| Biomanipulation has been applied in ecological restoration for eutrophication lakes.The traditional technology focused on the use of filter feeding trophic level,ignoring the regulation and control function of complete food chain in the aquatic ecosystem.In this study,in order to verify the controling function of multi-level trophic level,a species of fish,Xenocypris microlepis was introduced in the simulation ecosystems combined with silver carps and bigbhead carp.Xenocypris microlepis is bottom habitat,feed on organic detritus at the bottom of the water.The poly culture of Xenocypris microlepis with silver carps,bigbhead carp build a food chain based on on the traditional biomanipulation technology.According to the differet ecological niche of the three species of fish,silver carps,bigbhead carp are expected to eliminate the blue algae floating in the water bady,while Xenocypris microlepis is expected to prey on the excrement of silver carps and bigbhead carp.The combination of the fishes are expected to control the water bloom and improve water quality.However,the feeding effect of Xenocypris microlepis inthe food chain and its impact on water environment had been rarely reported.The experiment was carried out under indoor and outdoor simulation conditions,the 15N stable isotope tracer technique and chlorophyll fluorescence technology was used,to analyze the influence of feeding behavior of Xenocypris microlepis on algal activit changes after digested by silver carp and bighead carp and transferring of faeces-sourced nitrogen.Furthermore,the influence of Xenocypris microlepis with silver carps,bighead carps on the aquatic environments and the transferring of nitrogen were studied.The results provided the theory basis for the application of biomanipulation mode of polyculture of Xenocypris microlepis for elimination of algae blooms.The main conclusions are as follows:(1)By using the 15N stable isotope tracer technique,to analyze the influence of feeding behavior of Xenocypris microlepis on feces from silver carp,bighead carp feeding on algal,and its influence on water quality change of experimental system.Before 2 days of the experiment silver carp and bighead carp were feeded with 15N labeled microcystin algae,at the beginning of the experiment put silver carp,bighead carp and feces collected during the period of silver carp and bighead carp feeding into the corresponding experiment bucket,and for 20 days experimental cycle.After experiment,the isotope ratio in selected Xenocypris microlepis organs significantly increased,and the isotope ratio had a great difference between each organ.In the process of the whole experiment,the changing trend of each organ were similar.As a general result,?15N(intestines)>?15N(blood)>?15N(tail fin)>?15N(muscle).Beside the introduction of silver carp and bighead carp,the polyculture of Xenocypris microlepis could improve the water environment quality.In the late stage of the experiment,nutrient concentrations in Xenoypris microlepis introduced gruoup were significantly lower than those in silver carp and bighead carp groups(P<0.05).At the ending of the experiment,TN?TP?NO3-?NH4+ and PO43-in Xenocypris microlepis introduced group was 59.04%,46.33%,32.12%,33.15%and 45.42%of silver carp and bighead carp group.(2)Effects on the amounts of feces and the activity of microcystis by the introduction of the different combination of silver carp,bighead carp and Xenocypris microlepis were studied in indoor simulation experiments.The feces weight of Xenocypris microlepis introduced group was 16.08%of the silver carp,bighead carp group at the ending of the experiment.Algae digestibility of Xenocypris microlepis introduced gruoup reached 85.9%at the end of the experiment,and was significantly higher than that in silver carp and bighead carp group(P<0.01).Analysis of the feces,found that the amino acid and nitrogen content in the experimental groups were 33.17%,53.62%and 34.97%,54.27%respectively compared with the microcystis aeruginosa in the blank control.The introduced Xenocypris microlepis could reduce the activity of the algae by feeding and digestion.Chlorophya fluorescence parameters(except NPQ),EPS and Chl.a in Xenocypris microlepis introduced group was significantly lower than that in silver carp and bighead carp group(P<0.05).(3)Effects on the water environment quality and nitrogen migration and transformation by the introduction of the different combination of silver carp,bighead carp and Xenocypris microlepis were studied in outdoor simulation experiments for for 30 days.Results showed that introduced Xenocypris microlepis speeded up the transformation of nitrogen.In the late stage of experimental,NH4+??15N(ammonia)in the Xenocypris microlepis introduced group was rapidly declined,while in silver carp,bighead carp group,they maintained a higher level.The Xenocypris microlepis introduced group could improve the adsorption effect on waste organic detritus,avoid to water pollution caused by waste decomposition.On 15th day,?15N(sediment)in the polyculture of Xenocypris microlepis introduced group was significantly greater than that in the silver carps,bighead carp group(P<0.01).(4)Both of the indoor and outdoor experiments indicated that grazing fish can effectively reduce algae biomass,improve the transparency of the water body.Results of outdoor experiments showed that the collaborative control function of Xenocypris microlepis with silver carps and bighead carp played very well for cyanobacteria,but was not obvious for the green algae.At the end of the experiment,cyanobacteria biomass in Xenocypris microlepis introduced gruoup was 28.3%of silver carps,bighead carp group,was significantly lower than that of silver carps,bighead carp group,but green algae biomass showed no significant difference between two experimental groups. |
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