Spatial pattern analysis of Ni concentration in topsoils in the Campania Region (Italy)

Abstract

The objective of this study is to demonstrate the combined use of point pattern, multifractal and digital image processing analysis in order to recognise and characterise spatial patterns of Ni concentration in topsoil in the Campania Region (Italy). After an exploring univariate statistical analysis, spatial clusters and outliers were revealed by Moran-I autocorrelation among the original measurement points. The linear and accurate Triangular Irregular Network (TIN) interpolation of Ni concentrations fitted at 3663 sample points was used. Successive moving average smoothing was applied to generalise the TIN model and to suppress small irregularities. The resulting raster map was the subject of multifractal analysis to classify the TIN-based Ni raster concentration map and to define Ni-baseline values. Digital Image Processing including lineament density and spatial variability index calculation was performed not only on the TIN-based total Ni raster map but also on its baseline map to recognise spatial patterns. The Ni-baseline map was given particular attention because the spatial distribution and variance in this map are assumed to be related to different geogenic processes.The highest spatial variability zones of total Ni concentrations are located in Campi Flegrei and around Napoli where low Ni values and spatial outliers are clustered. The highest variability zones can be found in topsoils over volcanoclastic rocks and they are related to urbanised and agricultural land use areas. The lowest variability zones coincide with the Eocene-Miocene argillaceous sediments of the Apennine Mts where the highest Ni values were measured.The highest spatial variability in the Ni-baseline map is in a NW-SE zone following the carbonate outcrops of the Apennine Mts (e.g. Mt. Alburni, Mt. Picentini). Another interesting NW-SE trending moderate to high variability zone was also identified following the alluvial plains of the Apennine's rivers. The Apennine's rivers seem to have played a crucial role in the redistribution of Ni through sediment transport processes resulting in higher spatial variability of Ni in the studied soils. The lowest variability zone is located south of Campi Flegrei and Napoli and it occupies the vast area of the Campanian Plain.