| Excessive concentration of nitrogen(N)and phosphorus(P)is the main reason for the eutrophication of water bodies,and it is also a quite prominent problem in the water environment.At the same time,microplastic pollution in aquatic ecosystems has become an increasingly significant problem.Macrobenthos are an important part of the aquatic ecosystem and play an important role in maintaining the material circulation and energy flow of the aquatic ecosystem.Study on the removal of nitrogen and phosphorus by Macrobenthos can provide a theoretical basis for aquatic ecological restoration.Exploring the effect of macrobenthos on the removal of microplastics in water bodies is of great significance to the treatment of microplastics pollution in the water environment.Based on the existing research status,this study designs and carries out mesocosm experiment on the removal of nitrogen and phosphorus by macrobenthos.Through regular collection and measurement of water samples,the characteristics of nitrogen and phosphorus removal by different macrobenthos are explored.The differences of nitrogen and phosphorus removal effect were compared under different density and individual size combination.At the same time,by investigating the characteristics of microplastics of Chongming Inland River and its dominant macrobenthos,analyzing the correlation between macrobenthos microplastics and microplastics in the water environment,and evaluating and discussing the removal of microplastics from water bodies by dominant macrobenthos.The main research results and conclusions are as follows:1.The removal of N and P by macrobenthos(1)The removal effect of N and P from water was significant by Lamellibranchia,and that is varies among different combinations of density and individual size.The highest removal rates of TN and TP by Corbicula fluminea were 51%and 62%,respectively.The highest removal rate of TN and TP by Anodonta woodiana were 49%and 51%respectively.The density of Lamellibranchia has a significant effect on the removal rate of N and P in water.On the whole,the higher the density,the higher the removal rate of N and P from the water body.When the Corbicula fluminea exceed 1.08kg·m-2 and the Anodonta woodiana exceed 2.16kg·m-2,the removal rate will no longer increase,instead will decrease as the density continues to increase.The individual size of Lamellibranchia has different effects on the removal rate of N and P in water under different densities.For example,Corbicula fluminea at the density of 0.36kg·m-2 and0.72kg·m-2,the N and P removal rate of 10g individuals was significantly higher than that of 20g individuals,while at 1.08kg·m-2 and 1.44kg·m-2 density,there is no significant difference among different individual size.Under the densities of 0.72kg·m-2,1.44kg·m-2 and 2.16kg·m-2,the TN removal rate of 75g individuals was significantly higher than that of 150g individuals.But there was no significant difference in TP removal rate.The overall performance of the removal of N and P by Lamellibranchia was fast in the early stage of the experiment and slow in the later stage.The rapid removal mainly occurred on the 2nd to 7th days,and then gradually slowed down.By the end of the experiment,the removal rate remained stable or slowly decreased.Compared with the initial water body,the forms of N and P in water has changed significantly after the experiment.The proportion of TPN and TPP in TN and TP increased significantly,and the proportion of TDN and TDP decreased significantly.(2)Gastropoda have a certain effect on the removal of N and P from water.There are differences between combinations of different densities and individual sizes.When the density of Bellamya aeruginosa is lower than 0.96kg·m-2,the highest removal rate of TN and TP in water is 43%and 28%,respectively.When the density reached 0.96kg·m-2,the 2.5g individual significantly increased the N and P content of the water,and the corresponding removal rate showed a negative value,reaching-46%and-43%,respectively.The individual size of Bellamya aeruginosa has different effects on the removal rate of N and P in water under different densities.At the density of 0.24kg·m-2 and 0.48kg·m-2,there was no significant difference in the removal rate of N and P between 2.5g and 5g individuals.At the density of 0.72kg·m-2 and 0.96kg·m-2,the N and P removal rate of 5g individuals was significantly higher than that of 2.5g individuals.The removal rate of N and P by Bellamya aeruginosa increased at first,then stabilized or decreased slowly.Compared with the initial water body,the forms of N and P in water has changed significantly after the experiment.The proportion of TPN and TPP in TN and TP increased significantly,and the proportion of TDN and TDP decreased significantly.(3)The effect of Crustaceans on the removal of nitrogen and phosphorus in water is not obvious.Both Eriocheir sinensis and Procambarus clarkii have negative N and P removal rates.The N and P forms of the water did not change significantly before and after the experiment.Under lower density conditions,Eriocheir sinensis and Procambarus clarkii have little effect on the concentration of N and P in water.As the density increases and the experiment progresses,the concentration of N and P increases instead.It is not recommended to use Crustaceans alone to remove nitrogen and phosphorus from water.2.The removal characteristics of microplastics in water by macrobenthosThe detection rate of microplastics in the Macrobrachium nipponense and Exopalaemon modestus of the dominant macrobenthos in the Chongming inland river were 64.58%and 50.12%,respectively.It was estimated that the average removal rate of microplastics in the Macrobrachium nipponense and Exopalaemon modestus to natural water were 0.00041%and 0.00125%,respectively.There were significant differences in the removal rate of microplastics by macrobenthos in different river reaches in the same season and in different seasons in the same river reaches(P<0.01).There was a significant correlation between the resources of Macrobrachium nipponense and Exopalaemon modestus and the removal rate of microplastics(P<0.05),and there was a significant correlation between the abundance of microplastics and the removal rate of microplastics in the Exopalaemon modestus(P<0.05).The removal characteristics of microplastics in water by macrobenthos were significantly affected by the composition of microplastics in the water environment.The shape,color,material qualities and size of microplastics in Macrobrachium nipponense and Exopalaemon modestus were significantly correlated with the characteristics of microplastics in the water environment.Preference analysis showed that Macrobrachium nipponense and Exopalaemon modestus were selective in the removal of microplastics,both for fibers,green,transparent,rayon and polyethylene,and<100?m,the removal preference was strongest.Macrobenthos as a sustainable biological resource in the water environment,the potential to removal of microplastics in the water environment cannot be ignored. |
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