Effects Of Biomanipulation Control On Spirogyra

In the coastal zone of rivers,lakes and other waters,benthic algae are often distributed,and the overgrowth of benthic algae can not be effectively curbed.The main components of biofilm are slime attached to algae,bacteria and other materials.Therefore,the change of biofilm biomass will have an impact on the food chain and water environment.Its excessive accumulation may cause a series of environmental problems in most water bodies.When the biofilm dies,it will form flocs into the water body and block the filtration system of water supply companies.This paper aims at the biofilm control of benthic algae,combined with field observation and control experiments,to explore the factors affecting biofilm biomass,and clarify the regulation of aquatic animals on benthic algae from the perspective of biological manipulation,so as to provide scientific basis and effective suggestions for people to better manage water biofilm.The conclusions include the following four aspects:(1)To better understand the determinants of periphyton biofilms,we applied generalized linear models(GLMs)and structural equation modelling(SEM)to compare and quantify the relative importance of multiple factors on the periphyton biofilm biomasses in the SNWD canal and its upstream Danjiangkou Reservoir.The results show excessive accumulation of periphyton biofilms in the SNWD canal,which cannot be neglected.Water temperature is the most important abiotic factor.Biotic factors for explaining the biofilm biomasses are quite different in the two ecosystems.Evidence from GLMs and SEM shows that Macrobrachium nipponense have a significant negative direct effect on the reservoir biofilm biomass,while Rhinogobius giurinus have a significant positive indirect effect via molluscs on the canal biofilm biomass.The Bayesian mixing models from stable isotope data also verify that biofilms are a major component of the reservoir Macrobrachium nipponense diets(72.50±1.90%).However,in the canal,biofilms are the major component of the canal mollusc diets(70.20±19.80%),and a rather high proportional contribution of molluscs is found for the Rhinogobius giurinus diets(67.40±8.00%).In this study,we reveal the determinants of periphyton biofilm accumulation,which may provide useful information for biomanipulation in the SNWD and its upstream reservoir.(2)Benthic green algae are often the main components of biofilms,Spirogyra,as a representative of Spirogyra,will cause a series of ecological problems in most water bodies,so it is widely concerned by researchers.When Spirogyra breaks out in lakes,ponds and other waters,it will reduce the dissolved oxygen content of water body,which pose a threat to aquatic organisms.The feeding habits of Macrobrachium nipponense can be used to control Spirogyra to a certain extent.At present,there is no research on the relationship between the ecological function of Macrobrachium nipponense regulating Spirogyra and the density of Macrobrachium nipponense.In order to study the regulation mechanism of different densities of Macrobrachium nipponense on Spirogyra,control group(0.00g/L),low density group(0.13g/L),medium density group(0.26g/L)and high density group(0.52g/L)were set to study the controlling effects on Spirogyra.The results showed that Macrobrachium nipponense had significant inhibition on the benthic Spirogyra,the biomass of benthic Spirogyra in low density group was the lowest,the control effect is the best,but the inhibition effect of Macrobrachium nipponense on the Spirogyra was not more significant with the increase of Macrobrachium nipponense density;Increasing the density of Macrobrachium nipponense could significantly increase the biomass of planktonic Spirogyra;compared with the low density group and medium density group,the high density treatment group significantly promoted the increase of nutrient content in the water,and promoted the increase of other benthic algae,planktonic algae and zooplankton.(3)Since Macrobrachium nipponense can control the growth of benthic algae in water,the coexistence of Macrobrachium nipponense and a large number of benthic algae in the main canal of South to North Water Diversion Project may be related to the niche and competitive stress of Macrobrachium nipponense.In order to understand the competitive stress of Macrobrachium nipponense,the coexistence relationship between the two species was studied,and the seasonal succession mechanism was explored.Therefore,we studied the effects of temperature on the abundance changes of Rhinogobius giurinus and Macrobrachium nipponense,and explored the seasonal succession mechanism of the two species.Three treatment groups were set up:normal temperature14-22?,low temperature 10.00?,high temperature26.00?.Macrobrachium nipponense of the same body length and Rhinogobius giurinus were co cultured in the tank,and the abundance ratio was 1:1.The results showed that the total abundance of fish and shrimp in the low temperature treatment group was 86.67±5.77 individuals/m~3,which was the largest among the three groups.The ratio of Macrobrachium nipponense to Rhinogobius giurinus is 1.60:1 in the low temperature group,1:1 in the high temperature group and 0.58:1 in the medium temperature group.Both Rhinogobius giurinus and Macrobrachium nipponense fed on algae in the experimental barrel.To sum up,in the same habitat,the total abundance of the Macrobrachium nipponense and the Rhinogobius giurinus was the largest at the low temperature10.00?.The Macrobrachium nipponense had greater advantage in the low temperature water body,and the Rhinogobius giurinus had greater advantage in the medium temperature water body.(4)Benthic molluscs often attach to biofilms dominated by benthic algae,benthic molluscs may play an important role in the food chain as predators of immobilized algae.In order to explore the regulation of benthic molluscs and fish on Spirogyra.The feeding habits of Radix sp.,Rhinogobius giurinus,Rhodeus ocellatus and Macrobrachium nipponense were used to explore the control on Spirogyra.The control group(0.00g/L),Radix sp.group(0.13g/L),Rhinogobius giurinus+Radix sp.group(0.13g/L+0.13g/L),Rhodeus ocellatus+Radix sp.group(0.13g/L+0.13g/L),Macrobranchium nipponense+Radix sp.group(0.13g/L+0.13 g/L)were set up.The results showed that Radix sp.did not act as a potent inhibitor of benthic Spirogyra as well as planktonic Spirogyra,and tall Rhodeus ocellatuss could significantly control benthic Spirogyra and was a good candidate for biomanipulation to control Spirogyra.The effect of high Rhodeus ocellatus on total and soluble phosphorus concentrations was significant,which promoted the phosphorus cycle in water bodies.The inhibitory effect of Macrobranchium nipponenseo n Spirogyra was related to temperature in addition to density.