|Behaviour of polycyclic aromatic hydrocarbons in the Exe estuary, Devon|
Herrmann, R.; Hübner, D. (1982). Behaviour of polycyclic aromatic hydrocarbons in the Exe estuary, Devon. Neth. J. Sea Res. 15(3-4): 362-390
In: Netherlands Journal of Sea Research. Netherlands Institute for Sea Research (NIOZ): Groningen; Den Burg. ISSN 0077-7579, more
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PAH pollutant loads resulting from river runoff to a receiving estuary are associated with suspended sediments. This is explained by high sorption coefficients on suspended and bottom sediments. Thus, the highest concentrations of PAH are found along the tidal channel within the mixing zone. A principal component analysis of grain-size distribution, organic carbon content and PAH concentration in bottom sediments indicates no regional covariation between PAH concentration and adsorption capacity. This leads to the assumption that hydrodynamic rather than physicochemical factors influence the regional distribution of PAH in the Exe Estuary. The concentrations of PAH in suspended sediments are in the order of magnitude of the concentrations in bottom sediments. The dominant mechanisms for the regional distribution of PAH in bottom sediments are sedimentation of suspended PAH within the mixing zone along the tidal channel, resuspension of bottom sediments, and mixing of fluviatile and marine sediments. The regional and temporal variation ofsuspended PAH, which was measured at 4 anchor stations during complete tidal cycles and at 4 traverses along the main tidal channel, is characterized by an increase of suspended PAH concentration and net positive fluxes from the river into the mixing zone and a subsequent decrease toward the sea. Besides, the suspended PAH concentrations decrease from the tidal channel to the tidal flats where the flux was negative. With only few exceptions of PAH polluted plugs of river water, the highest concentrations of suspended PAH occur just above the bottom and coincide with strong tidal currents. In the upper water column higher concentrations per weight of suspended sediments have been observed than in the lower one. This may be explained by a greater adsorption coefficient of the upper fine suspended sediments and a dilution by landward transport of marine suspended sediments near the bottom. The field data plots of suspended PAH concentrations against salinity are above the theoretical mixing line, indicating a net concentration within the mixing zone. This is due to a zone of maximum turbidity produced by the estuarine circulation pattern. The field data of detergents and humic substances do not support increased solubilization of PAH, and those of iron do not show coprecipitation within the mixing zone. A laboratory experiment involving short term (2 hours) interaction of suspended PAH with increasing salinities did not show significant removal of PAH from suspension. However, in a long term (a few hours) interaction the importance of sea water electrolytes for the removal of suspended PAH could be proved. The connection between regional distribution of suspended PAH and estuarine circulation was demonstrated by a two-dimensional box model.