Pollutant Transport Via Sediments in Medium-Sized Meandering Rivers: The Example of Barium in Kupa River (Croatia)

Abstract The aim of our study is to expand the world-wide knowledge about pollutant transport in sediments of medium-sized meandering rivers and to explain barium distribution in Kupa River (Croatia), as it showed as an ideal “natural laboratory”. Sampling was performed twice at the same places with the time span of 15 years to see the changes in Ba concentrations after that period. Ba was analyzed using ICP-MS method on clay + silt sediment fraction (<63 µm). Modelling was performed in R environment (R version 3.5.1, 2018) and for solving the sediment transport equation of Ba in Kupa River a program based on finite differences is constructed. After barite mine ceased operation in 1990, Ba is still entering Kupica and Kupa rivers, as karstic underground still contains large amounts of barite waste. Ba concentrations in Kupa River sediments are still increasing consequently along the whole river length, except in Kupica River and first downstream sample in Kupa River. It seems that in this part of river course erosion exceeded deposition processes. Also, there is an indication of changing the way of underground Ba transport. Erosion and deposition processes lead to formation of peak of Ba concentrations in the lower course of the Kupa River. Most important conclusion is that the mentioned peak was formed under one or two flood episodes, when sediment eroded from the upstream locations and was brought and deposited in the lower course of the river. Our modelling predicts that Ba source will not cease completely during the next 20 years.