The Study Of The Restoration Effectiveness By Submerged Plants Emerged Plants & Plankton Feeders In Eutrophicated Fresh Water Ecosystems

Restoration of the damaged aquatic ecosystem has been becoming one of the important research projects in environmental science field.Eutrophication is due to the increase of nutrient concentrations nitrogen and phosphorus in water,and the explosive growth of phytoplankton as consequence.As many research shows,the treatment for eutrophicated aquatic ecosystem by controlling the biomass of aquatic advanced plants,benthic animals＆plankton -feeding fish had remarkable effectiveness,for aquatic advanced plants as the competitors of phytoplankton,benthic animals＆plankton-feeding fish as the predators of phytoplankton,according to trophic structure of aquatic ecosystem.In this research,submerged plants Ceratophyllum demersvm,and emerged plants Arundo donax var.versicolor,Typha orientalis Presl were selected for cultivation in eutrophicated water for the short-term experiments.The result showed that:1.In the short-term experiments,the final concentrations of TN,TP and final biomass were different.a.Both submerged plants,compared with Vallisineria spiralis,the final biomass of Ceratophyllum demersum were remarbly higher,particularly in the high concentration group.In the lower concentration group(ρ(N)=0.5-2mg/L,ρ(P)=0.05-0.2mg/L),the difference between final concentrations of TN,TP of V.spiralis and C.demersum was not remarkable.In the higher concentration group(ρ(N)=8-16mg/L,ρ(P)=0.8-1.6mg/L),the final concentrations of TN,TP and C. demersum was remarkable lower than that of V.spirali,which shows C.demersum had better absorptive capacity and higher tolerance of nitrogen and phosphorus than V.spiralis in the high concentrations of nitrogen and phosphorus conditions.b.Both emerged plants,compared with Typha orientalis Presl,the final biomass of Arundo donax var.versicolor were remarbly higher.In the lower concentration group(ρ(N)=0.5mg/L,ρ(P)=0.05mg/L), the difference between final concentrations of TN,TP of Typha orientalis Presl and Arundo donax var.versicolor was not remarkable.In the higher concentration group(ρ(N)=2-16mg/L,ρ(P)=0.2-1.6mg/L),the final concentrations of TN,TP of Arundo donax var.versicolor was remarkable lower than that of Typha orientalis Presl,the concentrations of chlorophyll a of implantation water of Arundo donax var.versicolor were remarkably lower than those of Typha orientalis Presl,which showed Arundo donax var.versicolor had better absorptive capacity and higher tolerance for nitrogen and phosphorus,and better inhibition of phytoplankton than Typha orientalis Presl in the high concentrations of nitrogen and phosphorus conditions.c.Compared with submerged plants,the biomass of emerged plants Typha orientalis Presl＆Arundo donax var.versicolor were remarkably higher than submerged plants Vallisineria spiralis.Tolerance for nitrogen and phosphorus,Arundo donax var.versicolor＞Typha orientalis Presl＞Ceratophyllum demersum＞Vallisineria spiralis2.Long-term experiments using river water and soil wa-li to build the simulated ecosystems,and Ceratophyllum demersum,Vallisineria spiralis Arundo donax var.versicolor,Typha orientalis Presl, snails were put into simulated ecosystems in different phases.a.The concentrations of TN,TP,chlorophyll a,COD of simulated ecosystems with Submerged plants, emerged plants,snails were remarkably lower than those of simulated ecosystems with none of them, which shows submerged plants,emerged plants,snails had remarkable effectiveness in improving water quality.b.The pure absorption by plants accounted for little(＜20%) in the decrease of the nitrogen concentration in simulated ecosystems,though that could be a majority(＞50%) in the decrease of the phosphorus concentration,when biomass was remarkable.Besides absorption,increasing DO, providing habitat for microorganism and zoobenthos,which facilitated decomposition,transformation of nitrogen＆phosphorus,were also important contributation of plants to the decrease of the nitrogen＆phosphorus.c.The density of Phytoplankton of simulated ecosystems with Submerged plants,emerged plants, snails were remarkably lower than those of simulated ecosystems with none of them,and the Shannon-Wiener index of phytoplankton of simulated ecosystems with Submerged plants,emerged plants,snails were remarkably higher than those of simulated ecosystems with none of them,which shows submerged plants,emerged plants,snails had remarkable effectiveness in reducing the density of phytoplankton and enhance its diversity.3.By comparing the water quality,habitation and communities of Liwa river before and after the approx-natural restoration engineering,it was found DO rosed to 9.09-11.18 mg/L,transparency rosed to 80cm-100cm,TN dropped from 1.85 mg/L to 0.41 mg/L,TP dropped from 0.23 mg/L to 0.03 mg/L, COD dropped from 33.25 mg/L to 21.5 mg/L.The harvesting of potamogeton crispus and lotus respectively accounted for 32.6%and 30.4%in nitrogen and phosphorus removal.Results indicated that the approx-natural restoration engineering was effective in treatment of urban river eutrophication.