The Effect Of Eutrophication And Environment On The Phototactic Index Of Daphnia Carinata

The serious aquatic pollution restricts the sustainable development of economy and is also dangerous to the human healthy and survival.In order to prevent water resources free from pollution, it is necessary to monitor aquatic pollution in real time in the management of water resource.Usually, there are two ways to monitor aquatic environments:physics/chemistry and biology.They have both advantages and disadvantages in the procuration of monitoring information and need to be cooperated and replenished mutually in order to provide accurate and correct information.The biomonitor methods are under developing and still have some limits such as poor accuracy,complex operation and difficult application,it is urgent to set up some accurate,quick and reliable methods for biomonitoring in present aquatic environment protection.Daphnia(Cladocero:crustacea),an important animal of the diet for many fish,is widespread in the world and has a critical role in aquatic ecology chains.It is quite sensitive to deleterious substances in water.Therefore,they are used to indicate and forecast the safety of water environments in acute toxicant test.The phototaxis of Daphnia is the character of light towards and against migration,which is genetically controlled and also influenced by environments.The utilization of phototaxis to mornitor the water qualities is a new developing technique in the world.This new technique is under investigation and has less information in theories and practical application.So,much fundamental research work needs to be done,including the selection of Daphnia as biomonitor sensitive to toxicants but less to environment changes,the exploitation of relationship between the phototactic behavior of Daphnia and pollutants such as heavy metal,pesticide and their mixtures,and the comprehension of the effect of environmental conditions such as fish kairomones on the phototactic behavior.At present,there was lack of systematic research on the influences of eutrophication and environments such as temperature,pH,hardness,light intensity and algae supplied and so forth on Daphnia's phototactic behavior.Although there are some reports of relations between the toxicants (heavy metals and pesticides)and the phototactic behavior,the mechanisms are necessary to explore. Therefore,we used Daphnia(carinata strain Dc4)collected in Three Gorges Area to study the influences of eutrophication pollutants,N and P,and environmental conditions on the phototactic behavior.Simultaneously,the relations between the activity of target enzyme,acety Icholinesterase, in nervous system and phototaxis were investigated under the presence of heavy metals and pesticides.The object of the experiment is to establish a fast,accurate and sensitive method for monitoring water qualities.The main conclusions are as follows:The phototactic index of Daphnia varied significantly in eutrophication water.Maximum phototactic index was observed in middle eutrophication water with 12-25 mg N L^-1and 2.5-5 mg P L^-1but greatly decreased in serious eutrophication water.The results indicate the survival adaptation of Daphnia in middle eutrophication water through natural evolution.Poor propagation of algae and bacteria in non eutrophication water with less nutrients present could result in short supply of food for Daphnia,which is unbeneficial their growth and reproduction.On the other hand,over propagation of algae in serious eutrophication water could lead the shortage of oxygen due to the consumption of oxygen in their life activities and the decomposition of their death bodies.Low oxygen,high volatile ammonium and toxicant effiuxes by algae are harmful to Daphnia.The phototactic index of Daphnia also varied significantly in different environments.Maximum phototactic index of Daphnia was found in the environments with temperature 20～25℃,pH 6.5～8.5,algae concentration1.7×10⁵～2.0×10⁵cell ml^-1,water hardness 15～18(Germany system),light intensity 9000～10000 lx and air pressure 980～1010pa.The activity of acety lcholinesterase in Daphnia reduced with the increments of hostathion and Cu²⁺concentrations,indicating the first action of two toxicants on nervous target enzyme and then changes of phototactic behavior.Taking in to account of time consumption,economic expensiveness and difficulties in site monitoring,the phototactic index of Daphnia could show perspective in the monitoring of water qualities in the future.