Spatial distribution patterns of chosen chemical elements with different spatial scales in London topsoils and Lake Taihu sediments

Abstract

As geographical information system (GIS) and spatial analysis techniques have been widely used in soil contamination, the methodologies applied in urbanized area and submillimetre profiles widened their utility. In this study, the spatial distribution patterns of phosphorus (P), aluminium (Al), calcium (Ca) and lead (Pb) in urban topsoils and labile P in lake sediments have been investigated using GIS-based techniques. The valuable results would provide information for soil management. The P is a necessary and limiting nutrient element for plants. The excessive P is becoming a worldwide environmental concern because it could cause water eutrophication, then threaten natural ecosystems and even human life. The hot spot map and results of analysis of variance (ANOVA) showed a mixed natural and anthropogenic control on P in the Greater London Authority (GLA) area based on analysis of 6467 topsoil samples. In the aspect of natural influences, alluvium and river terrace deposits had elevated P content. The hot spot map clearly demonstrated that the hot spots in the lower Thames Estuary disappeared suddenly, indicating the influences of the tidal dilution on the P-enriched soils. The high values clusters of hot spots in the city center and the built-up areas suggested that soil P content was heavily affected by human activities, which had also been revealed by the significant difference between the P concentration in urbanized area and that in non-urbanized area. The GIS techniques were used to visualize the labile P distribution in sediments of Lake Taihu at a submillimetre scale, showing low labile P in winter and high labile P in summer. The significant spatial autocorrelation in sediment profiles was revealed by the high values of Moran’s I. The distinct submillimeter-scale spatial patterns with seasonal changes were exhibited by the semivariograms. The impact of temperature on the mobility and spatial distribution of labile P in sediments was revealed by the apparently different levels of spatial variation during summer and winter. Except for P, the spatial distribution of chemical elements in urban topsoils can be changed with different degrees. Three metals, Al, Ca and Pb in urban topsoils of the GLA area, displayed different levels of geogenic and anthropogenic influences, revealed by ANOVA and GIS-based spatial analysis. The spatial distribution of Pb was remarkably changed by human activities; The inert element Al could still be able to reserve its natural spatial distribution in the highly urbanized London and Ca exhibited the hybrid spatial distribution affected by both natural factors and human activities. Since Pb is often affected by human activities and it is a toxic heavy metal that is detrimental to human health as well as social behavior, we attempted to prepare the investigation of the relationship between Pb and socioeconomic or healthy status in the GLA area in the future. The first challenge is the spatially misaligned data when linking point Pb concentration to the socioeconomic or healthy data of the ward. This study has highlighted the point-to-area transformation issue on the basis of review and comparison of various methodologies. The advantages and disadvantages of different methods have been pointed out. The method of median block inverse distance weighted (IDW) interpolation was recommended for our further investigations.