Impacts of Mesopotamian wetland re-flooding on the lipid biomarker distributions in sediments

Abstract Shallow sediment core samples from two locales in the Mesopotamian marshlands of Iraq were analyzed to characterize the extractable organic (lipid) compounds, and their sources and distributions after hydrological restoration by re-flooding of the marshes. Dried samples were extracted with a dichloromethane/methanol mixture before analysis by gas chromatography-mass spectrometry (GC–MS). The major compounds were n -alkanes, fatty acids and alcohols, steroids, terpenoids, hopanes, steranes, unresolved complex mixture (UCM), and plasticizers. The lipid compounds in Kurmashia (Al-Hammar marshes) were generally higher in concentration than in Abu Zirig (Central marshes), and decreased with core depths for both sites. This concentration decrease with core depth is attributed to transformation, biodegradation and variable input processes. The distribution patterns of the lipids in the sediment cores indicated that the Abu Zirig area was drier than Kurmashia before the re-flooding process. Furthermore, the concentration of the compounds in the surface sediment the Abu Zirig core was as high and similar to that in Kurmashia, reflecting the re-flooding impacts on the marsh and the revival of the wetland. The major sources of these lipids were from natural terrestrial vegetation (35–66% for Abu Zirig; 40–49% for Kurmashia), microbial (plankton) residues and bacteria (27–52% for Abu Zirig; 39–43% for Kurmashia), with a minor contribution from anthropogenic sources including plastic wastes and petroleum (6–13% for Abu Zirig; 9–18% for Kurmashia).