Influence of snow on the hydrology and hydrochemistry of the Allt a' Mharcaidh, Cairngorm mountains, Scotland

Abstract

Systematic studies of winter snow pack accumulation and melt have been carried out in the Allt a' Mharcaidh catchment in the western Cairngorms, Scotland since 1989/90. These reveal marked variations in the annual snow pack accumulation which, in terms of peak volume (in water equivalents), ranges from <25 mm in mild winters to >180 mm in severe ones. This volume, and the rate at which it melts, has a clear impact on the annual flow regime of the Allt a' Mharcaidh: major melt produces high peak flows, whilst the absence of a substantial snow pack in mild winters can result in low flows. The dynamics of snow pack chemistry have also been examined. In the severe winter of 1993/94 the results suggest enhanced acidic enrichment at greater altitude (>900 m). In contrast, the smallest concentrations of acid anions (NO 3, SO 4, and Cl) were recorded during the mild winter of 1991/92. Limited snowfall at this time resulted in minimal accumulation of pollutants through dry deposition. Snowmelt events cause dramatic changes in the chemistry of the Allt a' Mharcaidh. High flows are accompanied by major acidic episodes produced by preferential elution of pollutants from snow which may have severe consequences for aquatic life. The most direct link between the quality of snow and runoff is the release of SO 4 and Cl. Spatial variability in the extent and magnitude of melting produced a damped response in the stream signal over a short temporal scale. Ions derived from marine sources were enhanced by a factor of 2 in the snowpack compared to the damped concentration in the meltwater. The Cairngorm mountains is a high amenity area renowned for its outstanding natural beauty. It is widely recognised that this fragile environment is of national importance, which is further justification for continued research interest in this area.