Organotin levels in Nazaré canyon (west Iberian Margin, NE Atlantic) and adjacent coastal area

Organotin compounds (OTs) are ubiquitous in the marine environment and high concentrations (μg g(-1) range) in sediments from different coastal areas around the world have been reported. However, few reports have described the OTs contamination status in the offshore and deep sea environment. This work investigated organotin levels in Nazaré canyon for the first time. Levels of monobutyltin (MBT), dibutyltin (DBT), tributyltin (TBT), diphenyltin (DPT), triphenyltin (TPT), dioctyltin (DOT) and trioctyltin (TOT) were quantified in sediment samples from the upper flanks of the canyon and from the adjacent coastal area. TBT levels detected in the canyon flanks are about two to three orders of magnitude lower than those found in the coastal area. Nevertheless, when quantifiable, TBT levels in the canyon samples were higher than the Environmental Assessment Criteria set for TBT in sediments by the OSPAR Commission indicating that at those locations negative ecological impacts are likely to occur.     

Probabilistic landslide risk analysis considering direct costs in the area north of Lisbon (Portugal)

The purpose of the present study is the analysis of landslide risk for roads and buildings in a small test site (20 km²) in the area north of Lisbon (Portugal). For this purpose, an evaluation is performed integrating into a GIS information obtained from multiple sources: (i) landslide hazard; (ii) elements at risk; and (iii) vulnerability. Landslide hazard is assessed on a probabilistic basis for three different types of slope movement (shallow translational slides, translational slides and rotational slides), based on some assumptions such as: (i) the likelihood of future landslide occurrence can be measured through statistical relationships between past landslide distribution and specified spatial data sets considered as landslide predisposing factors; and (ii) the rainfall combination (amount–duration) responsible for past slope instability within the test site will produce the same effects (i.e. same type of landslides and similar total affected area), each time they occur in the future. When the return period of rainfall triggering events is known, different scenarios can be modelled, each one ascribed to a specific return period. Therefore, landslide hazard is quantitatively assessed on a raster basis, and is expressed as the probability for each pixel (25 m²) to be affected by a future landslide, considering a rainfall triggering scenario with a specific return period. Elements at risk within the test site include 2561 buildings and roads amounting to 169 km. Values attributed to elements at risk were defined considering reconstruction costs, following the guidelines of the Portuguese Insurance Institute. Vulnerability is considered as the degree of loss to a given element resulting from the occurrence of a landslide of a given magnitude. Vulnerability depends not only on structural properties of exposed elements, but also on the type of process, and its magnitude; i.e., vulnerability cannot be defined in absolute terms, but only with respect to a specific process (e.g. vulnerability to shallow translational slides). Therefore, vulnerability was classified for the three landslide groups considered on hazard assessment, taking into account: (i) landslide magnitude (mean depth, volume, velocity); (ii) damage levels produced by past landslide events in the study area; and (iii) literature. Finally, a landslide risk analysis considering direct costs was made in an automatic way crossing the following three layers: (i) Probabilistic hazard map for a landslide type Z, considering a particular rainfall triggering scenario whose return period is known; (ii) Vulnerability map (values from 0 to 1) of the exposed elements to landslide type Z; and (iii) Value map of the exposed elements, considering reconstruction costs.     

Contourites in the Gulf of Cadiz: a cautionary note on potentially ambiguous indicators of bottom current velocity

Facies associations in cores collected in the deep part of the Gulf of Cadiz, which is under the influence of the lower branch of the Mediterranean Outflow Water, are investigated in terms of the classical contourite model using grain-size analyses and thin sections of indurated sediment. Cores include both low-energy (contourite drift) and high-energy (channel) environments. The thin sections and grain-size distributions show that clayey fine silts and sandy coarse silts are the most common facies associations in the studied contourite sequences, while coarse-grained, gravelly contourites are less common. Grain-size distributions are unimodal in the fine-grained and bi- or trimodal in the coarser-grained contourites. This change in grain-size composition is related both to the partial removal of the fine-grained fraction and to the replenishment of the coarser-grained one. In addition, most of the contacts between individual facies are sharp rather than transitional. This suggests that the contourite sequence is only in part related to changes in bottom current velocity and flow competency, but may also be related to the supply of a coarser terrigeneous particle stock, provided by either increased erosion of indurated mud along the flanks of confined contourite channels (mud clasts), or by increased sediment supply by rivers (quartz grains) and downslope mass transport on the continental shelf and upper slope. The classical contourite facies association may therefore not be solely controlled by current velocity, but may be the product of a variety of depositional histories. The classical contourite depositional sequence should therefore be interpreted with greater care and in the light of the regional sedimentological background. In addition, the wisdom of exclusively using mean or modal particle size for the interpretation of depositional contourite processes is questioned. Instead, it is proposed that the vertical evolution of grain-size populations in the facies successions forming contourite sequences be assessed.     

Spatial and temporal variability of seawater properties,current velocity and SPM concentration off Cassino Beach-Rio Grande-Southern Brazil

Water column profiles and near-bed time series of pressure, current velocity, suspended-particulate matter (SPM) concentration and seawater temperature and salinity were collected during three short cruises carried out in May 2005 in the shoreface and inner shelf area adjacent to Cassino Beach, southern Brazil. The measurements were part of the Cassino Experiment, a project conducted at an open, sandy coastal area known for the occurrence of patches of fairly large amounts of muddy sediments that are sporadically fluidized, transported onshore and eventually stranded on the beach. The study area is close to the Patos Lagoon mouth, being influenced by its water and suspended-sediment discharge. The presence of the Patos Lagoon outflow on the inner shelf was detected in one of the cruises (May 13) through measurements of near-surface salinity: while close to shore salinity was 29.4, a minimum value of 13.8 was measured at ∼10 km from the coast. Four days later, no trace of the plume was detected in the area. Regarding seawater temperature, no large temporal or spatial variability was documented with measured values ranging from 19.3 to 20 °C. Water column currents were prominently to N and NE, except at the outermost station, located ∼42 km from the coast, where NW-directed flows were observed at surface and mid-depth. Maximum near-bed current velocity oscillated between 18 and 42 cm s⁻¹ in the east–west direction and between 14 and 42 cm s⁻¹ in the north–south direction. Near-surface concentration of SPM oscillated between 11 and 99 mg L⁻¹, in general one order of magnitude lower than near-bed values. However, near-bed concentration of SPM showed large spatial variability: the highest value (2200 mg L⁻¹) was yielded by a water sample collected at ∼8 m water depth, at a station located ∼2 km away from the shoreline; two water samples collected 500 m, apart from this station, yielded SPM concentrations of 148 and 205 mg L⁻¹, one order of magnitude lower. Spectral analyses of near-bed current speed and SPM concentration indicate the relevance of oscillations in the low-frequency (<0.05 Hz) range. Detailed sampling of bottom sediment indicated that in May 2005 the mud patch was centered at ∼8.5 m water depth.     

Sediment depth and habitat as predictors of the diversity and composition of sediment bacterial communities in an inter‐tidal estuarine environment

Saltmarshes, seagrass meadows and mudflats are key habitats in estuarine ecosystems. Despite being involved in key ecological processes, the influence of different estuarine habitats on sediment bacterial communities remains understudied. Few studies have analysed and compared the bacterial communities of more than one estuarine habitat at different depths. Here, we investigated to what extent different habitats (mudflats; mono‐specific plots of seagrass [Zostera noltei] and two saltmarsh plants [Juncus maritimus and Spartina maritima]) and sampling depth (0, 5, 10 cm) influence variation in sediment bacterial composition. Our results showed significant differences in the abundance of selected higher taxa amongst habitats and depths. Surface sediment was characterized by bacteria assigned to the Acidimicrobiia, Flavobacteriia, Thiotrichales, Alteromonadales and Rhodobacterales, whereas in deeper sediment Deltaproteobacteria and Anaerolineae were dominant. Juncus sediment, in turn, presented the most distinct bacterial community, with Myxococcales abundant in this habitat. Sampling depth and habitat proved significant predictors of variation in sediment bacterial composition. The compositional dissimilarities amongst habitats and depths suggest functional divergence and complementarity, thus enhancing ecosystem functioning and health. Given the compositionally distinct communities found in different habitats and depths, our study corroborates the importance of conserving a diverse array of estuarine habitats.     

Evaluation of community leaders’ perception regarding Alerta Rio,the warning system for landslides caused by heavy rains in Rio de Janeiro

Warning systems help reduce damage and save lives in disasters; however, there is a lack of research analyzing the population perception of these systems. In Rio de Janeiro (Brazil), because the city slums face the risk of landslides caused by heavy rains, a siren early warning system named “Alerta Rio” was installed in 102 areas. The purpose of this paper was to understand the perception of community leaders regarding this alert system. To this end, a survey was conducted with community leaders to collect data on whether and why the public do or do not attend to the alert. Results indicated that (1) public adherence to Alerta Rio is low despite the generally positive view of the system, (2) local violence was reported as the reason for staying at home to protect one’s property, and (3) problems with temporary shelters and the routes to them result in lack of people’s involvement in the system. Whereas these factors are similar to population perception regarding other warning systems, the community leaders also raised the public’s lack of trust in the city hall’s adopted concept of risk and in the politicians as a relevant factor in the population perception of Alerta Rio. These factors, together with the lack of prevention policies complementary with the alert system, led to perception of reduced importance of the system. For potential solutions to enhance alarm compliance, this study recommends improvement in communication, educational programs, and public engagement strategies tailored for each target group.     

The Role of Groundwater for Lake‐Water Quality and Quantification of N Seepage

The heterogeneous nature of both groundwater discharge to a lake (inflow) and nitrate concentrations in groundwater can lead to significant errors in calculations of nutrient loading. Therefore, an integrated approach, combining groundwater flow and transport modelling with observed nitrate and ammonium groundwater concentrations, was used to estimate nitrate loading from a catchment via groundwater to an oligotrophic flow‐through lake (Lake Hampen, Denmark). The transport model was calibrated against three vertical nitrate profiles from multi‐level wells and 17 shallow wells bordering a crop field near the lake. Nitrate concentrations in groundwater discharging to the lake from the crop field were on average 70 times higher than in groundwater from forested areas. The crop field was responsible for 96% of the total nitrate loading (16.2 t NO₃/year) to the lake even though the field only covered 4.5% of the catchment area. Consequently, a small change in land use in the catchment will have a large effect on the lake nutrient balance and possible lake restoration. The study is the first known attempt to estimate the decrease of nitrate loading via groundwater to a seepage lake when an identified catchment source (a crop field) is removed.     

The Extended Delaunay Method Applied to First Order Resonance

This paper is concerned with the extended Delaunay method as well as the method of integration of the equations, applied to first order resonance. The equations of the transformation of the extended Delaunay method are analyzed in the (p + 1)/p type resonance in order to build formal, analytical solutions for the resonant problem with more than one degree of freedom. With this it is possible to gain a better insight into the method, opening the possibility for more generalized applications. A first order resonance in the first approximation is carried out, giving a better comprehension of the method, including showing how to eliminate the ‘Poincaré singularity’ in the higher orders. This revised version was published online in July 2006 with corrections to the Cover Date.