Toxicity and bioaccumulation of sulphadimethoxine inArtemia (Crustacea,Anostraca)

To evaluate the effects of sulphonamide pollution in marine and brackish systems, and to assess the utility of a recently proposed test protocol, sulphadimethoxine toxicity was measured using naupli and cysts of anArtemia species. Nauplii mortality, evaluated between 24 and 96 h, indicated a relatively high toxicity of sulphadimethoxine toArtemia (96 h LC₅₀= 19.5 mg L⁻¹). In addition, test on cysts demonstrated that a nominal concentration of 300 mg L⁻¹ sulphadimethoxine significantly depressed hatching. Toxicity could depend on the high bioaccumulation rate of sulphadimethoxine measured in the organisms. The role of these tests in assessing the environmental risks of intensive farming and in determining suitable standards to improve water quality criteria is discussed together with the possible utilization of bioaccumulatingArtemia as ‘medicated feed’.     

GENETIC ALGORITHMS AS A STRATEGY FOR FEATURE SELECTION

Genetic algorithms have been created as an optimization strategy to be used especially when complexresponse surfaces do not allow the use of better-known methods (simplex, experimental designtechniques, etc.). This paper shows that these algorithms, conveniently modified, can also be a valuabletool in solving the feature selection problem. The subsets of variables selected by genetic algorithms aregenerally more efficient than those obtained by classical methods of feature selection, since they canproduce a better result by using a lower number of features.     

Enhancing the credibility of ecology: Interacting along and across hierarchical scales

A wide range of space and time scales characterize the processes and phenomena which interact to shape environmental condition and trends. Important perspectives of environmental space and time include the role of terrestrial and astronomical factors in shaping climatic change, insights to be gained from the pre-historical record, relations between disturbance and biotic responses, episodic extreme events and large-scale phenomena, cumulative impacts, fast — slow processes and memory reservoirs. Scales in physical, chemical and biological phenomena have parallels in human driving forces, societal relations and decision — making processes, and environmental scales of space and time thus have perceptual as well as physical (objective) dimensions. Scale is clearly more than just size and dimension, and there is a growing body of examples on how zooming along and across hierarchical scales can help in seeking explanation (how) and significance (why), and in revealing emergent properties. Scaling can also act as a motor for new approaches to scientific cooperation. Such evolving scales in scientific cooperation are examined in relation to three international research programmes (IBP, MAB, IGBP), to various sub-disciplines of ecology and biogeography, and to the restructuring of a largish research institute in Montpellier (France). An overall conclusion is that scaling issues may provide a stimulus to increased coherence within the science of ecology itself, and may facilitate mutually supportive links with other scientific domains and society at large.The views expressed are those of the authors and not necessarily those of the authors' employers.     

A typology of scientific bottlenecks to natural resources development

A preliminary systematic framework for considering the scientific bottlenecks to the development of natural resources is presented, as a basis for discussion and refinement. In giving particular attention to problems of resource use in developing countries, two main types of scientific bottlenecks are recognized. One concerns the quality and quantity of information on natural resources, and the use that is made of that information. The second relates to the quality and quantity of local manpower in the ecological and related sciences that is available to developing countries, and to the conditions that affect the promotion and stability of scientific endeavor in these countries.Action strategies for combatting these bottlenecks are proposed. These strategies emphasize the need to improve the scientific basis for the predictable use of natural resources, to facilitate multi-directional links of scientific cooperation between countries, and to help develop national self-reliance in research and management activities. They stress such principles of action as the promotion of a problem-oriented, interdisciplinary approach within specific geographic units, and the combination of research, training and demonstration within particular field activities. These features of suggested research run counter neither to scientific method nor to the freedom of scientific endeavor. They do, however, entail a change in the way that much research is conceived and organized. More particularly, they entail the incorporation of additional dimensions in the overall research effort, including that of a perception approach to problems.The views expressed in this article are the authors', and not necessarily those of Unesco.     

全球变化与地表参数的定量遥感

从全球变化研究对遥感获取地表时空多变要素信息的需求 ,论述定量遥感中对地表多尺度空间信息作地学描述的新思路和新方法。在分析了变差图描述方法的特点及其不足的基础上 ,提出了直方变差图的概念 ,通过定义驻点和边界点 ,尝试采用直方变差图分解的方法分析地物空间分布规律 ,并通过一个实验对此方法进行了说明。进而基于对地表空间分布信息的提取 ,将可见光、近红外波段遥感信息用于热红外遥感的地温反演 ,利用地表空间结构和大气温度空间分布模式的差异 ,将热红外遥感图像分为地表贡献和大气贡献两部分 ,通过空间相关性分析 ,寻求从热红外遥感图像中直接分离出大气的空间分布模式的方法 ,以解决地温反演中面临的困难。已有的研究结果说明了在全球变化和定量遥感研究中 ,对地表多尺度空间变化信息作简洁的地学描述的必要性及其重要的应用意义。     

Les récifs coniaciens à rudistes de Tunisie centro-occidentale: sédimentologie, cadre paléogéographique et interprétation séquentielle

Coniacian rudist-buildups have been discovered in the Dernaïa-Tamesmida area (west central Tunisia). They are sedimentologically studied in detail in this paper. Reefs sensu stricto are made up of rudists (Hippuritidae and Radiolitidae) and they show a height:lateral extension ratio of about 1:50. The fore-reef is composed of southwest progradang pelletoid sandwaves, whilst hemipelagic micrite has been deposited in the distal talus. The back-reef lagoons (NE side) include green algae and annelid, miliolid, ostracod and gastropod biotopes. Perilagoonal oolitic bars may border these environments.These reefs evolved in a shallow, relatively open environment. They correspond to barrier-reef complexes which developed at the margin of a generally shallow carbonate ramp.In terms of the sequence stratigraphy, they characterise late low sea levels and especially the high sea levels of the uppermost Turonien-Coniacian depositional sequence.     

A numerical exercise for the definition under undrained conditions of the deep tunnel front characteristic curve

In spite of the increasing diffusion of tunnel boring machines, conventional tunnelling is still largely employed in the excavation of both deep and shallow tunnels characterized by a particularly irregular tracing. Under difficult ground conditions, in conventional tunnelling, the front is frequently reinforced by using fibreglass tubes partially removed during the excavation. This technique is expensive, time-consuming and its design is based on either empirical or very simplified theoretical formulas. Thus, the ultimate objective of the research developed by the authors is to introduce a more sophisticated design approach for this front reinforcement technique. A first step in this direction is this numerical study, in which the mechanical response of deep tunnel faces under undrained conditions is analysed by employing the front characteristic curve: a useful tool largely employed in the literature in analogy with what done for the cavity. The main result of this paper is the “Front Mother Characteristic” curve, obtained by introducing appropriate non-dimensional variables, allowing the designer, once both the system geometry and the soil mechanical properties are assigned, to assess the displacements of tunnel fronts without performing any numerical analysis.     

Autochthonous and allochthonous plant contributions to coastal benthic detritus deposits: a dual-stable isotope study in a volcanic lake

The high numbers of primary producers represent multiple sources of organic matter accumulating onto lake bottoms. The difficulty of distinguishing the relative contribution to the mixture presents considerable challenges to the analysis of these organic deposits. In this study, dual-stable isotope analysis and IsoSource model were used to identify allochthonous and autochthonous components of detritus deposits (Particulate Organic Matter: POM) at two different bottom slope sites of a volcanic lake (lake Bracciano). Experiments were carried out to calibrate IsoSource on constructed plant mixtures and assess changes in isotope ratios during plant decomposition. IsoSource satisfactorily discriminated the constructed mixture sources with a few exceptions. Changes in isotopic enrichment during decomposition were low, and thus did not represent a confounding variable in the isotopic analysis. By contrast, chemical and geological differences of the study sites were associated with differences in plant δ¹³C and δ¹⁵N values (more than 2‰ within single plant species). At both sites, the isotopic signals of POM fell between polygons delineated by source end members with an evident shift of δ¹³C toward allochthonous sources. POM amount and diversity were greater at the flatter bottom site, where allochthonous contributions were larger than at the other site. In particular, IsoSource ranked species contributions as follows: A. glutinosa > P. australis > A. donax > S. alba > P. nigra > the benthic macroalga Chara sp. at the first site, and A. glutinosa > P. nigra > the aquatic macrophyte C. demersum at the latter. The composition of littoral POM was determined by allochthonous sources in proportion to their relative abundances (as percent land cover) with differences between sites due to bottom slope.     

Gravity contributions to the understanding of salt tectonics from the Jebel Cheid area (dome zone, Northern Tunisia)

Detailed gravity measurements integrated with geological data were computed to constrain the mechanisms that were active during the emplacement of the Triassic evaporite-bearing folds of Jebel Cheid from the salt-dome zone in the Atlassic region. The gravity analysis consists in mapping the contrasting gravity responses: complete Bouguer anomaly, residual anomaly and derivative maps; the main results display a positive amplitude gravity anomaly as the response of Triassic evaporite bodies and important NE–SW-trending features at the boundaries between the Triassic outcrops and their enveloping strata. In contrast with gravity calculations of a salt dome structure usually resulting in negative gravity anomaly models, the Jebel Cheid clearly expresses a positive gravity anomaly; furthermore, this result is supported by synthetic gravity interpretation.     

Dependence of eelgrass (Zostera marina) light requirements on sediment organic matter in Massachusetts coastal bays: Implications for remediation and restoration

Using a calibrated bio-optical model we determined that the optical water quality conditions in several nitrogen-impaired embayments and in one unimpaired system were within the range of values known to support eelgrass growth. We also used the model to identify a range of light requirements for eelgrass (Zostera marina). Higher eelgrass light requirements, expressed as a percentage of surface-incident irradiance, corresponded with higher sediment organic matter content. These results corroborated findings by previous studies which indicate a generalized relationship: seagrasses growing in turbid conditions with poorer water and sediment quality have higher light requirements than those growing in less degraded conditions. The mechanistic reason for the variation in light requirements is still not completely explained and cannot be attributed to a single independent variable. Varying light requirement have important implications for eelgrass protection and should be considered when setting restoration targets for eelgrass in water quality and nitrogen remediation programs.