Effects of combined pollution of Cd and Pb on soil enzyme activity under different types of land use.

In order to explore how to rationalize the use of land polluted by heavy metals,coupled with an indoor pot experiment,a field experiment was carried out on Chongming Island,Shanghai to study effects of combined pollution of Cd and Pb on soil enzyme activity under different types of land use.Results show that the soil enzyme activity is lower in farms,residential areas and some other lands seriously affected by human activities than in wetlands,forest lands and riversides and lands which are rich in water supply and less disturbed by human activities.Significant positive correlations were observed between soil urease,phosphatase and dehydrogenase in activity (P0.01),and soil urease was rather sensitive to Cd and Pb.Soil enzyme activity was also found to be positively related to organic matter (P0.05).At low concentration,combined pollution of Cd and Pb showed a positive effect on soil enzyme activity,while at high concentration a negative impact.