Implications of flow intermittency on sediment nitrogen availability and processing rates in a Mediterranean headwater stream

Most streams draining to the Mediterranean basin are temporary. As a result of their hydrological regime, temporary streams are affected by drying and rewetting periods. Drying can alter in-stream nitrogen (N) availability and reduce N processing rates and subsequent retention after re-wetting. We sought to determine if hydrologic drying modifies reach-scale sediment chemical properties and constrains the response of N processing to rewetting. We compared different abiotic characteristics of sediments and nitrification and denitrification rates between a perennial and intermittent reach in the same stream over a wet period, when surface water flowed in both reaches, and a dry period, when the intermittent reach dried up. We analyzed N processing rates by incubating sediments with stream water, thereby simulating a rewetting when sediments from the intermittent reach were dry. We found that drying increased the sediment nitrate (NO₃ ^?) content. Conversely, drying did not reduce the recovery of N processing rates to pre-dry levels after simulated flooding conditions. Our results suggest that dry reaches may act as a potential NO₃ ^? source by releasing downstream NO₃ ^? pulses after stream flow recovery. Given the European Water Framework Directive requirements to assess stream ecological status, these N pulses following rewetting should be considered when designing management plans in temporary streams. Our study highlights the rapid response of in-stream N processing to rewetting period following a drought. This high resilience to process N should be seen as a vital ecosystem service provided by temporary streams despite annual dry periods.     

Using the damage from 2010 Haiti earthquake for calibrating vulnerability models of typical structures in Port-au-Prince (Haiti)

After the 2010 Haiti earthquake, that hits the city of Port-au-Prince, capital city of Haiti, a multidisciplinary working group of specialists (seismologist, geologists, engineers and architects) from different Spanish Universities and also from Haiti, joined effort under the SISMO-HAITI project (financed by the Universidad Politecnica de Madrid), with an objective: Evaluation of seismic hazard and risk in Haiti and its application to the seismic design, urban planning, emergency and resource management. In this paper, as a first step for a structural damage estimation of future earthquakes in the country, a calibration of damage functions has been carried out by means of a two-stage procedure. After compiling a database with observed damage in the city after the earthquake, the exposure model (building stock) has been classified and through an iteratively two-step calibration process, a specific set of damage functions for the country has been proposed. Additionally, Next Generation Attenuation Models (NGA) and \(\hbox {Vs}^{30}\) models have been analysed to choose the most appropriate for the seismic risk estimation in the city. Finally in a next paper, these functions will be used to estimate a seismic risk scenario for a future earthquake.     

The contribution to IHY from the COST296 Action MIERS: Mitigation of Ionospheric Effects on Radio Systems

The objective of the COST296 Action MIERS (Mitigation of Ionospheric Effects on Radio Systems) is to develop an increased knowledge of the effects imposed by the ionosphere on practical radio systems, and for the development and implementation of techniques to mitigate the deleterious effects of the ionosphere on such systems (http://www.cost296.rl.ac.uk). The COST296 Community contributes to the international efforts of IHY with scientific and outreach activities as well. After the realization of a web site hosted by Istituto Nazionale di Geofisica e Vulcanologia (INGV), developed also to promote the ionospheric physics to the open public, the COST296 Community supported an initiative addressed to the pupils of the primary school of several European Countries: the realization of a school-calendar dedicated to the Sun and to the Sun-Earth connections.     

The Carancas meteorite impact crater,Peru: Geologic surveying and modeling of crater formation and atmospheric passage

Abstract— The recent Carancas meteorite impact event caused a worldwide sensation. An H4–5 chondrite struck the Earth south of Lake Titicaca in Peru on September 15, 2007, and formed a crater 14.2 m across. It is the smallest, youngest, and one of two eye‐witnessed impact crater events on Earth. The impact violated the hitherto existing view that stony meteorites below a size of 100 m undergo major disruption and deceleration during their passage through the atmosphere and are not capable of producing craters. Fragmentation occurs if the strength of the meteoroid is less than the aerodynamic stresses that occur in flight. The small fragments that result from a breakup rain down at terminal velocity and are not capable of producing impact craters. The Carancas cratering event, however, demonstrates that meter‐sized stony meteoroids indeed can survive the atmospheric passage under specific circumstances. We present results of a detailed geologic survey of the crater and its ejecta. To constrain the possible range of impact parameters we carried out numerical models of crater formation with the iSALE hydrocode in two and three dimensions. Depending on the strength properties of the target, the impact energies range between approximately 100–1000 MJ (0.024–0.24 t TNT). By modeling the atmospheric traverse we demonstrate that low cosmic velocities (12–14 kms^?1) and shallow entry angles (<20 °) are prerequisites to keep aerodynamic stresses low (<10 MPa) and thus to prevent fragmentation of stony meteoroids with standard strength properties. This scenario results in a strong meteoroid deceleration, a deflection of the trajectory to a steeper impact angle (40–60 °), and an impact velocity of 350–600 ms^?1, which is insufficient to produce a shock wave and significant shock effects in target minerals. Aerodynamic and crater modeling are consistent with field data and our microscopic inspection. However, these data are in conflict with trajectories inferred from the analysis of infrasound signals.     

Acropora coral colonies as microhabitats for sponges in Tayrona National Natural Park,Colombian Caribbean

Sponges are sessile organisms capable of colonizing diverse substrata. In the Caribbean, coral reefs have suffered a drastic decline, and branching corals of the genus Acropora have been widely decimated. On dead coral skeletons and around surviving tissue the settling of sessile organisms can be observed, sponges being common. In order to investigate whether or not sponges have a preference for a particular species of coral, or for specific microhabitats of the colonies, we evaluated species composition, cover, richness and diversity of sponges colonizing the dead parts of still live colonies of the branching corals Acropora palmata and Acropora cervicornis in five locations of the Tayrona National Natural Park in the Colombian Caribbean. Ten colonies of Ac. palmata were quantified in each of the five locations, and eight Ac. cervicornis colonies in each of two locations. Quantification was carried out using video taken within 0.625‐m² photoquadrats. Seventeen sponge species were found, 13 of them associated with Ac. palmata and seven with Ac. cervicornis. Desmapsamma anchorata, Clathria venosa and Scopalina rutzleri were found to be common to all Ac. palmata locations, while De. anchorata occurred in the two Ac. cervicornis locations. On Ac. palmata, encrusting sponges dominated, while on Ac. cervicornis branched and lobed sponges predominated. Significant differences in sponge cover were not found among locations but were observed in the sponge species present. On Ac. palmata the species with highest cover were D. anchorata and Cla. venosa, while on Ac. cervicornis it was De. anchorata. The richness and diversity of sponges were low for both coral species, and their varying distribution can be attributed to the differences in available substrate for attachment, given coral colony morphology; for Ac. palmata, sponges predominated on the underside of the branches, semi‐cryptic areas and colony bases, whereas for Ac. cervicornis, they were located over the entire area of the cylindrical branches. Surviving colonies of Ac. palmata and Ac. cervicornis that are still erect offer additional microhabitats for reef sponges, some of which can be found directly interacting with live coral tissue, further threatening their recovery.     

An analysis and interpretation of the current data collected in the strait of Juan de Fuca in 1973

Abstract

We evaluate a set of current measurements done in a section of the Strait of Juan de Fuca. The flow is of estuarine character, the upper layer flow usually being directed seaward. The RMS value of steady current exceeds its mean value appreciably in the upper layer; it also exceeds the mean near the bottom. The near‐surface currents do change their direction on occasions and can run landward for over five consecutive days, especially in the southern part of the channel. The lower layer flow (landward) and the upper layer flow (seaward) varied in magnitude from 90 to 160 thousand m³/sec, and their fluctuations were in phase; their difference, the net flow, is of the order of 5% to 10% of these flows and could not be calculated with any confidence. Tidal motion is barotropic in the section, with some deformation in the vertical caused by bottom friction and internal stresses. The M₂ tide in the system Juan de Fuca‐Georgia Strait can be represented by a standing Kelvin wave influenced by friction. The K₁ tide can also be represented by a standing Kelvin wave if some leakage is allowed in the northern end of Georgia Strait. Topographic effects mask the Coriolis influence on the intensity of tidal currents.     

Shallow velocity model of the Northern Flank of Stromboli Volcano, deduced by high frequency surface wave dispersion

The wavefield produced by the Stromboli volcano explosion quakes shows a significant amount of surface waves. Rayleigh waves recorded by a linear array have been investigated to infer the shear-wave velocity model of the Stromboli northern flank. The group velocity dispersion curve was obtained using the multiple filter technique, while the phase velocity dispersion curve was calculated both by phase-matched filtering and performing a p– stack on the observed waveforms. Through the inversion of these curves we were able to recover the shear-wave structure to a depth of about 190 m.     

Deforestation of water‐repellent soils in Galicia (NW Spain): effects on surface runoff and erosion under simulated rainfall

At three adjacent sites in steeply sloping woodland in Galicia (NW Spain), surface runoff and associated erosion under simulated rainfall (64 mm h^?1) were measured on five occasions between June 1998 and July 1999. Two of the three sites had recently been deforested and topsoil added, and one of these two had been sown with grass, which was germinating at the onset of the study. Deforestation greatly increased runoff and erosion rates, and the recovery of plant cover reduced erosion. All three soils were very hydrophobic due to high levels of poorly humified organic matter, which led to higher runoff rates than expected, especially during dry periods. However, great structural stability prevented there being a significant correlation between runoff rate and soil erosion. Copyright © 2003 John Wiley & Sons, Ltd.     

Comparing Loss Estimation with Observed Damage: A Study of the 1999 Kocaeli Earthquake in Turkey

Loss estimation from future earthquakes is of growing importance in planning earthquake protection strategies in high-risk areas. Loss models based on the spectral displacement approach are now widely used because of generally acknowledged deficiencies in earlier approaches using macroseismic intensity or peak ground-motion parameters. However, there has been to date rather little earthquake damage data by which the new generation of models can be assessed and which can be used to calibrate the parameters involved. The availability of several detailed damage surveys carried out following the 1999 Kocaeli earthquake in Turkey, provides a rare opportunity for such an assessment. In this paper the losses which would be predicted from two different approaches to loss assessment – one using predicted macroseismic intensity, the other using the spectral displacement method – are compared with actual observed losses in the Kocaeli event at two different locations where surveys were carried out. One of these sites was very close to the surface fault rupture (< 3 km distance), the other at a distance of about 4.5 km. It is shown that the predictive methods available generally overestimated the losses at these distances, and a number of possible reasons for these discrepancies are considered. The sensitivity of loss estimates to variations in the key parameters governing the estimation in each case are explored, in particular with respect to modifications in the parameters of the attenuation relationships and the vulnerability parameters. The implications of these results for estimating future losses are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.