Water quality of Scottish rivers: spatial and temporal trends.

The Harmonised Monitoring Scheme (HMS) was initiated in 1974 and represents the best-organised source of temporal and spatial data describing water quality for the major mainland rivers of Scotland, England and Wales. This paper presents the first detailed analysis of HMS data for Scotland, and identifies temporal changes in water quality from 1974 to 1995. From a concomitant analysis of catchment land cover characteristics, water quality indices have been linked with potential 'drivers' of change, influencing both point and diffuse sources. Nitrate concentrations between rivers are highly correlated with the amount of arable land, and relationships exist between grassland cover, orthphosphate-P and suspended solids concentrations. Similarly, urban catchments are highly correlated with ammonium-N, orthophosphate-P and suspended solids. Spatial and temporal trends in water quality for the rivers of Scotland are discussed.