The zinc load from the Dalälven River to the Baltic Sea is greater than for any other watercourse in Sweden. This paper investigates zinc mass flows into and through the Dalälven River from major mining areas within its drainage basin. Reported zinc mass flow data for this river are re-analyzed using an input-output flow analysis approach. Results show major inconsistencies in previous data interpretations which totally neglected possible zinc mass load contributions from the groundwater system to the river. This paper quantifies significant subsurface zinc load contributions that are consistent with all independently available data. Furthermore, a possible explanation for why these subsurface contributions may have been missed in previous studies and by the prevailing Swedish environmental monitoring system is provided. The study indicates that the input-output flow analysis approach may be generally useful for identifying and quantifying diffuse, unmonitored and uncertain pollutant load contributions from ground- to surface water systems.

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