Contamination characteristics of the confluence of polluted and unpolluted rivers - range and spatial distribution of contaminants of a significant mining centre (Kutná Hora, Czech Republic)

The study brings new insights into the topic of the contamination characteristics of the mining region of Kutná Hora (Central Bohemia). The previous meta-analysis of the contamination studies showed that there could be a surprisingly low spatial range of contaminated river sediment downstream of Kutná Hora. The study should answer the question as to whether it is justifiable to interpret the presence of contaminants as a result of Kutná Hora mining. There was found a rapid increase in concentrations between the background area and contaminated Kutná Hora. Increase of medians (in mg/kg) of As: 33 and 148, Cu: 34 and 57, Pb: 35 and 82, Zn: 85 and 232; means increased ca 10 times. Then a decrease between the contaminated area and the confluence area was observed. But this decrease was influenced by the presence of extreme values in the contaminated area and therefore it was observed only in means. Medians of the elements concentrations did not decrease. The concentrations of the elements decreased after the confluence to lower values, but they stayed at the contaminated area levels. The background levels were observed only in the probes related to Labe alluvium. But also in these probes, the contamination was traced by multivariate analyses - by clear separation of As, Cu, Pb, Zn from other elements. The contamination was manifested in probes after the confluence mainly in the topsoil levels of alluvium, ca. in 10 to 40 cm. The original starting point of this study, that the contamination is not firmly manifested in the areas after the confluence, based on meta-analysis of regional studies, is not valid.