Geochemical features of biomarkers in foam substances from the Chikugo River system in the Hita City area, Oita Prefecture

Abstract

We studied biomarkers (hydrocarbons, fatty acids and sterols) in foam substances from the Chikugo River system in the Hita City area, Oita Prefecture to elucidate their source organisms and materials. Normal-alkanes with a predominance of odd-carbon numbers were found together with unidentified branched alkanes and unresolved complex mixture of hydrocarbons (UCMH), and with small amount of isoprenoid alkanes. Abundance of short-chain n-alkanoic acids (C₁₂-C₁₉) and cholesterol were found, along with the small amounts of long-chain n-alkanoic adids (C₂₀-C₃₀) and branched acids (iso- and anteiso-C₁₃-C₁₇). Biomarkers in foam substances are, therefore, mainly derived from microalgae and cyanobacteria with small amounts of vascular plants and eubacteria. The occurrence of UCMH as well as epimerized triterpanes and steranes strongly suggest the contribution of petroleum products from automobiles and road runoff including asphalts in the Chikugo River basin. Branched alkanes may be derived from insects such as Chironomidae. These organic components are important in the formation of foam substances in the Chikugo River system of the Hita City area.