Effects of Sewage Discharge on Nitrification and Denitrification in Mangrove Constructed Wetlands

Effects of municipal sewage discharge on the mechanisms of nitrification and denitrification at different depths of mangrove wetlands in Futian District,Shenzhen were explored. The study showed that nitrification and denitrification could take place at the same time in the constructed wetlands, and nitrification, denitrification were significantly positively correlated with the counts of nitrifying and denitrifying bacteria,respectively. Compared with the effect of being treated with tap water,the nitrification/denitrification action was significantly boosted by sewage discharge;nitrification in the upper layer(0~10cm)of the soil was notably higher than that of the lower layer(10~20cm),but the denitrification was the other way round. Obviously,nitrification and denitrification in the substrate planted with mangroves was higher than that without any plants. As to the mangrove species,it proved strength of nitrification followed the order as K. candel A. corniculatum S.caseolaris,though the difference was not significant. However,denitrification was found very strong in S. caseolaris. The Pearson correlation analysis showed that both nitrification and denitrification were significantly correlated to the concentrations of organic matter,salinity and p H value in soil.