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  1. Article: Advancements in hydrochemistry mapping: methods and application to groundwater arsenic and iron concentrations in Varanasi, Uttar Pradesh, India

    Olea, Ricardo A / Juan José Egozcue / N. Janardhana Raju / Shubhra Singh / Vera Pawlowsky-Glahn

    Stochastic environmental research and risk assessment. 2018 Jan., v. 32, no. 1

    2018  

    Abstract: The area east of Varanasi is one of numerous places along the watershed of the Ganges River with groundwater concentrations of arsenic surpassing the maximum value of 10 parts per billion (ppb) recommended by the World Health Organization in drinking ... ...

    Abstract The area east of Varanasi is one of numerous places along the watershed of the Ganges River with groundwater concentrations of arsenic surpassing the maximum value of 10 parts per billion (ppb) recommended by the World Health Organization in drinking water. Here we apply geostatistics and compositional data analysis for the mapping of arsenic and iron to help in understanding the conditions leading to the occurrence of elevated level of arsenic in groundwater. The methodology allows for displaying concentrations of arsenic and iron as maps consistent with the limited information from 95 water wells across an area of approximately 210 km2; visualization of the uncertainty associated with the sampling; and summary of the findings in the form of probability maps. For thousands of years, Varanasi has been on the erosional side in a meander of the river that is free of arsenic values above 10 ppb. Maps reveal two anomalies of high arsenic concentrations on the depositional side of the valley, which has started seeing urban development. The methodology using geostatistics combined with compositional data analysis is completely general, so this study could be used as a prototype for hydrochemistry mapping in other areas.
    Keywords arsenic ; drinking water ; geostatistics ; groundwater ; hydrochemistry ; iron ; prototypes ; rivers ; uncertainty ; urban development ; watersheds ; wells ; World Health Organization ; Ganges River ; India
    Language English
    Dates of publication 2018-01
    Size p. 241-259.
    Publishing place Springer Berlin Heidelberg
    Document type Article
    ZDB-ID 1481263-0
    ISSN 1436-3259 ; 1436-3240 ; 0931-1955
    ISSN (online) 1436-3259
    ISSN 1436-3240 ; 0931-1955
    DOI 10.1007/s00477-017-1390-3
    Database NAL-Catalogue (AGRICOLA)

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  2. Article ; Online: Proportionality

    David Lovell / Vera Pawlowsky-Glahn / Juan José Egozcue / Samuel Marguerat / Jürg Bähler

    PLoS Computational Biology, Vol 11, Iss 3, p e

    a valid alternative to correlation for relative data.

    2015  Volume 1004075

    Abstract: In the life sciences, many measurement methods yield only the relative abundances of different components in a sample. With such relative-or compositional-data, differential expression needs careful interpretation, and correlation-a statistical workhorse ...

    Abstract In the life sciences, many measurement methods yield only the relative abundances of different components in a sample. With such relative-or compositional-data, differential expression needs careful interpretation, and correlation-a statistical workhorse for analyzing pairwise relationships-is an inappropriate measure of association. Using yeast gene expression data we show how correlation can be misleading and present proportionality as a valid alternative for relative data. We show how the strength of proportionality between two variables can be meaningfully and interpretably described by a new statistic ϕ which can be used instead of correlation as the basis of familiar analyses and visualisation methods, including co-expression networks and clustered heatmaps. While the main aim of this study is to present proportionality as a means to analyse relative data, it also raises intriguing questions about the molecular mechanisms underlying the proportional regulation of a range of yeast genes.
    Keywords Biology (General) ; QH301-705.5
    Subject code 310
    Language English
    Publishing date 2015-03-01T00:00:00Z
    Publisher Public Library of Science (PLoS)
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  3. Article: Compositional Data Analysis (CoDA) as a tool to study the (paleo)ecology of coccolithophores from coastal-neritic settings off central Portugal

    Guerreiro, Catarina / Anabela Oliveira / Aurora Rodrigues / Mário Cachão / Vera Pawlowsky-Glahn

    Sedimentary geology. 2015 Apr. 15, v. 319

    2015  

    Abstract: Whereas using the species percentages is the standard analytical procedure used to infer species ecological preferences, independently of taphonomical effects, the closure problem associated with closed number systems and subsequent inconsistency of ... ...

    Abstract Whereas using the species percentages is the standard analytical procedure used to infer species ecological preferences, independently of taphonomical effects, the closure problem associated with closed number systems and subsequent inconsistency of determining percentages may lead to spurious correlations, biased statistical analysis and misleading interpretations. To avoid these problems, we applied Compositional Data Analysis (CoDA) to investigate the (paleo)ecological preferences and spatial distribution of coccolith assemblages preserved in seafloor sediments, using as a case-study the central Portuguese submarine canyons and adjacent shelf-slope areas. Results from using the isometric log-ratio (ilr) approach from CoDA are compared with results from using classical analytical methods, and further discussed.While providing scale invariance and subcompositional coherence, CoDA is revealed to be a consistent statistical tool to infer the (paleo)ecological preferences of coccolithophores, corroborating earlier work based on from percentage determinations. Results of this study clearly confirmed the coastal-neritic distribution of coccoliths from Gephyrocapsa oceanica, Helicosphaera carteri and Coronosphaera mediterranea, whereas coccoliths from Calcidiscus leptoporus, Umbilicosphaera sibogae, Umbellosphaera irregularis and Rhabdosphaera spp. more typically occur offshore. Differences between canyons and adjacent shelf and slope areas were also confirmed, namely the (a) greater importance of the coastal-neritic assemblage possibly resulting from local and persistent nutrient pumping in these areas, and (b) stronger mixing of coccoliths from coastal and oceanic species in upper canyon reaches, resulting from the focused coastward advection of more oceanic water masses along their axes.Unlike the results from both ilr-coordinates and the percentage approaches, both coccolith concentrations and fluxes showed that spatial trends in which the species ecological inter-relationships appear to be masked by taphonomical phenomena, especially towards the coast and in the canyons, suggesting the two latter approaches are not suitable to perform (paleo)ecological inferences in more dynamic coastal-neritic settings.Our study suggests that the (paleo)ecological signal preserved in the studied sediment samples is persistent enough to be revealed by both CoDA and percentages. Yet, given that CoDA provides the only statistical solution to coherently draw (paleo)ecological interpretations from compositional data, our recommendation is that CoDA should always be used to test and validate any ecological signals obtained from percentage distributions.
    Keywords advection ; analytical methods ; Calcidiscus ; canyons ; coasts ; Coronosphaera ; data analysis ; Helicosphaera ; mixing ; paleoecology ; sediments ; statistical analysis ; Portugal
    Language English
    Dates of publication 2015-0415
    Size p. 134-146.
    Publishing place Elsevier B.V.
    Document type Article
    ZDB-ID 216739-6
    ISSN 0037-0738
    ISSN 0037-0738
    DOI 10.1016/j.sedgeo.2015.01.012
    Database NAL-Catalogue (AGRICOLA)

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