Biomarkers in the Siak River System, E. Sumatra, Indonesia

A total of 33 plant species and 122 surface sediments were obtained from March 2004 to November 2008 in the Siak River system including its major tributaries and coastal areas. Grain size distribution shows the sediments to be sands to silt with a general trend of coarser sediments in the upper reaches and fi ner ones in the estuary. The expected linear relationship between the content of organic carbon and the mud fraction of the sediments (<63 µm) is distorted by input of (a) clay-sized, organic-poor material from river bank erosion and (b) input of coarse plant detritus. All samples were analysed for n-alkanes and steroids. For all plant samples and a limited number of sediment samples, fatty acids were also determined. The data indicate a variety of organic carbon sources, the dominant one being river bank vegetation. Urban and industrial discharges, peat erosion and atmospheric deposition of black carbon and biomarkers might also play a role in controlling the lipid composition of the sedimentary organic carbon pool.