Dynamics Of Zooplankton Community Structure And Its Ecological Significance In Restoring Pulluted Waterbodies

The dynamics of zooplankton community structures in polluted water bodies, which were restored by measures of combined biological technicians and ecological engineering, were studied and the validity of restoration measures were evaluated based on zooplankton ecology. The restoration measures mainly included restoration of aquatic vegetation, tryout of microbial mixtures, application of constructed wetland and connection of rivers and lakes. In the course of restoration to water bodies, zooplankton community structures were influenced with change of water environment. .1) The effect of different combination system of constructed wetland (CW) on the community structure of zooplankton and the effect of the seasonal change were studied under different hydraulic loading (600 mm/d, 800 mm/d, 1000 mm/d). The results showed that the effect of CW system on the community structure of zooplankton was more effective under hydraulic loading 800 mm/d than others; the effects in spring, summer and autumn were more notable than that in winter, otherwise the effect in autumn was the most notable; the effect on macro-zooplankton was more obvious than that on micro-zooplankton and there were some species in the effluent water of wetland but not in influent water. The existence of the ponds in the system reduced the effects of the CW on zooplankton community structure and the effect of combination system(down-flow→aerobic and anaerobic pond) was the worst of all combination system. Contrastly, combined system of down-flow→up-flow→ horizontal-flow wetland and down-flow→horizontal-flow wetland presented obvious effects on zooplankton.2) Dynamics of zooplankton in aquiculture water by constructed wetland was studied. The results showed that zooplankton mostly were micro-zooplankton such as Trichocera pusilla, juveniles of Moina micrura, nauplii and copedide. Trichocera pusilla and Anuraeopsis fissa were dominant in Pond 1, and Brachionus angularis in Pond 3 in the same density of Channel Catfish (Ictalurus punctatus, 3×105ind/ha.). Moina micrura fluctuated periodically when cycled water volume was 15 percent of the whole water volume. They fluctuated analogously and showed a peak every 6-8 days in Pond 1 and Pond 3. Fluctuant periods of Moina micrura were longer and about 12 days in Pond 2. The density of Moina micrura was lower in Pond 4(average density≤1ind/L). Thermocyclops taihokuensis showed a peak every 12 days in Pond 1 and Pond 3, but only 4-8 days in Pond 4.3) The enclosure experiment of application of microbial mixtures showed that there was no significant difference of zooplankton species in the control and the treated enclosure whether in small enclosure and/or in large enclosure, and the variation of densities were similar. In the small enclosures, the density of zooplankton in the control was higher than that in the treated enclosure. The changes on densities of rotifer and copepoda were the same as total densities. But the density of cladoceran in the control was lower than that in the treated enclosure. In the large enclosure, changes on the densities of zooplankton were dominated by protozoa and rotifer. The densities cladoceran was not different. After stopping the application of microbial mixtures, the zooplankton density in the treated enclosure increased and was even higher than that in the control quickly. The effect of microbial mixtures on zooplankton community was temporary.4) Findings of experiment in Lake Yuehu showed in Lake Dayuehu, dominant protozoa were Difflugia, Tintinnopsis, Strobilidium and Halteria; dominant rotifer were Brachionus, Keratella valga and Polyarthra trigla; dominant cladoceran were Daphnia pulex in winter (from Nov. to Mar.) and Moina micrura in summer (from Apr. to Aug.) and Chydorus and Bosmina presented a peak when two species alternated; dominant copepoda were nauplii and copedide in density, and Cyclops vicinus in winter and Thermocyclops taihokuensis in summer. Protozoa and rotifer were dominant in richness and density. In Lake Xiaoyuehu, zooplankton community structure was similar to that in Lake Dayuehu, but the dominant protozoa was ciliate. Zooplankton density and diversity index in Lake Dayuehu were higher than those in Lake Xiaoyuehu, and biomass was contrarily. Biomass of zooplankton kept in lower lever in Lake Xiaoyuehu after constructed wetland was being operated. Zooplankton was disturbed by the restoration of macrophytes. A protozoa–rotifer-dominant peak presented in 1-2 months after macrophytes was replanted. Influence of macrophytes on the community of zooplankton was obviously.5) Findings of experiment in Lake Lianhuahu showed effects of constructed wetland on zooplankton were difficult from the front (protozoa﹥copepoda﹥rotifer﹥cladoceara). Species richness of zooplankton in Lake Xiaolianhuahu (101genera) was higher than that in Lake Dalianhuahu. Oligotrophic-prone genera were recorded in Lake Xiaolianhuahu such as Difflugia, Tintinnopsis, Ascomorpha, Chromagaster, Notholca labis, Lecane ludwigii, Eudactylota eudactyota and Calanoida. But some genera tolerant to contamination were recorded in Lake Dalianhuahu such as Maristentor and Colpoda. The average biomass of zooplankton in Lake Dalianhuahu (15 mg/L) were higher than that in Lake Xiaolianhuahu (6 mg/L) and the density in Lake Dalianhuahu was a little higher. Two peaks in density were found in Lake Xiaolianhuahu in November and May, it maybe resulted from the season succession of macophytes in the lake. Significance correlation was found between zooplankton density and macrophyte biomass.6) Water was transferred from Hangjiang River and Lake Houguan to Yangzi River via Lake Sanjiaohu and Lake Nantaizihu. Zooplankton community was investigated in the connecting rivers and lakes. The water quality was improved and zooplankton species richness decreased in lakes as soon as the water transfer finished. After one month, the zooplankton species richness increased except of the entrance in Lake Sanjiaohu. Before drawing water, the dominant species were contamination tolerated ones such as Brachionus sp., Polyarthra sp., Keratella sp. and Thermocyctops sp. in Lake Sanjiaohu. After drawing water oligotrophic-prone species were dominanted such as Tintinnopsis sp., Acanthocystis sp., Lecane ludwigii, Gastropus stylifer and Calanoida. The density and the biomass decreased in lakes by drawing water. But they increased at the entrance to Lake Sanjiaohu because of Landform geometry change. The densities of protozoa and rotifer decreased and the diversity indexes incresed in Lake Sanjiaohu and Qinduan Stream. Drawing water would be important measure for water quality improvement and ecosystem restoration. .In summary, zooplankton community would be disturbed moderately and the diversity could be increased in the water bodies treated by the CW with appropriate combination system and hydraulic loading. Zooplankton density was lower in the treated water body than in the control during using microbial mixtures. Dynamics of zooplankton in Lake Xiaolianhuahu with longer-time restoration was more disciplinary than those in Lake Yuehu with shorter-time restoration. Drawing water made zooplankton diversity increasing in lakes. So the measures for polluted water bodies restoration have showed their effects.