Acid episodes in the Allt a'Mharcaidh, Scotland: an investigation based on sub-hourly monitoring data and climatic patterns
Abstract. 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.
Bonjean, M. C., Hutchins, M. G., and Neal, C.: Acid episodes in the Allt a'Mharcaidh, Scotland: an investigation based on sub-hourly monitoring data and climatic patterns, Hydrol. Earth Syst. Sci., 11, 340-355, doi:10.5194/hess-11-340-2007, 2007.