Study On Fish And Plankton Resources In Dawangtan Reservoir In Guangxi Province

Dawangtan Reservoir is an important drinking water source protection area in Nanning.From November 2016 to September 2017,this study collected fish,plankton and water-quality samples quarterly through setting up five sampling sites(cross sections)in the Dawangtan Reservoir.Based on field measurements,laboratory operations,and statistical analysis,the experiment studied the species composition,diversity,and spatial and temporal distribution of fish and plankton.In the end,the study also evaluated the water quality of the reservoir.It also analyzed the relationship between fish,plankton and water environment in Dawangtan Reservoir.This study provided theoretical basis for the protection and restoration of fishery resources in Dawangtan Reservoir and the improvement of water quality in the water source area.The main results of this study were as follows:(1)There were 34 species belonging to 4 orders,9 families and 26 genera identified in the reservoir.Cyprinidae was the most abundant.The most dominant species were Oreochromis niloticus,Cyprinus carpio,Cirrhinus molitorella and Oreochromis mossambicus.The results of research on fish diversity in Dawangtan Reservoir were as follows:the Shannon-Wiener(H')was 1.213?2.279,the Margalef(D')was 1.995?3.412 and the Pielou(J')was 0.448?0.771 in space;the Shannon-Wiener of fish ranged from 2.167 to 3.738,Margalef ranged from 1.960 to 2.290 in seasonal.The difference in Pielou was small,which ranged from 0.636 to 0.764.According to Shannon-Wiener index,Pielou index,Margalef index and fish community cluster analysis,it was greater than 60.0%of the similarity of spatial composition of fish community in Dawangtan Reservoir,and the similarity of fish community was 60.0%approximately.There was no significant difference in the fish communities among seasons and sampling sites.(2)There were total of 7 orders,25 families and 43 genera of phytoplankton detected in Dawangtan Reservoir.The number of Chlorophyta species was the largest,which was 12 genera(27.9%).The dominant species of planktonic algae in the reservoir were Ankistrosmus,Synedra,Merismopedia,Melosira,Scenedesmus,Closterium,Oscillatoria,which was a total of seven species.In the reservoir,the mean density of phytoplankton was 2.79×105 ind./L and the mean phytoplankton biomass was 1.046 mg/L.Meanwhile the average of Shannon-Wiener(H')of phytoplankton was 2.24,and the average of Pielou(J')of phytoplankton was 0.76.According to the classification criteria,the reservoir was 2.00<H'<3.00 and 0.50<J<<0.80,the water quality of the reservoir was between lightly polluted and clean state(3)There were total of 4 orders,16 families and 23 genera(species)of zooplankton identified in the Dawangtan Reservoir.The dominant species(genus)of Zooplankton in the Dawangtan Reservoir were Nauplii,Cucurbitella,Brachionidae,Difflugia,Sinocalnus,Trichocerca and Keratella.In the reservoir,the average density of zooplankton was 2628.07 ind/L and the average biomass was 49.32 mg/L.Meanwhile the average Shannon-Wiener(H')of the reservoir zooplankton was 2.29 and the average Pielou(J')was 0.85.According to the Shannon-Wiener and Pielou of zooplankton,the quality of the water in the reservoir was in a slightly polluted state.(4)Comprehensive evaluation based on major water quality indicated that the quality of the water in the Dawangtan Reservoir was in a state of eutrophication and it was mildly polluted.The quality of the water in Dawangtan Reservoir were up to Grade ? in the Environmental Quality Standards for Surface Water.Indeed,several indicators were up to Type ?.According to the principal component analysis(PCA)test,the main environmental factors were BOD5,CODMn,WT,pH,NH4-N and TP.The correlation analysis showed that the phytoplankton biomass of the Dawangtan Reservoir was positively correlated with NH4-N,DO,TN,TP,N03-N,and WT,and the relationship was significant.Meanwhile zooplankton biomass was positively correlated with phytoplankton biomass,DO,CODMn,NH4-N,N03-N,and Chl.a.Based on the Canonical Correspondence Analysis(CCA),it concluded that the relationship between fish resources and its living environment factors in the Dawangtan reservoir area was significant.It also had clustering characteristics in temporal and spatial distribution.(5)Based on comprehensive analysis,the status of fishery resources in Dawangtan reservoir was the result of the joint action of water-quality factors,plankton and fish.According to present situation of fishery resources in the reservoir,it is suggested that stock enhancement should be strengthened within a reasonable range,biological invasion must be prevented.Meanwhile it is fishery management and water environmental protection that should be strengthened in the Dawangtan reservoir.