Dynamics of carbon pools in post-agrogenic sandy soils of southern taiga of Russia     

Olga Kalinina  Sergey V Goryachkin  Nina A Karavaeva  Dmitriy I Lyuri  Luise Giani 《Carbon balance and management》2010,5(1):1

Background  

Until recently, a lot of arable lands were abandoned in many countries of the world and, especially, in Russia, where about half a million square kilometers of arable lands were abandoned in 1961-2007. The soils at these fallows undergo a process of natural restoration (or self-restoration) that changes the balance of soil organic matter (SOM) supply and mineralization.  相似文献   

The effect of mantle composition on density in the extending lithosphere   总被引：1，自引：0，他引：1  

Nina S.C. Simon  Yuri Yu. Podladchikov 《Earth and Planetary Science Letters》2008,272(1-2):148-157

The density distribution of the lithosphere is non-linear and discontinuous due to complex mineralogy and, most importantly, phase transitions. We evaluate the influence of changes in mantle composition on lithospheric density and its evolution during horizontal stretching, using thermodynamic calculations of the density as a function of pressure, temperature and composition. We also develop a simple parameterization based on end-member mineral reactions and geometric relationships between the geotherm and the phase boundary for comparison. The garnet–spinel peridotite transition leads to a moderate decrease in density of the mantle part of the lithospheric column at the initial stages of stretching. When the crust is sufficiently thinned and temperature is relatively high, plagioclase peridotite becomes stable in the upper part of the mantle. The density reduction due to the plagioclase-in reaction is controlled by bulk Al₂O₃ in the mantle and by the depth of the plagioclase-in reaction, which is mainly governed by the Na₂O/Al₂O₃ ratio. Since Na₂O and Al₂O₃ increase with the fertility of the mantle the phase transition effect is most pronounced for relatively fertile mantle (and strong extension) and can lead to 2.3% density reduction. This is equivalent to heating the entire lithosphere by 700 °C if only the effect of thermal expansion on density is taken into account. The formation of plagioclase peridotite can explain syn-rift uplift in sedimentary basins that experienced large mantle stretching without invoking an unrealistically strong increase in temperature. It might also be responsible for the break-up unconformity observed at continental margins.  相似文献   

Abundance, Sources and Speciation of Trace Elements in Humus-Rich Streams Affected by Acid Sulphate Soils   总被引：3，自引：0，他引：3  

Mats Åström  Nina Corin 《Aquatic Geochemistry》2000,6(3):367-383

The behaviour of trace elements (Al, As, Cd, Co, Cr,Cu, Fe, Mn, Ni, V, Zn) was studied in five humus-richstreams (dissolved organic carbon = 14–40 mg/L)impacted by acid sulphate soils developed in marinesulphide-bearing fine-grained sediments. During heavyrainfalls in autumn, on which the study focusses, themetals Al, Cd, Co, Cu, Mn, Ni and Zn are extensivelyleached from these acidic soils (pH = 2.5–4.5), whileAs, Cr, Fe and V are not leached more strongly fromthis soil type than from areas of till and peat. Aspeciation experiment, based on anion and cationexchange of the stream waters in the field, showedthat (1) the metals Al, Cd, Co, Mn, Ni and Zn aretransported in the streams mainly as inorganiccations, (2) Cu exists mainly in cationic form but isalso to a significant extent associated with dissolvedhumic substances, (3) Fe occurs mainly in the anionicfraction explained by organic coating on colloidal Feoxyhydoxides and (4) the hydrochemistry of As, Cr andV is complex as these elements may exist in severalunquantified anionic fractions and to a minor extentin cationic species/forms. Whereas the proportion ofacid sulphate soils in the catchments had a largeimpact on concentrations levels of several elements inthe stream waters, these soils did not have a largeaffect on the speciation of elements in water.  相似文献   

Bathymetric patterns of megafaunal assemblages from the arctic deep-sea observatory HAUSGARTEN     

Thomas Soltwedel  Nina Jaeckisch  Nikolaus Ritter  Christiane Hasemann  Melanie Bergmann  Michael Klages 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(10):1856-1872

Five photographic transects, covering some 830 m² of seafloor in total, were analyzed to characterize the megabenthic community along a bathymetric gradient covering water depths from 1200 to 5500 m in the eastern Fram Strait. Megafaunal densities ranged between 11 and 38 ind. m⁻². The highest densities were found at 1650 m and the lowest densities occurred at 3000 m depth. The number of taxa and morphotypes ranged between 4 at 5500 m and 27 at 1650 m water depth. Ophiocten gracilis, a small white unidentified amphipod, Kolga hyalina, and Bathycrinus carpenteri were the dominant and characteristic species on the slope and continental rise. Elpidia heckeri dominated in the Molloy Hole, the deepest depression known in the Arctic Ocean. Megafaunal zonation patterns appeared to be mainly controlled by food availability, as indicated by phytodetrital matter measured at the seafloor, and by benthic biomass in the sediments, as indicated by sediment-bound particulate proteins and phospholipids. By contrast, physical factors, including water depth and seabed properties such as sediment porosity and hard substrata (e.g., dropstones), appear to play a secondary role in determining megabenthic zonation patterns along the bathymetric HAUSGARTEN gradient.  相似文献   

Growing up a geologist—John Phillips and William Smith     

Nina Morgan 《Geology Today》2019,35(5):179-185

William Smith's 1815 Map of the Geology of England and Wales was a ground‐breaking achievement that changed the understanding of geology forever. However, perhaps Smith's greatest contribution to science lay in nurturing the talent of his orphaned nephew, John Phillips, who grew up to become one of the most versatile and distinguished geologists and polymaths of the nineteenth century.  相似文献   

Cenozoic development of northern Svalbard based on thermochronological data     

Nina Drr  Frank Lisker  Karsten Piepjohn  Cornelia Spiegel 《地学学报》2019,31(3):306-315

Northern Svalbard represents a basement high surrounded by the Norwegian‐Greenland Sea/Fram Strait, Eurasian Basin, the Barents Shelf and the onshore Central Tertiary Basin (CTB). Published apatite fission track (AFT) data indicate Mesozoic differential, fault‐controlled uplift and exhumation of the region. Thermal history modelling of published and new AFT and (U–Th–Sm)/He ages of 51–153 Ma in the context of regional stratigraphy and geomorphology implies at least two, possibly three, uplift and exhumation stages since late Mesozoic, separated by episodes of subsidence and sediment deposition. Late Cretaceous/Palaeocene exhumation and subsequent burial appear to be related with the transition of compressional to transpressional collision of Svalbard and Greenland during the Eurekan Orogeny. Renewed exhumation since the Oligocene probably results from passive margin formation after the separation of Svalbard and Greenland, when a new offshore sedimentary basin opened west of Svalbard. Final uplift since the Miocene eventually re‐exposed the palaeosurface of northern Svalbard.  相似文献   

High-temperature neutron diffraction study of deuterated brucite     

Hongwu Xu  Yusheng Zhao  Donald D. Hickmott  Nina J. Lane  Sven C. Vogel  Jianzhong Zhang  Luke L. Daemen 《Physics and Chemistry of Minerals》2013,40(10):799-810

To study the structural behavior of brucite at high temperature, we conducted in situ neutron diffraction experiments of a deuterated brucite powder sample, Mg(OD)₂, in the temperature range 313–583 K. The sample was stable up to 553 K, above which it started to decompose into periclase (MgO) and D₂O vapor. Rietveld analyses of the obtained data were performed using both single-site and three-site split-atom hydrogen models. Our results show that with increasing temperature, unit-cell parameter c increases at a rate ~7.7 times more rapidly than a. This large anisotropy of thermal expansion is primarily due to rapid increase in the interlayer thickness along the c-axis on heating. The amplitudes of thermal vibration for Mg, O, and D increase linearly with increasing temperature; however, the rate of the increase for the lighter D is much larger. In addition, D vibrates anisotropically with a higher magnitude within the (001) plane, as confirmed by our first-principles phonon calculations. On heating, the interatomic distances between a given D and its associated O and D from the adjacent [MgO₆] layer increase, whereas the O–D bond length decreases. This behavior suggests weakened D···O and D···D interlayer interactions but strengthened O–D bonding with increasing temperature.  相似文献   

顾及排序差异的对象群邻近关系相似性计算     

孟妮娜  艾廷华  周校东 《武汉大学学报(信息科学版)》2013,38(6):737-741

针对空间邻近关系相似性的定量化计算问题,在确定邻近特征量的基础上,将相似性度量的要素模型和对准模型结合起来,建立了顾及排序差异的对象群邻近关系相似性计算方法,并验证了该方法的可用性。  相似文献   

Oxygen depletion and phosphorus release following flooding of a cultivated wetland area in Denmark     

Nina L. Grunth  Louise Askaer  Bo Elberling 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):17-25

Geografisk Tidsskrift, Danish Journal of Geography 108(2):17–25, 2008

The rewetting of altered wetlands is becoming increasingly widespread. When flooding cultivated soils, the oxygen (O₂) availability is reduced, subsequently, ferric hydroxides can dissolve and associated inorganic phosphorus (P) will be mobilized. This study shows the temporal and spatial dynamics of O₂ depletion following flooding using planar optodes and the subsequent release of Fe and P in two depth intervals in an experimental column set-up. The column was kept flooded for 48 days and thereafter partly drained and flooded again. Results document that large amounts of P (0.2 t P ha-¹) have accumulated in the present plough-layer (Ap) during the last 22 years, which represent roughly 15% of the present inorganic P stock in the Ap. As a result of flooding, fully anoxic conditions were observed within 3 days (within 10 h in Ap) and concentrations of dissolved Fe and P in the soil solution increased simultaneously after 7 days of flooding. Thus, P reaction kinetics was markedly delayed as compared to O₂ availability. P concentrations in soil water afterflooding (up to 0.15 mg L^?1) accounted for only 0.034% of the inorganic P stock in the Ap which is a significantly smaller fraction of the potential P-release as compared to previous investigations.

This is considered a result of only a minor fraction of the total inorganic P being directly associated with ferric hydroxides and thereby sensitive to short-term anoxic conditions as well as differences in the methodology used in this study (soil/water ratio). Finally, reactions releasing Fe and P were noted to be partly reversible upon draining.  相似文献   

Turn calculations for the indoor application of the fewest turns path algorithm     

Ann Vanclooster  Nina Vanhaeren  Pepijn Viaene  Kristien Ooms  Laure De Cock  Veerle Fack 《International journal of geographical information science》2013,27(11):2284-2304

ABSTRACT

Present-day indoor navigation systems are often not well adapted to the specific needs and requirements of its users. This research aims at improving those indoor navigation systems by providing navigation support that cognitively closer to user preferences and behaviour. More specifically, the focus is on the implementation of an accurate turn calculation method in a turn minimization algorithm, aiming to lower the complexity of routes and route instructions. This new-introduced perception-based turn calculation procedure is based on a direct door-to-door walking pattern, and, in contrast to previous algorithms, independent of the underlying indoor network type. It takes into account the effects of geometry of indoor space on human movement. To evaluate its functioning, both the traditional algorithm and the proposed perception-based algorithm are applied in the fewest turns path algorithm. It is demonstrated that the proposed algorithm accurately calculates turns in alignment with people’s perception. The implementation of the calculation algorithm in the fewest turns path algorithm also allows future applications in indoor simplest path algorithms, and overall contributes to cognitively richer indoor navigation systems.  相似文献