Seasonal snowpack influence on the hydrology of a sub-arctic catchment in Scotland

Snow cover, depth and water equivalent have been measured in each snow season between 1989/90 and 1993/94 in the Allt a' Mharcaidh catchment in the western Cairngorms. Spatial and temporal patterns of snow accumulation vary: the peak measured water equivalent held in the catchment snowpack ranged from around 50 mm in mild winters to 200 mm in more severe ones. Snow accumulation was concentrated on north and east lacing slopes in the parts of the catchment above 700 m. Point measurements of water equivalent in the areas of greatest accumulation exceeded 2000 mm as a result high densities produced by prolonged melt metamorphosis. Patterns of accumulation and melt strongly influenced the hydrology and hydrochemistry of the stream which has a distinct alpine-like regime. Low baseflows of high pH (>6.5) characterise cold periods of snow accumulation. Melt events are variable; slight increases in temperatures commonly melt all snow lying at low altitudes. More substantial melts involving the extensive snowpack at higher altitudes occur in the early spring as temperatures increase more significantly. Melt events strongly influence the hydrochemistry of the stream; preferential elution of Cl and SO₄ were distinct characteristics of each melt season. Moreover, the most acidic (pH < 5.5) streamflows, and the highest levels of inorganic aluminium, were usually observed during snowmelt.