Abstract: [Objective] To select the best herbaceous plants for preventing eutrophication, the effects of grass cover on runoff and sediment nitrogen (N) reduction rate were explored in Lijiang River,an aquatic-terrestrial ecotone. This provides a theoretical basis for ecological restoration.[Method] Runoff and sediment processes on four types of grass cover (Cynodon dactylon, Setaria viridis, Eremochloa ophiuroides and Alternanthera philoxeroides) were conducted in comparison to bare slope. Simultaneously, various forms of N were tested in runoff and sediment. Reduction rates of grass cover on runoff, sediment, N were calculated.[Result] Compared to bare slope, Cynodon dactylon, Setaria viridis, Eremochloa ophiuroides and Alternanthera philoxeroides reduced runoff by 17%, 35%, 29%, and 23%, respectively. They reduced total N in runoff by 37%, 43%, 40%, and 52% (P<0.05). Compared to bare slope, Cynodon dactylon, Setaria viridis, Eremochloa ophiuroides and Alternanthera philoxeroides reduced sediment yield by 17%, 32%, 26%, and 20%. They reduced TN in sediment by 31%, 48%, 41%, and 40%(P<0.05). Runoff reduction rate had significant positive correlation with reduction rates of NH₄⁺-N and TN, and was correlated closely with NH₄⁺-N reduction rate. However, rainfall intensity had significant negative correlation with reduction rates of NO₃^--N and TN.[Conclusion] Four types of grass cover all decreased the input of N to runoff. Setaria viridis and Alternanthera Philoxeroides had better function in reducing N loss with runoff. Positive relationship between N reduction rate and runoff reduction rate was established, therefore, conserve runoff loss from slope was an effective measure to prevent water pollution.

Key words: nitrogen, runoff, non-point source pollution, aquatic-terrestrial ecotone, reduction effect, ecological restoration, Lijiang River