Non-aromatic hydrocarbons in ‘dissolved’ phase (< 0·7 μm) and their fractionation between ‘dissolved’ and particulate phases in the changjiang (Yangtse River) Estuary

Abstract

Hydrocarbons were analyzed in water samples collected in the Changjiang River mouth and in the adjacent East China Sea in January and July 1986. Analyses were performed by gas chromatography and gas chromatography/mass spectrometry. Concentrations and characteristics of hydrocarbons varied largely according to the season. In January 1986 the river flow was low (9·5 × 10 3 m 3 s −1); it was much higher in July 1986 (47·3 × 10 3 m 3 s −1). In contrast, the mean suspended-sediment load in the river and the mixing zone was higher in winter (232·6 mg liter −1) than in summer (47·7 mg liter −1). ‘Dissolved’ non-aromatic hydrocarbon concentrations varied from 0·08 to 2·33 μg liter −1 in winter, whereas higher values were observed in summer, from 0·61 to 9·05 μg liter −1. n-Alkanes were distributed in the carbon range 15–38 and peaked up at different numbers of C max generally at n-C 29 in winter and at n-C 17, n-C 18, n-C 19, n-C 31 and n-C 33 in summer. A predominance of even carbon number n-alkanes (C 16–C 22) was observed in winter but only in a few samples in summer. CPI values were less than 1·5 in both seasons, reflecting degraded material from higher plants and algae, together with fossil inputs. In both seasons U/R ratio (unresolved/resolved compounds) values were less than 3, generally suggesting a limited petroleum contamination. A comparison of ‘dissolved’ and particulate hydrocarbons was carried out. Data suggested that in winter higher quantities of non-aromatic hydrocarbons were present in the particulate phase (1·02–21·55 μg liter −1) than in the ‘dissolved’ phase (0·08–2·33 μg liter −1), but in summer some opposite partitionings were encountered. Using several criteria, such as U/R ratio, it was observed that the petroleum and/or anthropogenic pollutants were preferentially associated with the particulate phase. Markers of microbial activities, such as two homologous series of iso- and anteiso- alkanes, were widely found in the ‘dissolved’ phase but not in the particulate phase.