title: Impact of grass cover on the magnetic susceptibility measurements for assessing metal contamination in urban topsoil.
abstract: In recent decades, magnetic susceptibility monitoring has developed as a useful technique in environmental pollution studies, particularly metal contamination of soil. This study provides the first ever examination of the effects of grass cover on magnetic susceptibility (MS) measurements of underlying urban soils. Magnetic measurements were taken in situ to determine the effects on κ (volume magnetic susceptibility) when the grass layer was present (κgrass) and after the grass layer was trimmed down to the root (κno grass). Height of grass was recorded in situ at each grid point. Soil samples (n=185) were collected and measurements of mass specific magnetic susceptibility (χ) were performed in the laboratory and frequency dependence (χfd%) calculated. Metal concentrations (Pb, Cu, Zn and Fe) in the soil samples were determined and a gradiometry survey carried out in situ on a section of the study area. Significant correlations were found between each of the MS measurements and the metal content of the soil at the p<0.01 level. Spatial distribution maps were created using Inverse Distance Weighting (IDW) and Local Indicators of Spatial Association (LISA) to identify common patterns. κgrass(ranged from 1.67 to 301.00×10-5SI) and κno grass(ranged from 2.08 to 530.67×10-5SI) measured in situ are highly correlated [r=0.966, n=194, p<0.01]. The volume susceptibility datasets in the presence and absence of grass coverage share a similar spatial distribution pattern. This study re-evaluates in situ κ monitoring techniques and the results suggest that the removal of grass coverage prior to obtaining in situ κ measurements of urban soil is unnecessary. This layer does not impede the MS sensor from accurately measuring elevated κ in soils, and therefore κ measurements recorded with grass coverage present can be reliably used to identify areas of urban soil metal contamination.
authors.affiliation: School of Geography and Archaeology, National University of Ireland Galway, Galway, Ireland.
authors.forename: Nessa
authors.initials: N
authors.lastname: Golden
authors.affiliation: School of Geography and Archaeology, National University of Ireland Galway, Galway, Ireland.
authors.forename: Chaosheng
authors.initials: C
authors.lastname: Zhang
authors.affiliation: School of Geography and Archaeology, National University of Ireland Galway, Galway, Ireland.
authors.forename: Aaron P
authors.initials: AP
authors.lastname: Potito
authors.affiliation: Environmental Geophysics Unit, Department of Geography, National University of Ireland, Maynooth, Ireland.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Gibson
authors.affiliation: Department of Mathematic & Statistics, University of Limerick, Limerick, Ireland.
authors.forename: Norma
authors.initials: N
authors.lastname: Bargary
authors.affiliation: Earth and Ocean Sciences, School of Natural Sciences and Ryan Institute, National University of Ireland Galway, Galway, Ireland. Electronic address: liam.morrison@nuigalway.ie.
authors.forename: Liam
authors.initials: L
authors.lastname: Morrison
mesh_terms: D002947:Cities; D004784:Environmental Monitoring; D007494:Ireland; D060328:Magnetic Phenomena; D019216:Metals, Heavy / Q000032:analysis*; D006109:Poaceae; D012989:Soil Pollutants / Q000032:analysis*
chemical_list: D019216:Metals, Heavy; D012989:Soil Pollutants
keywords: Environmental magnetism; Grass cover; Magnetic susceptibility; Soil metal contamination; in situ MS