Abstract
Remnant forests in urban areas provide vital ecosystem services but are susceptible to many human activities including heavy metal emissions. In this study, we collected 192 samples of mineral soils at depths of 0–3, 3–13 and 13–23 cm in 16 remnant forests (eight natural forests and eight plantation forests) in the urbanized Pearl River Delta, China. We assessed the potential risks of soil Cu, Zn, Pb, Mn, Ni and Cr to the vegetation in these forests based on their total and 0.1 M HCl extractable concentrations. The mean concentrations for all soil samples were 202.7, 102.0, 75.7, 24.3, 30.3, and 7.8 mg/kg for Zn, Mn, Pb, Cu, Cr, and Ni, respectively. Compared to background values, total soil Zn concentrations were higher for both the natural and plantation forests located near both industrial and non-industrial sites; total soil Cu and Pb concentrations were higher near industrial sites, particularly for the natural forests. Total soil Pb, Cu, and Mn concentrations and exchangeable soil Pb and Mn concentrations were higher in the natural forests than in the plantation forests. Total soil Cu and Pb concentrations and extractable soil Cu, Pb, Zn, and Mn concentrations decreased with soil depth. Based on these results and previous findings of continued acidification and low phosphorus availability of these soils, we recommend that the growth of these remnant forests can be improved by the application of phosphate rock.
Highlights
Remnants of forest ecosystems occur in urban areas around the world [1,2]
The mean total soil Mn concentration was much lower than its background value for both location types and forest types except for the natural forests in the industrial locations where the mean total soil Mn concentration was similar to the background concentration (Table 4)
The results of the previous and current study indicate that forest ecosystems in the urbanized areas of the Pearl River Delta (PRD) general suffer from Cu, Pb, and Because no heavy metal-containing fertilizers or agricultural or industrial wastes have been applied to these forests, the high concentrations of heavy metals in the soil may be largely attributed to atmospheric deposition [7,8,18]
Summary
Forest remnants are typically small patches, they can provide important ecological services that improve human well-being in urban areas They can, for example, improve urban air quality, ameliorate the heat island effect, preserve biodiversity, and provide wood products, recreational venues, and landscape aesthetics [1,2,3,4]. Soil total Pb (a) and extractable Mn (b) concentrations were relatively higher in the industrial locations than in the non-industrial locations for the natural forests. A horizon (generally about 20 cm depth) in Guangdong province, China where Foshan located, data is mean value, n = 167 [31]. Total soil Zn concentration was markedly higher than the background concentration for all soil depths, both forest types, and both location types (Table 4).
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