Studies On The Water Ecological Health Status And Effects Of Comprehensively Engineering Measures On Mingxin Lake In Campus Of Wenzhou University

Mingxin Lake of Wenzhou University is an artificial lake with serious eutrophication.In April 2020,Mingxin Lake underwent comprehensive treatment.The main engineering measures included sediment dredging,aquatic plant planting,aeration,and swan breeding ban.The main purpose of this study is to track and evaluate its treatment effects by comparing the changes in the water quality and phytoplankton community structure of Mingxin Lake before and after comprehensive treatment,so as to provide reference for the treatment of similar lakes in China or abroad.In order to eliminate the influence of seasonal changes on the water quality and phytoplankton community structure of Mingxin Lake,we selected the Wenruitang River tributary next to Mingxin Lake to conduct a synchronous sampling study as a control.In terms of water quality changes,before the comprehensive treatment,the chemical oxygen demand(COD)of Mingxin Lake was 50-60 mg/L,the content of total nitrogen(TN)was 2.6-4 mg/L,and the content of total phosphorus(TP)was 0.16-0.31 mg/L,the transparency(SD)was 0.04-0.18 m,and the dissolved oxygen(DO)was 8.6-11.0 mg/L.After comprehensive treatment,the COD,TN,TP,DO had all decreased significantly,and the COD decreased to 30 mg/L,the TN decreased to 0.5-1.6 mg/L,the TP decreased to 0.05-0.17 mg/L,the DO decreased to 7-9 mg/L.on the other hand,the SD increased to over 0.37 m,and the pH value did not change significantly before and after the treatment.The changes in these indicators reflect that the water quality of Mingxin Lake has been significantly improved after the comprehensive treatment.In terms of phytoplankton,the dominant species in Mingxin Lake throughout the year were Fragilaria sp.,Synedra sp.,Navicula sp.,Pediastrum simplex,Melosira granulata,Euglena sp.,Chlamydomonas sp.,Eudorina sp.,etc.Before and after the comprehensive treatment,there was no significant difference in the number of phytoplankton species in Mingxin Lake,and there was a strong consistency with the number of phytoplankton species in Wenruitang River.This may be due to the frequent pumping of water from Wenruitang River to Mingxin Lake.After the comprehensive treatment,the concentration of chlorophyll a,the abundance and biomass of phytoplankton in Mingxin Lake had all dropped significantly,which also indicated that the water quality of Mingxin Lake has been improved and the eutrophication level of the water body had decreased.After RDA analysis,the main reasons leading to the decrease of chlorophyll a concentration,phytoplankton,abundance and biomass are the reduction of nutrients and organic matter in the water body and the changes of DO.The monitoring results showed that after comprehensive treatment,the abundance of green algae such as P.simplex and Eudorina sp.was significantly increased,which also indicated that the water environment of Mingxin Lake was more suitable for the survival of green algae after the comprehensive treatment.In terms of zooplankton,before the comprehensive treatment,cladocera and other metazooplankton in the water body of Mingxin Lake accounted for a relatively large proportion,and a large number of Scapholeberis kingi often appeared.After the comprehensive treatment,the S.kingi in the water body disappeared,and the proportion of cladocera decreased.After RDA analysis,this change was found to be related to the changes in COD,TN,TP,and DO in the water body.After the comprehensive treatment,the dominance of the S.kingi and Diaphanosoma leuchtenbergianum was greatly reduced,while the dominance of Bosmina longirostris and Moina macrocopa was increased.For the rotifers,the dominance of Brachionus urceus significantly decreased after the comprehensive treatment.At the same time,after the comprehensive treatment,the aboundance and biomass of zooplankton in Mingxin Lake decreased significantly,this also denoted that the treatment effect of Mingxin Lake was good.