Principal component analysis Sediment

A sample may be characterized by the determination of a number of different analytes. For example, a hydrocarbon mixture can be analysed by use of a series of UV absorption peaks. Alternatively, in a sediment sample a range of trace metals may be determined. Collectively, these data represent patterns characteristic of the samples, and similar samples will have similar patterns. Results may be compared by vectorial presentation of the variables, when the variables for similar samples will form clusters. Hence the term cluster analysis. Where only two variables are studied, clusters are readily recognized in a two-dimensional graphical presentation. For more complex systems with more variables, i.e. //, the clusters will be in -dimensional space. Principal component analysis (PCA) explores the interdependence of pairs of variables in order to reduce the number to certain principal components. A practical example could be drawn from the sediment analysis mentioned above. Trace metals are often attached to sediment particles by sorption on to the hydrous oxides of Al, Fe and Mn that are present. The Al content could be a principal component to which the other metal contents are related. Factor analysis is a more sophisticated form of principal component analysis. 

To illustrate the environmental application of the SIMCA method we examined a set of isomer specific analyses of sediment samples. The data examined were derived from more than 200 sediment samples taken from a study site on the Upper Mississippi River (41). These analytical data were transferred via magnetic tape from the laboratory data base to the Cyber 175 computer where principal component analysis were conducted on the isomer concentration data (ug/g each isomer). 

Pere-Trepat, E., Petrovic, M., Barcelo, D., and Tauler, R., Identification of main microcontaminant sources of non-ionic surfactants, their degradation products and linear alky-lbenzene sulfonates in coastal waters and sediments in Spain by means of principal component analysis and multivariate resolution, Anal. Bioanal. Chem., 378, 642-654, 2004. 

Isaure, M.-P. et al., Quantitative Zn speciation in a contaminated dredged sediment by m-PIXE, m-SXRF, EXAFS spectroscopy and principal component analysis, Geochim. Cosmochim. Acta, 66, 1549, 2002. 

Panhli, F., Manceau, A., Sarret, G., Spadini, L., Bert, V., Kirpichtchikova, T., Matthew, M., and Ahamdach, N. (2005). Evolution of Zn speciation induced by phytostabilization in a contaminated sediment, using scanning electron microscopy, x-ray fluorescence, EXAFS spectroscopy, and principal component analysis. Geochim. Cosmochim. Acta 69, 2265-2284. 

Corresponding to the dimension d = 2, the poset shown in Fig. 19 can alternatively be visualized by a two-dimensional grid as is shown in Fig. 22. Both visualizations have their advantages. Structures within a Hasse diagram, e.g., successor sets, or sets of objects separated from others by incomparabilities, can be more easily disclosed by a representation like that of Fig. 19. In multivariate statistics reduction of data is typically performed by principal components analysis or by multidimensional scaling. These methods minimize the variance or preserve the distance between objects optimally. When order relations are the essential aspect to be preserved in the data analysis, the optimal result is a visualization of the sediment sites within a two-dimensional grid. 

Principal Component Analysis (PCA) is being used increasingly to interpret multivariate data, such as concentrations of metals in sediments. PCA could clearly separate metal patterns in clean, less-clean, and highly contaminated sediments and showed correlations between Co and Mn, Zn and Pb, and a relatively weak relationship between Cu and Cd [71]. 

Fig. 12. Principal components analysis of sediment data from Trinity Bay. All data used were concentrations per dry weight. Aik 2 alkanes, AMPL acetone-mobUe polar lipids, i + ai iso + anteiso, Iso 2 isoprenoid hydrocarbons, PAH 2 polycyclic aromatic hydrocarbons, PL phospholipid,POM particulate organic matter, TG triacylglycerol, 16 1/16 16 1/16 0,16/18 2Cij/2Ci8, 18 2 18 2oo6, 18 3 18 3oo3, 20 4 20 4oo6, 20 5 20 5oo3...

To determine the somce of heavy metals in sediments, mathematical statistics can be used to obtain the results except when it comes to the combination characteristics of elements. Factor analysis is employed to analyse the data of heavy metals in Bohai Bay sediment. Results showed that Cd, Zn, and As are seriously contaminated by human pollution. Pb, Cr, and Hg are partly contaminated by hmnans, while Cu, Fe, and Ni are from natural sources. Principal component analysis (PCA) was used to estimate source of heavy metal contamination in Jiaozhou Bay sediments. Results showed that heavy metal contamination somces in this bay could be divided into three groups, such as industrial wastewater, degradation of organic matter, and erosion of rocks, respectively. The Q-cluster analysis indicated that the degree of pollution near the estuary was heavy, but was light far away from the estuary (Li Y et al., 2006). 

Li Y, Yu JJ (1999) Geochemical characteristics of phosphorus near the Huanghe River Estuary. Chin J Oceanol Limnol 17(4) 359-365 Li Y, Yu, ZM, Song XX (2006) Application of principal component analysis (PCA) for the estimation of source of heavy metal contamination in marine sediments. Environ Sci 27(1) 137-141 (in Chinese with English abstract)... 

Fij ure Jl. A principal components analysis (PCA) biplol can be used for comparing sediment compositions from different sites. A range of sediment compositions is seen for lakes from the Jianghan Plain. Central China (Figure from Boyle et al. 1999),... 

The close link between lakes and their catchments was evident in a study of spatial variability in surface sediment composition in a small northern Swedish lake (Korsman et al., 1999). In this study, the information in the near-infrared spectra of surface sediment samples was used to determine how sediment composition varied over the lake bottom. The study showed that the NIR spectra per se provide information that can be used to study sediment characteristics as well as sediment focusing in a qualitative way. The variance in the NIR spectra (Fig. 7) was only to a minor extent explained by the variation in water depth or sediment organic content. More importantly, the spatial evaluation of the spectral data suggested that NIR analysis of lake sediments mainly reflects sediment properties that cannot be simply explained by water depth or amount of organic matter. Principal component modelling of NIR spectra from 165 coring sites, established along a 50m x 50m... 

Figure 7. Near-infrared spectral variation in surface sediments of Stor-Skdrtrdsket. The figure shows the spectral variance in the first principal component from a PCA-analysis based on 165 surface sediment samples. The bottom topography is presented as depth curves with a 2-m interval. Modified from Korsman et al. (1999).

The distinctive absorption bands associated with individual molecules enable the analysis of individual components in even complex mixtures by either evaluating isolated bands or by applying modern chemometric methods (e.g. Principal compound analysis), which process the entire spectral information. As a consequence, mid-IR spectroscopy represents a widely applicable tool for investigations of dynamic processes (e.g. chemical reactions, phase transitions, sedimentations, etc.). Moreover, information about interactions of the analyst with the surrounding media can be acquired because vibrational modes tend to be affected by the molecule s environment (Raichlin Katzir, 2008). 

By comparing the actual composition of sea water (sediments + sea -f- air) with a model in which the pertinent components (minerals, volatiles) with which water has come into contact are allowed to reach true equilibrium, Sillen in 1959 epitomized the application of equilibrium models for portraying the prominent features of the chemical composition of this system. His analysis, for example, has indicated that contrary to the traditional view, the pH of the ocean is not buffered primarily by the carbonate system his results suggest that heterogeneous-equilibria of silicate minerals comprise the principal pH buffer systems in oceanic waters. This approach and its expansion have provided a more quantitative basis for Forchbammer s suggestion of 100 years ago that the quantity of the different elements in sea water is not proportional to the quantity of elements which river water pours into the sea but is inversely proportional to the facility with which the elements in sea water are made insoluble by general chemical actions in the sea. 

In the investigation of organic compounds in sediments the experimental procedures invariably include a separation scheme to divide and simplify total sediment extracts into suitable fractions of different polarity. Typically, this experimental procedure will yield a number of fractions containing principally hydrocarbon, ketone, carboxylic alcohol or polar components. The reconstituted ion (RIC) from gc-ms analysis of three such discussed herein to illustrate the observed of marker compounds in marine sediments and inferred biological origins. 

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