Changes Of Periphyton Communities On Artificial Substrates And Effects On Water Quality

Periphyton is one of the most sensitive indicator organism for the variation of water environment.Quantity and community of periphyton are important water quality parameter of biological evaluation,since they can reflect the condition of water environment properly.The study of periphyton community dynamic variation of Dajingshan reservoir shows that diatom is dominant species in area A,B and C,Cymbella sp.,Achnanthes sp.,Gomphonema sp., Melosira.granulata var.angustissima and Navicula sp.are common species.Dactylococcopsis sp., Oscillatoria princeps,Linmothrix sp.of green algae,and Scenedesmus quadricauda and Tetraedron minimum of Cynaophyta also are important part of periphyton community in this reservoir.The results indicated that water quality is in mesotrophic level.At the same time,there is a positive correlation between periphyton biomass and nutrients contents.Nutrient content in area C is relatively higher,and periphyton biomass is also higher than the other two areas.In the terms of maintaining circulation of nutrients,periphyton on artificial substrate is a pool of nitrogen and phosphorus,and can keep numerous nutrients in water body.In-situ mesocosm experiments was set-up in Dajingshan reservoir,in order to study influences of artificial substrate on water quality.Results showed that artificial substate could improve water quality greatly which contains tilapia.Artificial substrates can eliminate 57.1%of TP,51.26%of particulate phosphorus,89.86%of chlorophyll-a and 65.17%of SS,also can improve water transparency.Artificial substrate could removed orthophosphate and various kinds forms of nitrogen,however,the differences was not significant.In nature water body, artificial substate can eliminate the various kinds of nitrogen,chlorophyll,SS and COD_Mn,but the effect is not significant,and all kinds of phosphorus concentration is higher than that of control.Through nutrient competition and allelopathy on phytoplankton growth,promotion of fish feces sedimentation and reducing of SS content,TP concentration in the water was reduced and water quality was improved by aitificial substate.In the non-tilapia water body,nutrients concentration was low and part of nutrients was eliminated by aritificial substrate,however,the effect was not significant.So results above showed that the effects of artificial substates was better in higher than in lower nutrient concentration water body.In the laboratory conditions,the study imitates how the exogenous nutrient(N:2 mg·L^-1·week^-1,P:0.1mg·L^-1·week^-1) influence nutrient circulation in the system of containing artificial adherences and snails.The result presented that periphyton could eliminate nutrients in water body effectively.,TP concentration and orthophosphate concentration reduced from about 0.4 mg·L^-1 and 0.036 mg·L^-1 At the beginning of this experiment to about 0.1 mg·L^-1 and 0.01 mg·L^-1 in the end,respectively;TN and ammonia nitrogen concentration reduced from about 4 mg·L^-1 and 2.3 mg·L^-1 to 1.2 mg·L^-1 and 0.4 mg·L^-1,respectively,and their removal rates were over 95%and 85%.Artificial substrate cart restrict phytoplankton growth and eliminate SS effectively,also can increase the saturation of DO and pH.Grazing effect of Bellamya sp. promoted circulation of nutrients,however,had little influence on periphyton community structure.