Changes in cetacean presence,relative abundance and distribution over 20 years along a trans‐regional fixed line transect in the Central Tyrrhenian Sea

From 1989 to 1992, systematic cetacean surveys were carried out twice weekly along a trans‐regional fixed transect in the Central Tyrrhenian Sea, utilising passenger ferries as research platforms. Using the same protocol and supervised by the same investigators, the research restarted in 2007, providing the opportunity to compare consistent data over a long 20‐year period. The monitored transect (Civitavecchia‐Golfo Aranci) runs along a strategic area just outside the southeastern border of the Pelagos Sanctuary. Over the last two decades, an increasing trend of temperature and salinity, in the deep and intermediate layers, has been documented in the region, as well as general changes over the Mediterranean basin. These changes, together with the increasing impact of some pressures (e.g. maritime traffic) may have led to changes in oceanographic and anthropogenic features and, subsequently, in cetacean presence and distribution. The research aimed to verify whether any changes occurred in the pattern of cetacean occurrence over the 20‐year period along the representative transect in the Central Tyrrhenian Sea. Data from 90 summer weekly runs undertaken in the 1990s were compared with data obtained from 95 runs undertaken in the 2000s. Each ferry run was considered an independent statistical unit: the encounter rate (ER = number of sightings per hour spent on effort) was calculated to compare relative abundance between periods, years and months. Spatial analysis was performed on geographical data using Kernel analysis to map the distribution of sightings. Logistic regression (GLM) was performed to compare habitat preference. Total encounter rate in the 1990s (ER = 0.59 ± CI 0.08) was significantly lower (P < 0.01) compared with the 2000s (ER = 0.94 ± CI 0.15). The same seven out of eight species known for their regular presence in the Mediterranean Sea were sighted in both the investigated periods. The most common species were striped dolphin (Stenella coeruleoalba), fin whale (Balaenoptera physalus) and common bottlenose dolphin (Tursiops truncatus). Neither the pilot whale nor any other rare or occasional species were sighted during the 6 years of the study. Despite the time span, no dramatic changes were observed for any species, bar fin whale, in terms of distribution, relative abundance, group size or habitat preference. Sightings of fin whale have surprisingly increased (+300%, P< 0.001), and their spatial and temporal distribution and habitat preference showed a radical difference between the two periods. The 2000s surveys confirmed the existence of high density areas of cetaceans, especially of fin whale, and the consequent necessity of specific legislative acts for cetacean conservation.     

Sensitivity analysis of CDOM spectral slope in artificial and natural samples: an application in the central eastern Mediterranean Basin

In the past two decades, optical properties of chromophoric dissolved organic matter (CDOM) in marine environments have been extensively studied. Many of these studies report CDOM properties for the offshore environment where this complex mixture of optically active compounds is strongly diluted. Nevertheless, autochthonous and allochthonous sources have been identified and sinks related to photodegradation and bacterial activity have been demonstrated. The calculation of the spectral slope of the CDOM absorption curve has been proven to be useful and is often reported. However, a rigorous uncertainty analysis of the slope calculation is rarely reported. In this paper, we propose a method to evaluate the uncertainty of CDOM spectral slope calculated between 270 and 400 nm, using both naturally sampled and artificial solutions. We use these results to study the ultra-oligotrophic waters of the Mediterranean Sea (central eastern basin), where little is known about CDOM spatial distribution. We show that dilutions of both artificial and natural samples produce a Gaussian distribution of spectral slopes, indicating that consistent values may be determined, with a typical uncertainty of ±0.0004 nm⁻¹ when absorption at 300 nm was greater then 0.1 m⁻¹ (0.1 m pathlength). Comparing the distribution of spectral slopes from central eastern basin samples to a Gaussian distribution, we show differences between measurements that were significantly different. These values allow us to distinguish possible sources (algal derived CDOM), sinks (e.g. photo-bleaching) at different depths. We propose a subdivision of CDOM compounds into refractory and semilabile/refractory pools and evaluate the CDOM spectral slope of algal derived CDOM released at or near deep chlorophyll maximum.     

Shaking‐table tests of flat‐bottom circular silos containing grain‐like material

According to Eurocode 8, the seismic design of flat‐bottom circular silos containing grain‐like material is based on a rough estimate of the inertial force imposed on the structure by the ensiled content during an earthquake: 80% of the mass of the content multiplied by the peak ground acceleration. A recent analytical consideration of the horizontal shear force mobilised within the ensiled material during an earthquake proposed by some of the authors has resulted in a radically reduced estimate of this load suggesting that, in practice, the effective mass of the content is significantly less than that specified. This paper describes a series of laboratory tests that featured shaking table and a silo model, which were conducted in order to obtain some experimental data to verify the proposed theoretical formulations and to compare with the established code provisions. Several tests have been performed with different heights of ensiled material – about 0.5 mm diameter Ballotini glass – and different magnitudes of grain–wall friction. The results indicate that in all cases, the effective mass is indeed lower than the Eurocode specification, suggesting that the specification is overly conservative, and that the wall–grain friction coefficient strongly affects the overturning moment at the silo base. At peak ground accelerations up to around 0.35 g, the proposed analytical formulation provides an improved estimate of the inertial force imposed on such structures by their contents. Copyright © 2015 John Wiley & Sons, Ltd.     

Rainfall-induced shallow landslides: a model for the triggering mechanism of some case studies in Northern Italy

The article relates the main findings of a recent investigation aimed at modeling the triggering of shallow landslides. A simplified model for assessing the safety factor of potentially unstable slopes, directly related with rainfall trends, was developed. Based on the geometric characteristics of the slope, the geotechnical properties, and strength parameters of the soil, the model makes it possible to define a safety factor of a slope as a function of time. The model is based on the limit equilibrium method and takes into account the seepage of underground water. The safety factor is, in turn, related to the seasonal rainfall. The model was applied on a local scale to some historical cases which had occurred recently in Northern Italy. The paper shows how the results of the application of the model on a local scale achieve a good agreement between the instability condition and the real date of each considered event.     

Population distribution and urban growth in Southern Italy, 1871–2011: emergent polycentrism or path-dependent monocentricity?

This study assesses changes in population distribution and the expansion of urban settlements in Southern Italy between 1871 and 2011. Four demographic phases are identified: (i) spatially balanced, mild population growth (1871–1921); (ii) moderate population increase concentrated in coastal and lowland areas (1921–1951); (iii) rapid and diffused population growth (1951–1981); and (iv) population stability with settlement dispersion (1981–2011). While urban growth in the years preceding the 1980s reinforced the polarization in rich and poor areas along the urban-to-rural gradient, since the early 1990s both urban and rural areas showed population dynamics that consolidated low-density settlements scattered around the largest cities. This path, however, does not reflect the evolution towards a more spatially balanced urban development, as observed in other European regions. Causes and consequences of the persistence of a fragmented urban hierarchy with dense settlements and sprawl concentrated around the main cities are finally discussed.     

Analysis and modelling of rainfall fields at different resolutions in southern Italy

Abstract

The spatial and temporal variability of the scaling properties and correlation structure of a data set of rainfall time series, aggregated over different temporal resolutions, and observed in 70 raingauges across the Basilicata and Calabria regions of southern Italy, is investigated. Two types of random cascade model, namely canonical and microcanonical models, were used for each raingauge and selected season. For both models, different hypotheses concerning dependency of parameters on time scale and rainfall height can be adopted. In particular, a new approach is proposed which consists of several combinations of models with a different scale dependence of parameters for different temporal resolutions. The goal is to improve the modelling of the main features of rainfall time series, especially for cases where the variability of rainfall changes irregularly with temporal aggregation. The results obtained with the new methodology showed good agreement with the observed data, in particular, for the summer months. In fact, during this season, rainfall heights aggregated at fine temporal resolutions (from 5 to 20 min) are more similar (relative to the winter season) to the values cumulated on 1 or 3 h (due to convective phenomena) and, consequently, the process of rainfall breakdown is nearly stationary for a range of finer temporal resolutions.

Editor D. Koutsoyiannis; Associate editor A. Montanari     

ESEEM of industrial quartz powders: insights into crystal chemistry of Al defects

A set of raw industrial materials, that is, pure quartz and quartz-rich mixtures, were investigated through electron paramagnetic resonance and electron spin echo-envelope modulation spectroscopies, with the aim of evaluating the effective role played by defect centres and of assessing whether they can be used to monitor changes in the physical properties of quartz powders with reference to their health effects. The obtained results point to two interactions of the Al defect centres with H⁺, hosted in sites within the channels parallel and perpendicular to the c axis of quartz, respectively. These two Al/H⁺ (h_Al) centres exhibit a weak chemical bond, and their relative amounts appear to be modified/controlled by the thermo-mechanical processes underwent by powders. Indeed, a mechanically promoted inter-conversion between the two kinds of site is suggested. As a consequence, the h_Al centres are effective in monitoring even modest activations of powders, through thermal or mechanical processes, and they are also supposed to play a specific, relevant role in quartz reactivity during the considered industrial processes.     

Numerical modelling of installation effects for diaphragm walls in sand

The scopes of this work are to study the mechanisms of load transfer and the deformations of the ground during slurry trenching and concreting in dry sand and to evaluate their effects on service structural loads, wall deflections and ground displacements behind the wall caused by subsequent excavation. A series of three-dimensional finite element analyses was carried out modelling the installation of diaphragm walls consisting of panels of different length. The soil was modelled as either linearly elastic-perfectly plastic or incrementally non-linear (hypoplastic) with elastic strain range. Plane strain analyses of diaphragm walls of identical cross section were also carried out in which wall installation was either modelled or the wall was wished in place (WIP). The analyses predict ground movements consistent with the experimental observations both in magnitude and trend. The results also show that the maximum horizontal wall deflections and structural loads reduce with increasing panel aspect ratio towards a minimum which is about twice the value computed for WIP analyses. Panel aspect ratios should be larger than about three to take advantage of the three-dimensional effects. The pattern and magnitude of surface vertical displacements obtained from linearly elastic-perfectly plastic analyses, no matter whether three- or two-dimensional, are unrealistic.     

Erosion rates and mechanisms of knickzone retreat inferred from 10Be measured across strong climate gradients on the northern and central Andes Western Escarpment

A steep escarpment edge, deep gorges and distinct knickzones in river profiles characterize the landscape on the Western Escarpment of the Andes between ~5°S and ~18°S (northern Peru to northern Chile). Strong north–south and east–west precipitation gradients are exploited in order to determine how climate affects denudation rates in three river basins spanning an otherwise relatively uniform geologic and geomorphologic setting. Late Miocene tectonics uplifted the Meseta/Altiplano plateau (~3000 m a.s.l.), which is underlain by a series of Tertiary volcanic‐volcanoclastic rocks. Streams on this plateau remain graded to the Late Miocene base level. Below the rim of the Meseta, streams have responded to this ramp uplift by incising deeply into fractured Mesozoic rocks via a series of steep, headward retreating knickzones that grade to the present‐day base level defined by the Pacific Ocean. It is found that the Tertiary units on the plateau function as cap‐rocks, which aid in the parallel retreat of the sharp escarpment edge and upper knickzone tips. ¹⁰Be‐derived catchment denudation rates of the Rio Piura (5°S), Rio Pisco (13°S) and Rio Lluta (18°S) average ~10 mm ky^?1 on the Meseta/Altiplano, irrespective of precipitation rates; whereas, downstream of the escarpment edge, denudation rates range from 10 mm ky^?1 to 250 mm ky^?1 and correlate positively with precipitation rates, but show no strong correlation with hillslope angles or channel steepness. These relationships are explained by the presence of a cap‐rock and climate‐driven fluvial incision that steepens hillslopes to near‐threshold conditions. Since escarpment retreat and the precipitation pattern were established at least in the Miocene, it is speculated that the present‐day distribution of morphology and denudation rates has probably remained largely unchanged during the past several millions of years as the knickzones have propagated headward into the plateau. Copyright © 2011 John Wiley & Sons, Ltd.