Benthic Macroinvertebratre Diversity of Urban Streams in Xitiaoxi Watershed, Anji County, Zhejiang Province, China

Using the exsiting data and data from field surveys in Xitiaoxi watershed, Zhejiang province, China, we explored the characteristic of bentic macroinvertebrate diversity of reference streams; the relationship of habitats, seasonal variation of water quality and dynamic of benthic macroinvertebrate assemblages among reference, moderately and severely disturbed streams and the mechanism of degradation of bnenthic macroivnertebrate diversity in urban streams. In addition, we evaluated the impact of urban stream dams on benthic macroivnertebrate assemblages. The detailed results were as follows:1.A total of 226 species, which belonging to 190 genera,74 families,7 classess (paltyhelm, gastropoda, lamellibranchia, oligochaeta, hirudinea, crustacea and insecta) and 4 phylums (platyhelminthes, mollusca, annelida and anthorpoda), were found based on investigations of 20 reference sites from 2004 to 2010. The dominant phylum was the anthropoda and dominant class was the insecta. A total of 207 species,178 genera and 8 orders of insecta were found, which composed of 91.59% total species. Ephemeroptera was the dominant order of insecta, which including 44 species,27 genera and 12 families, composed of 21.26% insecta species; followed by Coleoptera,43 speices,40 genera and 12 families, composed of 20.78% of insecta species. The three dominant species were Baeties sp. (7.19%), Cheumatopsyche sp. (9.21%) and Chorotopers sp. (7.19%). The ANOSIM analysis showed the significant seasonal difference (spring, summer, autumn and winter) of species composition of 3 reference sites from 2009 and 2010 (R=0.611,p=0.001).2.The dominant substrates of reference sites were boulders (35.92%) and cobbles (33.66%), moderately disturbed sites were gravels (60.25%) and the severe disturbed sites were dominated by sands and silts (98.5%). The total nitrogen, total phosphorus, COD, conductivity were much higher in disturbed streams than in reference streams. In contrast, dissolved oxygen was much lower in disturbed streams than in reference streams. The total taxa richness, EPT (Ephemeroptera, Plecoptera and Trichoptera) taxa richness, Shannon diversity index and B-IBI index were highest at reference sites, followed by moderately disturbed sites, lowest at severe disturbed sites. In contrast, biotic index has the highest values in severly disturbed streams and lowest values in refernce stream. Both the NMDS analysis (stress=0.17) and ANOSIM analysis showed that the composition of macroinvertebrate community greatly varied among the three groups (R=0.664, p=0.001). Moreover, they were significantly different in different seasons (R=0.342, p=0.001), except for spring and winter (p=0.064), autumn and winter (p=0.227).3.Canonical Correspondence Analysis (CCA) about the macroinvertebrate community and environmental factors suggested that elevation, the percentage of boulders, sand, total nitrogen, dissolved oxygen were the major factors that influenced the distribution of macroinvertebrate communities in Xitiaoxi watershed, which was similar with the results of Pearson’s correlation analysis. The results of CCA showed that the former three axises explained 27.4% of the benthic community structure. The macroinvertebrate assemblages of reference sites have significantly positive relationship with elevation and the percentage of boulders. The indicative species of this group were Styloperla sp., Nemoura spl, Gumaga sp., Phryganopsyche sp., Glossosoma sp. and other more sensitive species. The macroinvertebrate assemblages of moderately disturbed sites have significant relationship with temperature, pH, and the main dominant taxa were Caenis longispina, Caenis sinensis and Corbicula flumineaand so on. The macroinvertebrate assemblages of severe disturbed sites were significantly related to total nitrogen and the percentage of sand. The dominant taxa of this group were Chironomidae and Oligochaeta.4.We surveyed the macroinvertebrate assemblages of nine sites (six in urban streams with run-of stream dams [2-3m] and three in reference forest streams) in August, in Xitiao watershed. Our results showed that the main substrate components of the reference sites were boulders and cobbles, while the substrate of the urban streams was mostly gravel (57.97%). Water temperature, conductivity, and concentrations of total nitrogen and total phosphorous were all significantly (p<0.05) higher in urban streams than in reference streams, whereas total taxa richness and EPT taxa richness were significantly (p<0.05) lower in the urban streams than in the reference streams. Differences in velocity (p=0.273) and depth/width (p=3.92) between sites above and below the dams were not significant. Dissolved oxygen, pH, total nitrogen concentration, water temperature and conductivity were also very similar between sites above and below the dams. An exception to this was that total phosphorus concentration was greater below the dams than above the dams. Moreover, total taxa richness, EPT taxa richness, Shannon diversity index and evenness index of the sites above and below the dams were similar. However, the biotic index was higher below dams than above dams. In addition, the ratio of sensitive taxa to tolerant taxa was lower at sites below dams, and the ratio of predators to collector-gatherers was higher at the sites below dams. Furthermore, NMDS analysis demonstrated that the macroinvertebrate community composition greatly varied between the sites above and below the dams in these urban streams. These results suggested that the sediment composition, water quality and benthic community structure had been significantly degraded in urban streams, particularly downstream of the dams.