Transport and fate of hydrocarbons in rivers and their estuaries. Partitioning between dissolved and particulate phases: Case studies of the Rhône, France, and the Huanghe and the Changjiang, China

Abstract

In order to study the biogeochemistry of organic matter in estuaries at the freshwater/seawater interface, three rivers were selected for study: the Rhône and its Mediterranean delta, France (several cruises each year, since 1985), the Huanghe, China (two cruises, spring and summer 1985), and the Changjiang, also in China (two cruises, winter and summer 1986). These rivers were characterized by different contaminant levels and sources and different suspended matter loads, an important factor in determining partitioning between dissolved and particulate phases. During these cruises, water was sampled at key stations chosen as a function of salinity and turbidity, filtered and analyzed for both dissolved and particulate non-volatile hydrocarbons. Hydrocarbons, after separation from other lipids, were analyzed by gas chromatography, high pressure liquid chromatography and gas chromatography/mass spectrometry. Particulate non-aromatic hydrocarbon and n-alkane concentrations are compared with suspended matter concentrations and with the organic carbon content of the suspended matter (percent organic carbon, POC). A good correlation was found between hydrocarbon concentrations and POC, but no such correlation was systematically observed between hydrocarbon and suspended matter concentrations. The ratio between particulate and dissolved hydrocarbon concentrations varies with suspended matter load and season. The ratio is probably also modified by the biological activity of the waters, which influences the transport processes through the freshwater/seawater interface and the budget of hydrocarbon inputs carried by rivers to the ocean.