Principal component analysis (PCA) was used to deduce the common origin of trace contaminants in a slightly contaminated, strongly seasonal river of low-average discharge, aiming to ascertain the type of the pollution. Splitting of data into categories according to specific conductance was essential to reach conclusions. Dry-season data allowed the pinpointing of polluting sites by means of the biplots resulting from the representation of the scores on the components. Concentrations corresponding to the wet seasons yielded no useful results probably due to the high percentage of data below detection limits for 2 of the 6 variables. The Arenales River in NorthWest Argentina was monitored by means of 19 sampling campaigns between 2003 and 2005 comprising two hydrological cycles, at seven locations along a 25 km section of the river course across the city of Salta. Pollution of the river was not severe, overall mean values in µg/ℓ being: As 1.2; B 490; Cu 4; Fe 92; Pb 13; Zn 83. Simple correlation analysis revealed no significant correlation between these elements. The high positive loadings of variables B and As concentrations on the first principal component and the biplots indicate that their main common point sources are boron mineral deposits still existing in the urban area. Interpretation of the biplots shows that Cu, Fe and Zn contamination also originated at point sources, the contribution of the sewage treatment plant being negligible.
Hierarchical clustering and principal component analysis applied to chemical components and physicochemical properties of well water proved to be a useful tool for identification and characterisation of aquifers. Underground water of Lerma Valley (Salta, Argentina) was examined for its physical and chemical properties by sampling 46 wells located in two adjacent areas separated by hills, one of them polluted with boron since 1991. Hierarchical clustering splits sampled sites into two main clusters, corresponding to the two areas, establishing the fact that the aquifers should be considered as two different entities in spite of their common recharge area. Values of boron concentration in the eastern area decreased in most of the wells since the pollution sources were eradicated, while four of them experienced a substantial increase, proof of the slow self-recovery of the aquifer. The use of principal component analysis provided evidence of the incipient boron pollution of the aquifer of the western area.
En este trabajo se realizó un estudio estadístico de variablesfísico químicas asociadas al fenómeno de contaminación ambiental,en particular concentración media mensual de SO2, medidas en la ciudad Salta Capital, Argentina, simultáneamente a concentracionesde NO2 y O3. Las series bajo estudio presentaban comportamientosdinámicos no lineales, datos atípicos y cambios estructurales, lo quehizo imposible modelarlas con tipologías econométricas tradiciones(AR, MA, ARMA, ARIMA, entre otras). Una solución eficiente quese encontró, hace uso de la teoría de los perceptrones multicapa.Mediante el modelo estructural de series de tiempo, esta solución sepresenta como un proceso matemático iterativo que permite obtenerun modelado final el cual tiene una muy alta confiabilidad (95%),para realizar pronósticos a futuro sobre el comportamiento de lavariable estudiada.
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