A model for predicting chloride concentrations in river water in a relatively unpolluted catchment in north-east Scotland

The River Dee is an oligotrophic soft water system, in the NE of Scotland, with a catchment area of approximately 2100 km(2). The river rises in the C airngorm Mountains and enters the North Sea at Aberdeen, approximately 140 km from its source. Water chemical quality data was collected every 2 weeks over 12 months for 59 sites distributed throughout the catchment. River wa ter chloride concentrations increased significantly from west to east, In d epth investigation of the relationship with distance from the coast reveale d the significant difference in spatial distribution of river water chlorid e concentrations between upland and lowland/agricultural areas, suggesting the possible importance of agricultural practices to streamwater chloride c oncentrations. Thirty of the sample sites are independent and have been use d to develop a simple model for prediction of streamwater Cl- concentration throughout the catchment. The model has been validated using data from the remaining sub-catchments. The model shows that mean Cl- concentration may be reliably predicted from distance from the coast and the percentage of im proved grassland and arable land cover in each sub-catchment (r(2) = 0.98). It is postulated that the land use effects may be partly due to the evolve d link between landuse and catchment altitude characteristics, rather than just the direct effect of applied potassium chloride fertiliser on agricult ural land. It was noted that there was insufficient forestry within the Riv er Dee Catchment to reliably include % forest cover in the model. (C) 2001 Elsevier Science B.V. Ail rights reserved.