The Characteristics Of MC-LR Concentration In Urban River In Tianjin And Effects On Iris Pseudacorus L's Growth

In recent years,the algae blooms in the slow-flowing rivers of plain cities have become more and more concerned by the governments and the public because of the increasing scale of the algae blooms,the increasingly serious environmental and biological hazards.The secondary product of microcystis aeruginosa blooms,microcystin(MC)-LR,is extremely difficult to degrade efficiently.The growth of animals and plants and the health of the public are facing a huge threat.Therefore,the MC-LR concentration in urban river water was monitored for a long time in this research to understand its variation and existent forms,and to explore the effects of algal toxins on the growth and metabolism of other aquatic organisms,and to control the urban MC-LR concentration.This work means a lot to the ecological protection.A series of long-term samples were taken from the fixed points of the outer-river,the Jizhuangzi River and Wei-jin River in Tianjin.Then the continuous water quality indicators,MC-LR and acute biotoxicity of the samples were monitored.The overall concentration of microcystin in urban water i s very low,between 5-50 ?g/L.The distribution of the concentration of MC-LR in several rivers showed the characteristics of "more in summer and autumn,less in pring".The suitable temperature and light conditions in summer and autumn are favorable for the growth and reproduction of algae cells.There is a significant correlation between the concentration of nitrogen and phosphorus and the density of algae.There is a positive correlation between the density of algae and MC-LR in spring and summer,and there is a negative correlation between chlorophyll a and MC-LR in autumn.There is no correlation between the concentration of MC-LR and the acute toxicity of water.The results of Iris pseudacorus L experiments showed that the pH value of hydroponic system with high concentration of MC-LR(MC-LR concentration above 100 ?g/L)was alkaline.The oxidation-reduction potential was low and less than-20 mv.In addition,the high concentration of MC-LR limits oxygen exudation from roots.This phenomenon will become more and more obvious when the concentration of crude algal toxins increases.When the concentration of MC-LR was in the range of 40-100 ?g/L,the growth of Iris pseudacorus L was stagnant.When the concentration of MC-LR was lower than 40 ?g/L,the inhibition on the growth of Iris pseudacorus L was not obvious.In a hydroponic system with a MC-LR concentration of more than 100 ?g/L,the biomass of the plant showed a sharp shrinkage until the root died.The higher the concentration of crude algal toxins was,the more obvious the growth inhibition effect on Iris pseudacorus L was.