Abstract: To control the rainfall-induced runoff pollution in the urban sightseeing areas of Wuhan, a lawn system was constructed in the Deer Yard of Wuhan Zoo. In this paper, the roles of the lawn system in controlling rainfall-induced runoff nitrogen pollution and in reserving rainfall nitrogen were studied. The results showed that the concentrations of total nitrogen (TN), total dissolved nitrogen (DN), and ammonium nitrogen (NH₄⁺-N) in pretreated rainfall-induced runoff decreased by 16.0%, 13.9%, and 75.6%, respectively. The retention rates of influent nitrogen by the lawn system were >90% of NH₄⁺-N, >65% of TN and DN, and> 5% of nitrate nitrogen (NO₃^--N). Hydraulic loading rate affected the effluent TN concentration and its removal rate significantly. When the influent TN concentration was nearly the same while hydraulic loading rate increased from 3.3 to 8.3 cm·d^-1, the removal rate of TN decreased from 28.0% to 19.8%. Lawn width also affected the concentrations of effluent N pollutants. With the increase of lawn width, the effluent NH₄⁺-N concentration decreased, while NO₃^--N concentration increased. The DN concentration was the lowest at 10 m of lawn width. At the meantime of purifying rainfall-induced runoff, lawn system increased the nutrients re-use and rainwater recycling, and saved the cost of lawn maintenance.

Key words: Oxalate, Phosphatase, Soil colloid, Minerals, Adsorption, Activity