Abstract: According to the pollution gradient of Hengshishui River contaminated by the acid mine drainage (AMD) from Dabaoshan Mine of Guangdong, seven contaminated sites and three noncontaminated sites were selected from the upstream to the downstream of Hengshishui River and its branches. The leaf litters of Castanopsis fissa and Schima superba enclosed in 0.5 mm mesh bags were put in these sites to study their decomposition rate along the pollution gradient. With the increase of water pH and the decrease of heavy metals concentration in river water, the decomposition rates of the two species of leaf litters increased gradually, and were significantly lower in contaminated sites than in non-contaminated sites (P<0.05). At the non-contaminated site I, the decomposition rates of C. fissa and S. superba leaf litters were 6.5 and 10.5 times higher than those at the most contaminated site A which was closest to the Mine. The leaf litter decomposition rates were positively correlated with water pH, and negatively correlated with the Cu, Cd, Zn, and Pb concentrations in river water, suggesting that the lower water pH and the higher heavy metals concentration in river water could result in a lower leaf decomposition rate. Our results indicated that leaf litter decomposition rate was sensitive to the changes in water quality, and could be used as an indicator in the evaluation of stream ecosystem integrality.

Key words: Deep fertilization in autumn, Straw return to field, Efficiency of water and fertilizer, Dryland corn