The impact of environmental factors on the distribution pattern of aquatic plants along the Danube River corridor (Slovakia)     

Helena O&#x;aheov  Milan Valachovic   Richard Hrivnk 《Limnologica》2007,37(4):290-302

The aim of the study was to evaluate pattern of the aquatic macrophyte species distribution along the Danube fluvial corridor in Slovakia, and to identify the impact of environmental abiotic parameters on macrophyte species diversity. Field sampling was performed in the period 1999–2005 from the boat. Aquatic habitats were divided into 365 survey unit (SU). The survey of aquatic macrophytes and abiotic parameters followed the European standard approach EN 144184 2003. The plant mass estimate (PME – a semi-quantitative estimation of the amount of individual species in a SU, which takes into account three-dimensional development of plant stands) was estimated according to a five-point-scale in each SU; environmental pattern, were assessed over six abiotic parameters (river km, bank type, sediment type, flow velocity class, land-use type, and heavily man-modified water bodies). Altogether, four hydrologic connectivity types of aquatic habitats were distinguished: the Danube River, Open Arms, Separated Arms, and Seepage Water-bodies.

In total, 54 aquatic macrophytes were recorded for the whole data set of the Danube fluvial corridor. The PME data of true aquatic macrophytes and the length of SUs created a basis for numerical derivates, relative plant mass (RPM), mean mass indices (MMT, MMO) and the distribution ratio (d).

The results correspond with comparable studies on this topic: the highest macrophytes species diversity occurred in Separated Arms. On the contrary, macrophytes had the lowest richness in the Danube River main channel, although their diversity was slightly higher in heavily man-modified water bodies (such as the hydropower plant's reservoir and the abandoned main channel of the so-called Old Danube). Our results suggest that the lateral connectivity types of the river water bodies, primarily characterised by different hydrologic dynamics and human impact expressed as land-use types are responsible for the variability of aquatic macrophyte assemblages along the Danube corridor in Slovakia.  相似文献   

Sea-level changes during the Pleistocene-Holocene in the NW coastal zone of Portugal     

Helena Maria Granja  G. Soares de  Carvalho 《地学学报》1995,7(1):60-67

Research was undertaken to establish the present coastal dynamics of the area south of Espinho, Portugal, with special emphasis on the migration inland of beaches and the retreat of cliffs during at least the last century.
Besides the Holocene units (the Silvalde-Paramos tijuca Formation, 2310 ± 80 yr BP to 500 ± 80 yr BP, and the Cortegaca Beach Formation, 6850 ± 60 yr BP to 950 ± 80 yr BP), a Pleistocene unit (the Maceda Beach Formation, 29, 600 ± 690 yr BP to 14300 ± 160 yr BP) with trunks of Pinus sylvestris was recognized. The Cortegaca Beach Formation comprises a truncated podzol profile, the Al horizon dating from 3490 ± 60 yr BP to 950 ± 80 yr BP. The study and the dating of the Pleistocene and the Holocene formations suggest a model of evolution related to sea-level fluctuations and neotectonics, during the interval between 29,000 ± 690 yr BP and the post-XVth century (Little Ice Age).
The final purpose of the research is to apply the results to the prediction of the coastal zone evolution, and particularly to influence policy with respect to coastal zone management. This policy must take into account the inland migration of the beaches and the cliff retreat as a consequence of the natural dynamics of the earth that cannot be arrested or controlled by man.  相似文献   

SENSITIVITY OF THE RUSSIAN AGRICULTURE TO CHANGES IN CLIMATE, CO2 AND TROPOSPHERIC OZONE CONCENTRATIONS AND SOIL FERTILITY     

Oleg D. Sirotenko  Helena V. Abashina  Vera N. Pavlova 《Climatic change》1997,36(1-2):217-232

Russian agriculture sensitivity to changes in climate, soil and atmosphere chemistry were analyzed. Calculated data are presented on crop productivity of grain crops and grasses (C₃) under arid and humid scenarios of climate taking account of one-, two-, three and four-factor natural environment impacts. All four factors under studies (climatic parameters, CO₂ and tropospheric ozone concentrations, soil degradation extent) greatly impact agriculture productivity. The effect of interaction between all considered factors on agroecosystem productivity is studied. It is established that a simple additive scheme for explaining the complex effect of some factors can be much violated. In this case, not only variations in the mean crop yield levels but also variations in the degree of crop stability have been assessed in some regions, that may be more important for determining the social-economic consequences. It turned out that the recurrence of critically very low yields in steppe regions may increase two fold as a result of global warming.  相似文献   

Experimental modeling of native carbon formation in a C–O–H fluid system     

L. A. Ivanova  T. G. Shumilova  V. Ya. Medvedev  M. V. Marchuk  S. I. Isaenko  S. S. Shevchuk 《Doklady Earth Sciences》2016,466(2):196-198

Integrated data are presented on structure–morphology features, as well as on the material and phase composition, of a fluid-produced carbonaceous substance (CS) formed under known thermodynamic conditions of the experiment (C–O–H system, 500–800°C, and 500–1000 atm). Solid products of the synthesis were examined by means of X-ray phase and thermal analyses, scanning electron microscopy combined with microprobe analysis, transmission electron microscopy, high-resolution Raman spectroscopy, IR spectroscopy, and CHN-analysis. The characteristics of the experimental CS may be applicable in genetic modeling of natural ore-bearing fluidal carbonaceous systems.  相似文献   

Long-term TNT and DNT contamination: 1-D modeling of natural attenuation in the vadose zone: case study,Portugal     

Helena?I.?F.?AmaralEmail author  Ana Claúdia?Gama  Cláudia?Gon?alves  Judite?Fernandes  Maria?Jo?o?Batista  Manuela?Abreu 《Environmental Earth Sciences》2016,75(1):89

The vadose zone of a trinitrotoluene (TNT) and dinitrotoluene (DNT) contaminated site was investigated to assess the mobility of those explosives under natural conditions. Located in the left margin of the River Tejo Basin, Portugal, the site is located on unconsolidated sediments. Wastewaters associated with the 50-year explosives production were disposed in excavated ponds, from where water would infiltrate and pollute the unsaturated and saturated parts of the local aquifers. Two boreholes were drilled to 9 m depth in such a former waste pond to investigate the contaminant’s fate in the vadose zone. Sediment samples were taken every 1–2 m for analysis of the poly-nitroaromatics (p-NACs) and organic volatile compounds, pH, organic carbon content, cation exchange capacity and grain size analysis. The main contaminant was TNT representing >70 % of the total p-NACs concentration that peaked approximately 7 mg/kg in one borehole, even if the median in both boreholes was of ~1 mg/kg. DNT was 4–30 % of the total p-NACs and nitrotoluene (NT), up to 5 %. No other (volatile) organic compound was detected. The predominance of TNT as the main contaminant implies that any natural mass reduction has been inefficient to clean the site. Several 1-D model simulations of p-NACs cleaning of the vadose zone under natural conditions indicated that the most probable scenario of combined advection and partitioning will only remove TNT after 10’s of years, whereas DNT and NT will hardly be removed. Such low concentrations and long times for the p-NACs removal, suggest that by now those compounds have been washed-out to a level below standard limits.  相似文献   

A green space between life and death – a case study of activities in Gamlebyen Cemetery in Oslo,Norway     

Grete Swensen  Helena Nordh  Jan Brendalsmo 《Norsk geografisk tidsskrift. Norwegian journal of geography》2016,70(1):41-53

The amount of green space in urban areas is shrinking. Densification and the introduction of new user groups in most cities today is leading to more intensive use of public spaces and the need for more space. Urban cemeteries constitute a unique type of public space: while some may consider them primarily religious and contemplative spaces, others see them as primarily recreational or as heritage sites steeped in history. The authors examine the extent to which the pressure on cities’ open green areas combined with influences from intercultural encounters is mirrored in the use and character of cemeteries today – exemplified by Gamlebyen Cemetery (Gamlebyen Gravlund) in Oslo, Norway. They used observations in combination with short semi-structured interviews with those using the cemetery. The findings of pilot study conducted in 2013 suggest that religious aspects played a minor role and that the recreational aspects were more important to most of the interviewees. Many of them considered that the cemetery provided a pleasant green walkway on their way to work, busses or city services. The cemetery offered a combination of calmness, an aesthetically pleasant environment, and ‘cultivated nature’ in an urban context, and was thus an arena that invited respect and esteem.  相似文献   

Evolving coastal character of a Baltic Sea inlet during the Holocene shoreline regression: impact on coastal zone hypoxia     

Wenxin Ning  Anupam Ghosh  Tom Jilbert  Caroline P. Slomp  Mansoor Khan  Johan Nyberg  Daniel J. Conley  Helena L. Filipsson 《Journal of Paleolimnology》2016,55(4):319-338

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Sensitivity of cork growth to drought events: insights from a 24-year chronology     

Vanda Oliveira  Alexandra Lauw  Helena Pereira 《Climatic change》2016,137(1-2):261-274

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Paleoproterozoic subduction-related metasomatic signatures in the lithospheric mantle beneath NE Brazil: inferences from trace element and Sr–Nd–Pb isotopic compositions of Neoproterozoic high-K igneous rocks     

Maria Helena Bezerra Maia de Hollanda  Mrcio Martins Pimentel  Emanuel Ferraz Jardim de S 《Journal of South American Earth Sciences》2003,15(8):885-900

Late Neoproterozoic (ca. 580 Ma), high-K, mafic-intermediate rocks represent voluminous bimodal magmatism in the Borborema Province, northeast Brazil. These rocks show the following chemical signatures that reflect derivation from a subduction-modified lithospheric mantle source: (1) enrichment in large ion lithophile elements (Rb, Ba, K, Th) and light rare-earth elements (REE) (La/Yb_CN=11–70), (2) pronounced negative Nb anomalies, and (3) radiogenic Sr (0.71202–0.7059) and unradiogenic Nd (_Nd from −9.3–−20.1) isotopic compositions. T_DM model ages suggest that modification of the lithospheric mantle source (metasomatised garnet lherzolite) may have occurred in the Paleoproterozoic during the Transamazonian/Eburnean tectonics that affected the region. Interaction with asthenospheric fluids is believed to have partially melted this enriched source in the Neoproterozoic, probably as a result of asthenosphere-derived fluid percolation in the Brasiliano/Pan-African shear zones that controlled the emplacement of these mafic-intermediate magmas. The involvement of this asthenospheric component is supported by the nonradiogenic Pb isotopic ratios (²⁰⁶Pb/²⁰⁴Pb=16–17.3, ²⁰⁷Pb/²⁰⁴Pb=15.1–15.6, ²⁰⁸Pb/²⁰⁴Pb=36–37.5), which contrast with the enriched Sr and Nd compositions and thereby suggest the decoupling of Rb–Sr, Sm–Nd, and U–Pb systems at the time of intrusion of the mafic-intermediate magmas in the crust.  相似文献   

Stress measurements in soft rocks     

Robert Corthsy  Maria Helena Leite  Denis E. Gill  Bernard Gaudin 《Engineering Geology》2003,69(3-4):381-397

The objective of this paper is to demonstrate that accurate and reliable in situ stress measurements can be performed in soft rocks. A quick overview of the mechanical behaviour of soft rocks is presented. After reviewing stress measurement techniques that have been used in soft rocks, the modified doorstopper technique is presented and the advantages it has over other techniques in soft rocks are underlined. Results from laboratory simulations in controlled conditions show that the technique is reliable and accurate. It is then shown, through field applications in a potash mine in Brazil, in an underwater tunnel in shales in Canada and in an exploratory drift in molassic rocks of the French Alps, how the technique yields results that can sometimes be confirmed by field observations.  相似文献