Trends in concentrations of solutes in an upland catchment in Scotland

Hydrochemical datasets from an upland catchment at Glensaugh, north-east Scotland, for the period 1989–1994 were used to compile input:output budgets to allow an assessment of the annual variation in amounts and concentrations of solutes. Rainfall amounts dominated the annual chemical budgets, but there was evidence of changes in concentration of SO4-S and Ca with time. A smoothing spline statistical technique was applied to examine and model the variation in streamwater quality due to changes in flow, season and long-term trend. The relative magnitude of the three components, along with the variance due to each, are presented for concentrations of SO4-S, NO3-N and Ca. An advantage of this, over similar techniques, is the ability to allow both the seasonal amplitude and the flow:concentration relationship to vary smoothly through time.