Abstract
Coastal zones receive upstream runoff and sediments, as well as the contaminants transported with sediments and flow. Constant urban growth in many coastal areas has raised an increasing concern about stream and floodplain contamination. This is a particularly challenging issue because fluvial hydraulics in the coastal zone is complex, due to the presence of backwater (BW) conditions which alter flow patterns and sediment transport regime. Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants that are widely distributed in urban areas and can be transported through stormwater runoff and by sediment facilitated transport. Even though this is a widespread problem in urban areas, the relationship between fluvial deposition and concentrations of PAHs is largely uninvestigated. To fill this gap, this paper investigates the correlation between PAHs concentration and sediment deposition in a backwater zone, using the lower Darby Creek, PA as a case study. A BW geomorphologic model was used to simulate the hydraulics of the flow in Darby Creek. The model identified locations of high and low shear stresses, erosion, and deposition of fluvial sediment. Twenty-eight core sediment samples, capturing a range of soil depths, were collected from the bed, the banks, and the floodplains of the creek and were analyzed for PAHs on a GC-MS. The results showed that PAHs concentrations were generally highest on depositional banks and were highly variable on the channel bed and in the floodplain. Further, PAH concentrations were more uniform across the cross section (bed, bank, and floodplain) at downstream sites compared to upstream. The results also showed that in erosional sites, unlike the depositional sites, there was little variation in PAHs concentration in the soil column. This analysis provides deeper insight into the transport and fate of PAHs in urban streams and floodplains, ultimately helping mitigate the impacts of pollutants on the environment.
Highlights
Polycyclic aromatic hydrocarbons (PAHs) are widely distributed persistent organic pollutants (Hong et al, 2020; Patel et al, 2020) that result mainly from urbanization and anthropogenic activities coupled with coal and petroleum combustion (Li et al, 2020b; Wang et al, 2020)
To illustrate the spatial variations in the measured PAHs concentrations, the cross sections of the sampling sites were extracted from the Digital Elevation Model (DEM) of the study area1
The findings suggest that the sample type tends to control how much change in PAHs concentration there is in the soil column
Summary
Polycyclic aromatic hydrocarbons (PAHs) are widely distributed persistent organic pollutants (Hong et al, 2020; Patel et al, 2020) that result mainly from urbanization and anthropogenic activities coupled with coal and petroleum combustion (Li et al, 2020b; Wang et al, 2020). PAHs pollutants adversely affect the health of humans as well as animals (Gou et al, 2020; Patel et al, 2020) and many PAHs are subject to worldwide mandatory regulations (Sushkova et al, 2019). One of the least understood aspects of PAHs in urban environment is the transport of such pollutants through urban fluvial systems This makes the study of the transport and accumulation of the PAHs (Sushkova et al, 2019) in urban rivers of great importance
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