Nutrients and heavy metals in urban soils under different green space types in Anji, China

Abstract

Anji, located in the northwest of Zhejiang Province, was chosen as the first eco-county in China in 2006, as it met the requirements of the ecological assessment criteria enacted by the Ministry of Environmental Protection P.R. China. Soil quality, however, is not included in the environmental criteria of the eco-county assessment. In 2009, a field survey was conducted to evaluate the soil quality in the built-up area of Anji. We investigated the soil pH, bulk density, nutrient content and the concentrations of Cr and Pb in the four main green space types, namely park green (PARK), street green (STREET), attached green space (ATTACH) and protective green (PROT). We believe that this soil quality information will provide a sound basis for eco-county selection in the future. The pH was alkaline, and the bulk density was much higher, in these four green space types than in the local natural soils. Although the soils were fertilized with NPK fertilizer, the amount of soil organic matter, total nitrogen (TN) and total phosphorus (TP) fell into low, moderate to low or extremely low categories in the four green space types. The amount of organic matter is important to restore the soil structure. The TN and TP concentrations were correlated with the concentrations of organic matter (P<0.01). In the PARK and PROT sites, soil organic matter and TN concentrations were higher than in the STREET and ATTACH sites (P<0.05), most likely because the amount of tree coverage was at least 20% in the PARK and PROT. The content of organic matter should be in line with the site conditions. Owing to past use of leaded petrol, the soils of the four green space types have been polluted by Pb in Anji, especially in the STREET and PROT sites. As an eco-county, Anji needs to adapt a soil replacement method and a biological treatment technology to reduce soil Pb pollution to create a favorable environment for the residents of the area. We suggest that soil quality indicators should be brought into the assessment criteria for eco-country establishment in China.