Home About us Contact
|
Home About us Contact | ||
|
|
||
Irreversible Effects (irreversible + effects)
Selected AbstractsSorption irreversibility of 1,4-dichlorobenzene in two natural organic matter,rich geosorbentsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2009Michael Sander Abstract Hysteresis, a frequently observed phenomenon in sorption studies, is inconsistent with the key assumption of sorption reversibility in most fate and bioavailability models. Therefore, a study of the underlying causes of hysteresis is essential. Carbon-radiolabeled 1,4-dichlorobenzene (DCB) isotope tracer exchange was carried out at select points along the isotherms of DCB in a brown coal and a peat soil, holding total DCB concentration constant. Tracer exchange was performed both in the forward (sorption) and reverse (desorption) directions at the bulk sorption points and in the desorption direction at the corresponding bulk desorption points. Bulk DCB isotherms showed concentration-dependent hysteresis. However, tracer reequilibration in all cases was consistent with free exchange between sorbed and aqueous-phase molecules. These results rule out common experimental artifacts and demonstrate that sorption of bulk DCB is truly hysteretic (i.e., irreversible). The differences in rates between bulk and tracer sorption and desorption are consistent with the coupling of bulk DCB diffusion to other processes that retard equilibration, which we assign to matrix swelling or shrinking. Hysteresis is attributed to matrix deformation,specifically, to inelastic expansion and creation of voids accommodating sorbate molecules in the matrix, which leads to enhanced affinity in the desorption step. Comparing the results to previous results for naphthalene in the coal, we find that irreversible effects are similar for DCB and naphthalene in the coal but differ for DCB between the two sorbents. An explanation based on the different physical properties of these sorbents is provided. Solid-phase extraction of equilibrated DCB with Tenax® revealed a highly desorption-resistant fraction. While too small to account for the observed hysteresis, this fraction may represent molecules that become trapped as the matrix collapses and simultaneously stiffens during abrupt desorption. [source] Test of a developmental trade-off in a polyphenic butterfly: direct development favours reproductive outputFUNCTIONAL ECOLOGY, Issue 1 2008Bengt Karlsson Summary 1Evolutionary theory predicts that resource allocation decisions taken during development are adjusted to an organism's life-history. These decisions may have irreversible effects on body design and strong fitness consequences. Holometabolous insects that have a long expected life span typically postpone reproduction, and so are expected to allocate resources for somatic maintenance prior to investing in reproduction. In contrast, insects that have a short expected life span are expected to allocate relatively less to soma and more to reproduction. In support of this theory, an earlier investigation of resources allocated to soma vs. reproductive reserves in the comma butterfly, Polygonia c-album, revealed that short-lived females indeed allocate more resources to reproductive reserves as compared to longer lived females that hibernate before reproduction suggesting that short-lived females should have higher fecundity. 2Here we test this prediction, using the comma butterfly as our study organism. Depending on daylength and temperature this butterfly produces one of two morphs: (i) a light summer morph that reproduces directly after adult eclosion and has a short expected life span of a couple of weeks; or (ii) a darker winter morph that normally lives for 8,9 months before the onset of reproduction. Our test is based on experimental manipulation that allowed us to induce reproduction without prior hibernation in winter morph comma butterflies, and comparing lifetime fecundity among three groups: (i) directly reproducing summer morph commas; (ii) directly reproducing winter morph commas; and (iii) winter morph commas reproducing after overwintering. This protocol allowed us to tease apart trade-offs during development and the hibernation period. 3The results showed that the short-lived summer morph had a substantially higher fecundity (total number of eggs = 586 ± 19, mean ± SE) than the winter morph females manipulated to reproduce without hibernation (total number of eggs = 334 ± 42). We argue that this is a consequence of a resource allocation trade-off during early development observed in this species; females with a short expected life as adults allocate relatively more of their resources to reproductive parts and thereby reach a higher reproductive output compared to females predisposed for a long adult life. 4There was no significant difference in lifetime fecundity between winter morph females that did, or did not, hibernate before reproduction. This suggests that the cost of hibernation per se is small and hence corroborates our conclusion that the life-history implemented trade-off made during early development underlies the lower reproductive output of the winter morph butterflies. [source] Similarities and differences in the historical development of flood management in the alluvial stretches of the Lower Mississippi Basin and the Rhine Basin,§IRRIGATION AND DRAINAGE, Issue S1 2006Dick de Bruin ingénierie hydraulique fluviale; développement historique des bassins du Rhin et du Mississippi inférieur; plaines alluviales Abstract Although the rivers Rhine and Mississippi cannot be compared as features of nature,the Mississippi River as a feature of nature is much bigger and more impressive than the Rhine,one can still observe striking similarities on flood management in both river basins, in particular in the alluvial flat reaches. But there are also some fundamental differences, not only technically but also institutionally. Since industrialization (around 1800), inland navigation became a major user on both river systems and later flood control started developing more fundamentally. Large intervention works were needed, mainly developed and based on trial and error. In both cases it has led to irreversible effects, which demand continuous attention. For the alluvial stretches in both river basins, a review is given on the most important developments in river engineering over the last two centuries. For both rivers, nautical management and flood control were held in one institutional hand at national/federal level, because both uses/sectors need the creation and regular maintenance of one similar issue: a stable and deep main channel. But the way in which in particular flood management gradually developed institutionally, as an essential part of integrated water management in the alluvial flat lower reaches of both river systems, has diverged. Discussions on financing, priorities, public disclosure, multifunctional aspects, etc. have led in both basins to lengthy procedures and complicated policy making. This paper elaborates on the historic development of fundamentals in river engineering and river management in the alluvial plains of the Rhine Basin and the Lower Mississippi Basin, more in particular focusing on the development of flood protection dikes, and on the stabilization of major channels. Copyright © 2006 John Wiley & Sons, Ltd. Bien que le Rhin et le Mississippi ne puissent pas être comparés en termes physiques,le Mississippi est beaucoup plus grand et impressionnant que le Rhin,on peut pourtant observer des similitudes saisissantes dans la protection contre les inondations des deux bassins, en particulier dans les plaines alluviales. Mais il existe également quelques différences fondamentales, non seulement techniques mais institutionnelles. Depuis les débuts de l'industrialisation (vers 1800), la navigation est devenue un usage très important sur les deux fleuves et la protection contre les inondations à commencer à se mettre en place de façon plus systématique. De grands travaux d'intervention ont été nécessaires, principalement basés sur la règle empirique de l'essai/erreur. Dans les deux cas, ceci a entraîné des effets irréversibles, qui nécessitent une surveillance permanente. Pour les plaines alluviales des deux bassins, l'article passe en revue la plupart des développements de l'ingénierie hydraulique fluviale des deux cent dernières années. Pour les deux fleuves, la gestion de la navigation et la protection contre les inondations ont été regroupées dans une même institution au niveau national/fédéral, parce que les deux usages/secteurs demandaient la création et l'entretien régulier d'une même infrastructure: un canal principal stable et profond. Mais la manière dont la protection contre les inondations s'est progressivement développée sur le plan institutionnel, comme élément essentiel de la gestion intégrée de l'eau dans les plaines alluviales des deux fleuves, s'est différenciée. Des débats sur le financement, les priorités, l'information du public, les aspects multi fonctionnels, etc., ont conduit les deux bassins à mettre en place des procédures lourdes et des prises de décision complexes. Cet article présente le développement historique des principes fondamentaux de l'hydraulique fluviale et de la gestion de fleuve dans les plaines alluviales du bassin du Rhin et du bassin inférieur du Mississippi, en mettant l'accent sur le développement des digues de protection et la stabilisation des canaux principaux. Copyright © 2006 John Wiley & Sons, Ltd. [source] Impact of periodontal preventive programmes on the data from epidemiologic studiesJOURNAL OF CLINICAL PERIODONTOLOGY, Issue 2005Per E. Gjermo Abstract This report provides only circumstantial evidence for the impact of programmes on periodontal epidemiology. The prerequisites for programmes and campaigns are described, and epidemiologic data on periodontal disease are compared with known changes in factors that may be affected by such activities. Unfortunately, parameters for periodontal disease as a process are not available. Only variables indicating irreversible effects on the periodontal status can be obtained. A lack of appropriate studies creates additional problems. This review indicates that preventive programmes and campaigns to improve oral hygiene have affected periodontal epidemiologic data concerning gingivitis and mild/moderate periodontitis favourably. Severe periodontitis seems not to have been influenced by such activities. Smoking is strongly associated with the severity of periodontitis. Therefore, a positive effect may be anticipated following the smoking cessation campaigns currently introduced worldwide. However, because of the irreversible nature of our epidemiologic parameters, it will take decades before any effect may be evident. It is recommended that periodontal epidemiology should be revitalized by introducing a nominalistic categorization instead of the changing essentialistic approaches used so far in order to facilitate the interpretation of data. [source] Forest Fragment and Breeding Habitat Characteristics Explain Frog Diversity and Abundance in SingaporeBIOTROPICA, Issue 1 2010David Bickford ABSTRACT Habitat loss and fragmentation can have severe negative and irreversible effects on biodiversity. We investigated the effects of forest fragmentation on frog diversity in Singapore because of its high rates of deforestation and the demonstration that frogs are some of the most sensitive species to habitat degradation. We surveyed frog species in 12 forest fragments varying from 11 to 935 ha. We compared differences in species richness, abundance, and Shannon's index in relation to forest fragment size, connectivity (distance between fragments), and breeding habitat heterogeneity. A total of 20 species from 12 genera and five families were encountered in 12 fragments. Larger fragments and those closer to larger fragments had higher species richness. Abundance, however, was not correlated with forest area or connectivity, but we found fewer individual frogs in the larger fragments. We also found that breeding habitat heterogeneity best explained frog species diversity and abundance in forest fragments. Fragments with a high diversity of breeding habitats had more species. We found no evidence to suggest that abundance and diversity are strongly correlated, particularly in disturbed areas, but that breeding habitat heterogeneity is an under-appreciated factor that should be considered when prioritizing areas for anuran conservation. Enriching breeding habitat heterogeneity, creating corridors between fragments, and reforesting degraded areas are some of the most beneficial strategies for preserving urban frog biodiversity. [source] | ||||||||||