The Study Of Zoobenthos During The Ecological Restoration Process In Suzhou Creek

As an important part of the aquatic ecosystem, zoobenthos are indispensable to its substance cycling and energy flowing. In the seriously polluted aquatic ecosystem, the structure of zoobenthos is simple, and the function is bereaved.,but as the restoration of ecosystem, the succession of zoobenthos community happens ,which make the species abundant.We can not only know the comtaminated degree of the water body by the study of community structure of zoobenthos ,but also know the status of ecosystem restoration by the restoration of zoobenthos. But in the process of river ecological restoration ,the studies of zoobenthos restoration dynamic in long time are few in China, mostly in one year.The sampling sites chosen for this study were four different reaches in Suzhou creek, including Zhaotun,Huangdu,Beixinjing and Zhejiangluqiao from headstream to downstream, and detailed investigation about zoobenthos in Suzhou creek was made from Spring in 2005 to Spring in 2006.Base on the general know of zoobenthos structure in Suzhou creek ,the impact on zoobenthos by environmental factors was analysed. Besides these, the dynamic of zoobenthos community restoration during the process of ecological restoration in Suzhou creek was studied by comparing the zoobenthos investigation data in 1999,2001 and 2003 with the current investigation data, and the evaluation of zoobenthos community restoration was made to explain the degree of ecological restoration in Suzhou creek. The main findings are as follows:1. Zoobenthos in Suzhou creek was not abundant, only nine species were found, including three kinds of Oligochaeta, five kinds of Mollusk, one kind of Insect, accounting for 33.3%,55.6%,11.1% respectively, and the dominant groups was Oligochaeta, while the indicators was Limnodrilus hoffmeisteri. Nine kinds of zoobenthos only belonged to two functional groups: collectors and grazers, and mostly were grazers.The seasonal changes of zoobenthos species were slight, whilethe changes of density and biomass were great. The highest density and biomass happened in Spring ,up to 22990 个/m² and 45.56 g/m² respectively, while the lowest density occurred in Winter ,up to 12463 个h/m²,and the lowest biomass occurred in Summer up to 19.70 g/m²o2 .Environmental factors had a great impact on zoobenthos in Suzhou creek, and different environmental factors affected zoobenthos in Suzhou creek differently. The main physicochemical factors which affected community structure of zoobenthos directly including species, density, biomass, diversity were DO and SS.DO and zoobenthos density, diversity had a negative correlation relationship, while SS and zoobenthos biomass had a negative correlation relationship. Other factors such as water temperature,BOD₅,NH₃-N affected zoobenthos density and diversity indirectly by influencing DO.The main sediment indeies that affected zoobenthos community structure directly were types of sediment, size of the granule ,CODcr,NH₃-N and organic matter. Types of sediment and size of the granule were remarkedly negative correlated with zoobenthos biomass in Suzhou creek, while CODcr, NH₃-N and organic matter were remarkedly negative correlated with zoobenthos diversity. Sediment affected different groups of zoobenthos differently. CODcr, NH₃-N and organic matter were markedly positively correlated with the distribution of Oligochaeta density, but had no marked correlation relationship with density of Mollusk and Insect. NH₃-N was markedly negative correlated with biomass of Mollusk and Insect. Besides hydrophyte, other biologic factors such as phytoplankton, fish had no great impact on zoobenthos in Suzhou creek.3. The changes of the zoobenthos community structure in Suzhou creek from 1999 to 2005 indicated that the restoration of zoobenthos community underwent two different phases, and the restoration in 2001 could be seen as a turning point. The restoration in 1999 and 2001 was better, because the species of zoobenthos amounted to 12 and 14 respectively, including Oligochaeta, Mollusk and Insect, and the number of Mollusk was more than that of Oligochaeta and Insect, but the density of Oligochaeta was dominant. The restoration in 2003 and 2005 was worse, and went with the trend of degradation, charactering with the reduction of species,increase ofthe density but reduction of the biomass and diversity. The number of species reduced from 14 in 2001 to 9 in 2005,and most of the species that disappeared were Mollusk. Shannon-Weinner diversity index decreased from 1.20 in 2001 to 0.70 in 2005,and the evenness index decreased from 0.67 in 2001 to 0.41 in 2005.The dynamic of zoobenthos restoration in Suzhou creek during the seven years showed that the process of zoobenthos restoration in Suzhou creek was very slow and iterative. Now the restoration of zoobenthos stays between the second phase and the third phase.4. At present the ecological restoration in Suzhou creek is slow and devious, staying between the second phase (phase of the water quality restoration) and the third phase (initial stages of ecological restoration) .The degree of the ecological restoration and the achievement we got are only a good beginning, and lots of work about ecological restoration needs to be done further. It will take long time to realize the ecological restoration in Suzhou creek.