Acid episodes in the Allt a'Mharcaidh, Scotland: an investigation based on sub-hourly monitoring data and climatic patterns

• Published in: Hydrology and earth system sciences Vol. 11; no. 1; pp. 340 - 355
• Main Authors: Bonjean, M. C., Hutchins, M. G., Neal, C.
• Format: Journal Article
• Language: English
• Published: Copernicus Publications 01.01.2007
• Subjects: British Isles, Scotland; ANE, British Isles, Scotland; AN, North Atlantic, North Atlantic Oscillation
• ISSN: 1607-7938; 1027-5606; 1607-7938
• DOI: 10.5194/hess-11-340-2007

Stream waters in the Allt a'Mharcaidh catchment (Cairngorms, Scotland) have been monitored for flow, conductivity and pH at sub-hourly resolution; and for a range of chemical, biological and physical parameters, less intensively, since the mid-1980s. The Allt a'Mharcaidh stream is subject to acidic events (pH<5.5) triggered by both hydrology and sea-salt inputs from the atmosphere. This paper investigates the drivers of these acidic events using variables derived from sub-hourly monitored data. It also examines the influence of the North Atlantic Oscillation (NAO) on episode severity. Sub-hourly datasets are used to derive multiple regression models expressing stream H+ concentration as a function of the sea-salt conductivity and the peak instantaneous flow rate amongst other explanatory variables. The relationship between sea-salt conductivity and the NAO is significant but hidden due to issues such as time lags and the influence of atmospheric patterns other than the NAO.