Comparative analysis of a new assessment of the seismic risk of residential buildings of two districts of Barcelona

Natural Hazards - There are personal and institutional decisions that can increase the seismic resilience of the buildings in a city. However, some of these decisions are possible if we have basic...     

Metal levels in estuarine macrophytes: Differences among species

With the aim of studying the interspectific differences in the bioaccumulation of a series of elements in six species of estuarine macrophytes, we measured the concentrations of various metals (Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn), as well as C and N, in several species of macroalgae and one species of seagrass in estuaries in northwest Spain. To facilitate the interpretation of the results, we also determined the concentrations of the same metals in sediments. Contamination by particulate metal did not appear to be important. The levels of Cu in the different species were generally high in comparison with those found in similar studies; in contrast, the concentrations of Pb and Zn were relatively low. The metal concentrations showed greater variability and a distibution that was further from normal than those of C and N. In general the highest concentrations of elements were found inEnteromorpha spp. andZostera noltii, and the lowest occurred inUlva spp. There were several significant positive correlations among tissue concentrations of Cr, Cu, and Ni. There were also significant correlations between tissue concentrations of N and Zn, suggesting possible synergetic effects between them. Cluster analysis clearly revealed that the chemical composition ofZ. noltii differed from that of the macroalage. Macroalgae were not grouped according to their taxonomic position, therefore it appears that the concentrations of the elements depended more on the ecological traits of the macroalgal species rather than on any possible, physiological differences among different taxonomic groups. Of the species studied,Ascophyllum nodosum andEnteromorpha spp. appeared to be the best biomonitors of metal contamination.     

The 1997–1998 Activity of Volcán de Colima,Western Mexico: Some Aspects of the Associated Seismic Activity

Volcán de Colima, the most active volcano in Mexico, had a climactic episode on 20 November, 1998. On this date, a dome formed on the small summit crater during the previous few days, collapsed generating block-and-ash flows. The event was preceded by almost twelve months of seismic activity, which continued afterwards for several more months. We analyzed the main seismic activity, which occurred from 20 March, 1998 to 31 March, 1999. The seismicity was dominated by volcano-tectonic earthquakes before the climax, and subsequently by hybrid and long-period earthquakes. We determined the frequency of events for the entire period, and located most of the volcano-tectonic events. To assess the possibility that these earthquakes were generated by the same source, they were tested for their similitude through cross correlation in the time domain. Six groups of similar events, or earthquake families, were generated. The members of these families appeared before the 20 November event, apparently ceasing afterwards. We examined the location of the families' events with respect to an existing gravity model in which an anomalous body of negative density contrast suggests the presence of the magma chamber. Most of the family events occur on top of the anomalous body, which suggests they were associated with the passage of magma through the feeding conduits of the volcano.     

Geometric harnessing of precipitation records: reexamining four storms from Iowa City

Complex geometries often present in hydrologic data sets such as precipitation records have been difficult to model in their totality using classical stochastic methods. In recent years, we have developed extensions of a deterministic procedure, the fractal-multifractal (FM) method, whose patterns share fine details and textures of individual data sets in addition to the usual key statistical properties. This work discusses our latest efforts at encoding four geometrically distinct storms gathered in Iowa City with parameters found running a modified particle swarm optimization procedure. The results reaffirm the capabilities of the FM method as all storms are closely fitted within measurement errors. All sets may be encoded with a compression ratio exceeding 350:1, have a maximum error in cumulative distribution less than 2.5 %, and closely preserve the autocorrelation, power spectrum, and multifractal spectrum of the records.     

Medium-term assessment of the effects of the Prestige oil spill on estuarine benthic communities in Cantabria (Northern Spain, Bay of Biscay)

A specific monitoring program was implemented in the estuaries of Cantabria (northern Spain) in order to assess the medium-term effects (2003-2005) of the Prestige oil spill (POS) on benthic macroinvertebrate communities. A control-impact design was adopted, examining four unaffected and five oil-affected estuaries. High mortalities and significant differences in overall richness and diversity between the control and impacted estuaries were not detected. Some changes in the temporal evolution of species abundance were observed for some key species, but these could not be related to the spillage event. It was not possible to ensure that low magnitude effects had not occurred, due to the high range of natural variability of benthic communities, the confounding effects of other contamination sources and the absence of previous reference conditions.     

Is it possible to assess the ecological status of highly stressed natural estuarine environments using macroinvertebrates indices?

Several biotic indices have been proposed for the assessment of the ecological status of benthic macroinvertebrates in marine waters, although none have been generally accepted. When it comes to assessing highly stressed natural environments, such as estuaries, the controversy and uncertainty is much higher than for any given normal index. In this article, we test the behavior and suitability of different biotic indices proposed under the perspective of the Water Framework Directive (S, H, AMBI, M-AMBI, BQI, W-statistic, Taxonomic distinctness) for the assessment of estuaries in northern Spain. The low species richness and dominance of a few tolerant species in the characteristic community of these estuaries presented a challenge to the application of the biotic indices tested. Combined approaches that integrate different aspects of water quality and ecosystem functionality could increase the reliability of the ecological assessment of these transitional waters.     

An ecological classification of rocky shores at a regional scale: a predictive tool for management of conservation values

The ecological classification of coastal waters has become an important issue in ecosystem water quality assessment. Previous studies have suggested that abiotic variables seem to be a suitable alternative to biological data for classifying coastal areas at different scales. The study presented here proposes a downscaling methodology for the classification of coastal waters at a regional scale within the NE Atlantic based on standardized data and objective decision rules. Physical variables (temperature, wave exposure, tidal range and radiation) were selected because of their ecological role, availability and statistical decision rules. This information was based on satellite data and mathematical modelling of natural coastal processes. The N and NW Spanish coastline was subdivided into 41 20‐km segments that were classified according to physical variables using the self‐organizing map and k‐means algorithms. To validate the classification with biological data, 21 sites representing the entire range of physical typologies in the study area were simultaneously and consistently sampled. Intertidal macroalgae were identified in each of 10 quadrats of 50 × 50 cm for two to three transects per site, according to a stratified sampling procedure. The coverage of macroalgae was obtained by photographic analysis. The physical classification shows four typologies: Lower Rias, Upper Rias, West Cantabric and East Cantabric. Statistical analyses confirmed the ecological significance of these typologies at the tidal levels where seaweeds were the major structural element (lower and middle intertidal). According to the biological data, the greatest differences were found between the Upper Rias and the rest of the N and NW Iberian Peninsula coast. Thus, the classification methodology has potential application as a management tool.