The impact of urban areas on the water quality gradient along a lowland river.

The effects of five towns on river water pollution were examined along the Łyna River (southern watershed of the Baltic Sea, northern Poland). The relationships among the spatially derived indicators of urbanization, environmental variables, and physico-chemical and microbiological data (heterotrophic plate count at 22 and 37 °C, and fecal coli) obtained from longitudinal river profiling have been examined with the use of multivariate analyses such as principal component analysis with factor analysis (PCA/FA) and hierarchical cluster analysis (HCA). We recognized the river channel as an environmental path that links serial urban areas into an "urban river continuum." An overall increasing trend in nutrients and indicator bacteria from suburban headwaters to urbanized sections of the river was detected despite a significant decrease in those between the towns. We concluded that the role of a multicity is equally as important as a single urban area in predicting the impacts of man-made pollutants on river water quality.