Study On Nitrogen And Phosphorus Removal By Newly Restored Wetland And Its Biological Regulation Mechanism

Coastal wetland is an ecological transition zone between land and ocean.It is one of the most productive ecosystems on earth.Due to the intensification of human activities such as reclamation and the rise of sea level,coastal wetlands are being seriously threatened.The practice results of coastal zone ecological restoration at home and abroad show that if the measures are appropriate,the newly restored wetland can regain its ecological function and promote its further development.How to combine wetland restoration,strengthen ecological function and give full play to ecosystem services beneficial to human beings is one of the hotspots in the field of ecological restoration.Based on this,relying on the ecological remediation and restoration project of Jinshan section on the North Bank of Hangzhou Bay,taking the built Yingwuzhou wetland as the research area,this study studies the water quality restoration function of the newly restored wetland.On this basis,combined with the long-term monitoring and control experiment of the wetland hydrological regulation area,this study further analyzes the mechanism of water quality restoration and biological regulation mechanism of the wetland,It provides a theoretical basis for the further development of coastal ecological restoration.The main conclusions are as follows:(1)The newly restored yingwuzhou wetland has an obvious purification effect on nutrients such as nitrogen and phosphorus in the incoming water.In terms of seasons,the removal efficiency of nitrogen and phosphorus by wetland is affected by seasonal changes.It is higher in spring and summer than in autumn and winter.The average removal rate of DIN,TN,dip and TP is 44%,33%,61% and 56%,respectively;From the concentration along the process,different units of the wetland can remove nitrogen and phosphorus to a certain extent,and each unit is organically complementary.The plankton in the wetland fluctuates slightly with seasons,but it is relatively stable on the whole.The species of phytoplankton are mainly diatom,accounting for 74% in the four seasons,followed by Chlorophyta,and other categories account for a relatively low proportion;Rotifers are the main species of zooplankton,accounting for an average of65% in four seasons;The second is copepods,and the proportion of cladocerans is relatively low.(2)Water flow has an important impact on wetland plant growth and nitrogen and phosphorus removal.Water flow can promote the growth of Phragmites australis.The average plant height of Phragmites australis in mobile area is 44.8 cm higher than that in static area in April and 61.6 cm higher than that in static area in September.In addition,water flow can also promote the absorption of nitrogen and phosphorus by wetlands.From the seasonal point of view,the removal rate of nitrogen and phosphorus in the mobile area in spring and summer is higher than that in autumn and winter.The average removal rates of DIN,DTN and TN are 48%,30% and 15% respectively,and the average removal rates of dip,DTP and TP are 45%,56% and 56% respectively,;In terms of the concentration along the process,the removal of nitrogen and phosphorus in the flow zone is mainly concentrated in the front end,accounting for more than 40%of the total removal rate.The concentration of nitrogen and phosphorus in the static area was higher than that in the flow area,and the change of concentration in the year was not obvious.(3)In situ control experiments showed that although the water body was in the state of mesotrophic and oligotrophic,phytoplankton could still absorb nitrogen and phosphorus in wetland waters.The removal amount of DIN and dip by phytoplankton increased with the addition of nitrogen and phosphorus.When the addition amount was the highest,the removal amount was the largest.In addition,the study also found that the proportion of ultra microalgae in phytoplankton community is high,with an average annual proportion of 52%.The average removal rates of DIN and dip by ultra microalgae are about 45% and 27%.The regulation of zooplankton will affect the removal rate of nitrogen and phosphorus.When the biomass of zooplankton increases,the nitrogen removal rate of phytoplankton decreases.