Abstract:Agricultural drainage ditches are a reflection of the disturbance caused by agriculture and other human perturbations associated with agricultural activities, and the density of them can be seen as an important gradient reflecting local disturbance. When appropriately selected, drainage ditch density gradient represents an ideal opportunity for differentiating the long-term effects of agricultural activity from other environmental patterns. Unfortunately, to date, few published studies have assessed the variation in species composition and diversity of wetland communities along the agricultural drainage ditch density gradient, yet such information is urgently needed for the conservation of wetland ecosystems under intensive cultivation. In this study, ditch density was chosen as an indicator of disturbance intensity, and four sites with different ditch density was chosen to compare species composition and diversity among them. Sixty-seven quadrats and four transects were sampled along the ditch density gradient. The results showed that there existed a significant negative relationship between disturbance intensity and species parameters, while species diversity did not differ greatly among sites, but species composition varied considerably. With increasing disturbance intensity, the wetlands tended to be reduced in plant species diversity, and an increasing loss of indigenous wetland species was paralleled with an increasing invasion of upland species. The results also show that the rate of species turnover within communities differed among communities under different disturbance intensities. The communities with intermediate ditch density（0.6-1.2 km/km2）had higher rates than the other communities.