Abstract: With incubation test, the effects of cadmium (Cd) and mercury (Hg) combined pollution on the urease and acid phosphatase activities in marine sediment silty loam soil (S₁) and yellowish red soil (S₂) were studied. The results indicated that during the whole incubation period, Cd and Hg, whether singly or combined together, had significant inhibitory effects on the urease and phosphatase activities in the two test soils, and the effects increased with their increasing concentration (except for Cd ≤1 mg·kg^-1). Compared with that under Cd or Hg pollution, the net change rates of soil urease and acid phosphatase activities under the same level Cd and Hg combined pollution were higher than 0, suggesting the synergistic effects of these two heavy metals on the inhibition of soil urease and acid phosphatase activities. In all treatments, the activities of urease and acid phosphatase were higher in S₂ than in S₁, possibly due to the higher contents of organic matter and clay particle in S₂.

Key words: lake-water total organic carbon, sediment, diatoms, eutrophication, Chenghai Lake, water regulation