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Substrate enzyme plays an important role in the transformation and the degradation processes of nutrients in constructed wetlands. The spatial distribution of the substrate enzymes, including urease, dehydrogenase and phosphatase, was monitored systematically. Meanwhile, the spatial distribution of dissolved oxygen and the spatial degradation rule of nutrients were investigated. The relationship between the enzyme activities and wetland operation characteristics was analyzed. Results showed that there was a close relationship between the spatial distribution of dissolved oxygen, the spatial degradation regularity of nutrients, and the enzyme activities. The activity of urease, dehydrogenase and phosphatase in the upper layer of soil was generally higher than that in the lower layer. The distribution regularity of the urease activity was similar with that of dissolved oxygen. The activity of dehydrogenase and phosphatase declined gradually along the flow in the wetland. The urease activity influenced the nitrification intensity significantly, showing a remarkable positive correlation with the nitrification intensity in the wetland. The dehydrogenase activity had no significant correlation with the nutrient removal, but was associated with the accumulation of organic matters in the substrates. The phosphatase activity was closely related to degradation of organophosphorus. [ABSTRACT FROM AUTHOR]

Seven subsurface flow constructed wetlands were constructed through different combinations of four plants (iris, bulrush, radix ophiopogonis and canna) and three substrates (slag, zeolite and gravel), aiming at studying the operation characteristics of urban sewage treatment during the wetlands' start-up under the conditions of different plants, same substrate as well as different substrates, same plant. The results indicated that regarding the average re-moval rates of CODcr, gravel>slag>zeolite, canna>iris> bulrush>radix ophiopogonis; regarding the average removal rates of TN, zeolite>gravel>slag, canna>bulrush>radix ophiopogonis>iris; as for the average removal rates of NH4+-N, zeolite>gravel>slag, bulrush>canna>radix ophiopogonis> iris; as for the average removal rates of TP, slag>gravel> zeolite, bulrush>canna>iris>radix ophiopogonis. There were no significant differences regarding the removal rates of CODcr among the three substrate wetlands with or without plants; as for the removal rates of TN and NH4+-N, zeolite was far better than slag and gravel. After planting, the removal rates of TP by the three substrates were all about 10.75%. The removal rates of CODcr by three plants (iris, radix ophiopogonis and canna) increased with the operation time, while the removal rate of CODcr by bulrush declined due to its bad growing situation. The removal rate of TN by canna wetland was higher than that by the other three; the differences among plant wetlands on the removal rates of NH4+-N were not significant. The removal rates of TP by the four plants were around 9.24%. [ABSTRACT FROM AUTHOR]