Biomarkers on Sediments in a Highly Saline Aquatic Ecosystem: Case of the Moknine Continental Sebkha (Eastern Tunisia)

Abstract

Surficial sediments from 18 sites throughout Moknine sebkha, one of the largest urbanized sebkha in the sahel of tunisia, were analyzed for biomarkers ( n-alkanes, hopanes and steranes ) to track the origin of organic inputs. A distinct spatial distribution of aliphatic hydrocarbons in sediments was observed in Moknine sebkha which subdivide this environment in two area . The submerged area is characterized by high concentration of OC 1-4.9%, EOM 2%-49% CO, aliphatic hydrocarbons 1350 µg.kg-1to 3700 µg.kg-1sediment dry weight. Emerged area is characterized by low concentration (OC<1%, EOM<12%OC and F1<1200 µg.kg-1sediment dry weight. Several ratios (e.g. CPI, ACL, NAR, TAR, Pr/Ph…) were used to evaluate the possible sources of terrestrial-lacustrine inputs of these hydrocarbons in the sediments. The various origins of aliphatic hydrocarbons were generally biogenic, including both terrigenous and cyanobacteria. The source of contamination is not petroleum. , the predominance of biogenic in combination with petrogenic hydrocarbons was indicated by the biomarkers. αβ trishomohopane C33 indicate an anthropogenic contribution (wastewater) in two stations (treated domestic wastewater (ssm1-2) and untreate industrial wastewater ssm6). The presence of biogenic hopanes (17β(H), 21β(H)-hopanes) indicate the biogenic origin of organic matter in the Moknine sebkha. The UCM not indicate petrogenic origin but high activities of bacteria in highly saline system.