Early warning system for rainfall-triggered landslides based on real-time probabilistic hazard assessment

Natural Hazards - A methodology to define rainfall-landslide thresholds, using a probabilistic model in which the accumulated rainfall at any time is treated as a random variable, is proposed. The...     

The Intertidal Burrowing Crab <Emphasis Type="Italic">Neohelice</Emphasis> (=<Emphasis Type="Italic">Chasmagnathus</Emphasis>) <Emphasis Type="Italic">granulata</Emphasis> Positively Affects Foraging of Rodents in South Western Atlantic Salt Marshes

The role of positive and indirect interactions is often crucial in communities with intense abiotic stress such as salt marshes. The burrowing crab, Neohelice (=Chasmagnathus) granulata, is the dominant benthic macroinvertebrate of southwest Atlantic marshes (southern Brazil to Northern Argentinean Patagonia), having strong direct and indirect effects on marsh soil and, in consequence, on marsh vegetation and primary consumers. In this work, we investigate if this crab indirectly modifies habitat use by the granivorous rodents, Akodon azarae and Oligoryzomys flavescens, by increasing nutrient availability and thus enhancing seed production by the marsh plant Spartina densiflora. The study was conducted at the Mar Chiquita Coastal Lagoon, Argentina (37°32′ S). Rodent frequencies in S. densiflora were positively correlated with crab densities throughout the low and middle marsh. Additionally, the highest quality of S. densiflora and inflorescence density was recorded at the highest crab densities. Experimental manipulation of crab densities shows that N. granulata indirectly enhances the performance of S. densiflora (e.g., decreased fiber content and C/N ratios) and increases density of seeds. Moreover, N. granulata also facilitates S. densiflora seed availability to rodents by concentrating them in sediment mound at their burrows entrances. Experimental rodent exclusions showed that rodent species used S. densiflora seeds, a variable positively related to crab burrow density. Thus, our results show that N. granulata drives the granivorous rodent distribution and the intensity of seeds–rodent interaction trough facilitative and indirect interactions in marsh community.     

The Southwest Atlantic intertidal burrowing crab Neohelice granulata modifies nutrient loads of phreatic waters entering coastal area

Along the coastal areas of the Southwest Atlantic estuaries and embayments, phreatic water often circulates through very extended areas (up to several hundred meters perpendicular to the coast), dominated by dense assemblages of deep burrows of the crab Neohelice granulata (formerly Chasmagnathus granulatus). This crab inhabits the intertidal area, from mudflats to marshes vegetated by species of Spartina, Sarcocornia and Juncus, generating extensive burrowing beds where burrow density may reach up to 60 burrows m⁻². Since the lower limit of the crab burrows is usually the water table, we investigated through field experiments the effect of N. granulata and their burrows on the chemical characteristics of this phreatic water. Water analysis from experimental (1) occupied burrows (with crabs), (2) unoccupied burrows (where crabs were excluded), and (3) sediment pore water show remarkable differences. Water oxygenation, and nitrate, ammonium and sulphate concentrations inside occupied burrows were higher than in the water inside unoccupied burrows or pore waters. Moreover, directed sampling of phreatic water entering and leaving the crab bed, shows that dissolved inorganic nitrogen concentration is enhanced as the water crosses the crab bed. These results may be ascribed to the fact that in the salt marsh the crabs spend most of their time within burrows, where presumably they store food (plants) and defecate. These activities generate an area of accumulation of excrements and nutrients in different decomposition states. The present work shows a novel way by which bioturbating organisms can affect nutrients exportation from salt marshes to the open waters.     

Fundamental frequency of tapered plates by the method of eigensensitivity analysis

The fundamental frequency of a rectangular isotropic plate having a linear thickness variation is computed using the method of eigensensitivity analysis. The approach incorporates eigen derivatives to evaluate a Maclaurin series representation of the desired eigenvalue, here the fundamental frequency. Comparison with published results, for various taper ratios, aspect ratios, and support conditions, demonstrates the accuracy and utility of the expression and methodology.     

Predicting the optical properties of the West Florida Shelf: resolving the potential impacts of a terrestrial boundary condition on the distribution of colored dissolved and particulate matter

Predicting the distribution of Inherent Optical Properties (IOPs) in the water column requires predicting the physical, chemical, biological, and optical interactions in a common framework that facilitates feedback responses. This work focuses on the development of ecological and optical interaction equations embedded in a 2D hindcast model of the shallow water optical properties on the West Florida Shelf (WFS) during late summer/fall of 1998. This 2D simulation of the WFS includes one case with a Loop Current intrusion above the 40-m isobath and one with the Loop Current intrusion in addition to a periodic terrestrial nutrient supply below the 10-m isobath. The ecological and optical interaction equations are an expansion of a previously developed model for open ocean conditions (Bissett, W.P., Carder, K.L., Walsh, J.J., Dieterle, D.A., 1999a. Carbon cycling in the upper waters of the Sargasso Sea: II. Numerical simulation of apparent and inherent optical properties. Deep-Sea Research, Part I: Oceanographic Research Papers, 46 (2), 271–317; Bissett, W.P., Walsh, J.J., Dieterle, D.A., Carder, K.L., 1999b. Carbon cycling in the upperwaters of the Sargasso Sea: I. Numerical simulation of differential carbon and nitrogen fluxes. Deep-Sea Research, Part I: Oceanographic Research Papers, 46 (2), 205–269). The expansion includes an increase in the number of elemental pools to include silica, phosphorus, and iron, an increase in the number of phytoplankton functional groups, and a redevelopment of the Dissolved Organic Matter (DOM) and Colored Dissolved Organic Matter (CDOM) interaction equations. It was determined from this simulation that while the Loop Current alone was able to predict the water column conditions present during the summer, the Loop Current alone was not enough to simulate the magnitude of optical constituents present in the fall of 1998 when compared to satellite imagery. Simulating terrestrial inorganic and organic nutrients and CDOM pulses coinciding with significant meteorological events and high freshwater pulses released from the major rivers feeding the WFS were required to accurately predict the distribution and scale of the inherent optical properties at the surface during the fall months. Modeling the in situ light field for phytoplankton growth and community competition requires addressing the CDOM optical constituent explicitly. The majority of the annually modeled CDOM on WFS was created via in situ production; however, it was also rapidly removed via advection and photochemical destruction. A pulse of terrestrial nutrient and organic color was required to simulate the dramatic changes in surface color seen in satellite imagery on the WFS. The dynamics of the biogeochemical portion of the simulation demonstrate the importance of nonstoichiometric supplies of terrestrial nutrients on the WFS to the prediction of nutrient and CDOM fluxes.     

Variations of tidally driven three-layer residual circulation in fjords

Residual, or tidally averaged, circulation in fjords is generally assumed to be density driven and two layered. This circulation consists of a thin surface layer of outflow and a thick bottom layer of sluggish inflow. However, development of different vertical structures in residual circulation in fjords can arise from wind, remote, and tidal forcing that may modify the two-layer circulation. Particularly, theoretical results of tidal residual flows in homogeneous semienclosed basins indicate that their vertical structure is determined by the dynamical depth of the system. This dynamical depth can be considered as the ratio between the water column depth and the depth of frictional influence in an oscillatory flow (inverse of Stokes number). When the frictional depth occupies the entire water column, the tidal residual flow is one layered as in shallow basins. But when the frictional depth is only a small portion of the water column (>6 times smaller), the tidal residual is three layered. In relatively deep fjords (say deeper than 100 m), where frictional depths typically occupy a small portion of the water column, the tidal residual flow is expected to be three layered. Ample observational evidence presented here shows a three-layered exchange flow structure in fjords. On the basis of observational and theoretical evidence, it is proposed that the water exchange structure in deep fjords (more than six frictional layers deep, or inverse Stokes number >6) is tidally driven and is three layered. The tidally driven three-layer structure of residual flows could be regarded in some cases as the fundamental structure. However, this structure will only be observed sporadically as it will be masked by wind forcing, remote forcing from the ocean, and freshwater pulses.     

Evaluation of combination rules for peak response calculation in three‐component seismic analysis

The responses, r_e, given by several multicomponent combination rules used in seismic codes for determining peak responses to three ground motion components are evaluated for elastic systems and compared with the critical response r_cr; this is defined as the largest response for all possible incident angles of the seismic components and obtained by means of the CQC3‐rule when a principal seismic component is vertical, or the GCQC3‐rule when it departs from the vertical direction. The combination rules examined are the SRSS‐, 30%‐, 40%‐ and IBC‐rules, considering different alternatives for the design horizontal spectrum. Assuming that a principal seismic component is along the vertical direction, the upper and lower bounds of the ratio r_e/r_cr for each combination rule are determined as a function of the spectral intensity ratio of the horizontal seismic components and of the responses to one seismic component acting alternately along each structural axis. Underestimations and overestimations of the critical response are identified for each combination rule and each design spectrum. When a component departs from the vertical direction, the envelopes of the bounds of the ratio r_e/r_cr for each combination rule are calculated, considering all possible values of the spectral intensity ratios. It is shown that the inclination of a principal component with respect to the vertical axis can significantly reduce the values of r_e/r_cr with respect to the case when the component is vertical. Copyright © 2003 John Wiley & Sons, Ltd.     

Non-extensive framework for earthquakes: The role of fragments

The inclusion of fragment-asperity interaction inside tectonic plates to find a frequency magnitude relation for earthquakes, and the need for non-extensive statistics in this case is exposed. The usefulness of this formulation is shown. A comparison with seismic observations is also discussed.