Mineral magnetic properties of urban forest soils tailored to soil quality indicator

Abstract

Ecosystem surveys reveal the benefits to society, provided by the natural environment, which in turn is chiefly regulated by the geodiversity. Thus, physico-chemical processes regulating the solid rock/sediment response to environmental changes comprise an important part in the assessment of natural ecosystems. Environmental magnetism provides a wide set of field and laboratory data able to discover natural and anthropogenic processes affecting different environmental compartments. Despite this, geosciences and environmental magnetism in particular, are under-represented in ecosystem assessment tools due to the lack of unified and clearly articulated application template. In this study, we propose a new mineral magnetic indicator of soil’s quality, based on detailed appraisal of field- and laboratory mineral magnetic characteristics of a collection of 453 urban topsoil samples. Field magnetic susceptibility (Kfield) and laboratory measurements of magnetic parameters revealed that soil magnetism reflects sensitively soils affected by vehicle traffic and park’s alleys foot load from semi-natural soil. Geochemical analyses of the content of Potentially Toxic Elements (PTEs) on a sub-set of samples was used for magnetic data validation. Correlation analysis showed strong positive link between magnetic parameters and the main PTEs, the strongest being obtained between magnetic susceptibility and the complex pollution load index (PLI). Factor analysis suggested that three factors account for the 74% of data variability. They were assigned to: 1) traffic emissions, 2) pedogenic contribution and 3) lithogenic input plus anthropogenic organic waste additions. Novel mineral magnetic Indicator (MAG) was defined, combining information on composition, concentration and grain size of ferrimagnetic iron oxides, using scored contributions from five magnetic parameters and grain size sensitive ratios. Evaluation of the spatial MAG map showed its suitability as a complex indicator of soils’ contamination with PTEs. Kfield reflected sensitively overall anthropogenic load not necessarily related to PTEs contamination but also to foot trampling and application of fertilizers.