Soil resource supply influences faunal size–specific distributions in natural food webs

The large range of body-mass values of soil organisms provides a tool to assess the ecological organization of soil communities. The goal of this paper is to identify graphical and quantitative indicators of soil community composition and ecosystem functioning, and to illustrate their application to real soil food webs. The relationships between log-transformed mass and abundance of soil organisms in 20 Dutch meadows and heathlands were investigated. Using principles of allometry, maximal use can be made of ecological theory to build and explain food webs. The aggregate contribution of small invertebrates such as nematodes to the entire community is high under low soil phosphorus content and causes shifts in the mass–abundance relationships and in the trophic structures. We show for the first time that the average of the trophic link lengths is a reliable predictor for assessing soil fertility responses. Ordered trophic link pairs suggest a self-organizing structure of food webs according to resource availability and can predict environmental shifts in ecologically meaningful ways

Recent Northern Hemisphere stratospheric HCl increase due to atmospheric circulation changes

The abundance of chlorine in the Earth’s atmosphere increased considerably during the 1970s to 1990s, following large emissions of anthropogenic long-lived chlorine-containing source gases, notably the chlorofluorocarbons. The chemical inertness of chlorofluorocarbons allows their transport and mixing throughout the troposphere on a global scale1, before they reach the stratosphere where they release chlorine atoms that cause ozone depletion2. The large ozone loss over Antarctica3 was the key observation that stimulated the definition and signing in 1987 of the Montreal Protocol, an international treaty establishing a schedule to reduce the production of the major chlorine- and bromine-containing halocarbons. Owing to its implementation, the near-surface total chlorine concentration showed a maximum in 1993, followed by a decrease of half a per cent to one per cent per year4, in line with expectations. Remote-sensing data have revealed a peak in stratospheric chlorine after 19965, then a decrease of close to one per cent per year6, 7, in agreement with the surface observations of the chlorine source gases and model calculations7. Here we present ground-based and satellite data that show a recent and significant increase, at the 2σ level, in hydrogen chloride (HCl), the main stratospheric chlorine reservoir, starting around 2007 in the lower stratosphere of the Northern Hemisphere, in contrast with the ongoing monotonic decrease of near-surface source gases. Using model simulations, we attribute this trend anomaly to a slowdown in the Northern Hemisphere atmospheric circulation, occurring over several consecutive years, transporting more aged air to the lower stratosphere, and characterized by a larger relative conversion of source gases to HCl. This short-term dynamical variability will also affect other stratospheric tracers and needs to be accounted for when studying the evolution of the stratospheric ozone layer

Aircraft Decompression with Installed Cockpit Security Door

A zero-dimensional model of cockpit and cabin decompression with cockpit security door is presented. The hinged panels in the security door were modeled to account for the pressure-equalization dynamics in the case of cockpit decompression. A comprehensive isentropic and isothermal theoretical analysis is presented with many closed-form and asymptotic solutions. New analytical estimates for the total decompression time and the pressure half-time were derived. The simulations for typical corporate and large-transport-category airplanes with different cabin geometries, discharge coefficients, rupture cross-sectional areas, pressure altitudes, and cabin altitudes have been obtained. The case in which the cockpit depressurizes first and its effect on the cabin decompression and on the security door integrity has been extensively studied. The recently required cockpit doors may be hazardous for flight crew in the case cockpit depressurizes first and other venting and blowout panels malfunction or are too slow to respond. The resulting pressure differential between the cockpit and the cabin can create instantaneous forces in excess of 80 kN on the cockpit security door. In addition, this puts the crew in danger due to explosive decompression on the time scale of 100 ms and increases the possibility of the security door being blown out of the frame