Environ Monit Assess (2013) 185:9857–9869 DOI 10.1007/s10661-013-3297-x Source and distribution of organic matter in surface sediments from mangroves on the island of Itaparica, Bahia/Brazil Elisângela Costa Santos & Joil José Celino & Vera Lúcia Cancio Souza Santos & José Roberto Bispo De Souza Received: 30 September 2012 /Accepted: 4 June 2013 /Published online: 16 June 2013 # Springer Science+Business Media Dordrecht 2013 Abstract Elemental analysis and isotopic composi- the presence of oil also showed in Misericordia and tion evaluated the impact of human activity at the Cacha Prego districts for both periods and Ponta surface sediments in the largest island of Todos os Grossa during the rainy season. Principal component Santos Bay, northeastern Brazil. Saturated hydrocar- analysis, using a correlation matrix, revealed the latent bons (n-alkanes and isoprenoids) by gas chromatogra- relationships among all the surface sediment stations phy coupled with a flame ionization detector and 13C investigated and confirmed our analytical results. by mass spectrometer were determined from 30 sur- face sediment samples in mangroves at the Itaparica Keywords Saturated hydrocarbons . δ13C . Organic Island (Bahia-Brazil) in the rainy and dry season. carbon . Mangroves . Estuary These data, distribution, and ratio of carbon/nitrogen showed a mixture of sources: continental, marine, and anthropogenic ones. From the chromatographic pro- Introduction files, light oil contamination was observed in the dry regions of Baiacu, Campinas, and Ponta Grossa, while In the mangrove ecosystem, tidal power is bland and in Jiribatuba it was observed during the rainy season. current velocity is low which favor the intense depo- However, δ13C results during dry and rainy season in sition of fine sediments and organic matter (Rossi and Mattos 2002; Zagatto and Bertoletti 2008). The chemical composition of sedimentary organic : E. C. Santos (*) J. J. Celino matter may vary depending on the weather on the Instituto de Geociências, Núcleo de Estudos Ambientais, coast and the contributions of marine and continental Universidade Federal da Bahia, organic matter residues (Queiroz and Celino 2008; Rua Barão de Geremoabo, Campus Ondina, 40170-290 Salvador, Bahia, Brazil Pait et al. 2012). The anthropogenic influence on the e-mail: [email protected] environment modifies the composition and concentra- tion of organic matter, potentially affecting the local V. L. C. S. Santos biota (Queiroz and Celino 2008; Ekpo et al. 2012). Instituto de Química, Universidade Federal da Bahia, Campus Ondina, Carbon and nitrogen are the two main components of 40170-115 Salvador, Bahia, Brazil organic matter. The carbon content in the pellet surface depends on a number of factors such as sedimentary J. R. Bispo De Souza characteristics, the rate of microbial degradation, col- Instituto de Física, Universidade Federal da Bahia, Rua Barão de Geremoabo s/n, umn of water and land ratio of entries (Costa et al. 2011). CEP 40170-115 Salvador, Bahia, Brazil The organic material from higher plants has low 9858 Environ Monit Assess (2013) 185:9857–9869 nitrogen content and therefore a high carbon/nitrogen fuels, forest fires, and diagenetic degradation of bio- (C/N) ratio. Therefore, high C/N ratios in marine genic precursors (Readman et al. 2002; Killops and sediments indicate a predominantly terrestrial source Killops 2005; Celino and Queiroz 2006), constitute an of organic matter, while sediments rich in marine important amount of the organic material that reaches organic matter have lower C/N ratios (Burone et al. the sediments. 2003; Gonsalves et al. 2011). According to Bordovsky Concentrations of total aliphatic hydrocarbons in (1965), marine sediments near the river exhibit the unpolluted intertidal and estuarine sediments are nor- highest C/N ratios, indicating entry of terrestrial mally lower than 10 μgg−1 (Volkman et al. 1992). In material in the area. The input of inorganic nitrogen organically enriched sediments, when there is a signifi- from sewage can contribute to the reduction of C/N cant input of n-alkanes derived from higher plants, total proportion. aliphatic hydrocarbon concentrations may have reached The carbon isotope ratio distinguish between sources values up to 100 μgg−1 (Venturini et al. 2004). of sedimentary organic matter, either in marine or ter- The positive correlation (p<0.05) between total or- restrial plants, mainly reflecting the dynamics of assim- ganic carbon and total aliphatic hydrocarbons could be ilation during photosynthesis and the isotopic composi- related to the input of terrestrial plant materials tion of carbon source (Meyers 1997). According to (Venturini et al. 2004) as well as to the input of Mahiques et al. (1999), using the values of δ13C, based petroleum products (McGroddy and Farrington 1995). on the subscriptions of different isotopes in C3 plants Preferred Carbon Index evaluates the maturity of (higher land plants), and C4 (grass), in benthic organ- thermal oil and may be used to verify the origin of isms, zooplankton, and phytoplankton led to an increas- organic matter. Values much higher than 1 indicate a ing number of studies and better understanding of sed- contribution of higher plants which is considered an iment dynamics in continental and coastal areas. immature oil; however, values equal to 1 indicate an Hydrocarbons present in the sediments originate increasing maturity of oil, thus presenting the presence from petroleum inputs, partial combustion of fossil of oil (Killops and Killops 2005). CPI ¼ § n−C25—n−C33 n−C24—n−C32 þ n−C25—n−C33 n−C26—n−C34 ð1Þ (Moldowan et al. 2007) loss in the total variance of the data. The load of each Todos os Santos Bay, with an area of approximately variable in the original data contributes to the major 927 km2, is the largest on the northeastern Brazilian components and allows the grouping of data with sim- coast, with an approximate volume of 6.39×109 m3,a ilar behaviors (Celino et al. 2012; Praveena et al. 2012). medium depth of 6.9 m and currents with medium The aim of this study was to investigate saturated speed of 41.0 cm s−1 (1.476 m h−1). These factors hydrocarbons (n-alkanes and isoprenoids) and stable contribute to the low water residence time in the bay, carbon isotopic (δ13C) composition in the different minimizing the effects of the industrial effluents to be seasons, in surface sediments samples, from various discharged into the bay (Lessa et al. 2008). mangroves of Itaparica Island (Bahia–Brazil), in order Since 1950, the area around Todos os Santos Bay to assess their possible origins, especially with respect (TSB) has been suffering increasing industrialization to contamination from anthropogenic sources. and exploitation of its natural resources (Queiroz and Celino 2008). Presently, the extraction, transportation, and refinement of petroleum at TSB are the most prom- Materials and methods inent industrial activities. The Itaparica Island is outside the area of petroleum activities, at the extreme south of The TSB has two entrances separated by Itaparica TSB (Fig. 1). Island (Fig. 1). The Itaparica Channel, on the south- Principal component analysis (PCA) reduces the west, which presents a smoother topography with number of variables in the original data set into fewer an average depth of 10 m (Lessa et al. 2008). The factors (or principal components) without significant circulationinsidethebayismostlytidallydriven. Environ Monit Assess (2013) 185:9857–9869 9859 (1) TSB (2) (1) (3) 6 5 BRAZIL (4) sland 1 2 3 4 (5) (6) (A) Atlantic Ocean (B) (C) (7) (3) 4 6 6 5 5 1 4 1 2 3 2 3 (2) 5 (4) 2 3 4 (5) 5 4 3 2 1 1 (6) (7) 1 1 2 3 2 5 5 3 4 6 6 4 Fig. 1 Map of collecting stations Mocambo, Misericórdia, Baiacu, Cacha Prego, Ponta Grossa, Jiribatuba, and Campinas in Itaparica Island, Bahia, Brazil During summer, the waters inside the bay have oce- The climate is tropical humid, with a 10-year aver- anic characteristics, while during winter there is a age mean air temperature of 25.3 °C close to Salvador, significant increase in freshwater fluxes (Souza et al. and a 30-year mean rain fall of about 1,900 mm/year 2011). for the bay area (Lessa et al. 2008). 9860 Environ Monit Assess (2013) 185:9857–9869 Sampling occurred in the sample. The samples washed and centrifuged three times with ultrapure water, dried Surface sediments (0.0 to 2.0 cm depth) were sampled below 50 °C, and weighed. Each sediment sample twice (dry and rainy seasons) during low tide at the (10–12 mg) weighed into a tin capsule, sealed, and intertidal zone. Seven stations sampled from the then subjected to elemental analysis (Costa et al. Mocambo (MB), Misericórdia (MD), Baiacu (BI), 2011). Organic carbon and nitrogen isotope values Ponta Grossa (PG), Campinas (CA), Jiribatuba (JI), were determined by elemental analyzer ECS 4010 and Cacha Prego (CP) (Fig.1). Composite sediment CHNS-O Analyser Costech Instruments. Isotopic samples, within a 90×90-cm square, were collected analysis determined by the elemental analyzer coupled from each station along a horizontal transect (0.1 km to a Finnigan Delta Plus mass spectrometer. The gases long), at every 10 m, by using a stainless steel spatula used in the product showed high purity (300 kPa of He and transported to the laboratory in ice boxes (4±2 °C). and O2 where He is the carrier gas). In the equipment, Each sediment sample was well mixed and kept frozen it was used a thermal conductivity detector whose until analysis. combustion gas used in the samples was O2 at 30 mL min−1 for 5 s and oven operating temperature Bulk sediment characteristics of 900 °C. pH measurements obtained with a SCHOTT Geräte Instrumental analyses Handylab 1, L7137A pH meter, by inserting the plat- inum electrode (pH) directly into the sediment The methodology used for the extraction of the fraction (Berrêdo et al.