Application of the self-organizing mapping in exploration of the environmental impact of a tsunami disaster

A self-organizing map (SOM) algorithm was applied to evaluate the geochemical and environmental impact of 26th December 2004 tsunami, based on interelemental and intersite relations of sediment chemistry. The study was carried out based on data sets, including contents of salts (K, Na, Ca, Mg, Cl and SO4) leached with deionized water, heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) in acid leachable fraction, metalloids (As, Sb and Se) in exchangeable fraction, as well as both total Hg and mercury in the form of various species (organomercury, water-soluble, acid-soluble, bound to humic matter and bound to sulfides) in sediment samples. SOM-supported exploration were performed for two separate data sets. The first run was applied for analytical results concerning sediments taken less than 50 days after tsunami event while the second one concerned results obtained for samples collected in the same location one year later, after rainy season. In the case of the 2005-run, based on mutual linkage, complete set of variables could be conditionally divided into general groups showing of their patterns related to their major source as salt and wastewater. Classification results revealed natural clusters of sediment samples in relation to their location and to the magnitude of the impact of tsunami wave. Numerous clusters reflect general chemical composition of tsunami sediments while clusters containing isolated sampling locations reflect site-specific conditions, partially related to anthropogenic impact. The cleaning effect of the rainy season in Thailand was observed, based on 2006-run exploaration results. The chemical composition of tsunami sediments was unified for 93% of samples. General patterns related to major source of analytes were analogous compared to the 2005-run. These studies demonstrate that SOM has the potential to successfully assist the assessment of the environmental impacts of a tsunami disaster and the role of a tsunami sediments as potential carriers of pollution.