Impacts Of Urbanization On Stream Water Quality And Macroinvertebrate Communities

Urbanization is a common phenomenon of land use change. The ecological effects of urbanization are well concerned recently. Urban steam ecosystem is one of the most impacted aquatic ecosystems disturbed by urbanization.Investigations of stream physico-chemical characters, macroinvertebrate communities as well as watershed land use were carrying out in89sites of1-3rd order streams in the tributaries of middle section of Qiantang River in April,2010and April,2011. The detailed results were as follows:The dominant substrates of reference streams were boulders and cobbles, disturbed streams were dominated by sands and silts. The water temperature, CODMn,total nitrogen, total phosphorus, conductivity, NH4+-N, PO43--P, Ca and Mg 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, Sensitive taxa%and predators%, shredders%, filterers%, scrapers%were higher at reference streams than disturbed streams. In contrast, BI, collectors%, tolerance taxa%and oligochaeta%were higher in disturbed streams than in refernce streams.The relationships of environmental and biological variables with percentage of impervious area (PIA) and as an indicator of urban intensity were explored. Spearman correlation analysis showed that NH4+-N, PO43--P, TP, CODMn, conductivity, stream wet width, depth and sand%were positively correlated with PIA (P<0.01) and negatively correlated with forest%(P<0.01). Fitted nonlinear regression equations revealed that all tested macroinvertebrate metrics had significant relationships with PIA (P<0.01). Of which, the total number of taxa, Shannon diversity index, richness index, EPT%, Sensitive taxa%, predators%, shredders%, filterers%, scrapers%was negatively correlated to PIA (P<0.01) and positively correlated to forest%(P<0.01). However, BI, collectors%, tolerance taxa%and oligochaeta%were positively correlated to PIA (P<0.01).Patterns in stream macroinvertebrate assemblages are the result of the combined influence of processes acting on different spatial scales. Based on the environmental and biotic data, the aims were to analyze the stream macroinvertebrate assemblages, indentify the key environmental factors that are linked to variation in macroinvertebrate assemblages and to partition the influence of watershed-scale and reach-scale variables, alone and in combination, on macroinvertebrate community composition. Principal Components Analysis (PCA) were used to explore the major environmental gradients. PC A showed the watershed land use and with the changing of watershed land use, streams suffered from high level of nutrient and degradation of physical habitats. Canonical Correspondence Analysis (CCA) were adopted to determine the relationships between environmental variables and macroinvertebrate composition, while variation partitioning was performed using partial Canonical Correspondence Analysis (pCCA) to understand the relative importance of different scale factors in macroinvertebrate variation. CCA suggested that in watershed scale Latitude location, altitude, sub-basin area, forest%, cropland%, PIA and in reach scale water temperature, pH, DO, Vmean, TP, the concentrations of Ca and the mean substrate score (MSUBST) were the most important variables structuring macroinvertebrate assemblages. The total explained variation is31.52%, and the results of pCCA indicated that the relative proportions of explained variation of macroinvertebrate communities attributable to watershed scale and reach scale environmental variables were30.43%and21.61%, respectively. The results of pCCA suggested that both scale variables play more important role in stream macroinvertebrates variation of this study region, and could have potential in biodiversity conservation and restoration, land management, environmental monitoring and assessments.Our study indicated that with the increasing of urbanization intensity, urban streams suffered from the urban syndrome in terms of high level of nutrient of nitrogen and phosphorus, degradation of physical habitats, loss of sensitive macroinvertebrate species and dramatically increase of tolerant species individuals. Stream macroinvertebrate assemblages were affected both by watershed scale and reach scale environmental variables, and variables of watershed scale play more important role than reach scale in shaping benthic maroinvertebrate community composition and structure.