The Synergistic Effect Between Submerged And Artificial Macrophytes On Pollutant Removal Efficiency In Eutrophic Water Bodies

Submerged plants（SMs）and artificial plants（AMs）have been widely used in water ecological engineering to improve the water quality of eutrophic water.However,existing studies only favored the single use of SMs or AMs.In highly eutrophicated aquatic ecosystems,the outbreak of blue-green algae often interferes with the growth of SMs,thus affecting the purification function of SMs.AMs mainly uses microbial membranes attached to the surface to purify water,but microbial activity is affected by the lack of carbon sources.The purpose of this project is to study a synergistic effect of SMs and AMs and to develop a strategy for the purification of eutrophic water based on this synergistic effect.On September 8,2019,a pilot test of SMs and AMs collaboration was conducted in Hongze Experimental Base of Nanjing University on November 28,2019.The experiment included three treatments:SMs and AMs collaboration group（S&A）,SMs alone group（SO）and AMs alone group（AO）.The environment,plant,water quality,algae and microorganisms were dynamically monitored during the growth and decline stages of SMs,respectively,in order to determine the water quality improvement potential produced by the synergistic use of SMs and AMs with SMs or AMs alone,the potential promoting effect of AMs on the growth status and possible pathways of SMs,and the effect of SMs on the microorganism attached to AMs surface.The experimental results are as follows:（1）The potential for water quality improvement resulting from the combined use of SMs and AMs,and the use of SMs or AMs alone was determined.During SMs growth period,S&A treatment can improve the RE of total nitrogen（TN）and chemical oxygen demand（COD）88.9%and 48.1%,respectively.By contrast,the REs for TN and COD are 77.4%and 81.2%respectively in SO treatment,and-13.7%and39.0%respectively in AO treatment.In SMs decay stage,S&A treatment can improve the REs of NH₄⁺-N,NO₃^--N,TN and TP.By 97.23%,64.95%,76.73%and 91.8%,respectively.In contrast,the REs for NH₄⁺-N,NO₃^--N,TN and TP were 80.75%,17.1%,38.45%,69.6%in SO treatment respectively,and 86.08%,42.5%,55.1%,89.4%,respectively in AO treatment.（2）The potential promoting effect of AMs on the growth status and possible pathways of SMs was determined.During SMs growth period,S&A treatment could promote the growth of biomass,leaf chlorophyll concentration and root activity of SMs.Compared with SO,S&A treatment was beneficial to the growth of biomass,leaf chlorophyll concentration and root activity of SMs by inhibiting the growth of algae.During SMs decay stage,S&A treatment can promote SMs root activity.SMs root activity in S&A treatment group was 54.14%higher than that in SO treatment group in theⅣcycle.（3）The effect of SMs on the microorganism commuity attached to AMs surface was determined.During the growth period of SMs,S&A treatment could increase the biomass and relative abundance of the biofilm on AMs surface.Compared with the AO treatment,the biomass and relative abundance of Nitrosomonadaceae and Nitrospira on AMs surface were increased under the treatment of S&A.In SMs decay stage,S&A treatment can increase the relative abundance of nir K,nos Z,nar G and AMX on AMs and SMs surface biofilm.Therefore,through the mutual promotion of SMs and biofilm on AMs,the synergistic application of SMs and AMs is an effective strategy to improve the RE of pollutant in eutrophic water bodies such as rivers and constructed wetlands.