Influence of Mussel Culture on the Vertical Export of Phytoplankton Carbon in a Coastal Upwelling Embayment (Ría de Vigo,NW Iberia)

The goal of this paper is to find out whether suspended mussel culture affects the vertical fluxes of biogenic particles in the Ría de Vigo on a seasonal scale. With this aim, vertical fluxes of particulate organic carbon (POC) and the magnitude and composition of vertical export of phytoplankton carbon (Cphyto) collected in sediment traps were examined by comparing data obtained inside a mussel farming area (RaS) with those found at a reference station (ReS) not affected by mussels. Our results indicate that mussel farming has a strong impact on sedimentation fluxes under the rafts, not only increasing POC flux but also altering the magnitude and composition of Cphyto fluxes. Average POC flux at RaS (2564?±?1936 mg m^?2 day^?1) was four times higher than at ReS (731?±?276 mg m^?2 day^?1), and much of this increase was due to biodeposit fluxes (Cbiodep) which accounted for large proportion of POC flux (35–60 %). Indeed, because of this high Cbiodep flux, only a small proportion of the POC flux was due to Cphyto flux (3–12 %). At the same time, we observed an increased sedimentation of phytoplankton cells at RaS that could be explained by a combination of mechanisms: less energetic hydrodynamic conditions under mussel rafts, ballast effect by sinking mussel feces, and diatom aggregates. Moreover, mussel farming also altered the quality of the Cphyto flux by removing part of the predatory pressure of zooplankton and thus matching diatom composition in water column and sediment traps.     

Linear discriminant analysis to describe the relationship between rainfall and landslides in Bogotá, Colombia

Bogotá is located in the central Andean region of Colombia, which is frequently affected by landslide processes. These processes are mostly triggered during the rainy season in the city. This fact remarks the importance of determining what rain-derived parameters (e.g. intensity, antecedent rain, daily rain) are better related with the occurrence of landslides. For this purpose, the linear discriminant analysis (LDA), a technique derived from multivariate statistics, was used. The application of this type of analysis led to obtain simple mathematical functions that represent the probability of occurrence of landslides in Bogotá. The functions also allow to identify the most relevant variables derived from records of rainfall linked to the generation of landslides. A proof of concept using the proposed methodology was done using historic rainfall data from a 9-km² area of homogenous climatology and geomorphology in the south part of Bogotá. Landslides needed to be grouped for the LDA. Each one of these grouping categories represents landslides that occurred in similar geomorphologic conditions. Another set of events with no landslides was generated synthetically. Results of the proof of concept show that rainfall parameters such as normalized rainfall intensity I _MAP, normalized daily rainfall R _MAP and rainy-days normal RDN have the best statistical correlation with the landslides observed in the zone of analysis.     

The Juchatengo complex: an upper-level ophiolite assemblage of late Paleozoic age in Oaxaca,southern Mexico

International Journal of Earth Sciences - The Juchatengo complex (JC) suite is located between the Proterozoic Oaxacan complex to the north and the Xolapa complex to the south, and was amalgamated...     

Site scale modeling of slow-moving landslides,a 3D viscoplastic finite element modeling approach

This paper presents an advanced 3D numerical methodology to reproduce the kinematics of slow active landslides, more precisely, to reproduce the nearly constant strain rate (secondary creep) and the acceleration/deceleration of the moving mass due to hydrological changes. For this purpose, finite element analyses are performed in a large area covering a long time-span (12 years), in order to exhibit different interacting slope movements. First, we perform a stability analysis using the shear strength reduction (SSR) technique with a Mohr-Coulomb failure criteria. It is done in order to compute factors of safety (FS) and to identify two different scenarios, the first one being stable (FS > 1) and the second one being unstable (FS < 1). In the studied test case, the Portalet landslide (Central Spanish Pyrenees), the first scenario corresponds to an initial stable configuration of the slope and the second one to an unstable excavated configuration. Second, taking the first scenario as an initial condition, a time-dependent analysis is performed using a coupled formulation to model solid skeleton and pore fluids interaction, and a simplified ground water model that takes into account daily rainfall intensity. In this case, a viscoplastic constitutive model based on Perzyna’s theory is applied to reproduce soil viscous behavior and the delayed creep deformation due to the excavation. The fluidity parameter is calibrated to reproduce displacements measured by the monitoring systems. Our results demonstrate that 3D analyses are preferable to 2D ones for reproducing in a more realistic way the slide behavior. After calibration, the proposed model is able to simulate successfully short- and medium-term predictions during stages of primary and secondary creep.