Modelling of E. coli transport in an oligotrophic river in northern Scandinavia

•We model E. coli transport in cold and oligotrophic river water.•Low inactivation rates lead to considerable transport distances of E. coli.•A clear seasonal structure of transport distances was observed.•Breakthrough of lake retention is pronounced during spring.•The model is a powerful tool for water management decisions in oligotrophic rivers.

This paper presents the development of a model for calculation of Escherichia coli transport in oligotrophic river waters, using temperature dependent inactivation rate for E. coli and flow velocity characteristics of the river and lakes. A total of 209 temperature measurements from 11 years surveillance were used to calculate transport distances until 90% inactivation of the E. coli. Three scenario sets of different site specific values for the first order reference inactivation rate constant k20 (0.145, 0.230 and 0.555 day−1) and temperature coefficient of the rate constant Q10 (2.07, 1.50 and 1.86) were tested in the upper parts of river Indalsälven, in northern Scandinavia. The first and third parameter sets represented respectively pristine water and lake water while the second setting was considered most representative of river Indalsälven. All three scenarios demonstrated considerable transport distances of E. coli with a clear and structured seasonal variation. The longest transport distances observed during late winter and spring are caused by a combination of low water temperature and high water velocity. The results have implications for water management decisions within the watersheds of oligotrophic rivers in cold and temperate climate.