Factors regulating the spatial and temporal distribution of solute concentrations in a major river system in NE Scotland

Abstract

The River Dee in NE Scotland, an oligotrophic soft water system, has a catchment area of approx. 2100 km 2, its source in the Cairngorm mountains being approx. 140 km from its outlet to the North Sea at Aberdeen. A comprehensive sampling strategy and analytical programme, commensurate with the size and nature of the Dee system, have been established for major water quality determinands to identify the controls on, and origins of, dissolved species throughout the system at a range of catchment scales and over a range of flow regimes. Fifty-nine sites covering a range of catchment types and scales were therefore sampled bi-weekly for 1 year. At the basin scale, there is a general downstream increase in determinand concentrations. This produces strong linear relationships between many determinands which are unrelated in terms of a common terrestrial process or origin. At the sub-catchment scale, however, specific hydrochemical processes control streamwater chemistry. The Dee basin divides into two distinct geographic regions in terms of land use (upland and lowland) which produce clear differences in water chemistry. Individual sub-catchments can also be grouped in terms of temporal variations in streamwater chemistry. The strength of the relationship between weathering-derived ionic concentrations and flow in the upland sub-catchments has lead to the identification of specific concentration limits in sub-catchments which can be used as characteristics of soil water and groundwater end-members. This provides a basis for the prediction of upland weathering-derived component concentrations for each sub-catchment at a range of flows.