The distribution of pond snail communities across a landscape: separating out the influence of spatial position from local habitat quality for ponds in south-east Northumberland, UK

Ponds support a rich biodiversity because the heterogeneity of individual ponds creates, at the landscape scale, a diversity of habitats for wildlife. The distribution of pond animals and plants will be influenced by both the local conditions within a pond and the spatial distribution of ponds across the landscape. Separating out the local from the spatial is difficult because the two are often linked. Pond snails are likely to be affected by both local conditions, e.g. water hardness, and spatial patterns, e.g. distance between ponds, but studies of snail communities struggle distinguishing between the two. In this study, communities of snails were recorded from 52 ponds in a biogeographically coherent landscape in north-east England. The distribution of snail communities was compared to local environments characterised by the macrophyte communities within each pond and to the spatial pattern of ponds throughout the landscape. Mantel tests were used to partial out the local versus the landscape respective influences. Snail communities became more similar in ponds that were closer together and in ponds with similar macrophyte communities as both the local and the landscape scale were important for this group of animals. Data were collected from several types of ponds, including those created on nature reserves specifically for wildlife, old field ponds (at least 150 years old) primarily created for watering livestock and subsidence ponds outside protected areas or amongst coastal dunes. No one pond type supported all the species. Larger, deeper ponds on nature reserves had the highest numbers of species within individual ponds but shallow, temporary sites on farm land supported a distinct temporary water fauna. The conservation of pond snails in this region requires a diversity of pond types rather than one idealised type and ponds scattered throughout the area at a variety of sites, not just concentrated on nature reserves

The response of perennial and temporary headwater stream invertebrate communities to hydrological extremes

The headwaters of karst rivers experience considerable hydrological variability, including spates and streambed drying. Extreme summer flooding on the River Lathkill (Derbyshire, UK) provided the opportunity to examine the invertebrate community response to unseasonal spate flows, flow recession and, at temporary sites, streambed drying. Invertebrates were sampled at sites with differing flow permanence regimes during and after the spates. Following streambed drying at temporary sites, dewatered surface sediments were investigated as a refugium for aquatic invertebrates. Experimental rehydration of these dewatered sediments was conducted to promote development of desiccation-tolerant life stages. At perennial sites, spate flows reduced invertebrate abundance and diversity, whilst at temporary sites, flow reactivation facilitated rapid colonisation of the surface channel by a limited number of invertebrate taxa. Following streambed drying, 38 taxa were recorded from the dewatered and rehydrated sediments, with Oligochaeta being the most abundant taxon and Chironomidae (Diptera) the most diverse. Experimental rehydration of dewatered sediments revealed the presence of additional taxa, including Stenophylax sp. (Trichoptera: Limnephilidae) and Nemoura sp. (Plecoptera: Nemouridae). The influence of flow permanence on invertebrate community composition was apparent despite the aseasonal high-magnitude flood events

Laser Patterning Pretreatment before Thermal Spraying: A Technique to Adapt and Control the Surface Topography to Thermomechanical Loading and Materials

Coating characteristics are highly dependent on substrate preparation and spray parameters. Hence, the surface must be adapted mechanically and physicochemically to favor coating–substrate adhesion. Conventional surface preparation methods such as grit blasting are limited by surface embrittlement and produce large plastic deformations throughout the surface, resulting in compressive stress and potential cracks. Among all such methods, laser patterning is suitable to prepare the surface of sensitive materials. No embedded grit particles can be observed, and high-quality coatings are obtained. Finally, laser surface patterning adapts the impacted surface, creating large anchoring area. Optimized surface topographies can then be elaborated according to the material as well as the application. The objective of this study is to compare the adhesive bond strength between two surface preparation methods, namely grit blasting and laser surface patterning, for two material couples used in aerospace applications: 2017 aluminum alloy and AISI 304L stainless steel coated with NiAl and YSZ, respectively. Laser patterning significantly increases adherence values for similar contact area due to mixed-mode (cohesive and adhesive) failure. The coating is locked in the pattern

Vers une approche cycle de vie de revêtements métalliques destinés à des applications industrielles

Les dépôts électrolytiques de chrome dur, utilisés pour protéger certaines pièces contre l’usure et la corrosion, vont disparaître à cause de l’utilisation de Cr(VI). L’évaluation environnementale de meilleures technologies en traitements de surface semble nécessaire pour innover dans ce domaine. Elle repose dans cette étude sur une analyse de cycle de vie (ACV), prenant en compte l’environnement au niveau des matériaux et des procédés. Parmi les solutions étudiées, la projection thermique, d’ores et déjà utilisée industriellement présente certains atouts bien que les résultats ne soient pas toujours satisfaisants pour des raisons de porosité et de microstructure des dépôts. L’apport du laser permettant la construction de dépôts plus denses est ici également étudié. Les deux procédés sont en fait très complémentaires et les résultats, techniques et environnementaux obtenus avec ces deux technologies, sont comparés. L’ACV réalisée sur les différents dépôts élaborés par projection plasma, projection HVOF, rechargement laser et par un procédé hybride couplant projection plasma et refusion laser in situ démontre leur avantageuse propreté par rapport aux dépôts de chrome dur. Une étude mécanique approfondie, qui justifie la durée de vie des dépôts, prouve également que ces alternatives plus écologiques sont également pertinentes pour certaines applications industrielles

Laser hybred plasma spray processes : tools to adjust coating structural characteristics

International audienceFive groups of closely interrelated operating parameters (power parameters, feedstock injection parameters, geometric parameters, kinematics parameters and environmental parameters) have to be optimized and controlled during Atmospheric Plasma Spraying (APS) to control the coating structure and its properties in service. Nevertheless, in some cases, the multiple possible combinations of operating parameters do not permit to reach the required coating structural characteristics. Auxiliary systems, such as lasers, can help to decouple interrelated effects and introduce new degrees of freedom to the process. Combining a plasma torch with a laser beam forms a hybrid process. In such a case, several strategies can be implemented, depending on the one hand on the laser irradiation characteristics and, on the other hand, on the location of the laser F irradiation area in regards with the particle impact footprint on the surface. This paper intends to develop several works carry out on laser hybrid plasma spray processes. Substrate surface and coating interface ablation, substrate surface and coating layers preheating and coating layers remelting are presented. Mechanisms resulting from laser irradiation are detailed and some resulting coating structures analyzed