Tomasz Kalicki

Based on the results of detailed geological-geomorphological studies, old maps from the past 200 years, and historical data, the paper is the first to present the structure of the valley floor in the estuary of the Nida River, an upland tributary of the Vistula, and discuss changes in the development and course of their channels. The aim of the study was to grasp the importance of local factors, both natural (palaeogeographical, lithological and tectonic) and anthropogenic, in the morphogenesis of this section, where a relatively small upland stream crossed in the medieval and modern periods by important overland and water routes of the Polish-Lithuanian Commonwealth flows into the Vistula River, which is ten times larger. The discussed section is not deltaic in character. The branching of the Nida into several simultaneously functioning outlet arms may have been caused by the blocking of outflow from the valley during floods and the drainage of the flood waters at the valley mouth in several directions, via channels both permanent and periodic. Changes in the numbers and locations of the Nida estuaries in recent centuries have both natural and anthropogenic causes. The interaction between the main stream and its many-times smaller tributary in the studied section has resulted in a complex mosaic of forms and cut-and-fills of both streams, but with the Vistula playing the dominant role. The cut-and-fills of the Vistula “enclose” the Nida alluvium inside its valley on the Winiary-Nowy Korczyn line, while the cut-and-fills of the Nida only occur in a very narrow strip under the edge of the terrace. The Nida followed abandoned channels of the Vistula on Holocene cut-and-fill IIA, flowing parallel to the Vistula for 9 km. The floor of the Nida Valley lacks Holocene mineral-organic and mineral sediments, characteristic of other upland tributaries from loess areas. The regulation of the Vistula in the mid-19th century and the Nida in the first half of the 20th century fixed the courses of the rivers, completely changing the sedi­mentation regime in the estuarine section of the Nida, where backflow and associated sedimentation of fine-grained deposits occurred.

The study area is located in the gorge section of the Upper Vistula river valley between Tyniec and Piekary near Kraków, where natural and industrial overbank alluvia with a different radionuclide activity, heavy metals content and grain size composition occur. Overbank deposits cover three levels of the floodplain where three cores of deposits were  collected. Alluvia of the lowest level along the channel are more heterogeneous and coarser than those on the middle and the highest level. Most of the overbank deposits were accumulated in the lower regime of water flow. On the basis of luminescence dating it was determined that the accumulation of overbank deposits on the first level started  200 years ago and on the highest level – 3,000 years ago.
All the three alluvium cores investigated in this study show a similar and regular vertical pattern of 137Cs and 210Pb activity. The vertical distribution of 137Cs in the profiles reflects its postdepositional migration and soil mixing due to ploughing. At the same time the vertical distribution of 210Pb seems not to be disturbed by this process. Moreover,  he peaks of 137Cs are concomitant with a decrease in heavy metal concentration in the top part of all profiles. This reflects the diminishing of industrial activity in Poland after the early 80’s of the 20th century. The vertical profile of 210Pb activity in the two cores from the upper levels of the floodplain wasused for the estimation of accumulation rates which occur to be approximately 0.4 cm/year. The vertical differentiation of heavy metals concentration in these profiles reflects both the economic changes in this region over the last century as well as the fluvial activity of the Vistula river. The higher pollution in the upper parts of the two profiles can be correlated with the industrial period which began at the end of the 19th century and lasted up to the middle of the 20th century in the upper Vistula river basin (Silesian Upland and Kraków Upland). The decrease of pollution at the top of all the profiles have results from economic recession and pro-ecological activities since the 1990’s.