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

摘要

The Mundaú-Manguaba estuarine-lagoon system (MMELS) constitutes one of the most representative ecosystems in the state of Alagoas, NE Brazil. Approximately 30% or 60,000ha 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), Mundaú Lagoon (C07) and Mundaú River (C08) in order to characterize the delivery and deposition of n-alkanes over the past 40yr. The n-alkanes ranged from C_(15) to C_(35), with total aliphatic hydrocarbon (TAH) concentration in the range 27.8-139.5μgg~(-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 (δ~(13)C) values of individual n-alkanes (C_(16)-C_(33)) varied between -22.6‰ and -34.2‰, suggesting a dominance of ~(12)C-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.