The channelization has caused severe degradation of aquatic ecosystems during the past decades of rapid urbanization in metropolitan areas of China. The re-construction of the in-stream habitat of aquatic organisms and the restoration of aquatic ecosystems were more difficult in the urban stream than in the natural stream with the effluence of nutrient enrichment, water contamination, and in-stream habitat loss. Considering the ecological effects of the submerged macrophyte replantation on macroinvertebrate communities, one of the urban streams that used replantation restoration strategy was seasonally monitored from October 2012 to July 2013. There were four sampling sites, two located at the upper region and two in the middle region. Due to the relatively high levels of organic matter contamination, there are no sites in the downstream region of Qinghe River. Four types of submerged macrophyte were planted at each site to restore the in-stream habitat of two years ago, including Potamogeton pectinatus, Potamogeton crispus, Hydrilla verticillate, and Ceratophyllum demersum. Because of the unexpected development, Myriophyllum spicatum and Acorus calamus appeared at the upper reach of Qinghe River. Considering the average water depth of 30-40 cm, the revised Surber net with the enlarged net was used to collect macroinvertebrate samples. At each sampling site, three replicates of macroinvertebrates were carefully collected for each type of macrophyte. Three replicates were sampled for the comparison at the imperviously concrete sections of each site. The community composition of the macroinvertebrate was determined by cluster analysis and ordination analysis. The density, biodiversity, and community stability were higher in the sampling sections with the replantation of macrophyte than in impervious concrete sections. The occurrence of intermediate tolerant taxa such as Ephemera sp., Caenis sinensis Gui, Ecnomus sp., and Hydropsyche sp. indicated the recovery and restoration of macroinvertebrates in Qinghe River. However, the differences in the community structure, density, taxa richness, biodiversity index, and the composition of functional feeding groups of macroinvertebrates among different types of submerged macrophyte were not identified. Unlike providing extra habitats for macroinvertebrates in the vertical direction in natural streams and lakes, the submerged macrophyte provided more stable benthic habitats in urban streams. The stem and leaf of macrophytes could adjust the hydraulics and continually absorb, fix, and accumulate the suspended solids in the sediment and water interface. The root systems could stabilize the microhabitat of the sediment for macroinvertebrates, benthic algae, and microorganisms. Those aquatic organisms played an important role in the decomposition, transformation, and mineralization of nutrients and organic matter in urban streams. Following the recovery of stabilized microhabitats, community restoration and secondary succession of macroinvertebrates could continually and slowly happen. This study improved the understanding of the ecological effects of macrophytes on the restoration of aquatic organisms and ecosystems in urban streams.
Keywords: ecological restoration; macroinvertebrate; macrophyte replantation; microhabitat; urban stream.