The research region is located in the retiform fluvial region of west Taihu Lake. With the pressure of increasing population and fast economical development, riparian buffer zones were gradually reclaimed to farmlands. In this study, the ecological and environmental functions between restored and degraded riparian wetlands were compared. The survey results show that the ecological indices of restored wetlands are higher than those of degraded ones, including species biodiversity, biomass of plants, the content of nitrogen and phosphorus nutrients in plants, the concentrations of nitrogen and phosphorus nutrients in water and the denitrification effects.
The species and plant numbers in restored area were high, the biodiversity and even indices reached to 1.7-3 and 0.5-0.9, respectively, indicating the relative good integrity of community structure. On the contrary, numbers of species and plants in the degraded wetland were low, the biodiversity and even indices varied between 0.3-1.5 and 0.15-0.65, respectively. In the community invaded by alternanthera philoxeroides, the value of biodiversity and even indices were only 0.3-1.0 and 0.1-0.3, respectively, indicating serious occurred degradation of the community structure. During the growing season, the individuals per square meter of Phragmites communis, Typha orientalis and Zizania latifolia in wetland area were 42, 18 and 17, respectively. The biomasses of these three species in restored wetlands were 4692, 5142 kg and 2182 kg, respectively. The average nitrogen and phosphorus contents per unit dry biomass of these three species contained 2.88 mg/g and 2.09 mg/g, respectively. In addition, the submerged macrophytes, which were the necessary components of wetland community, inherited strong absorbency capacities and high biomass. The average nitrogen and phosphorus contents of five dominant submerged macrophytes were 7.27 mg/g and 4.14 mg/g, respectively.
The concentrations of dissolved inorganic nitrogen of the outlet water of restored wetland reduced to 0.15-0.89 mg/L, which were about 85% lower than that of the inlet water. The concentrations of TP of the inlet water were 90% higher than that of the outlet water of restored wetland, mainly due to the salimentation and sedimentation functions of the restored wetland system. The SS contents of the upriver water were 90% lower than that of the downriver, because of the obstruction and adsorption of SS by the restored wetland.
In the restored wetland, the number of denitrifying bacteria in the terrestrial area and the transition area from water to terrene area were higher than that of water area. The flux of N₂O from the river center to the riverside increased gradually, N2O flux of riverside was 35% higher than that of river center. This result demonstrated that denitrification play an efficient role in eliminating the nitrogen content of the upriver water.