Mediating effect of stream geometry on the relationship between urban land use and biological index

Numerous studies have stated that land use in urbanized areas can adversely affect water quality of streams. Previous studies reported that edges may play important roles in controlling flow rate of material in two systems. In this study, we examined the mediating effects of streamline geometry on the relationships between urban land use and the index of biological integrity (IBI) of the Nakdong River in Korea. Two mediation models with streamline geometry, including the partial mediation effect model and the full mediation effect model, were estimated to explore the mediating effect of streamline geometry. To measure streamline geometry, we calculated the fractal dimension of a streamline within a 1 km buffer from the sampling sites. The proportion of urban land use within a 5 km buffer of the sampling sites was also computed by GIS. We used biological assessment data from the National Aquatic Ecological Monitoring Program in Korea to delineate the IBI at the sampling sites. The results showed that urban land use significantly degraded stream morphology and IBI in the Nakdong River. It was also observed that streamline geometry mediated the influence of urban land use on the IBI. The results of structural equation modeling analysis for the two mediation models with the fractal dimension and IBI suggested that only two paths were significant in the partial mediation model, whereas all paths were significant in the estimated full mediation model.