Temporal And Spatial Pattern Of Phytoplankton Community And Water Environment Quality Assessment Of Dingguo Lake In Xinxiang City

Dingguo Lake in Xinxiang city is located in the eastern of Xinxiang center city,it is one of the important projects of the ecological construction project of water system connection in the central urban area of Xinxiang city.The lake is built on the Zhaoding River in Xinxiang City and covers an area of 41.65 hectares,of which the water surface area is 20.13 hectares.The lake area has a capacity of about 500,000 cubic meters and the maximum water depth is not more than 6 meters.It is an artificial shallow lake in the city.The lake was built in April 2016 and has been basically completed and impounded by April 2017.In order to fully understand the water environmental quality of Dingguo Lake in Xinxiang and provide theoretical basis and reference for the protection and scientific management of newly built artificial lakes,a sampling survey was conducted on Dingguo lake from July 2017 to November 2018.The main results showed that:1.Temporal and spatial pattern of physical and chemical indicators of water and sedimentsThe transparency of Dingguo Lake fluctuated greatly during the sampling period,ranged from 46 to 154 cm,with an average of 92 cm;The pH ranged from 7.81 to 8.96,which was weakly alkaline;the DO content ranged from 8.72 to 13.41 mg/L,and the average value was 11.58 mg/L;The fluctuation of the ORP was large,the variation range between 58.5-208.5mV,and the average value was 110.6mV;the temperature of water showed obvious seasonal changes,wherein the summer water temperature was the highest and the winter water temperature was the lowest;The turbidity ranged from 5.832 to 36.17 NTU with an average of 14.44 NTU;the CODCr ranged from 19.56 to 63.21 mg/L with an average of 32.80 mg/L;the TN content varied significantly.The range of variation was 0.298-4.19 mg/L with an average of 1.22 mg/L;the TP content ranged from 0.015 to 0.064 mg/L with an average of 0.030 mg/L;the NH3-N content ranged from 0.066 to 0.372 mg/L,the average value was 0.199mg/L;Chl-a content had obvious seasonal changes,including higher content in summer and autumn,and relatively low in spring and winter.The pH of the sediments in Dingguo Lake varied from 8.49 to 8.68 during the sampling period,which was weakly alkaline;the contents of TN,TP and organic matter were relatively low.The TN content varies between 0.034%and 0.075%,with an average of 0.052%;the TP content varied between 0.036%and 0.072%,with an average value 0.055%;the organic matter content ranged from 0.372%to 0.735%,and the average was 0.483%.2.Water quality evaluation by fuzzy comprehensive evaluationThe water quality level of Dingguo Lake varies from 2.486 to 4.989,with an average of 3.931,which was in line with the national Class ? water quality standards of surface water environmental quality standards.Among them,spring and winter water quality was better.However the water quality was poor in summer and autumn.The weighting results of water quality assessment factors showed that CODCr and TN were the main environmental factors,which affected the water quality of Dingguo Lake.3.Temporal and spatial pattern of phytoplankton community and bioassessment of water qualityA total of 124 species of 8 phylum 72 genus of phytoplankton were found during the sampling period.There were 19 genera and 32 species of Bacillariophyta,accounting for 25.8%;and Cyanobacteria 16 genera and 33 species,accounting for 26.6%;Chlorophyta 24 genera and 42 species,accounting for 33.8%;Xanthophyta 3genera and 3 species accounting for 2.4%;Pyrrophyta 3genera and 3 species accounting for 2.4%;Cryptophyta 2 genera and 4 species accounting for 3.2%;Euglenophyta 3 genera and 5 species accounting for 4%;Chrysophyta 2 genera and 2 species accounting for 1.6%.Among them,there were more phytoplankton species in summer and spring,and fewer species in autumn and winter.There were more phytoplankton species in sampling spot No.1(near estuary)and No.2(the viewing platform on the side of the main entrance)sampling point,and relatively few sampling points in No.3(near outlet)and No.4(inside viewing platform)sampling points;The number of phytoplankton species was higher in April and May 2018 in sampling spot No.5(near the center of lake),and the number of phytoplankton species in February and September 2018 was relatively small.The average abundance of Dingguo Lake was autumn>spring>summer>winter,and there was no significant spatial difference among the various points in abundance and realative abundance.From July '2017 to December 2017,Cyanophyta was dominated phytoplankton in Dingguo Lake;Bacillariophyta and Cyanophyta were dominated phytoplankton in January 2018;Bacillariophyta,Cyanophyta and Chlorophyta were dominated phytoplankton in March 2018;Bacillariophyta was dominated phytoplankton from April 2018 to September 2018.According to the Dominance Value Formula got 32 dominant species in Dingguo Lake during the sampling period,including 9 Bacillanophyta,15 cyanophyta,4 chlorophyta,2 Cryptophyta,one Pyrrophyta and one Euglenophyta.There were more dominant species in August and September 2017 and fewer dominant species in October 2017.The results of biological evaluation of water quality of Dingguo Lake by using phytoplankton diversity index showed that the water quality of Dingguo Lake was better in spring and summer,worse in autumn and winter,and the average pollution level was slight.There was no obvious spatial difference in the pollution level of different points.4.The relationship between phytoplankton and environmental factorsThe correlation analysis between phytoplankton abundance and environmental factors,and the CCA analysis between dominant species of phytoplankton and environmental factors showed that ORP,WT,turbidity and TP were the main influencing factors of phytoplankton community composition in Dingguo Lake.