Research On The Interaction Of Vegetation Succession And Nutrient Removal In Near Nature Restoring Wetlands

Wetland degradation seriously affects the ecological function of wetlands,which is one of the important ecological and environmental problems faced by humankind.Wetland ecological restoration can restore the function ecosystem and improve the degraded wetland ecosystem.Based on the long-term field monitoring of Qixinghu near-nature restoring wetland,the characteristics of plant community succession in near-nature restoring wetland were studied,and the responses of typical aquatic plants to submerged water depth and nutrient level were discussed.The effects of vegetation biomass,vegetation area,coverage,and plant community diversity index on the nutrient removal of wetlands were studied in the process of wetland vegetation succession.Research indicates:(1)The abundance of plant species and community diversity declined in the near-nature restoration wetlands for many years,but increased in wetland effluent areas.In the near-nature restoring wetland,under the high pollution stress of influent load,the vegetation community tended to develop simpler structure.When the environmental conditions were suitable,the wetland vegetation pattern became diversified.(2)Depth of water had an important influence on the distribution of aquatic plants in the wetlands.The typical aquatic plants in wetland showed self-adjustment and different characteristics of distribution along with the water depth.After 6 years of natural succession,plant adaptation to water depth in the constructed wetland performed following the order: floating plant ? floating leaf plant> submerged plants> emergent plants.The plant community gradually developed its own suitable water depth,and the competition among different plant communities in the same water depth area resulted in the succession of the community.(3)Nutrient levels had a significant effect on the distribution of aquatic plants in the near-nature restoring wetland,while the plants responsed differently to nutrient levels.Phragmites australis and Typha angustifolia grew well in all areas of the wetland.High concentrations of nitrogen and phosphorus went against the growth of Lotus,Gorgon and submerged macrophytes.The tolerance of submerged macrophytes to nurtients stress in the near-nature restoring wetland was highest in Potamogeton crispus,followed by Ceratophyllum demersum> Myriophyllum verticillatum> Hydrilla verticillata.Water chestnut grew well in the region with high nutrient content,while Nymphoides grew better in the effluent area with less pollutants.(4)Plant communities significantly influenced the water temperature,pH and dissolved oxygen.There was a significant negative correlation between water temperature and vegetation area,coverage,vegetation biomass in summer.pH was positively correlated with vegetation area,biomass and species richness,and negatively correlated with vegetation coverage.Dissolved oxygen was negatively correlated with vegetation area,coverage and biomass in both summer and autumn,and positively correlated in spring and winter.Dissolved oxygen contents increased with species richness.There was no significant trend of plant diversity index with water temperature,pH or dissolved oxygen.(5)Vegetation succession affected nitrogen and phosphorus removal efficiency of the near-nature restoring wetland.The removal rates of nitrogen and phosphorus in different wetland units showed different changes with the vegetation distribution.The removal efficiency was significantly positively correlated with the biomass and vegetation area of wetland vegetation in the process of vegetation succession.With the increase of vegetation coverage,the removal rate of nitrogen and phosphorus in wetland increased first and then decreased.Coverage rate of 75%~80% was optimal for the removal of the nitrogen and phosphorus.Species richness and removal of nitrogen and phosphorus were significantly positively correlated.Plant community diversity index H and dominance index D were weakly related with the nitrogen removal efficiency,but were significantly related with the removal efficiency of dissolved phosphorus.The correlation of evenness index J and phosphorus removal rate is poor,but the evenness index J was negatively correlated with nitrogen removal rate of wetland.The structure and function of aquatic macrophytes in wetland have been changed greatly during the long-term operation of near-nature restoring wetlands.In this research,the response and mechanism of typical aquatic plant communities to nutrient and water level in the near-nature restoring wetlands were studied.The relationship between vegetation succession and nutrient removal in near-nature restoring wetlands was studied,and it can provide theoretical basis and technical support to the adaptability pattern of wetland vegetation or wetland restoring.