Phosphorus is an important pollutant affecting the quality of water and aquatic biodiversity. As such, control of phosphorus loading to waters is required in order to meet the terms of the EU Water Framework Directive (WFD), whose purpose is to achieve good ecological status of all water bodies across Europe (2000/60/EC, EC 2000). The Upper Greensand (UGS) is a formation of middle Cretaceous age, ranging from a few meters up to 75m in thickness, located in southern England. It is mainly composed of calcareous sandstones and calcarenites with varying amounts of silica and occasionally contains glauconite and shell debris. Additionally, recent studies have shown that UGS also contains high concentrations of phosphorus (P) due to a mixture of P exported to the UGS from overlying agricultural soils and plumes from septic tanks, and to the presence of the phosphate mineral apatite. Those concentrations, along with a proportion of P derived from diffuse agricultural and point source sewage discharged directly to the river or via the soils, create important environmental implications such as eutrophication in the surface waters of the Hampshire Avon catchment, which are drained, in part, from the UGS aquifer. Consequently, assessing the proportion of P coming from both UGS and separating this from anthropogenic sources is of major importance to determining the natural ecological health of the Upper Avon. This study aims to investigate the source and distribution of P by sampling representative areas of the UGS in order to identify and distinguish the primary apatite that is originally hosted in the UGS, from the secondary apatite that is of anthropogenic origin. In this context, the project involves LOWTEX and AQUALAB suites for P speciation analysis in the aqueous samples and SEM-EDS, EPMA and μXRF for chemical analysis of apatite in the bulk UGS samples. Finally, oxygen isotopes will also be employed to distinguish primary from secondary apatite in the UGS. The outcome of this study will be the identification of the primary apatite in the UGS, the determination of the rate at which soluble P fractions are released from the primary apatite through weathering, the characterisation of the primary versus secondary apatite in the UGS and, finally, an estimation of the amount of P coming from natural P bearing sources in the UGS.