Abstract
Abstract At the Svartberget Research Catchment in northern Sweden, stream pH had risen to 5.7 after a period of dry summer weather in 1987 before it dropped to below 4.4 during three ensuing storm events. To clarify the relationship between flow pathways and episodic acidity, the sources of storm runoff and its acidity in one of the catchment hillslopes were investigated. Hydrological considerations locate the origins of the runoff within the upper four decimeters of the soil in a swath some 50m wide along the stream. Groundwater remained alkaline throughout the episodes. Increases in the total organic carbon content of runoff appeared to play a central role in the stream pH decline. The episode's acidity and distinctive chemical ‘fingerprint’ originated in the runoff's passage through the organic-rich forest mor and/or streambank vegetation. Results from a column-leaching experiment supported this hypothesis. Such localized origins of runoff and especially of acidity may be of significance when calculating the rate at which acid episodes in other catchments respond to changes in acid deposition. A better understanding of the interaction between runoff and organic material is needed to determine whether the acidity at Svartberget is natural or if it has been affected by atmospheric inputs of anthropogenic origin.
Published Version
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