The influence of different land uses on mineralogical and chemical composition and horizonation of urban soil profiles in Qingdao, China

Background, Aims and Scope. Urban soils are important sinks and sources of pollutants. Furthermore, urban soils are often much more heterogeneous than natural, agricultural or forest soils. This is due to the highly diverse land uses occurring in small distances. Different land uses specifically affect the mineralogical and chemical composition of urban soils causing various, often negative impacts on the environment. Therefore, sustainable urban development has to be based on comprehensive knowledge on the urban 'basis' of life: the soils. Till today, knowledge on urban soil is generally limited and more often linked to environmental assessments than to soil profiles and their genesis. During the last decades, some studies were carried out in the so-called developed countries, but little is known about the genesis and pollution of Chinese urban soils. Therefore, in April 2004, a soil survey was carried out to investigate land use-related influences on soil formation at Qingdao. Materials and Methods. Five locations were chosen for detailed pedological, mineralogical and geochemical investigations. These five locations represent anthropogenic impacts of different land uses and comprise one natural soil, one soil from an industrial site, two soils from the city center and of different ages, and one soil from an abandoned construction site. Results. The soils investigated showed various impacts of anthropogenic activities. Whilst natural soil just showed signs of diffuse pollution by some atmospheric inputs of heavy metals, peculiar impacts of construction activities, construction waste and coal disposal were identified in cases of the urban soils investigated. Thin layers of technical materials (lime, coal) divided two older, inner urban soil profiles into geogenic and anthropogenic sections. Both of the soils showed elevated concentrations of Cu, Zn and Pb owing to admixtures of construction rubble and coal particles. Furthermore, it was found out that Ba is a fairly good indicator for the pollution of soil horizons by other heavy metals. Discussion. The impact of construction activities especially could be identified by two features: (i) The pedological description identified upper soil layers, which were filled with artificial materials or mixtures of excavated soil and artificial materials. (ii) Elevated concentrations of Ca and calcite and higher pH values characterized soil horizons influenced by human activities since the natural soil has developed from granitic rock. A typical feature of Qingdao urban soils is the missing of the natural Ah horizon. Instead of this horizon, several horizons comprising various technogenic materials were filled on top of the parent rocks or natural B horizons. Expandable phyllo-silicates and interstratified clay minerals naturally indicate weathering processes and they consequently were found in the geogenic soil horizons. Considerable amounts of phyllo-silicates were also found in the anthropogenic horizons contributing to a potential lower mobility of pollutants. Conclusions. The geogenic parent materials in Qingdao are granitic rocks and sediments of those rocks. Thus, the natural soil investigated is an Endoleptic Cambisol, whereas the inner urban soil and the industrial soil are Urbic Technosols. Qingdao urban soils are intensively disturbed and contain considerable amounts of construction waste and frequently coal particles. Construction activities are the most destructive impacts on the Qingdao soils investigated. The oldest soils are most heavily contaminated, but pH values often between 7 and 8 indicate low mobilities of heavy metals. Atmospheric pollution is superimposing soil pollution caused by the fillings. Recommendations and Perspectives. The implementation of a construction and building waste management preventing uncontrolled spreading of building rubble would be necessary to protect soils from pollution and would be a useful contribution to a sustainable urban development. Since the state of knowledge on Chinese urban soils is limited, much more intensive research is necessary to develop a comprehensive understanding of the dynamics of Chinese urban soils with respect to genesis, composition, pollution and future development.