MODELLING THE IMPACT OF LAND USE CHANGE ON WATER QUALITY IN AGRICULTURAL CATCHMENTS

✍ Scribed by P. J. JOHNES; A. L. HEATHWAITE

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 359 KB
• Volume: 11
• Category: Article
• ISSN: 0885-6087
• DOI: 10.1002/(sici)1099-1085(19970315)11:3<269::aid-hyp442>3.0.co;2-k

✦ Synopsis

Export coecient modelling was used to model the impact of agriculture on nitrogen and phosphorus loading on the surface waters of two contrasting agricultural catchments. The model was originally developed for the Windrush catchment where the highly reactive Jurassic limestone aquifer underlying the catchment is well connected to the surface drainage network, allowing the system to be modelled using uniform export coecients for each nutrient source in the catchment, regardless of proximity to the surface drainage network. In the Slapton catchment, the hydrological pathways are dominated by surface and lateral shallow subsurface ¯ow, requiring modi®cation of the export coecient model to incorporate a distance±decay component in the export coecients. The modi®ed model was calibrated against observed total nitrogen and total phosphorus loads delivered to Slapton Ley from in¯owing streams in its catchment. Sensitivity analysis was conducted to isolate the key controls on nutrient export in the modi®ed model. The model was validated against long-term records of water quality, and was found to be accurate in its predictions and sensitive to both temporal and spatial changes in agricultural practice in the catchment. The model was then used to forecast the potential reduction in nutrient loading on Slapton Ley associated with a range of catchment management strategies. The best practicable environmental option (BPEO) was found to be spatial redistribution of high nutrient export risk sources to areas of the catchment with the greatest intrinsic nutrient retention capacity.