The Ecological Structure Of The Limnodrilus In The YaLuRiver And The Analysis For Its Poisonous Experiment

Limnodrilus is the most common benthos in fresh water,we can often see plenty of Limnodrilus hoffmeisteri individual when eutrophication is serious,which mainly because this species can endure the environment that is in low oxygen or lack of oxygen.Caused by organic compound's being resolved in a great quantity,while under the same environment,other benthos can always be restrained or even die.A lot of research at home and abroad would determine the quota of the water polution degree according to the munber of Limnodrilus in per unit area.The superior species of Limnodrilus in the YaLuRiver in Dandong is Limnodrilus hoffmeisteri.To measure the ecological structure of the Limnodrilus in the YaLu River,we set up three sampling stations along the YaLu River bank,the yearly average value of fourteen chemical quota in three sampling stations:Total-Nitrogen,Total-DN,Petroleum-degrading Bacteria,Fingerling Cyprinus,Total-Phosphorus,Dissolved Total-Phosphorus and Super Phosphorus presents varying differences.That is:â… >â…¡>â…¢station,but Dissolved Oxygen presents opposite changeable trend whether it is from the surface or from the bottom.That isâ… <â…¡<â…¢station,there is not obvious changeable trend in PH,Alkalinity,Hardness and SiO₂ density,At stationâ… ,where its eutrophication is the most sirious,Limnodrilus hoffmeisteri is the obsolutely superion species(occupying 65.6%of all the benthos at this station),and its yealy average density is 3215 ind.·m^-2.Compared with stationâ… ,stationâ…¡is also in eutrophication,but less in degree,and its yearly average density can also be up to 2766 ind.·m^-2,Compared with stationâ… and stationâ…¡,the nutritious level in stationâ…¢is lower,and the density of Limnodrilus hoffmeisteri is 2684 ind.·m^-2,From above analysis,we can see that the density of Limnodrilus hoffmeisteri and its water hutritious level tend to be positive.The acute poisonous data on fish is one of the most common basis to judge the poisinous chemical material and industrial waste water endangering the water creatures. Adopting acute poisonous method,we can measure the density of Limnodrilus LD50 poisoned by Dimethoate with different density.We can also measure the changeable relationship between the dosage of carassius auratus and its death rate after Limnodrilus being poisoned.(1)Dimethoate virsus Limnodrilus 48h LD50 is 4.5mg·L^-1.(2)Using 3～5mg·L^-1Dimethoate poisoned Limnodrilus to feed carassius auratus,we know within fourteen days,the death rate increases with the density.The result of the experiment shows that Dimethoate can threaten the existence of Limnodrilus and within a certain density,it can also influence directly or indivectly the existence of other animals living on the Limnodrilus.To make matters worse,it can even endanger its life.