Investigation into the fate and transport in groundwater of agriculturally derived phosphorus compounds.

Investigation into the fate and transport in groundwater of agriculturally derived phosphorus compounds Phosphates are ubiquitous in the environment, where they are essential for life however at excessive levels they can cause significant environmental damage. This project investigates the spatial and temporal occurrence of phosphorus in groundwater, and phosphorus transport through the vadose zone. Concentrating on agriculturally-derived phosphates, the research elucidates the geochemical relationships between phosphorus species and geology. The project has two study locations. A section of the Lower Usk Valley in Monmouthshire was the principal site the Eden Valley in Cumbria was used as a comparison case study. With highly heterogeneous distributions, phosphorus often showed significant concentrations in both soil and groundwater. In groundwater Soluble Reactive Phosphorus (SRP) ranged from 1.07 mg I1 to undetectable. Maximum soil leachable SRP was measured at 55 mg kg1 and soil Total Phosphorus (TP) 113 mg kg1 while in an adjacent borehole groundwater SRP was undetectable. Phosphorus was found at intermediate concentrations beneath potential hotspots created by large manure piles effluent 85 mg I1. Analysis by X-ray diffraction and analytical scanning electron microscopy did not identify soil phosphate minerals at these and other sites this suggests that precipitation reactions are not a dominant source or sink of agricultural phosphorus in local soils. The results of the geochemical investigations indicates that iron and manganese oxides are providing sorption sites for phosphates, influencing their mobility and observed concentration in groundwater. Data obtained from in-situ borehole loggers were used to characterise the aquifer zone of the study area and understand the groundwater response to external drivers such as fertilizer application and rainfall. Groundwater and species transport modelling of the Usk area indicates that local parameter heterogeneity is critically important. The groundwater modelling, supported by a statistical analysis of the data, has increased and refined our conceptual understanding of the fate and transport of phosphorus in groundwater.