Abstract: The 59 1st-3rd order tributaries in the middle reach of Qiantang River are negatively affected by different intensities of urbanization. In April 2010, an investigation was conducted on the water bodies’ physical and chemical properties and macrobenthos communities of the tributaries, with the relationships between the tributaries’ water quality and biological communities and the percentage of ground surface impervious area (PIA), an indicator of urbanization intensity. The Spearman correlation analysis showed that the water bodies’ NH₄⁺-N, PO₄^3--P, TP, COD_Mn, conductivity, width, depth, and fine sand/ silt ratio were positively correlated with PIA, and negatively correlated with forest land area. The fitted nonlinear regression equations revealed that all the test macrobenthic invertebrate’s parameters had significant relationships with PIA, of which, the total number of taxa, Shannon diversity index, richness index, EPT (%), predators (%), shredders (%), filterers (%) and scrapers (%) were negatively correlated to PIA but positively correlated to forest land area, and the BI, ollectors (%), tolerance taxa (%) and oligochaeta (%) were positively correlated to the PIA. Our study indicated that under the impact of urbanization, these tributaries presented the common features of degradation, i.e., high concentrations of nitrogen and phosphorus, degradation of physical habitat, disappearance of pollution-sensitive macro-benthic invertebrate species, and dramatic increase of pollution-tolerant species individuals.

Key words: Qiantang River, urbanization, macro-benthic invertebrate, ground surface impervious area.