Ammonia, Nitrite And Algal Toxins Two Daphnia Life History Characteristics

Blue-green algae will release intracellular microcystin and produce secondary pollutants such as nitrite and ammonia during the degradation after cyanobacterial blooms accumulated in local region, and thus cause serious water quality problems. In order to evaluate which materials are harmful to zooplankton among nitrite,ammonia and microcystin, D. similoides and D.obtusa, the common species of zooplankton in Lake Taihu, were used in the experiments. From the acute and chronic exposure experiments of nitrite,ammonia and microcystin to D. similoides and D. obtusa,we can get the following conclusions:1 The acute toxicity of ammonia and nitrite to D. similoides at different developmental stages (0.5,1,3,5,7 d)The 24-h and 48-h LC50 of nitrite to D. similoides at different developmental stages increase as the instar grows, the other instar all have significant difference (P< 0.05) except 5 and 7 days;a modified Gaussian model was used to describe the trends of changes in LC50s at different stages in D. similoides, we can get the maximum LC50 of nitrite at 24h and 48h which were 156.99 and 63.09 mg.L-1 respectively;the age that LC50s of nitrite at 24h and 48h reached the maximum values were 6.25 and 5.74 days,respectively.The 24-h and 48-h LC50 of ammonia to D. similoides at different developmental stages will not vary with instar increasing when it was over 3 days old, and there were no significant difference between 5days and 3days on the 24-h and 48-h LC50. a modified Gaussian model was used to describe the trends of changes in LC50s at different stages in D. similoides, we can get the maximum LC50 of ammonia at 24 h and 48 h which were 1.74 and 1.33 mg L-1,respectively; the age that LC50s of ammonia at 24 and 48 h reached the maximum values were 3.98 and 4.03 days,respectively.Using the modified Gaussian model, we can describe the trends of changes in LC50s of nitrite and ammonia to D. similoides at different developmental stages.we can gain an insight into the maximum LC50 and the age that has the maximum LC50 and predict LC50s at any specific ages. We suggest that such a model might be used to describe the trend in acute toxicity of some other zooplankton species at different stages.2 The chronic toxicity effect of ammonia and nitrite to D. similoides and D. obtusaDuring the 21 days chronic experiment of ammonia and nitrite to D. similoides and D. obtusa, we evaluate the following parameters:time to first eggs/clutches,body length at first eggs/clutches,number of moults,number of clutches,mean number of offspring per clutch,mean number of offspring per female,mean survival days. And four-parameter logistic model was chosen to fit the indexes'data, we can get the indexes'EC50,respectively, contrast the LOEC,NOEC and EC50 among the indexes, The order of sensitivity of all indexes was as following:Ammonia to D. similoides:time to first eggs/clutches=mean number of total offspring per clutch> mean number of total offspring per female> mean number clutches> mean survival days> mean number moults.Ammonia to D. obtusa:mean number of total offspring per female>mean number of total offspring per clutch>time to first clutches=body length at first eggs/clutches>mean number clutches> mean survival days> mean number moults.Of the all indexes of ammonia to D. similoides and D. obtusa, the time to first eggs/clutches of D. similoides and time to first clutches of D. obtusa was significantly delayed with ammonia increasing, ammonia to D. similoides body length at first eggs/clutch have no significantly effect, but to D. obtusa' body length at first eggs/clutch have a stimulation at low concentration (0.01076,0.0538 mg/L), the body length is longer than other concentrations'. To mean number of offspring per clutch and mean number of total offspring per female stimulation effect also appear at low concentration. From the order of sensitivityof all indexes,we know mean number of offspring per clutch and mean number of total offspring per female was the most sensitive indexes in both D. similoides and D. obtusa,the two index's NOEC and LOEC is 0.0538 mg/L and 0.1076mg/L respectively,it suggests both Daphnia has the same sensitivity to low ammonia concentration,then assessing the EC50,mean number of offspring per brood of D. similoides was 0.58 mg/L,mean number of total offspring per female of D. obtusa was 0.27 mg/L, it suggests D. obtusa was more sensitive than D. similoides.Nitrite to D. similoides:mean number of total offspring per female> mean number of total offspring per clutch>mean number clutches>mean number moults>mean survival days.Nitrite to D. obtusa:body length at first clutches= mean number of total offspring per female> mean number of total offspring per clutch>time to first eggs/clutches>mean number moults>mean number clutches>mean survival days.During the nitrite to D. similoides and D. obtusa' experiment,the time to first eggs/clutches,body length at first eggs/clutches of D. similoides and time to first eggs/clutches,body length at first eggs of D. obtusa was not effected.through the order of sensitivity of all indexes, mean number of total offspring per female and mean number of total offspring per clutch was the most sensitive.Contrast the LOEC and EC50 of mean number of total offspring per female among the two species, D. similoides was 1 mg/L and 1.56 mg/L respectively, D. obtusa was 0.1 mg/L and 1.59 mg/L respectively,it suggests D. obtusa was more sensitive than D. similoides to low nitrite concentration, but the value at which they reach the EC50 concentration was almost the same3 Combined effects of nitrite and microcystin to D. obtusaDuring the 15days combined experiment,the parameters time to first eggs(P=0.020)and time to first clutches (P=0.021) all have significant interaction, the influence of time to first eggs/clutches not only depends on nitrite concentration,but also depends on microcystin concentration,during the combined effects of nitrite and microcystin, microcystin can reduce the harmful effects caused by nitrite on delaying time to first eggs/clutches. On the remaining parameters:body length at eggs/clutches,mean number of offspring per clutch, mean number of total offspring per female, mean number moultes,mean number clutches, nitrite and microcystin represent single effect, because microcystin didn't exert significant influence on the parameters, we think the harmful effects was caused by nitrite.4 Combined effects of ammonia and microcystin to D. similoides and recovery experimentDuring the combined effects of ammonia and microcystin to D. similoides,we evaluate the parameters as following:time to first eggs/clutches, body length at first eggs/clutches, mean number of offspring per brood, mean number of total offspring per female, mean number clutches, mean number moultes. On the time to first eggs ammonia and microcystin represent interaction (P=0.026) and microcystin can reduce ammonia to delay time to first eggs. On the time to first clutches ammonia and microcystin don't represent significant interaction effect but both influence the parameters depending on each other. On the mean number of offspring per clutch, ammonia and microcystin don't represent significant interaction effect, ammonia can influence the parameter itself, but microcystin influence it depending on ammonia. On the mean number of offspring per female, ammonia and microcystin represent independently, both influence it respectively. On the mean number clutches, ammonia and microcystin represent independently,but microcystin don't represent significant influence, we think the all harm was affected by nitrite. On the remaining parameters, ammonia and microcystin didn't represent any harmful effects.In the recovery experiment, we evaluate mean number moultes,mean number clutches, mean number of offspring per clutch, mean number of offspring per female.there was no significant difference between different concentrations on mean number moultes and mean number clutches in recovery,from this,we could conclude that ammonia and microcystin didnt have influence on the two parameters.as for the remaining two parameters, the offspring of high concentration treatments is higher than that of low concentration treatments in recovery experiment, it showed that individuals exposed to higher concentrations in chronic experiment had more fast recovery speed on reproduction index in recovery experiment,which is called'catch-up reproduction'theory. Maybe these two parameters are very sensitive, they will recovery rapidly when the suppression disappeared.