts usually focused on the impacts within the Amazon biome only, while the effects that spill over to other areas (e.g., displacement of environmental pressure from one area to another) were rarely considered. Ignoring spillover effects may lead to biased or even wrong conclusions about the effectiveness of these conservation efforts because the hidden cost outside the target area of conservation may offset the achievement within it. It is thus important to assess the spillover effects of these supply-chain agreements. In this study, we used the two supply-chain agreements (i.e., Soy Moratorium and zero-deforestation beef agreement) implemented in the Amazon biome as examples and evaluated their spillover effects to the Cerrado. To achieve a holistic evaluation of the spillover effects, we adopted the telecoupling framework in our analysis. The application of the telecoupling framework includes the interactions between distant systems and extends the analytical boundaries beyond the signatory areas, which fill the gap of previous studies. Our results indicate that the supply-chain agreements have significantly reduced deforestation by half compared to projections within the sending system (i.e., Pará State in the Amazon, which exports soybeans and other agricultural products), but at the cost of increasing deforestation in the spillover system (i.e., a 6.6 time increase in Tocantins State of the Cerrado, where deforestation was affected by interactions between the Amazon and other places). Our study emphasizes that spillover effects should be considered in the evaluation and planning of conservation efforts, for which the telecoupling framework works as a useful tool to do that systematically.  相似文献   

Hydroclimatic change disparity of Peruvian Pacific drainage catchments     

Pedro?RauEmail authorView author&#;s OrcID profile  Luc?Bourrel  David?Labat  Frédéric?Frappart  Denis?Ruelland  Waldo?Lavado  Boris?Dewitte  Oscar?Felipe 《Theoretical and Applied Climatology》2018,134(1-2):139-153

Peruvian Pacific drainage catchments only benefit from 2% of the total national available freshwater while they concentrate almost 50% of the population of the country. This situation is likely to lead a severe water scarcity and also constitutes an obstacle to economic development. Catchment runoff fluctuations in response to climate variability and/or human activities can be reflected in extreme events, representing a serious concern (like floods, erosion, droughts) in the study area. To document this crucial issue for Peru, we present here an insightful analysis of the water quantity resource variability of this region, exploring the links between this variability and climate and/or anthropogenic pressure. We first present a detailed analysis of the hydroclimatologic variability at annual timescale and at basin scale over the 1970–2008 period. In addition to corroborating the influence of extreme El Niño events over precipitation and runoff in northern catchments, a mean warming of 0.2 °C per decade over all catchments was found. Also, higher values of temperature and potential and actual evapotranspiration were found over northern latitudes. We chose to apply the Budyko-Zhang framework that characterizes the water cycle as a function of climate only, allowing the identification of catchments with significant climatic and anthropogenic influence on water balance. The Budyko-Zhang methodology revealed that 11 out of 26 initial catchments are characterized by low water balance disparity related to minor climatic and anthropogenic influence. These 11 catchments were suitable for identifying catchments with contrasting change in their hydroclimatic behavior using the Budyko trajectories. Our analysis further reveals that six hydrological catchment responses can be characterized by high sensitivity to climate variability and land use changes.  相似文献   

A GRASS GIS parallel module for radio-propagation predictions     

Lucas Benedičič  Felipe A. Cruz  Tsuyoshi Hamada  Peter Korošec 《International journal of geographical information science》2014,28(4):799-823

Geographical information systems are ideal candidates for the application of parallel programming techniques, mainly because they usually handle large data sets. To help us deal with complex calculations over such data sets, we investigated the performance constraints of a classic master–worker parallel paradigm over a message-passing communication model. To this end, we present a new approach that employs an external database in order to improve the calculation–communication overlap, thus reducing the idle times for the worker processes. The presented approach is implemented as part of a parallel radio-coverage prediction tool for the Geographic Resources Analysis Support System (GRASS) environment. The prediction calculation employs digital elevation models and land-usage data in order to analyze the radio coverage of a geographical area. We provide an extended analysis of the experimental results, which are based on real data from an Long Term Evolution (LTE) network currently deployed in Slovenia. Based on the results of the experiments, which were performed on a computer cluster, the new approach exhibits better scalability than the traditional master–worker approach. We successfully tackled real-world-sized data sets, while greatly reducing the processing time and saturating the hardware utilization.  相似文献