The main objective of this project is to develop a methodology to assess the contribution of phosphorus runoff from clay-rich soils at reference conditions, for use as a management tool in the implementation of the European Water Framework Directive (WFD) in agricultural river basins.Sub-objectives;- Estimate levels of P losses from forested arable areas with clay-rich soils.- Estimate the bioavailability of P in runoff from clay-rich soils, soil-water/ground water, and surface water in forested areas. - Evaluate reference conditions in areas dominated by clay-rich soils based on palaeolimnological studies.- Develop an improved methodology and management tool for estimating background contributions of P in areas dominated by clay-rich soils.Although the WFD focuses on ecological aspects, nutrient concentrations are still important when designing appropriate abatement plans. In Norway large agricultural areas consist of marine clays with apatite-phosphorus. Waters in these areas are expected to have h igher reference levels of total phosphorus (TP). Several abatement plans to reduce TP from agricultural streams have pointed out that the presently assumed reference conditions are based on insufficient knowledge. The result may be too strict goals, with subsequent requirements for abatement measures and, thus, negative economical consequences for the agricultural sector.The project will seek to assess reference conditions of phosphorus through more than one approach to develop a robust methodology and m anagement tool for finding reference conditions. It is expected that this will have implications for the implementing of the WFD in Norway, and also be of interest in other European countries. The project will result in at least four peer reviewed scienti fic papers, and popularized information will also be prioritized so that management and stakeholders will be informed about the project through several info channels. The project will also result in a Ph.D. thesis.