Study On The Characteristics Of Aquatic Community Before And After The Reservoir Decommissioning

In order to study the structure characteristics of phytoplankton and benthos before and after decommissioning of the reservoir and their correlation with environmental factors,this paper takes Pingshan reservoir in Fushun City,Liaoning Province as the research object.From 2015 to 2018,three typical sections were set up in Pingshan reservoir to collect and analyze the samples of phytoplankton and benthos,and monitor the water quality indicators.On this basis,the community structure characteristics of phytoplankton and zoobenthos before and after the retirement of Pingshan reservoir were analyzed,and the redundancy analysis method was further used Analysis,RDA)explored the main environmental factors affecting the community structure of phytoplankton and benthos in Pingshan reservoir.?1?Before the retirement of Pingshan reservoir?2015?,39 species of 6 phyla of phytoplankton were identified.The average cell density of phytoplankton was8.017×10⁵ cells/L,in which the average cell density of Bacillariophyta was the largest,reaching 3.45×10⁵ cells/L;27 species of phytoplankton from 4 phyla were collected in the year when Pingshan reservoir was decommissioned?2016?.The average cell density of phytoplankton was 3.37×10⁶ cells/L,among which the average cell density of Cyanophyta was the largest,reaching 2.46×10⁶ cells/L;In September 2017,a small number of phytoplankton species were identified,with only 5 phyla and 18 species.The average cell density of phytoplankton was 2.95×10⁶ cells/L,among which the average cell density of Cyanophyta was the largest,2.46×10⁶ cells/L;In 2018,79 species of 7phyla of phytoplankton were detected,and the average cell density of phytoplankton was 2.137×10⁶ cells/L,among which the average cell density of Bacillariophyta was the largest,2.1194×10⁶cells/L.Before and after the reservoir decommissioning,the Shannon Weiner index?H??,Pielou index?J?and Margalef index?D?did not change significantly.?2?In 2015,18 species,15 genera,12 families,3 classes,6 orders and 12 orders were found in Pingshan reservoir.In 2016,20 species,15 genera,8 families,3 classes,5 classes,5 orders and 8 orders were found in benthos.In 2017,10 species,7 families,7 genera,7 classes,4 classes,7 orders and 7 orders were found in benthos.In 2018,25species,15 genera,6 orders,3 classes,6 orders and 6 orders were found in benthos;Before and after the decommissioning of Pingshan reservoir,arthropods were the most abundant species and numbers of benthos.Before the decommissioning of the reservoir?2015?,the proportion of arthropods was 84.62%,and the proportion of arthropods in the decommissioning year?2016?was 75%.The proportion increased to 80.82%in two years?2018?after the reservoir was decommissioned.The proportion of molluscs in total increased first and then decreased.The proportion of annelids is on the rise,compared with that before the decommissioning of the reservoir,the change trend of the quantity proportion of the reservoir after the decommissioning in one year?2017?is the largest,with an increase of 12.43%;Shannon Wiener diversity index and BI index were used to evaluate the water quality before and after the decommissioning of the reservoir.The results showed that the water quality before and after the decommissioning of the reservoir was medium pollution.?3?According to the water quality monitoring data,before the retirement of the reservoir?2015?,the water quality grade is poor V,after the retirement of the reservoir?2016-2017?,the water quality has improved,and the water quality grade is V,while in2018,the overall water quality grade is reduced to poor V.According to the correlation analysis of phytoplankton community and environmental factors before and after the retirement of Pingshan reservoir,the main environmental factors affecting phytoplankton and benthos are TP,NH₃-N and other nutrients.