Episodic stream water pH decline during autumn storms following a summer drought in northern Sweden

• Published in: Hydrological Processes
• Main Authors: Laudon, Hjalmar, Bishop, Kevin
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2002
• Subjects: Northern Sweden
• Online Access: http://dx.doi.org/10.1002/hyp.360; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fhyp.360; https://onlinelibrary.wiley.com/doi/pdf/10.1002/hyp.360

Abstract The sources of episodic pH decline in four streams from northern Sweden during the autumn of 1996 were quantified. The events, in which pH dropped by between 1·0 and 2·4 units, were preceded by an extensive summer drought. Total organic carbon, which increased 100% to 160% during peak flow, was the most important driving mechanism of the episodic pH decline. Sulphate, however, was relatively more important during these autumn events than during spring flood. In the sites where past and present anthropogenic deposition were believed to be the main source of sulphate in stream water, sulphate contributed less than 0·3 pH units to the pH decline. In catchments where natural sources of sulphate are known to be important, sulphate contributed up to 0·6 units of pH decline. The export of sulphate during the episodes was two to nine times higher than what was expected from deposition only. The drought preceding the study episodes resulted in some of the lowest ground water levels during the 1990s in that region. The large export of sulphate was probably due to oxidation of natural sulphate bearing minerals in the soil and/or previously deposited sulphate driven by the low ground water level preceding the episodes. Copyright © 2002 John Wiley & Sons, Ltd.