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

The River Dee in NE Scotland, an oligotrophic soft water system, has a catc hment area of approx.: 2100 km(2), its source in the Cairngorm mountains be ing approx. 140 km from its outlet to the North Sea at Aberdeen. A comprehe nsive sampling strategy and analytical programme, commensurate with the siz e and nature of the Dee system, have been established for major water quali ty determinands to identify the controls on, and origins of, dissolved spec ies throughout the system at a range of catchment scales and over a range o f flow regimes. Fifty-nine sites covering a range of catchment types and sc ales were therefore sampled bi-weekly for 1 year. At the basin scale, there is a general downstream increase in determinand concentrations. This produ ces strong linear relationships between many determinands which are unrelat ed in terms of a common terrestrial process or origin. At the sub-catchment scale, however, specific hydrochemical processes control streamwater chemi stry. The Dee basin divides into two distinct geographic regions in terms o f land use (upland and lowland) which produce clear differences in water ch emistry. Individual sub-catchments can also be grouped in terms of temporal variations in streamwater chemistry. The strength of the relationship betw een weathering-derived ionic concentrations and flow in the upland sub-catc hments has lead to the identification of specific concentration limits in s ub-catchments which can be used as characteristics of soil water and ground water end-members. This provides a basis for the prediction of upland weath ering-derived component concentrations for each sub-catchment at a range of flows. (C) 1998 Published by Elsevier Science B.V. All rights reserved.