Epigenetic salt accumulation and water movement in the active layer of central Yakutia in eastern Siberia   总被引：1，自引：0，他引：1  

C. M. Larry Lopez  A. Brouchkov  H. Nakayama  F. Takakai  A. N. Fedorov  M. Fukuda 《水文研究》2007,21(1):103-109

Observations of soil moisture and salt content were conducted from May to August at Neleger station in eastern Siberia. Seasonal changes of salt and soil moisture distribution in the active layer of larch forest (undisturbed) and a thermokarst depression known as an alas (disturbed) were studied. Electric conductivity EC_e of the intact forest revealed higher concentrations that increased with depth from the soil surface into the active layer and the underlying permafrost: 1 mS cm^?1 at 1·1 m, to 2·6 mS cm^?1 at 160 cm depth in the permafrost. However, a maximum value of 5·4 mS cm^?1 at 0·6 m depth was found in the dry area of the alas. The concentration of ions, especially Na⁺, Mg²⁺, Ca²⁺, SO₄^2? and HCO₃^? in the upper layers of this long‐term disturbed site, indicates the upward movement of ions together with water. A higher concentration of solutes was found in profiles with deeper seasonal thawing. The accumulation of salts in the alas occurs from spring through into the growing season. The low concentration of salt in the surface soil layers appears to be linked to leaching of salts by rainfall. There are substantial differences between water content and electric conductivity of soil in the forest and alas. Modern salinization of the active layer in the alas is epigenetic, and it happens in summer as a result of spring water collection and high summer evaporation; the gradual salt accumulation in the alas in comparison with the forest is controlled by the annual balance of water and salts in the active layer. Present climatic trends point to continuous permafrost degradation in eastern Siberia increasing the risk of surface salinization, which has already contributed to changing the landscape by hindering the growth of forest. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Input of Nutritionally Rich Organic Matter from the Mississippi River to the Louisiana Coastal Zone     

Lawrence M. Mayer  Linda L. Schick  Mead A. Allison 《Estuaries and Coasts》2008,31(6):1052-1062

Isotopes have often been used to discern riverine subsidies to coastal food chains, but there are few direct measurements of nutritional quality of riverine particulates. We tested for nutritionally enriched organic matter in the Mississippi River suspended sediment and evidence for its delivery to Louisiana coastal sediments by measuring enzymatically hydrolysable amino acids (EHAA). Riverine suspended sediments contained EHAA concentrations of up to 5 mg g^?1, higher than reported in any coastal sediment. Pigment concentrations indicated that EHAA in some river samples were dominated by phytoplankton, but many samples contained significant non-algal EHAA. Coastal sediments showed EHAA concentrations lower than riverine sediments but still higher than most reported shelf values. Incubation of riverine sediment showed losses of 28–34% of their EHAA over 6 days, similar to differences found between riverine and coastal sediments. EHAA concentrations decreased more rapidly than total nitrogen, indicating the relative lability of this pool of material in the studied region. These EHAA-enriched materials provide fuel for various coastal biota whose composition likely depends on factors such as disturbance regimes.  相似文献   

Groundwater in civil engineering : L. Rétháti. Developments in Geotechnical Engineering, 35, Elsevier, Amsterdam, 1983, 500 pp., US $104.25 (USA and Canada)/Dfl. 245.00 (rest of world). Hardcover. Co-edition with Akademiai Kiado, Budapest, 1983     

Larry D. Agenbroad 《Engineering Geology》1984,20(4):346

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A geochemical survey of St. Lucia, West Indies     

Larry W. Maassen  Stephen L. Bolivar 《Journal of Geochemical Exploration》1987,28(1-3)

The Los Alamos National Laboratory conducted a reconnaissance-scale geochemical exploration program on the island of St. Lucia during September 1983. Totals of 307 stream-sediment and 55 beach-sand samples were collected and analyzed for a suite of 44 elements. Data interpretation utilized computer-generated color images. Several anomalies were delineated, the most significant of which indicate previously unrecognized Au mineralization in two areas.  相似文献   

Trace elements in fines from the Apollo 15 deep drill     

Philip A. Helmke  Karen M. Telander  Charles K. Weiss  Larry A. Haskin 《Geochimica et cosmochimica acta》1973,37(3):706-708

No systematic variations in concentrations with depth were found for 1O trace elements in samples from the Apollo 15 deep drill. Presence of a significant amount of KREEP is indicated.  相似文献   

The simulation of European heat waves from an ensemble of regional climate models within the EURO-CORDEX project   总被引：4，自引：1，他引：3  

Robert Vautard  Andreas Gobiet  Daniela Jacob  Michal Belda  Augustin Colette  Michel Déqué  Jesús Fernández  Markel García-Díez  Klaus Goergen  Ivan Güttler  Tomáš Halenka  Theodore Karacostas  Eleni Katragkou  Klaus Keuler  Sven Kotlarski  Stephanie Mayer  Erik van Meijgaard  Grigory Nikulin  Mirta Patarčić  John Scinocca  Stefan Sobolowski  Martin Suklitsch  Claas Teichmann  Kirsten Warrach-Sagi  Volker Wulfmeyer  Pascal Yiou 《Climate Dynamics》2013,41(9-10):2555-2575

The ability of a large ensemble of regional climate models to accurately simulate heat waves at the regional scale of Europe was evaluated. Within the EURO-CORDEX project, several state-of-the art models, including non-hydrostatic meso-scale models, were run for an extended time period (20 years) at high resolution (12 km), over a large domain allowing for the first time the simultaneous representation of atmospheric phenomena over a large range of spatial scales. Eight models were run in this configuration, and thirteen models were run at a classical resolution of 50 km. The models were driven with the same boundary conditions, the ERA-Interim re-analysis, and except for one simulation, no observations were assimilated in the inner domain. Results, which are compared with daily temperature and precipitation observations (ECA&D and E-OBS data sets) show that, even forced by the same re-analysis, the ensemble exhibits a large spread. A preliminary analysis of the sources of spread, using in particular simulations of the same model with different parameterizations, shows that the simulation of hot temperature is primarily sensitive to the convection and the microphysics schemes, which affect incoming energy and the Bowen ratio. Further, most models exhibit an overestimation of summertime temperature extremes in Mediterranean regions and an underestimation over Scandinavia. Even after bias removal, the simulated heat wave events were found to be too persistent, but a higher resolution reduced this deficiency. The amplitude of events as well as the variability beyond the 90th percentile threshold were found to be too strong in almost all simulations and increasing resolution did not generally improve this deficiency. Resolution increase was also shown to induce large-scale 90th percentile warming or cooling for some models, with beneficial or detrimental effects on the overall biases. Even though full causality cannot be established on the basis of this evaluation work, the drivers of such regional differences were shown to be linked to changes in precipitation due to resolution changes, affecting the energy partitioning. Finally, the inter-annual sequence of hot summers over central/southern Europe was found to be fairly well simulated in most experiments despite an overestimation of the number of hot days and of the variability. The accurate simulation of inter-annual variability for a few models is independent of the model bias. This indicates that internal variability of high summer temperatures should not play a major role in controlling inter-annual variability. Despite some improvements, especially along coastlines, the analyses conducted here did not allow us to generally conclude that a higher resolution is clearly beneficial for a correct representation of heat waves by regional climate models. Even though local-scale feedbacks should be better represented at high resolution, combinations of parameterizations have to be improved or adapted accordingly.  相似文献   

Spatial gradients in the flow over an estuarine channel   总被引：3，自引：0，他引：3  

Arnoldo Valle-Levinson  Larry P. Atkinson 《Estuaries and Coasts》1999,22(2):179-193

Acoustic Doppler current profiles were measured for a twelve-hour period on February 21, 1997 across Thimble Shoal channel, lower Chesapeake Bay, for the purpose of determining bathymetrically-induced spatial gradients in the flow and their implications for the lateral momentum balance in estuaries. A least-squares fit to semidiurnal and quarter-diurnal harmonics was used to separate the tidal and subtidal contributions to the observed flow. The period of observation was characterized by onshore winds and subtidal inflow everywhere along the transect sampled but strongest in the channel. Spatial gradients in both the tidal and subtidal horizontal flows showed that the greatest lateral shears and convergences were found where the bathymetric changes were sharpest, i.e., on the shoulders of the channel. The ratio of the quarter-diurnal to the semidiurnal tidal amplitudes was greatest over the channel shoulders, for both the along- and across-estuary flow components, and indicated the importance of non-linear effects there. The nonlinear term caused by across-estuary divergence was larger than the Coriolis term over the channel shoulders. The nonlinear contribution was comparable to the Coriolis acceleration in the subtidal and tidal lateral momentum balances. For the tidal balance, the local accelerations were also as important as the Coriolis accelerations. Equivalent results in the momentum balances were obtained with another data set of October 1993. Contrary to the customary assumption, the across-estuary momentum balance in this area was ageostrophic.  相似文献   

W. G. Bailey, Timothy R. Oke, and Wayne R. Rouse (eds.), The Surface Climates of Canada     

Larry Mahrt 《Boundary-Layer Meteorology》1999,90(2):339-340

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Weathering of archaeological cherts: A case study from the Solomon Islands     

Peter J. Sheppard  Larry A. Pavlish 《Geoarchaeology》1992,7(1):41-53

Weathering of chert artifacts from three Lapita sites (ca. 3000–2000 B.P.) in the Southeast Solomons is examined. It is shown that the rate of weathering is strongly influenced by soil pH, mineralogy, and prehistoric burning of the material. The concentrations of some major elements (Na, Cl, K, Al) are shown to have been altered during the weathering process. Implications of this work for the sourcing and dating of cherts are discussed.  相似文献   

Semipermeable membrane devices link site-specific contaminants to effects: PART II - A comparison of lingering Exxon Valdez oil with other potential sources of CYP1A inducers in Prince William Sound, Alaska   总被引：1，自引：1，他引：0  

Short JW  Springman KR  Lindeberg MR  Holland LG  Larsen ML  Sloan CA  Khan C  Hodson PV  Rice SD 《Marine environmental research》2008,66(5):487-498

We deployed semipermeable membrane devices (SPMDs) on beaches for 28 days at 53 sites in Prince William Sound (PWS), Alaska, to evaluate the induction potential from suspected sources of cytochrome P450 1A (CYP1A)-inducing contaminants. Sites were selected to assess known point sources, or were chosen randomly to evaluate the region-wide sources. After deployment, SPMD extracts were analyzed chemically for persistent organic pollutants (POPs) and polycyclic aromatic hydrocarbons (PAH). These results were compared with hepatic CYP1A enzyme activity of juvenile rainbow trout injected with the same extracts prior to clean-up for the chemical analyses. Increased CYP1A activity was strongly associated with PAH concentrations in extracts, especially chrysene homologues but was not associated with POPs. The only apparent sources of chrysene homologues were lingering oil from Exxon Valdez, asphalt and bunker fuels released from storage tanks during the 1964 Alaska earthquake, creosote leaching from numerous pilings at one site, and PAH-contaminated sediments at Cordova Harbor. Our results indicate that PWS is remarkably free of pollution from PAH when nearby sources are absent as well as from pesticides and PCBs generally.  相似文献