Direct evidence of imbalanced seagrass (Posidonia oceanica) shoot population dynamics in the Spanish Mediterranean     

Núria Marbà  Carlos M. Duarte  Elena Díaz-Almela  Jorge Terrados  Elvira Álvarez  Regino Martínez  Rocío Santiago  Esperança Gacia  Antoni M. Grau 《Estuaries and Coasts》2005,28(1):53-62

Direct census of shoots tagged in permanent plots was used to assess the present (2000–2002)Posidonia oceanica population dynamics in 25 meadows along the Spanish Mediterranean Coast. Shoot density ranged from 154±8 to 1,551±454 shoots m⁻², absolute shoot mortality from 5±0 to 249±53 shoots m⁻² yr⁻¹, and absolute shoot recruitment from <5 ±1 to 62±42 shoots m⁻²yr⁻¹. Specific shoot mortality and recruitment rates, which are mathematically and statistically (p>0.05) independent of shoot density, varied from 0.015±0.006 to 0.282±0.138 yr⁻¹ and 0.018±0.005 to 0.302±0.093 yr⁻¹, respectively. Absolute shoot mortality rate was scaled to shoot density (Pearson correlation, r=0.78, p<0.0001), and variability in specific shoot recruitment rate was partially due to differences in the percentage of growing apexes, which produce most of the recruits within the population (Pearson correlation, r=0.50, p<0.001), demonstrating the existence of structural constraints on shoot demography. Shoot half-life was estimated to range from 2.5 to 60.4 yr and meadow turnover times between 6.7 yr and more than a century, provided current estimates of shoot mortality, recruitment rates, and density remain uniform. There were differences in shoot mortality and recruitment at the regional scale, with the meadows developing along the coast of the Spanish mainland experiencing the highest shoot mortality (Tukey test, p<0.05) and tending to exhibit the highest shoot recruitment. The low shoot recruitment did not balance shoot mortality in most (60%) of the meadows, showing a prevalence of declining populations among the 25 meadows studied (Wilcoxon ranked sign test, p<0.0005). This study demonstrates the power of direct census of seagrass shoots in permanent plots to evaluate the present status of seagrass meadows, to detect on-going population decline, and to provide some insight onto the possible factors involved. The incorporation of direct census of seagrass meadows to monitoring programs will help provide the early-warning signals necessary to support management decisions to conserve seagrass meadows.  相似文献   

Depth of crustal conducting layer and asthenosphere in the Pannonian basin determined by magnetotellurics     

A. Ádám  L.L. Vanyan  D.A. Varlamov  I.V. Yegorov  A.P. Shilovski  P.P. Shilovski 《Physics of the Earth and Planetary Interiors》1982,28(3):251-260

On the basis of numerical modelling and statistical investigations of the horizontal electrical inhomogeneities (narrow fractures, change of conductance of the surface sediments) ρ_min magnetotelluric (MT)-sounding curves were found to be less distorted and, therefore, they can be used for the determination of deep conducting formations in the crust and upper mantle.Carefully selected MT curves indicate the crustal conductive layer at depths of 7–13 km and the conductive asthenosphere between 50 and 80 km.The relatively shallow position of the asthenosphere corresponds to the high heat flow (q > 80 mWm^?1) in the Pannonian basin according to the empirical relation derived by Ádám (1978).  相似文献   

Foreword     

Antal Ádám 《Surveys in Geophysics》1982,4(4):335-336

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Das Erdstrom-Observatorium bei Nagycenk (Ungarn)     

Anton Ádám  Josef Verö 《Pure and Applied Geophysics》1958,39(1):126-151

Zusammenfassung Im ersten Teil des Artikels werden — nach einem kurzen geschichtlichen Rückblick — die Anlage und die technischen Einrichtungen des im IGJ bei Nagycenk (Ungarn) errichteten tellurischen Observatoriums dargelegt. Der zweite Teil beschäftigt sich mit der Bearbeitung der Registrierungen. Wir wollen in erster Richtung die Verteilung der Variationen von verschiedenen Perioden untersuchen, und wir ordneten deshalb, teils auf Grund der Gegebenheiten der Registrierungen, hauptsächlich aber der Untersuchung bei verschiedenen Typen wegen, die Variationen in 5, bzw.9 Klassen ein. Ausserdem führen wir die tellurischen Äquivalenten der magnetischen Phenomena (Bay, Sturm, usw) und die Grundlagen deren Einteilung an. Die Publikationen über Karakteristiken und Graphikons zweccks Erkennung der Eigenschaften der Variationen werden wir von Zeit zu Zeit forsetzen.

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Summary In the first part of the article the writers — after a brief historical note — acquaint with the question of the location of the telluric observatory, established during the IGY near Nagycenk (Hungary) and with its technical arrangements. The second part presents the preparation of the records. It was chiefly the distribution of the different periodic variations in our mind, and this is why we included the variations, partly based on the given conditions of the recording, but in first line on the examination of periods of the different types in 5, respectively in 9 classes. Moreover, we specify the telluric equivalents of magnetic phenomena (bay, storm, etc.) and the basic principles of the classification. We shall report periodically on the characterics and graphs concerning the feature of the variations.

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Assessment of soil erosion in a small watershed covered by loess     

Ádám Kertész  Béla Márkus  Gerold Richter 《GeoJournal》1995,36(2-3):285-288

Loose sediments like loess are easily erodable especially on hillslopes used for agriculture. Erosion contributes to the sedimentation and pollution of lakes such threatening quasi-natural ecosystems. On the other hand soil erosion damages fertile soils.The aim of the present paper is the assessment of soil and nutrient loss in a tributary catchment of Lake Balaton, including geoecological aspects of the lake ecosystem and of the slopes mantled by loess.The USLE is applied for small topological units, for the so called erotops. Rainfall simulation experiments were applied for the determination of the erodibility of soils. The calculation is based on a new, GIS aided method. Control measurements have been going on for four years at a gauging station to check how much sediment and water actually leaves the catchment.Results of sediment yield measurements were compared with the results obtained by the application of USLE for the whole catchment. According to this comparison only 2% leaves the catchment so that redeposition processes within the catchment are very important whereas the contribution of soil erosion to the eutrophication of the lake is not very significant in the small tributaries in the northern part of Lake Balaton catchment.  相似文献   

PHYSICAL IMPACTS OF CLIMATIC CHANGE ON DELTAIC COASTAL SYSTEMS (I): AN APPROACH     

AGUSTIN SÁNCHEZ-ARCILLA  JOSÉ A. JIMÉNEZ 《Climatic change》1997,35(1):71-93

The evaluation of the impact of climate change on deltaic systems implies studying a multi-component system in which the complexity of links is high enough to present doing it as a whole. Because of this, it is a reasonable approach to study separately the behaviour of each element, to be afterwards linked into a general conceptual model for deltaic behaviour. Moreover, in the case of largely regulated deltas, the main impacts of climatic change will be marine-related since those related to the catchment areas will be severely damped by river regulation and management policies. This fact implies that coastal fringes may become the main frontier between the delta and climatic change effects. In this context, a methodology to study climatic change impacts on deltaic coastal fringes is here presented. It will be further developed on two companion papers dealing with the study of driving terms and coastal response. As coastal processes act at different time and space scales, determining the reference – initial – situation must be done taking into account the inherent system dynamics. It is thus unrealistic to characterize the initial stage as a static one. In order to avoid this simplistic approach, a comprehensive approach to the coastal system must be employed, with three different scales (long-term/large scale, medium term/scale and episodic).  相似文献   

PHYSICAL IMPACTS OF CLIMATIC CHANGE ON DELTAIC COASTAL SYSTEMS (II): DRIVING TERMS     

JOSÉ A. JIMÉNEZ  AGUSTIN SÁNCHEZ-ARCILLA 《Climatic change》1997,35(1):95-118

The evaluation of the impact of climatic change on deltaic coastal systems requires establishing a reference situation. As deltaic coastal zones are highly dynamic areas, it is necessary to define the reference situation as a function of their present evolutive stage. This implies characterizing coastal processes as a complex system defined by the links between driving or forcing terms and the coastal response at different temporal and spatial scales (long/large, medium and episodic scales). Starting from classical previous works on deltaic systems and including all available field and conceptual knowledge to properly consider present conditions (largely regulated rivers, subsidence, etc.) a detailed methodology to analyse forcing or driving agents at the three mentioned scales is presented. This methodology which developed the general approach presented in a companion paper, will be followed by a future paper focusing on the analysis of the coastal response.  相似文献   

SPATIO‐TEMPORAL SPECIFICS OF HYDRO‐GEOMORPHIC PROCESSES IN HEADWATER PARTS OF MID‐MOUNTAINS RECONSTRUCTED BASED ON TREE‐RING DATA: A CASE STUDY FROM THE HRUBÝ JESENÍK MOUNTAINS (CZECH REPUBLIC)          下载免费PDF全文

RADEK TICHAVSKÝ  KAREL ŠILHÁN 《Geografiska Annaler: Series A, Physical Geography》2016,98(4):369-388

Debris flows and debris floods cause frequent geomorphic hazards, even in the mid‐mountains of Central Europe. In the Hrubý Jeseník Mountains (Eastern Sudetes, Czech Republic), strong anthropogenic interventions have created specific conditions for erosion, transport and accumulation of material released by debris flow/flood events. We present a detailed spatio‐temporal reconstruction of the hydro‐geomorphic process activity in two adjacent sub‐catchments using dendrogeomorphic methods applied to the steep, narrow channels. An analysis of 172 sampled trees [Picea Abies (L.) Karst.] revealed 14 torrential events since 1943 in the Klepá?ský stream sub‐catchment and 11 events since 1897 in the Keprnický stream sub‐catchment. Identical events were identified in 1965, 1991, 1997, 2002 and 2010. The event return periods were comparable with return periods from the foothills of the European Alps. A higher frequency of events in the first sub‐catchment may be caused by the presence of a deep‐seated landslide, steeper slopes and a higher susceptibility to shallow slope deformations. Different spatial patterns of events were presented using the Kernel Density analysis in ArcMap 10.1. Clusters of affected trees in the valley floor during the last decades may be due to increased erosion below the check dams and increased accumulation above. The presence of check dams and slope stabilization works since the 1960s has mitigated the processes in several gullies, but due to the current non‐interventional management, the risk of their damage is increasing, particularly when increased activity is observed in the adjacent unprotected gullies.  相似文献   

Holocene evolution of the Xagó dune field (Asturias,NW Spain) reconstructed by means of morphological mapping and ground penetrating radar surveys     

G. Flor-Blanco  D. Rubio-Melendi  G. Flor  J. P. Fernández-Álvarez  D. W. T. Jackson 《Geo-Marine Letters》2016,36(1):35-50

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Resistivity methods in geothermal prospecting in Iceland     

Hjálmar Eysteinsson  Knútur Árnason  Ólafur G. Flóvenz 《Surveys in Geophysics》1994,15(2):263-275

Resistivity techniques have been used successfully to identify and delineate geothermal resources in Iceland. The most frequently used techniques include Schlumberger, central loop TEM and head-on profiling. Geothermal systems in Iceland are located both within and outsite the active volcanic regions. Outsite the active volcanic regions the temperature in the upper most kilometer of the geothermal systems is below 150° C whereas the temperature in the geothermal fields within the active volcanic regions exceeds 200° C. The resistivity of the rock in geothermal fields located outside the active volcanic regions ranges from about 10 m to some hundreds of m, and are characterized by considerably lower resistivity than of the surrounding rocks. Most of the geothermal systems within the active volcanic regions, show common resistivity structure with low resistivity of 1–5 m surrounding an inner core of higher resistivity. This increasing resistivity with depth is associated with a change in the conduction mechanism, from interface conduction to electrolyte conduction due to a change in alteration minerals at about 240° C. Examples of resistivity surveys of geothermal fields from both outsite and within the active volcanic regions are discussed.  相似文献