Characterization of the water and sediment quality of the lower course of the Mrežnica River: the effect of long-term historical contamination

The lower course of the Mrežnica River has long been exposed to different types of industrial loads. In Duga Resa, the cotton industry was active for more than a century, and a few kilometres downstream, industrial wastewaters of Karlovac entered the river until approximately a decade ago. Our aim was to determine the main inorganic and organic contaminants of river-water and sediments at two differently polluted sites compared to upstream reference site. Turbidity, chemical oxygen demand, and total nitrogen were somewhat increased in Karlovac, whereas total phosphorus was increased at the reference site. Although dissolved metal concentrations in the water were rather low, indicating a pristine river, an increasing trend towards Karlovac existed for several elements (e.g., Fe, Mn), where the highest metal concentrations in finer sediment fraction (