Comparison Of The Nutrition Adaptability And Alga-gra Zing Ability Of Several Common Large Cladocerans

Eutrophication is one of the major environmental problems in our country, in Europe and America have a lot of success experiments show that traditional bio manipulation can effectively control the eutrophication of lakes, but the case is rarely implemented in China. Prior in this research group have studied the impact of China major fish species on the traditionalal biomanipulation, but also through their investigation proved eutrophic shallow lakes concentrated Yunnan-Guizhou Plateau and the eastern plains lake sediments and lake waters are riched in large Cladocera dormant eggs, indicated that the traditional biomanipulation has the potential feasibility in these lakes, so on this basis, furtherly compare of the nutrition adaptability and alga-grazing ability of several common large cladocerans have important significance.Large zooplankton species and quantity is the foundation of traditional biomanipulation, By controlling the laboratory experiments, compared the influence of the main environmental factors including the food, the water temperature and the pH on Daphnia magna., Daphnia carinata, Daphnia hyalina, Daphnia pulex four large Cladoceras’population.The results showed that:four large cladocerans growth relatively good in the concentration of105cell/mL Chlorella pyrenoidosa. Of Microcystis sp.,Hubei Cyclotella hebeiana and Microcystis aeruginosa have shown poor ingestion, and even appeared all deaths. Temperature has a significant influence on Daphnia pulex quantity and body size (p<0.05), Daphnia pulex populations reached69.3at20℃, but it’s body size become smaller;Daphnia carinata and Daphnia hyalinethe population fecundity rate are rapid under the condition of25℃; the effect of temperature on Daphnia magna is not obvious (p>0.05). Daphnia magna’s amplification was the fastest at pH7, also the body size; Daphnia carinata and Daphnia hyaline’s amplification was the fastest at pH6, the body size are respectively larger at pH8and7, Daphnia pulex populations expanded fastest in the pH7condition, but the body size maximumed at pH6. So, Daphnia magna., Daphnia carinata, Daphnia hyaline and Daphnia pulex optimal culture conditions were20℃, pH7;25℃, pH6;25℃, pH6;20℃, pH7, the density of feeding food is105cell/mL pyrenoidosa.Further compared the four large cladocerans’adaptability to water quality and their ability to control algal growth in different trophic state of water through the situ experiment. Experiments in Wuhan in East Lake botanical garden and Ziyang lake, representing the moderate eutrophication and severely eutrophic water, the initial inputting density is40ind./L.The results showed that, during the whole experimental period the four large cladocerans can well adapt to survive in two kinds of nutritional status, population density is mainly affected by the seasonal temperature, the population density is relatively high in the summer, tand decreased in the autumn season, the cladocerans priority feeding Chlorophyta, they are poorly digest the Bacillariophyta and Cyanophyta. Daphnia magna and Daphnia carinata performance more prominent,at the same time, adding different large cladocerans makes the water in each enclosure different changes on physical and chemical index in different nutritional conditions.At the East Lake Botanic Garden, Daphnia magna significantly increased transparency, with the blank group, Daphnia pulex, Daphnia hyalina showed significant difference (p<0.05) after imputting, at october, both Daphnia magna, carinata Daphnia hyaline and Daphnia pulex with blank group have significant difference (p<0.05);while in Ziyang lake,20days inputting afer cladocera, each experimental group transparency increased significantly and compared with the blank group have significant difference (p<0.05). In Ziyang lake, addition of Daphnia pulex, Daphnia magna and Daphnia carinata water chlorophyll a content decreased significantly (p<0.05); in the botanical garden, since the initial chlorophyll a content is lower, so there is no difference between the experimental group and the blank group (p>0.05). In Ziyang Lake TP have great changes after the experiment, but there is no significant difference (p>0.05) between experimental group and the blank group, TP in botanical garden experimental group and the blank group only shows differences(p<0.05) in November;similarly, Ziyang Lake Daphnia carinata experimental group with the blank group showed differences (p<0.05) in March alone at TN, Permanganate index change is not obvious during the whole experimental period.In the blank enclosure, the experimental stage, transparency, total nitrogen, total phosphorus and Permanganate index decreased significantly, and the number of large zooplankton also increased significantly, showed that in these waters, even without adding large zooplankton, can also improve water quality through recovery of the large zooplankton communities in original water, they have the the potential implement biomanipulation.To sum up, apply the traditionalal biomannipulation to our lake to govern the eutrophication is feasible...