The biogeochemistry of lipids in rivers of the Orinoco Basin

Abstract Water samples from rivers in the Orinoco Basin were examined in order to assess the biogeochemistry of particle-associated and dissolved lipids. Lipid fractions were characterised so as to determine their origin, speciation, variability in individual rivers, and their flux to the lower Orinoco River. Aliphatic hydrocarbons, ketones, alcohols, triterpenoids, and fatty acids were ubiquitous in the rivers, and a large proportion of these compounds were found to be autochthonous in origin. The relative loadings of particle-associated and dissolved lipids were of the same order of magnitude in most of the rivers, indicating the importance of the dissolved phase. Apparently, true equilibria between water and particulate phases were not reached, probably as a result of the high amounts of colloidal and humic materials associated with the dissolved phase in most of the rivers. Preliminary data indicate that there were considerable seasonal variabilities in the distributions and concentrations of lipids in some of the rivers, but that each of these showed different behaviour.