Sources and Distribution of Particulate Organic Matter of a Tropical Estuarine-Lagoon System from NE Brazil as Indicated by Lipid Biomarkers

Abstract

In the present work, we evaluated the origin of organic matter in the tropical estuarine-lagoon system of Mundaú-Manguaba, NE Brazil, by considering the bulk (organic carbon and chlorophyll-a) and lipidic (n-alcohols and sterols) composition of suspended particles. Water samples were collected in August 2006 from 24 stations covering the salinity gradient from the rivers down to the sea outlet. Chlorophyll-a (Chl-a) varied from 22.7 to 134.1 lg L -1 in the lagoons, indicating eutrophic to hypertrophic conditions at the time of sampling. The high correlation between Chl-a and phytol together with the molar C:N ratio indicated the presence of fresh and recently produced autochthonous particulate organic matter throughout the system, except for the river samples. The elevated concentrations of short-chain n-alcohols and phytosterols, mainly 24-methylcholesta-5,24(28)-dien-3b-ol, also corroborated the predominance of autochthonous organic matter in the lagoons but were generated by distinct sources: cianobacteria in the freshwater Manguaba lagoon and diatoms in the brackish Mundaú lagoon compartments. Input of terrestrial organic matter was only detected in the rivers themselves or at the upper river-lagoon interfaces. Coprostanol indicated contamination by sewage in Mundaú lagoon and in some rivers, but at lower levels when compared to other Brazilian coastal lagoons and estuaries.

Fontes e distribuição de matéria orgânica sedimentar no complexo estuarino-lagunar de Mundaú-Manguaba/AL, utilizando esterois e alcoóis como indicadores

“…Considerando-se apenas os nalcoóis de cadeia longa, marcadores robustos de vegetação terrestre, 17 não houve predomínio entre compostos individuais. Esta distribuição difere da maior contribuição de 22OH encontrada por Costa e colaboradores 25 em amostras de material particulado do CELMM. Possivelmente, a diferença na distribuição de n-alcoóis no sedimento obtida no presente trabalho e a observada no material particulado por Costa e colaboradores 25 resulta do transporte diferenciado de restos de plantas, ocasionado pela seleção hidrodinâmica de materiais com densidades distintas (p.ex., galhos, folhas, talos, etc.…”

“…[20][21][22] No entanto, apenas recentemente vêm sendo realizados trabalhos mais detalhados para caracterizar, sob o ponto de vista químico, as alterações ambientais na região. [23][24][25][26] …”

Investigation of sewage contamination using steroid indexes in sediments of the Guajará Estuary (Amazon coast, Brazil)

“…Despite the precarious sanitary conditions of the area, there is still a paucity of studies on the identification and monitoring of sewage organic contamination that could help to prevent potential adverse effects to both public health and environmental quality standards. Alternative indicators derived from cholesterol such as coprostanol, epicoprostanol, cholestanol, coprostanone and cholestanone have been applied for the identification of the chemical composition of sedimentary organic matter and particularly for tracking sewage contamination in diverse environments (GRIMALT et al, 1990;MIRSADEGHI, 1992;EGANHOUSE;SHERBLOM, 2001;MARTINS et al, 2008;COSTA et al, 2011). Cholesterol is reduced by bacteria in the intestinal tract of most mammals and birds resulting in coprostanol, the main fecal sterol (BULL et al, 2002).…”

Input of organic matter in a large south american tropical estuary (Paranaguá Estuarine System, Brazil) indicated by sedimentary sterols and multivariate statistical approach

“…3 One approach to investigate the geochemistry of organic matter in marine environment is based on information of specific organic compounds, known as molecular markers or biomarkers. 4,5 Sterols are one of the categories of molecular markers currently in use to elucidate the presence of marine, terrestrial and fecal input of organic matter in sediments. They are source-specific, relatively resistant to microbial degradation and may be quantified at low levels.…”

“…4,5 Sterols are one of the categories of molecular markers currently in use to elucidate the presence of marine, terrestrial and fecal input of organic matter in sediments. They are source-specific, relatively resistant to microbial degradation and may be quantified at low levels.…”