Particulate phosphorus transport by sub-surface drainage from agriculturalland in the UK. Environmental significance at the catchment and national scale

Phosphorus (P) is the key limiting nutrient in most UK freshwater systems. With increased legislation controlling point source inputs, dissolved (DP) and particulate P (PP) derived from diffuse sources are making a more signi ficant contribution to the total P loading of surface waters. Recent resear ch has focused on pathways linking diffuse sources to the fluvial system an d sub-surface field drains have been shown to transport both sediment and P rapidly to watercourses. Preliminary results are presented from an ongoing study using environmental tracers to identify the source of the drain sedi ment and its potential as a carrier of PP. These results suggest that the m ajority of sediment in drains is topsoil derived, but the significance of P loss via this pathway in a regional or UK context has yet to be evaluated. A protocol to study the potential problem at a regional/national scale is discussed and initial data presented. (C) 2001 Elsevier Science B.V. All ri ghts reserved.