Meiobenthic diversity in space and time: The case of harpacticoid copepods in two Mediterranean microtidal sandy beaches

Meiobenthic data from two microtidal sandy beaches of the eastern Mediterranean (Crete, Greece) were used to investigate patterns of both alpha and beta diversity in space and time. Copepod assemblages and environmental variables related to sediment characteristics, morphodynamics and food were studied over a year at four distinct habitats at each beach; the retention, resurgence and saturation zones of Salvat's intertidal scheme (midlittoral zone), and the surf zone of the sublittoral. Αlpha diversity analysis indicated similar species richness at both beaches when the whole 13-month data set was considered but was higher at the sheltered site when each sampling period was examined separately. Both beaches supported higher diversity in the sublittoral zone. Species richness increased seawards at the midlittoral zone of the sheltered site whereas, no pattern was evident at the exposed site, where the intense hydrodynamic conditions homogenized the sediments. Beta diversity increased markedly towards the sublittoral, indicating greater differences in alpha diversity between the sublittoral and the midlittoral zone. Species turnover was more variable at the exposed beach and at the most landward stations, where environmental conditions change often between extremes. A proportion of the variation in alpha diversity was explained by food availability at both beaches and additionally by grain size at the sheltered site. However, no environmental variable explained beta diversity patterns. Although the results of our study support the hypothesis of Multicausal Environmental Severity proposed for sandy beach macrofauna, we believe the classic Intermediate Disturbance Hypothesis is a more appropriate framework for the meiofauna communities of the studied sites.     

Short-term seaward fish migration in the Messolonghi–Etoliko lagoons (Western Greek coast) in relation to climatic variables and the lunar cycle

In the present study we analysed the daily seaward migratory behaviour of four dominant euryhaline fish species (Mugilidae: Liza saliens, Liza aurata, Mugil cephalus and Sparidae: Sparus aurata) in the Messolonghi–Etoliko lagoon system (Western Greek coast) based on the daily landings' time series of barrier traps and assessed the relationship between their migratory behaviour and various climatic variables (air temperature and atmospheric pressure) and the lunar cycle. A 2-year time series of daily fish landings (1993 and 1994), a long time series of daily air temperature and daily temperature range (1991–1998) as well as a 4-year time series of the daily atmospheric pressure (1994–1997) and daily pressure range were used. Harmonic models (HM) consisting of annual and lunar cycle harmonic components explained most (R² > 0.80) of the mean daily species landings and temperature variations, while a rather low part of the variation (0.18 < R² < 0.27) was explained for pressure, daily pressure range and daily temperature range. In all the time series sets the amplitude of the annual component was highest. The model values of all species revealed two important migration periods (summer and winter) corresponding to the spawning and refuge migrations. The lunar cycle effect on species' daily migration rates and the short-term fluctuation of daily migration rates were rather low. However, the short-term fluctuation of some species' daily migration rates during winter was greater than during summer. In all species, the main migration was the spawning migration. The model lunar components of the species landings showed a monthly oscillation synchronous to the full moon (S. aurata and M. cephalus) or a semi-monthly oscillation synchronous to the new and full moon (L. aurata and L. saliens). Bispectral analysis of the model values and the model residuals' time series revealed that the species daily migration were correlated (coherencies > 0.6) to the daily fluctuations of the climatic variables at seasonal, mid and short-term scales.     

Empirical relationships between aftershock area dimensions and magnitude for earthquakes in the Mediterranean Sea region

Fault dimension estimates derived from the aftershock area extent of 36 shallow depth (≤ 31 km) earthquakes that occurred in the Mediterranean Sea region have been used in order to establish empirical relationships between length, width, area and surface-wave/moment magnitude. This dataset consists of events whose aftershock sequence was recorded by a dense local or regional network and the reported location errors did not exceed on average 3–5 km. Surface-wave magnitudes for these events were obtained from the NEIC database and/or published reports, while moment magnitudes as well as focal mechanisms were available from the Harvard/USGS catalogues. Contrary to the results of some previously published studies we found no evidence in our dataset that faulting type may have an effect on the fault dimension estimates and therefore we derived relationships for the whole of the dataset. Comparisons, by means of statistical F-tests, of our relationships with other previously published regional and global relationships were performed in order to check possible similarities or differences. Most such comparisons showed relatively low significance levels (< 95%), since the differences in source dimension estimates were large mainly for magnitudes lower than 6.5, becoming smaller with increasing magnitude. Some degree of similarity, however, could be observed between our fault length relationship and the one derived from aftershock area lengths of events in Greece, while a difference was found between our regional and global fault length relationships. A calculation of the ratio defined as the fault length, derived from our relationships, to the length estimated from regional empirical relationships involving surface ruptures showed that it can take a maximum value of about 7 for small magnitudes while it approaches unity at Ms 7.2. When calculating the same ratio using instead global empirical relationships we see the maximum value not exceeding 1.8, while unity is reached at Mw 7.8, indicating the existence of a strong regional variation in the fault lengths of earthquakes occurring in the Mediterranean Sea region. Also, a relationship between the logarithms of the rupture area and seismic moment is established and it is inferred that there is some variation of stress drop as a function of seismic moment. In particular, it is observed that for magnitudes lower than 6.6 the stress drop fluctuates around 10 bar, while for larger magnitudes the stress drop reaches a value as high as 60 bar.     

Development and verification of a 3-D integrated surface water–groundwater model

Coupled modelling of surface and subsurface systems is a valuable tool for quantifying surface water–groundwater interactions. In the present paper, the 3-D non-steady state Navier–Stokes equations, after Reynolds averaging and with the assumption of a hydrostatic pressure distribution, are for the first time coupled to the 3-D saturated groundwater flow equations in an Integrated suRface watEr–grouNdwater modEl (IRENE). A finite-difference method is used for the solution of the governing equations of IRENE. A semi-implicit scheme is used for the discretisation of the surface water flow equations and a fully implicit scheme for the discretisation of the groundwater flow equations. The two sets of equations are coupled at the common interface of the surface water and groundwater bodies, where water exchange takes place, using Darcy’s law. A new approach is proposed for the solution of the coupled surface water and groundwater equations in a simultaneous manner, in such a fashion that gives computational efficiency at low computational cost. IRENE is verified against three analytical solutions of surface water–groundwater interaction, which are chosen so that different components of the model can be tested. The model closely reproduces the results of the analytical solutions and can therefore be used for analysing and predicting surface water–groundwater interactions in real-world cases.     

Investigation of ‘equal displacement’ rule for bridges subjected to differential support motions

The ‘equal displacement’ rule is employed in seismic design practice to predict inelastic displacements from analyses of the corresponding linear elastic structural models. The accuracy and limitations of this rule have been investigated for ordinary structures but not for bridges subjected to spatially varying ground motions. The present study investigates this rule for moderate levels of inelastic behavior for four highway bridges in California accounting for the effects of spatial variability of the support motions due to incoherence, wave passage and differential site response. The bridge models vary significantly as to their fundamental periods and their overall configurations. Statistical analyses of pier‐drift responses are performed using as input simulated arrays of nonstationary ground motions in accordance with prescribed coherency models. It is found that the ‘equal displacement’ rule is fairly accurate for cases when the fundamental period of the bridge is longer than the transition period between the acceleration‐controlled and velocity‐controlled ranges of the response spectrum. Otherwise, the rule is non‐conservative for cases with large ductility factors and conservative for cases with small ductility factors. Wave passage and incoherence tend to reduce ratios of mean peak inelastic to elastic pier drifts, whereas incorporation of the differential site‐response effect by locating piers on softer soils tends to increase the same ratios. Mild or moderate positive correlation between these ratios and ductility demands is observed in most cases. Effects of spatial variability are more pronounced for longer and stiffer bridges. Copyright © 2013 John Wiley & Sons, Ltd.     

Reverse flood and pollution routing with the lag-and-route model

ABSTRACT

Reverse routing can be used to transfer flood- or pollution-related information monitored at a downstream gauging station to an ungauged upstream cross-section. This signal identification problem is ill-posed and, as such, is sensitive to perturbations in the data to be inverted; therefore, the amplification of errors, e.g., those befalling measurements, must be controlled. Storage routing models are parsimonious diffusion wave substitutes and well suited for conversion to direct reverse routers. We present efficient inversion frameworks based on the lag-and-route (single reservoir plus exact reverse lag-step) and the reservoirs-in-series models. In both cases we invert a centred finite difference scheme of the reservoir storage balance equation that involves only one value of the unknown signal; signal values identified in previous reverse time steps, which would carry perturbations, are absent. This simple structure endows the reverse scheme with robustness. Procedures are verified with perfect and with error-seeded data; solution oscillations caused by the latter are damped by low-pass filtering. Both inverse routing models regain the upstream signals with high fidelity. Reverse storage routing is exemplified in a demonstration of reservoir control and in a field case of solute transport in a stream.

Editor M.C. Acreman; Associate editor X. Chen     

Time delays in the correlation between solar activity and the F2 region plasma frequency

The upper ionosphere electron density characterized by the critical frequency foF2 is correlated with solar activity when using monthly medians or averages from longer intervals. When shorter intervals are studied, time delays of different lengths in solar activity effects in the ionosphere are observed. The correlation between the foF2 values and the solar radiation intensity, given by the F10.7 index, is studied using the 1967–2003 data of mid-latitude ionosonde stations spaced at distances greater than 100° in geographical longitude. At which longitude the reaction of foF2 to the changes in solar activity appears sooner depends on the position of the interval studied in the 22-year solar cycle.     

Coherency analysis of accelerograms recorded by the UPSAR array during the 2004 Parkfield earthquake

Spatial variability of near‐fault strong motions recorded by the US Geological Survey Parkfield Seismograph Array (UPSAR) during the 2004 Parkfield (California) earthquake is investigated. Behavior of the lagged coherency for two horizontal and the vertical components is analyzed by separately examining the decay of coherency with frequency and distance. Assumptions, approximations, and challenges that are involved in estimation of the coherency from recorded data are presented in detail. Comparison of the UPSAR coherency estimates with coherency models that are commonly used in engineering practice sheds light on the advantages and limitations of different approaches to modeling the coherency, as well as on similarities and differences in the spatial variability exhibited by seismic ground motion arrays at different sites. Copyright © 2013 John Wiley & Sons, Ltd.     

A new GIS-compatible methodology for visibility analysis in digital surface models of earth sites

As a GIS tool,visibility analysis is used in many areas to evaluate both visible and non-visible places.Visibility analysis builds on a digital surface model describing the terrain morphology,including the position and shapes of all objects that can sometimes act as visibility barriers.However,some barriers,for example vegetation,may be permeable to a certain degree.Despite extensive research and use of visibility analysis in different areas,standard GIS tools do not take permeability into account.This article presents a new method to calculate visibility through partly permeable obstacles.The method is based on a quasi-Monte Carlo simulation with 100 iterations of visibility calculation.Each iteration result represents 1% of vegetation permeability,which can thus range from1% to 100% visibility behind vegetation obstacles.The main advantage of the method is greater accuracy of visibility results and easy implementation on any GIS software.The incorporation of the proposed method in GIS software would facilitate work in many fields,such as architecture,archaeology,radio communication,and the military.     

Regional non-hazardous landfill site selection by integrating fuzzy logic, AHP and geographic information systems

This study presents a geographic information systems-based multi-criteria site selection of non-hazardous regional landfill in Polog Region, Macedonia. The multi-criteria decision framework integrates legal requirements and physical constraints that relate to environmental and economic concerns and builds a hierarchy model for landfill suitability. The methodology is used for preliminary assessment of the most suitable landfill sites by combining fuzzy set theory and analytic hierarchy process (AHP). The fuzzy set theory is used to standardize criteria using different fuzzy membership functions while the AHP is used to establish the relative importance of the criteria. The AHP makes pairwise comparisons of relative importance between hierarchy elements grouped by environmental and economic decision criteria. The landfill suitability is achieved by applying weighted linear combination that uses a comparison matrix to aggregate different importance scenarios associated with environmental and economic objectives. The results from the study suggested that a least suitable landfill area of 1.0% from the total is generated when environmental and economic objectives are valued equally while a most suitable landfill area of 1.8% area is generated when the economic objective is valued higher. Such results are aimed for enhancement of regional landfill site selection in the country that is compliant with modern EU standards.