Phosphorus in UK Rivers: The Impact of Urban Waste Water Treatment Directive

Abstract

Excessive phosphorus levels leading to eutrophication in natural waters as a result of growing population, urbanisation and intensified agriculture has long been a major environmental concern at a global scale. Many remediation strategies and actions have been undertken since the implementation of Urban Waste Water Treatment Directive (UWWTD) in 1992. The UWWTD was implemented to reduce direct phosphorus inputs into rivers from effluents of sewage treatment works. Nevertheless, the long-term outcomes and effectiveness of theses actions still remain unknown. An understanding of the prospective results and effectiveness of these implementations is only possible with a retrospective analysis of riverine phosphorus dynamics.
Therefore, this thesis explored the evolution of P concentration and flux from across the UK with datasets available from 230 river sites between the period of 1974 and 2012. These datasets were examined with the purpose of detecting the traces of the events that are likely to be governing the changes in phosphorus levels over the this time period i.e. the implementation of the UWWTD. Trend and change point analyses conducted on Total reactive phosphorus (TRP) and Total phosphorus (TP) data indicated that the concentrations and fluxes have been declining since the mid-1980s correlatingwith declining phosphate-fertilizer usage. The sites with the largest declines were from the Midlands and South East regions of England, whereas Scotland has seen almost no change. Significant step changes were encountered in most of the TRP concentration records, and most of these step changes were detected in the period 1993-1997 suggesting that the UWWTD was the key factor leading to these step changes. To validate this hyphothesis, Principal component analysis (PCA) was conducted to be able to track down the urban source contributor. Water quality (TRP, BOD, Suspended solids, Nitrate concentration and Conductivity) data from 5 example sites were analysed however, in none of the case examples was there an explicit principle component that could be construed with an urban or any other source contributor. Therefore, the PCA technique was not found to be a suitable technique to analyse this type of datasets.