Antonella Buccianti

Compositional data analysis in the geosciences : from theory to practice

Since Karl Pearson wrote his paper on spurious correlation in 1897, a lot has been said about the statistical analysis of compositional data, mainly by geologists such as Felix Chayes. The solution appeared in the 1980s, when John Aitchison proposed to use Iogratios. Since then, the approach has seen a great expansion, mainly building on the idea of the ‘natural geometry’ of the sample space. Statistics is expected to give sense to our perception of the natural scale of the data, and this is made possible for compositional data using Iogratios. This publication will be a milestone in this process. This book will be of interest to geologists using statistical methods. It includes the intuitive justification of the methodology, convincing through case studies and presenting user-friendly software, which includes a section for those who need to see the proof of the mathematical consistency of the methods used.

Exploratory compositional data analysis

Abstract This paper presents the first steps that should be performed whenever the study of a compositional dataset is initiated. Centre, variation matrix and total variance of a compositional dataset are introduced. In addition the biplots are also introduced as a powerful tool to analyse and discover special features related to subcompositions. The exploratory methodology is applied to a dataset consisting of the major, minor and trace elements composition of soil samples from several places in Tuscany (Italy). The structure of the data, collected from three different known country rocks of ophiolitic nature (basic and ultrabasic rocks), represent an interesting case study for experimenting on new methodologies of statistical investigation and for pointing out differences related to parental chemistry and mineralogy as well as the nature of processes to be related to the subsequent evolution.

1980–1990: Ten years of geochemical investigation at Phlegrean Fields (Italy)

Abstract A systematic geochemical investigation on the thermal manifestations of the volcanic area of Phlegrean Fields started in 1980, with the aim of obtaining useful information about the changes possibly occurring at the same time of vertical ground movements, termed as “bradyseismic”, which frequently interested this area. The attention was initially given to the fumaroles and the boiling pools of Solfatara and Pisciarelli, then subsequently extended to thermal springs, dug wells, and crater lakes. Analytical data pertaining to a period preceding the last crisis of 1982–1984 were then available, as well as other data collected during the previous crisis of 1970; a comprehensive picture of the variations observed before, during and after the acceleration of vertical movement has been drawn. According to the results obtained, the intrusion of a magmatic body as the trigger of the observed ground deformation is considered unrealistic. The whole area appears now in a quiet stage, and no further perturbation is expected without previous significant tectonic activity; chemical precursors appear suitable for an early detection of changes occurring at depth, to forecast possible consequences to be expected in the surface environment.

Biotic signals from nannoflora across the iridium anomaly in the upper Eocene of the Massignano section: evidence from statistical analysis

Abstract Strong evidence for a major late Eocene impact, including an iridium-rich layer and shocked quartz, has been found in the Massignano section (central Italy), stratotype of the Eocene/Oligocene boundary. Quantitative calcareous nannofossils analyses have been performed and classical and multivariate statistical techniques have been applied to assess the paleonvironmental effect of this impact on the nannoflora. Abundance patterns indicate: (1) a warming episode just above the iridium layer; (2) a subsequent slight cooling trend, probably related to the global cooling during late Eocene to early Oligocene; (3) marked fluctuations in the trophic resources and an increase in near-shore taxa in the upper part of the interval; (4) increase in low-nutrient taxa in biotite-rich layers, just above the iridium level, possibly related to lowered productivity linked to volcanic activity. All these signals appear most likely to be the result of long-term climatic changes rather than to short-term effects of extraterrestrial impact. In addition, cluster analysis was performed on the assemblage data. This delineated similarities among different taxa and grouped samples with similar assemblages. Several groups related to temperature-, trophic- and unknown-preference conditions have been distinguished. A consistent difference in the abundances of the taxa and in their correlation has been detected between samples above and below the iridium level. This change appears to be related to two important sedimentary features which are found in the interval above the iridium occurrence: (1) the presence of biotite-rich layers linked to increasing volcanism and (2) a conspicuous color transition from reddish to greenish related to changes in sedimentary environments (e.g. variations in trace element abundance). These environmental changes rather than the impact may have affected the nannoflora assemblages.

The 87Sr/86Sr strontium isotopic systematics applied to Glera vineyards: A tracer for the geographical origin of the Prosecco

Glera vineyards from the Prosecco wine district in northern Italy have been characterised in terms of the (87)Sr/(86)Sr isotope-ratio of musts from the 2010, 2011 and 2012 vintages, coupled with the isotopic analysis of Sr in the labile fraction of the soils of provenance. For a single vineyard, detailed Sr isotopic analyses were carried out in sequentially extracted soil fractions at three different depths, and in the grape components (skin, seeds, must and stem), in order to verify the lack of Sr isotopic fractionation within the plant. The (87)Sr/(86)Sr in must, seeds and stem overlaps within experimental uncertainties; skins are shifted towards a lower Sr isotopic composition. A large range of Sr isotopic compositions ((87)Sr/(86)Sr between 0.70706 and 0.71215) characterizes musts from the different vineyards, notwithstanding the relatively limited extension of the investigated geographic area. A statistically significant correspondence between the soil labile fraction and must is observed.

Exploring element accumulation patterns of a metal excluder plant naturally colonizing a highly contaminated soil.

This work investigates the element distribution in Silene paradoxa growing on the mine dump of Fenice Capanne (Tuscany, Italy). The accumulation of As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn in root apoplast and symplast and in shoot was assessed and compared to the levels of the same metals in the respective rizosphere soils, analyzing both the total and the phytoavailable fractions. Levels of As, Cu, Fe, Pb and Zn, were above toxicity thresholds in both soil and shoot samples. Inter- and intra-element correlations were analyzed in plant and soil using different statistical methods. Soil total and phytoavailable metal concentration were shown not to be dominant in determining metal accumulation by the plant, since no significant positive correlation was found between metal concentration in soils and plants. Moreover, results indicated that S. paradoxa was able to cope with the studied multi-metal contaminated soil excluding the elements from its tissues and preferentially accumulating them into the root compartment, thus suggesting this species as possible good candidate for phytostabilization purposes.

Morphometrical characterization of the Austropotamobius pallipes species complex

Genetic studies have shown that the threatened crayfish Austropotamobius pallipes species complex is composed of two lineages (A. italicus and A. pallipes), both occurring in Italy. However, the issue surrounding their taxonomic status has not yet been solved even though the confused taxonomy may hamper attempts to conserve indigenous crayfish. The aim of this study was to develop methods for the morphometrical characterization of the A. pallipes species complex. Having analysed 18 morphometric variables on a total of 44 specimens of each lineage, we showed that the tip of the rostrum could be used to discriminate A. italicus and A. pallipes. Such discrimination was also obtained by analysing the size and shape of both the female spermatophoric plate and the male gonopods. These results confirm the potential to adopt morphometric studies to complement the genetic characterization of cryptic species.

Determination of Organic Acids in Plants of Silene paradoxa L. by HPLC

According to the general behavior that organic acids steadily bind metals, a specific and highly reproducible HPLC separation method with photodiode array detection has been improved for their determination and quantification in biological materials. The separation was carried out on an Alltima C-18 reverse phase column. The mobile phase was 125 mM KH2PO4, adjusted to pH 2.5 with concentrated H3PO4, and optimum separation efficiency was obtained by using a 2 mL min(-1) flow rate. Detection wavelength for quantitative measurement was 210 nm. The run time of each sample was 20 min, with a spectra collection frequency of 5 spectra s(-1). Organic acids were identified by comparing the retention times of the samples against retention times of the standards and confirmed with spectral (190-700 nm) signature. Because organic acids could steadily bind metals in plant tissues and due to the strong matrix effect observed, the addition method was applied for quantitative analysis and its performance evaluated.

Insights into Late Quaternary calcareous nannoplankton assemblages under the theory of statistical analysis for compositional data

Abstract The investigation of changes in abundance of calcareous nannofossil associations is fundamental for palaeoclimatic and palaeoceanographic reconstructions. In general, since the number of recognised species is high, the numerical and graphical treatments of the data play an important role to validate hypotheses about the influence of physico–chemical factors on the quality of past environments, as reflected by changes in abundance. Moreover, the application of multivariate procedures may be useful for improving interpretation of the overall data structure. Calcareous nannofossil associations analysed in this work are related to core GNS84-C106 collected in the Gulf of Salerno (Campania, southern Italy) under a national interdisciplinary research programme aimed at recognising the impact of natural events on biological communities during the last 20 kyr. Biplot analysis of compositional data was applied to indicate the presence of subcompositions or, in other words, to identify strong relationships among a limited number of species that can be interpreted from a palaeoenvironmental point of view. This investigation was followed by the application of simplicial principal component analysis with the aim of determining, from a numerical point of view, the laws for describing and modelling the behaviour of the species involved in these subcompositions. In this work, all statistical methods were applied by taking rigorously into account the sample space of compositional data (i.e. data matrices whose rows sum to 100%). From a general point of view, the results obtained, related to the detection of new parameters to be used for monitoring the quality of the past environment, have encouraged us to promote the application of statistical methodologies that take into account the correct sample space for compositional data. In this context, inferential applications and modelling can be developed under a correct theoretical framework.

Group specific vocal signature in free-ranging wolf packs

Acoustic communication conveys a variety of information that is a helpful tool for animal conservation. The wolf is an elusive species, which can be detected through the howls that individuals emit. In this study we investigated the acoustic features of wild wolf pack howls from five locations in the province of Arezzo, Italy. We tested the hypothesis that each group had a distinctive vocal signature. Our results showed that these wolf packs emitted howls with significantly distinctive acoustic structures. We hypothesized that group-specific vocal signatures require temporal stability to be functional. Indeed, we did not find any statistical differences in howls collected from the same location during the same season or for 2 consecutive years. We suggest that the acoustic features of howls can be used to distinguish wolf packs in the wild.