http://hdl.handle.net/10256/617 2025-08-13T20:51:37Z http://hdl.handle.net/10256/710 A compositional approach to stable isotope data analysis Tolosana Delgado, Raimon; Otero Pérez, Neus; Soler i Gil, Albert Mateu i Figueras, Glòria; Barceló i Vidal, Carles Isotopic data are currently becoming an important source of information regarding sources, evolution and mixing processes of water in hydrogeologic systems. However, it is not clear how to treat with statistics the geochemical data and the isotopic data together. We propose to introduce the isotopic information as new parts, and apply compositional data analysis with the resulting increased composition. Results are equivalent to downscale the classical isotopic delta variables, because they are already relative (as needed in the compositional framework) and isotopic variations are almost always very small. This methodology is illustrated and tested with the study of the Llobregat River Basin (Barcelona, NE Spain), where it is shown that, though very small, isotopic variations comp lement geochemical principal components, and help in the better identification of pollution sources 2005-10-01T00:00:00Z http://hdl.handle.net/10256/709 Statistical Analysis of Eco-Toxicologic Data of Mammals from a Polluted Area Sánchez-Chardi, Alejandro; López Fuster, María José; Egozcue, Juan José Mateu i Figueras, Glòria; Barceló i Vidal, Carles Several eco-toxicological studies have shown that insectivorous mammals, due to their feeding habits, easily accumulate high amounts of pollutants in relation to other mammal species. To assess the bio-accumulation levels of toxic metals and their in°uence on essential metals, we quantified the concentration of 19 elements (Ca, K, Fe, B, P, S, Na, Al, Zn, Ba, Rb, Sr, Cu, Mn, Hg, Cd, Mo, Cr and Pb) in bones of 105 greater white-toothed shrews (Crocidura russula) from a polluted (Ebro Delta) and a control (Medas Islands) area. Since chemical contents of a bio-indicator are mainly compositional data, conventional statistical analyses currently used in eco-toxicology can give misleading results. Therefore, to improve the interpretation of the data obtained, we used statistical techniques for compositional data analysis to define groups of metals and to evaluate the relationships between them, from an inter-population viewpoint. Hypothesis testing on the adequate balance-coordinates allow us to confirm intuition based hypothesis and some previous results. The main statistical goal was to test equal means of balance-coordinates for the two defined populations. After checking normality, one-way ANOVA or Mann-Whitney tests were carried out for the inter-group balances 2005-10-01T00:00:00Z http://hdl.handle.net/10256/707 Application of discriminant function analysis and change-point problem in dating volcanic ashes Lee, Bik-wa; Bacon Shone, John Mateu i Figueras, Glòria; Barceló i Vidal, Carles The application of Discriminant function analysis (DFA) is not a new idea in the study of tephrochrology. In this paper, DFA is applied to compositional datasets of two different types of tephras from Mountain Ruapehu in New Zealand and Mountain Rainier in USA. The canonical variables from the analysis are further investigated with a statistical methodology of change-point problems in order to gain a better understanding of the change in compositional pattern over time. Finally, a special case of segmented regression has been proposed to model both the time of change and the change in pattern. This model can be used to estimate the age for the unknown tephras using Bayesian statistical calibration 2005-10-01T00:00:00Z http://hdl.handle.net/10256/705 The chemical variability at the surface of Mars: implications for exogenic processes Kolb, Christopher; Martín Fernández, Josep Antoni; Abart, Rainer; Lammer, Helmut; Thió i Fernández de Henestrosa, Santiago; Pawlowsky-Glahn, Vera Mateu i Figueras, Glòria; Barceló i Vidal, Carles The chemical composition of sediments and rocks, as well as their distribution at the Martian surface, represent a long term archive of processes, which have formed the planetary surface. A survey of chemical compositions by means of Compositional Data Analysis represents a valuable tool to extract direct evidence for weathering processes and allows to quantify weathering and sedimentation rates. clr-biplot techniques are applied for visualization of chemical relationships across the surface (“chemical maps”). The variability among individual suites of data is further analyzed by means of clr-PCA, in order to extract chemical alteration vectors between fresh rocks and their crusts and for an assessment of different source reservoirs accessible to soil formation. Both techniques are applied to elucidate the influence of remote weathering by combined analysis of several soil forming branches. Vector analysis in the Simplex provides the opportunity to study atmosphere surface interactions, including the role and composition of volcanic gases 2005-10-01T00:00:00Z