A three-dimensional biophysical model of Karenia brevis dynamics on the west Florida shelf: A look at physical transport and potential zooplankton grazing controls

The development of accurate predictive models of toxic dinoflagellate blooms is of great ecological importance, particularly in regions that are most susceptible to their detrimental effects. This is especially true along the west Florida shelf (WFS) and coast, where episodic bloom events of the toxic dinoflagellate Karenia brevis often wreak havoc on the valuable commercial fisheries and tourism industries of west Florida. In an effort to explain the dynamics at work within the maintenance and termination phases of a red tide, a simple three-dimensional coupled biophysical model was used in the analysis of the October 1999 red tide offshore Sarasota, Florida. Results of the numerical experiments indicate that: (1) measured and modeled flowfields were capable of transporting the observed offshore inoculum of K. brevis to within 16 km of the coastal boundary; (2) background concentrations (1000 cells L⁻¹) of K. brevis could grow to a red tide of over 2×10⁶ cells L⁻¹ in little more than a month, assuming an estuarine initiation site with negligible offshore advection, no grazing losses, negligible competition from other phytoplankton groups, and no nutrient limitation; (3) maximal grazing pressure could not prevent the initiation of a red tide or cause its termination, assuming no other losses to algal biomass and a zooplankton community ingestion rate similar to that of Acartia tonsa; and (4) the light-cued ascent behavior of K. brevis served as an aggregational mechanism, concentrating K. brevis at the 55 μE m⁻² s⁻¹ isolume when mean concentrations of K. brevis exceeded 100,000 cells L⁻¹. Further improvements in model fidelity will be accomplished by the future inclusion of phytoplankton competitors, disparate nutrient availability and limitation schemes, a more realistic rendering of the spectral light field and the attendant effects of photo-inhibition and compensation, and a mixed community of vertically-migrating proto- and metazoan grazers. These model refinements are currently under development and shall be used to aid progress toward an operational model of red tide forecasting along the WFS.     

A stochastic model for daily subsurface CO2 concentration and related soil respiration

Near-surface soil CO₂ gas-phase concentration (C) and concomitant incident rainfall (P_i) and through-fall (P_t) depths were collected at different locations in a temperate pine forest every 30 min during the 2005 and 2006 growing seasons (and then averaged to the daily timescale). At the daily scale, C temporal variations were well described by a sequence of monotonically decreasing functions interrupted by large positive jumps induced by rainfall events. A stochastic model was developed to link rainfall statistics responsible for these jumps to near-surface C dynamics. The model accounted for the effect of daily rainfall variability, both in terms of timing and amount of water, and permitted an analytical derivation of the C probability density function (pdf) using the parameters of the rainfall pdf. Given the observed positive correlation between daily C and soil CO₂ fluxes to the atmosphere (F_s), the effects of various rainfall regimes on the statistics of F_s can be deduced from the behavior of C under different climatic conditions. The predictions from this analytical model are consistent with flux measurements reported in manipulative experiments that varied rainfall amount and frequency.     

Long-period seismicity during magma movement at Volcán de Colima

During the period from February to September 2005, Volcán de Colima produced 30 Vulcanian explosions of sufficient magnitude to produce pyroclastic flows of variable size, with a total volume of at least 2.5 × 10⁶ m³. Swarms of long-period events were associated with each event, their duration ranging from about 6 h to 3 days and each swarm containing up to 886 events. The characteristics of the swarms have been studied to understand the source mechanism and their relationship with the Vulcanian explosions. In total, 12,548 long-period events were analysed using various comparative and statistical methods. Patterns were not apparent in the data with no correlation between different properties of the swarms (duration, magnitude or frequency of occurrence of LP events) and the magnitude of the associated Vulcanian explosion, whether recorded by seismicity, volume of pyroclastics or altitude of the eruption column. This, along with other characteristics of the swarms, such as the continuation of the swarm after the explosion, with an increase in long-period event amplitude in some cases, suggests that the mechanism is not merely associated with the pressurization under an impermeable cap and resulting pressure differentials between adjacent volumes within the system. It is more likely that the production of long-period events is dominated by brittle fracturing on the margins of an ascending magma body. A model is proposed whereby the unloading above the ascending magma column produced by a Vulcanian explosion resulted in an increase in ascent rate, reflected in the increasing amplitude of long-period events. The results reflect the complexity of non-linear processes involved during magma ascent, degassing, crystallization and rupture of the impermeable plug during the Vulcanian process. At Volcán de Colima, as at many volcanoes, long-period events represent a useful precursor for eruptive activity. For monitoring, this paper highlights some useful analyses that can be carried out, which could illustrate certain characteristics of an eruptive episode. A preliminary model is presented of the conduit processes at work during the cyclic extrusive and explosive activity during 2005.     

A physical model for dynamic analysis of wine barrel stacks

This paper deals with the earthquake response of wine barrel stacks using a physical model of rigid‐body components with discrete flexible and damped contact elements. An analytical 3D formulation of the complex dynamic behavior of different barrel stack configurations is presented. Such behavior includes the real geometry of the bodies, large displacements and rotations, the use of non‐linear contact elements to account for impact and sliding between bodies, and the resulting local energy dissipation at contact. The parameters defining the physical and mathematical model were calibrated experimentally, and the dynamic behavior of a benchmark barrel stack configuration was compared with the experimental results obtained from the literature. It was found that the model is able to predict the exact mode of collapse and the overall behavior of the system. Copyright © 2010 John Wiley & Sons, Ltd.     

Susceptibility to gravitational processes due to land cover change in the Río Chiquito-Barranca del Muerto subbasin(Pico De Orizaba Volcano,México)

Land cover change can lead to slope instability by accelerating erosive processes associated with agriculture, forestry, and infrastructure. The Rio Chiquito-Barranca del Muerto subbasin has experienced an increase in land cover change due to government programs and the establishment of agricultural and urban areas. The aim of this study was to provide a model to map the susceptibility to gravitational processes along sites where anthropogenic land cover change has occurred. The method was based on the stratification of the subbasin according to landforms and cartographic variables. These variables were used in a multi-criteria assessment to assign weights according to their contribution to the onset of new gravitational processes. Those weights were used to create a susceptibility map based on a weighted linear sum. The accuracy of the resulting map was validated in an error matrix with a random stratified design based on susceptibility classes per landform. The results produced a map of areas with susceptibility to gravitational processes due to land cover change; this susceptibility is very high in the undifferentiated pyroclastic slope and limestone mountain, where it derives not only from anthropogenic effects on natural vegetation cover, but also from steep slopes, weathered materials, low apparent density, high erosivity, and previous gravitational processes. The results support other studies that concluded that loss of vegetation is a triggering factor in the formation of gravitational processes, but also show that excessive reforestation can increase gravitational processes.     

Exploring the policy and social factors fueling the expansion and shift of sugarcane production in the Brazilian Cerrado

Within the past decade, the sugarcane ethanol industry in Brazil has increased its production capacity to meet rising domestic demand for ethanol. However, to achieve this growth the industry has had to expand into new frontiers in the Brazilian Cerrado, specifically in the states of Goiás and Mato Grosso do Sul, which is now the second largest producing area of ethanol in Brazil. We argue that the expansion into the Brazilian Cerrado is a result of the interactions between the increase in demand, governmental policies, infrastructure, and factors that have prevented traditional sugarcane producing regions from meeting the increasing demand for ethanol. This paper analyzes the policies that have shaped the sugarcane industry in Brazil and the expansion of the industry across the country. The policies and issues examined include those that led to the concentration and consolidation of the sugarcane industry in the state of São Paulo and the consequences of this consolidation; the influence of governmental policies on the decision-making process of producers and industry; the state-level policies designed to expand the industry into Goiás and Mato Grosso do Sul states; infrastructure development; and the Sugarcane Agroecological Zoning policies. Through this study we conclude that the ethanol industry identified the Cerrado states as an opportunity for investment, given the good agricultural conditions for producing sugarcane, affordable land prices and favorable state-level fiscal incentive policies. In addition, there is a need for further regional development policies as the interaction between the sugarcane sector and regional government is likely to continue into the future.     

Probabilistic assessment of annual repair rates in pipelines and of direct economic losses in water and sewage networks: application to Manizales,Colombia

A methodology for the development of fully probabilistic seismic risk assessments on water and sewage networks is presented in this paper together with a case study for the system of Manizales, Colombia. These kinds of assessments require the development of probabilistic seismic hazard analysis, the consideration of local site effects, when relevant, the assembly of databases to identify and characterize the exposed elements and the development and assignment of vulnerability models for each type of component. For the case of Manizales, a high-resolution exposure database has been developed (element by element, segment by segment) based on the information and data provided by the owner and operator of the network, Aguas de Manizales. Losses due to earthquakes are obtained after convoluting the hazard and vulnerability inputs in a fully probabilistic manner, using the state-of-the-art methodologies incorporated in the CAPRA risk assessment module. Several risk metrics such as the loss exceedance curve, the loss exceedance probabilities for different time frames and the average annual loss are obtained for the system as a whole as well as disaggregated by component. In addition, repair rates for the pipelines were also calculated. The risk results obtained in this study have been useful for the company in designing and implementing expansion and maintenance plans that explicitly account for seismic risk mitigation issues, as well as to explore and negotiate financial protection alternatives by means of risk transfer and retention schemes, thus becoming a valuable input in the continuous development of good disaster risk management practices in this city.