Flash flood occurrence and magnitude assessment in an alluvial fan context: the October 2011 event in the Southern Apennines

Natural Hazards - This study presents the analysis of flash floods triggered by an extreme rainfall event that occurred on 7 October, 2011, over the Marzano carbonate massif (Southern Apennines)....     

In situ high-temperature X-ray and neutron powder diffraction study of cation partitioning in synthetic Mg(Fe<Subscript>0.5</Subscript>Al<Subscript>0.5</Subscript>)<Subscript>2</Subscript>O<Subscript>4</Subscript> spinel

The intra-crystalline cation partitioning over T- and M-sites in a synthetic Mg(Fe,Al)₂O₄ spinel sample has been determined as a function of temperature by Rietveld structure refinements from powder diffraction data, combining in situ high-temperature neutron powder diffraction (NPD; POLARIS diffractometer, at ISIS, Rutherford Appleton Laboratory, UK), to determine the Mg and Al occupancy factors, with in situ high-temperature X-ray powder diffraction, to fix the Fe³⁺ distribution. The results obtained agree with a two-stage reaction, in which an initial exchange between Fe³⁺ and Mg, the former leaving and the latter entering tetrahedral sites, is successively followed by a rearrangement involving also Al. The measured cation distribution has then been compared and discussed with that calculated by the Maximum Configuration Entropy principle, for which only NPD patterns have been used. The cation partitioning has finally been interpreted in the light of the configuration model of O’Neill and Navrotsky.     

Late quaternary tephra layers along the Cilento coastline (southern Italy)

The results of stratigraphic and tephrostratigraphic analyses of several pyroclastic levels, collected along the coastal sector of the Cilento region (southern Italy), are presented. Some of these levels are here described for the fist time, others, already known in literature, were reconsidered in order to better understand their stratigraphic position and to point out the possible volcanic sources.     

On the incipient formation of bars and channels on alluvial fans

The morphodynamics of topographic expansion has been recently investigated both experimentally, by Sittoni et al., (2014) Shaw et al., (2018), and numerically Sittoni et al., 2014. Here, we study the basic mechanism that governs the evolution of topographic and expansions and explore the instability of the bottom topography under conditions of steady but spatially expanding flow. We model the expanding flow via a by configuration where water and sediments are supplied from a central hole and flow on a cone shaped surface confined by lateral walls. The governing equations are the shallow-water equations coupled with the Exner equation, written in cylindrical coordinates. We initially approach the problem analytically by considering the conditions required for the basic state, consisting of a pure radial flow and bottom profile, to lose stability to small amplitude perturbations. This analysis suggests that more than one mode may be unstable, encouraging us to extend the analysis to the nonlinear regime. We do this through numerical modeling of the full governing equations, which allows us to predict the establishment of a bar pattern whose features are similar to those experimentally observed. Two prominent features of the finite-amplitude bar pattern are (1) bar apices are distributed at a radial distance from the inflow consistent with work of Shaw et al. (2018); and (2) that the flow aspect ratio of the interbar areas remain high without provoking further instability. Both features imply that in general expansion acts to reduce bar development relative to an equivalent rectilinear flow. © 2019 John Wiley & Sons,  Ltd.     

Microphytobenthic primary production as C uptake in sublittoral sediments of the Gulf of Trieste (northern Adriatic Sea): Methodological aspects and data analyses

From January 2003 to December 2004 microphytobenthic primary production was estimated both from in situ (MPPs) and in the laboratory (MPPp) ¹⁴C-incubation of slurries collected in a coastal site of the Gulf of Trieste (northern Adriatic Sea). MPPs values varied from −7.54 ± 3.12 to 34.59 ± 7.66 mg C m⁻² h⁻¹ over the whole period. The lowest MPPs were observed in November 2003 and August 2004, while the highest MPPs in July 2003 and May 2004, in correspondence with high PAR at the bottom. Significant correlations between MPPs and the microphytobenthic biomass (BIOM) (r = 0.75, p < 0.001), between MPPs and PAR at the bottom (r = 0.54, p < 0.01) and between MPPs and OXY (r = 0.50, p < 0.05) were revealed. MPPp values were higher than MPPs ones in 15 out of 23 observations, with the highest MPPp recorded in July 2003. At 17 m depth a seasonal pattern of sampling months was revealed by the cluster analysis. The role of abiotic parameters in determining this seasonal pattern was highlighted by the PCA, with the first axis correlated with MPPs and PAR, and the second one with temperature. Applying the fuzzy sets it resulted that spring months showed a higher degree of membership with MPPs, summer months with temperature and autumn–winter months with OXY. The microphytobenthic community did not seem to be photosynthetically active throughout the study period. From August–September to December low or negative MPPs values were recorded. We infer that during these months a shift from the autotrophic to heterotrophic metabolism of the benthic microalgae occurred in correspondence with low PAR and/or high temperature at the bottom. Despite the progressive lowering of the trophy of the study area occurred during the last 20 years, we found higher primary production values than those estimated two decades earlier.     

Ecological status in the Ligurian Sea: the effect of coastline urbanisation and the importance of proper reference sites

The assessment of the ecological status, as required by the Water Framework Directive (WFD), plays an important role in coastal zone management, but only a small number of ecological indices are applicable on rocky bottoms. In this study, we apply a previously defined ecological quality index based on the cartography of littoral and upper-sublittoral rocky-shore communities (CARLIT), based on the sensitivity of algae dominated communities to anthropogenic impacts along a moderate urban gradient. We also apply this index in four Marine Protected Areas (MPAs), proposed as reference sites at a regional scale. After comparing the outputs with water variables and other quality indices, we can affirm that (1) the CARLIT index is suitable to detect different kinds of anthropogenic pressures, that (2) the choice of proper reference sites is a focal point in the fulfilment of the WFD (Water Framework Directive) and that (3) historical data are important to define reference conditions and the degradation of ecological status.     

Flood Hazard Assessment for a Hyper-Tidal Estuary as a Function of Tide-Surge-Morphology Interaction

Astronomical high tides and meteorological storm surges present a combined flood hazard to communities and infrastructure. There is a need to incorporate the impact of tide-surge interaction and the spatial and temporal variability of the combined flood hazard in flood risk assessments, especially in hyper-tidal estuaries where the consequences of tide and storm surge concurrence can be catastrophic. Delft3D-FLOW is used to assess up-estuary variability in extreme water levels for a range of historical events of different severity within the Severn Estuary, southwest England as an example. The influence of the following on flood hazard is investigated: (i) event severity, (ii) timing of the peak of a storm surge relative to tidal high water and (iii) the temporal distribution of the storm surge component (here in termed the surge skewness). Results show when modelling a local area event severity is most important control on flood hazard. Tide-surge concurrence increases flood hazard throughout the estuary. Positive surge skewness can result in a greater variability of extreme water levels and residual surge component, the effects of which are magnified up-estuary by estuarine geometry to exacerbate flood hazard. The concepts and methodology shown here can be applied to other estuaries worldwide.     

Spatial and temporal variation of biomarkers in mussels (Mytilus galloprovincialis) from the Lagoon of Venice, Italy

A multiple biomarker approach was adopted in a seasonal study carried out in the Lagoon of Venice, with the double aim of evaluating the natural and anthropic stresses influencing the biological responses of mussel (Mytilus galloprovincialis) and of assessing the effects due to spatial rather than temporal variations.Biochemical (aldehyde dehydrogenase and catalase activities), cellular (neutral red retention time) and physiological (survival in air and condition index) biomarkers were determined in mussels collected in four differently impacted lagoon areas.Multivariate analysis showed that samples were distributed mainly according to temperature and four seasonal groups were identified. The combination of spatial and temporal information enabled us to distinguish physiological variations due to natural causes from those due to anthropic stress, and to identify the sampling period when several biomarkers are less influenced by both natural and endogenous factors.     

Spatial and temporal variation of biomarkers in mussels (Mytilus galloprovincialis) from the Lagoon of Venice, Italy

A multiple biomarker approach was adopted in a seasonal study carried out in the Lagoon of Venice, with the double aim of evaluating the natural and anthropic stresses influencing the biological responses of mussel (Mytilus galloprovincialis) and of assessing the effects due to spatial rather than temporal variations. Biochemical (aldehyde dehydrogenase and catalase activities), cellular (neutral red retention time) and physiological (survival in air and condition index) biomarkers were determined in mussels collected in four differently impacted lagoon areas. Multivariate analysis showed that samples were distributed mainly according to temperature and four seasonal groups were identified. The combination of spatial and temporal information enabled us to distinguish physiological variations due to natural causes from those due to anthropic stress, and to identify the sampling period when several biomarkers are less influenced by both natural and endogenous factors.