Dissolved, particulate and sedimentary hydrocarbons in a deltaic environment

Abstract

A study of biolipid indicators in the Ebro Delta (Spain) involving the analysis by computerized GC-MS of dissolved, particulate and sedimentary hydrocarbons (saturated and unsaturated) was carried out. Three different depositional environments were considered, namely the river mouth, the open sea and the delta bays. The water column was sampled with a recently designed filtering and extraction system based on a Teflon impeller pump which passed water through a glass fibre filter and a Teflon column packed with polyurethane foam plugs, where respectively particulate and dissolved material was collected. The decoupling of lipids between the different marine compartments was closely dependent on their sources and exhibited seasonal and spatial variations reflecting environmental conditions. Anthropogenic HCs (UCM, 17α(H),21β(H) hopanes) were mainly concentrated in the dissolved phase. Allochthonous continental inputs ( n-C 27- n-C 31 alkanes and alkenes) were recognized in particulates collected in the open sea, whereas autochthonous planktonic inputs ( n-C 15, n-C 17, pristenes, HEH) were identified mainly in the bays. Bacterial activity was recognized by the presence of 17β(H), 21β(H) hopanes and hopenes. A bioconversion of petroleum short chain n-alkanes was observed during spring in the bays. New di- and tri-unsaturated HCs related to C 20 and C 25 multibranched isoprenoids were identified in particulates, pointing to planktonic and metabolic or diagenetic origins. A series of sesquiterpenoid cycloalkenes (cadinene derivatives) not previously reported in the marine environment affords evidence of inputs of higher plant resins. The corresponding aromatic derivatives were found in the sediments together with abietane and pimarane aromatized HCs. The results presented illustrate that the study of lipids in dissolved and particulate phases of the marine environment may provide a better understanding of this environment in terms of both sources of organic matter, transport routes and depositional conditions.