Predicting the effect of land use on stream water quality in the UK

The effect of land use change at both long (90 year) and short (single water year) time scales are discussed. Current annual sediment and solute export from this area of arable and grassland farming in SW Devon is of the order: 61 for NH4-N, 2821 for N03-N, 21 for P and 14401 for suspended sediment. Sediment cores from the lake receiving these catchment inputs provides long-term evidence for an increase in erosion and nutrient export since the 1950s. A significant increase in stream NO3" load is also recorded over the past 30 years. As a result of catchment inputs, the lake is now hypertrophic. Models currently used to predict the effect of land use change on stream water quality are limited because they fail to account for the effect of hillslope hydrological pathways and the physical and biochemical modification of the potential nutrient and sediment load