Understanding catchment phosphorus pressures using an innovative monitoring system

Biles, Emma and Quinton, John and Zhang, Hao (2026) Understanding catchment phosphorus pressures using an innovative monitoring system. PhD thesis, Lancaster University.

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Abstract

Freshwater phosphorus pollution is recognised as a cause for concern worldwide due to its relationship with eutrophication, and the first challenge faced is its monitoring. This is because the most common method for monitoring is infrequent (monthly) grab sampling – which is discrete both spatially and temporally. A lack of data makes identifying sources and incidents of phosphorus pollution difficult. Techniques capable of collecting spatial and temporal phosphorus data are therefore of interest to water stewards and researchers. DGT (diffusive gradients in thin-films) passive sampling is thought to be capable of meeting such needs. It is, by design, a time-weighted average sampler that can be easily deployed in multiple locations. However, there have been few field studies demonstrating the technique for phosphorus monitoring. This thesis therefore aimed to establish DGT as a reliable, scalable monitoring tool for the field measurement of phosphorus in rivers and catchment systems. Different deployment systems were investigated for impacts upon DGT measured concentrations. It was demonstrated that deployment system had no impact upon DGT measured concentration and therefore recommended that DGT samplers be deployed in whichever system best suits site conditions. After comparison with high-frequency data it was preliminarily demonstrated that DGT successfully monitor temporal changes in phosphorus concentrations, and that DGT measure labile phosphorus concentrations, which are lower than total reactive and soluble reactive fractions in most cases. Incidences of spatial and temporal phosphorus pollution were reported according to DGT sampling results and diffuse and point sources of phosphorus pollution were identified within catchments by the technique. Additionally, DGT effectively measured significant decreases in river phosphorus concentrations following the implementation of mitigation technologies in wastewater treatment plants/storm dilution. This thesis therefore preliminarily demonstrated DGT as a versatile monitoring tool capable of spatial and temporal catchment investigations, and for use in monitoring mitigation effectiveness and phosphorus pollution control.