Determination of the nature and origins of riverine phosphorus in catchments underlain by Upper Greensand Aquifer

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.