Source characterization using molecular distribution and stable carbon isotopic composition of n-alkanes in sediment cores from the tropical Mundau-Manguaba estuarine-lagoon system, Brazil

The Mundau-Manguaba estuarine-lagoon system (MMELS) constitutes one of the most representative ecosystems in the state of Alagoas, NE Brazil. Approximately 30% or 60,000 ha of the lower surrounding drainage basin of the MMELS are covered by sugar cane and a total of 250,000 inhabitants contribute untreated effluent to the system. Short sediment cores from MMELS were collected in 2007 at three sites: Manguaba Lagoon (C03), Mundau Lagoon (C07) and Mundau River (C08) in order to characterize the delivery and deposition of n-alkanes over the past 40 yr. The n-alkanes ranged from C-15 to C-35, with total aliphatic hydrocarbon (TAH) concentration in the range 27.8-139.5 mu g g(-1). An unresolved complex mixture (UCM) was observed in all sediments. The terrigenous/aquatic ratio (TAR), carbon preference index (CPI) and average chain length (ACL) showed that the terrigenous input dominated. The (delta C-13) values of individual n-alkanes (C-16-C-33) varied between -22.6% and -34.2%, suggesting a dominance of C-12-enriched n-alkanes that originated from C-3 plants and lacustrine algae. The data reflect how anthropogenic input (via sewage, industrial pollution and agriculture) has influenced the organic content of the system through time. (C) 2012 Elsevier Ltd. All rights reserved.