Mesocosm studies to resolve the fate of polycyclic aromatic hydrocarbons in grass swales as components of Sustainable Drainage System (SuDS) treatment trains

Student thesis: Doctoral Thesis


Urban runoff from impervious surfaces, such as roads, pathways and car parks, causes increases in localised flooding and is a source of pollution entering the aquatic environment. Sustainable Drainage (SuDS) are systems that can mitigate these impacts by mimicking pre-development hydrology, often using swales and detention ponds. Organic pollutants, such a polycyclic aromatic hydrocarbons (PAHs), are particularly found in road runoff and the understanding of their fate in SuDS has been limited due to of a number of factors including the heterogeneity in storm events, site conditions, local traffic, environmental conditions and natural changes in the PAHs themselves.
The aim of this study was to establish a large scale mesocosm to replicate environmental conditions of storm flow through vegetated swales and study the behaviour and fate of particle bound PAHs. A 10 m long physical model of a vegetated swale was constructed in a controlled environment, and a repeatable storm event runoff simulation pattern established. This was to allow observation of the transport and movements of the PAHs along the swale. A method was created for artificially producing road runoff dust, dosed with creosote containing PAH pollutants. Water samples were tested to establish the reduction in PAH aqueous concentrations after passage through the swale soil. Soil samples were collected from locations along the swale, and PAH concentrations established. Results showed that the swale mesocosm provides an effective simulation of storm hydrograph patterns. Aqueous PAH concentrations were significantly reduced after filtration through the swale system. Soil PAH behaviour showed that high molecular weight PAHs, (benzo(a)pyrene, chrysene and pyrene) reduced in concentration with distance along the swale. These PAHs began to accumulate in the 5 – 10 cm soil depth, just below the vegetated root zone. The profiles of the PAHs in the controlled mesocosm environment provide a reference point for field studies and will allow the fates of PAHs to be more precisely predicted for designs on sites where PAH discharges are sensitive. The unique model swale has allowed for the control of variables found in the environment that normally affect field research. This, however, means that results found may not be truly representative of those found in natural environment.
Date of AwardMay 2020
Original languageEnglish
Awarding Institution
  • University of Portsmouth
SupervisorJohn Williams (Supervisor), Fay Couceiro (Supervisor) & Joy Watts (Supervisor)

Cite this