The Community Structures Of Plankton And Its Relationship With Water Environmental Factors In A Integrated Aquaculture System

With the development of intensive aquaculture and high-density breeding,the excessive input of forage leads to the deterioration of pond water quality and disease outbreaks occur frequently in the cultured animals.Meanwhile,aquacultural wastewater was being discharged directly into the aquatic environment without treatment.A new,more ecological,culturing method,the integrated pond aquaculture-constructed wetland system,improves the quality of the products while conserving water resources and effectively treating the aquacultural wastewater.In this research,a modern integrated system was studied,consisting of a constructed wetland(0.68mu)and a culture pond(5mu).In the system,Carassius auratus gibelio fingerlings(650ind/mu)with a small number of Hypophthalmichthys molitrix(60ind/mu),Aristichthynobilis(30ind/mu),Ctenopharyngodon idellus(30ind/mu),and Mylopharyngodon Peter(8ind/mu)were mix-cultured in the pond.The wastewater was filtered and purified through the constructed wetland and recirculated back to the pond.The fingerlings were fed on an artificial diet four times daily.From June to September 2015,we investigated the community structure of phytoplankton,zooplankton,temperature(T),pH,dissolved oxygen(DO),secchi depth(SD),total nitrogen(TN),ammonia nitrogen(NH3-N),nitrate nitrogen(NO2--N),total phosphorus(TP),orthophosphate(PO43--P)in the pond.The relationship between plankton community structure and water quality parameters was analyzed.The main results as below:A total of 87 phytoplankton species from 7 phyla were identified in the pond,including,Bacillariophyta,Chlorophyta,Cyanophyta,Cryptophyta,Euglenophyta,Chrysophyta,and Pyrrophyta.Among them,Chlorophyta(47species)accounted for 54.02%of the total phytoplankton species,with absolute dominance,while the phytoplankton density was dominated by Cyanophyta,accounting for 62.42%of the total phytoplankton density.During the entire study,the phytoplankton density varied from 1.96×108cells/L to 7.36×108cells/L with an average of 2.84×108cells/L and the phytoplankton biomass ranged from 8.27 mg/L to 27.95mg/L with an average of 16.32mg/L.The phytoplankton community was dominated by 17 species,including Merismopedia tenuissima,Gloeathece linearis,Oscillatoria limosa,Oscillatoria formosa,Phorimidium tenus,Anabaena circinalis,Gloeathece linearis,Microcystis flos-aquae,Merismopedia elegans,Chroococcus minutus,Spirulina princeps and Microcystis incerta from Cyanophyta,Chlorella vulgaris,Crucigenia tetrapedia and Scenedesmus quadrricaudu from Chlorophyta,Cyclotella from Bacillariophyta and Euglena oxyuris from Euglenophyta.The Shannon-Wiener diversity index,Margalef richness index and Pielou evenness index of the phytoplankton community were in the range of 3.95-4.19,3.53-3.93,and 0.63-0.67,respectively,indicating that the phytoplankton community structure in the pond was very stable.Correlation analysis showed that the species number of phytoplankton had a significant positive correlation with TN,but significant negative correlation with pH;the phytoplankton density had a significant positive correlation with PO43--P,TP and NH3-N,but significant negative correlation with NO2--N;the phytoplankton biomass had a significant positive correlation with T and pH,but significant negative correlation with TN;The Shannon-Wiener diversity index had a significant positive correlation with SD and N/P,but significant negative correlation with pH.Redundancy analysis showed that most algae were mainly affected by TP,PO43--P and NH3-N,Cyclotella,Spirulina princeps,Anabaena circinalis and Euglena oxyuris were mainly affected by T and NO2--N.The zooplankton were identified belonging to 40 species,24 gena,among them,Rotifer(30 species)accounted for 69.77%of the total zooplankton species,with absolute dominance.During the entire study,the zooplankton density varied from 5137.30ind/L to 37057.60ind/L with an average of 23247.56ind/L and the zooplankton biomass ranged from 3.11 mg/L to 21.50mg/L with an average of 13.99mg/L.The zooplankton community was dominated by 16 species including KeratelIa valga,Polyarthra trigla,Brachionus budapestiensis,Filinia longiseta,Brachionus angularis,Brachionus urceus,Keratella cochlearis,Trichocerca lophoessa,Keratella cochlearis,Brachionus calyciflorus,Diurella collaris,Trichocerca similis,Diurella brachyura,Trichocerca sp.3,Anuraeopsis fissa and Asplachna priodonta.The Shannon-Wiener diversity index,Margalef richness index and Pielou evenness index of the zooplankton community were in the range of 2.58-3.36,1.87-2.76,and 0.63-0.75.Correlation analysis showed that the species number of zooplankton had a significant positive correlation with T and pH,but significant negative correlation with TN,DO and PO43--P;both the zooplankton density and biomass had a significant positive correlation with T and pH,but significant negative correlation with SD and TN;The Shannon-Wiener diversity index had a significant positive correlation with pH,but significant negative correlation with SD and N/P.Redundancy analysis showed Rotifer and Copepoda density had a positive correlation with pH and T,but negative correlation with TN,DO and SD;Cladocera density had a positive correlation with pH and NO2--N,but negative correlation with TN,NH3-N,N/P,SD and DO.This experiment provided some theoretical criterion for the structure of the integrated pond aquaculture-constructed system and the change of plankton structure in the future.