Using stable isotopes to resolve transit times and travel routes of river water: a case study from southern Finland †

The Kokemäenjoki River is dominated by great lake basins whereas the Vantaanjoki River has been reported having a significant groundwater component. The mean residence time of the young surface flow component could be resolved by sine function fitting onto the annual fluctuations of the isotopic signal, and the amount of base flow was estimated by using the isotopic composition of the river and groundwater.

In this study, we found that the methods work for simple two component catchments. In more complex cases with three different components mixing, the solution becomes increasingly difficult and requires more study.