Sr isotope tracing of multiple water sources in a complex river system, Noteć River, central Poland

Anthropogenic impact on surface waters and other elements in the environment was investigated in the Noteć River basin in central Poland. The approach was to trace changes in the Sr isotope composition ((87)Sr/(86)Sr) and concentration in space and time. Systematic sampling of the river water shows a very wide range of (87)Sr/(86)Sr ratios, from 0.7089 to 0.7127. This strong variation, however, is restricted to the upper course of the river, whereas the water in the lower course typically shows (87)Sr/(86)Sr values around 0.7104-0.7105. Variations in (87)Sr/(86)Sr are associated with a wide range of Sr concentrations, from 0.14 to 1.32mg/L. We find that strong variations in (87)Sr/(86)Sr and Sr concentrations can be accounted for by mixing of two end-members: 1) atmospheric waters charged with Sr from the near-surface weathering and wash-out of Quaternary glaciogenic deposits, and 2) waters introduced into the river from an open pit lignite mine. The first reservoir is characterized by a low Sr content and high (87)Sr/(86)Sr ratios, whereas mine waters display opposite characteristics. Anthropogenic pollution is also induced by extensive use of fertilizers which constitute the third source of Sr in the environment. The study has an important implication for future archeological studies in the region. It shows that the present-day Sr isotope signatures of river water, flora and fauna cannot be used unambiguously to determine the "baseline" for bioavailable (87)Sr/(86)Sr in the past.