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Anuário do Instituto de Geociências - UFRJ www.anuario.igeo.ufrj.br Modern Diatom Distributions in Guanabara Bay Sediment and Oceanic Areas, Rio de Janeiro (Brazil) Distribuição das Diatomáceas Modernas nos Sedimentos da Baía de Guanabara e Áreas Oceânicas, Rio de Janeiro (Brasil) Lazaro L.M. Laut1; Vanessa M. Laut2 3; Frederico S. Silva3 & Alberto G. Figueiredo Jr.1 1 Universidade Federal do Estado do Rio de Janeiro, Departamento de Ciências Naturais, Laboratório de Micropaleontologia – LabMicro. Av. Pasteur, 458, IBIO/CCET sala 500 Urca, 22.240-490. Rio de Janeiro, Brasil 2 Universidade do Estado do Rio de Janeiro, Faculdade de Geologia Programa de Pós-Graduação em Análises de Bacias e Faixas Móveis. Av. São Francisco Xavier, 524, sala 400A, Maracanã. 20550-013. Rio de Janeiro – RJ, Brasil 3 Universidade Federal do Rio de Janeiro, Departamento de Geologia, Laboratório de Palinofácies e Fácies Orgânicas. Av. Athos da Silveira Ramos, 274 - Bloco F Ilha do Fundão - Cidade Universitária. 21.949-900. Rio de Janeiro – RJ, Brasil 4 Universidade Federal Fluminense, Departamento de Geologia – LAGEMAR. Av. General Milton Tavares de Souza, 4º andar - Campus da Praia Vermelha – Gragoatá. 24210-346. Niterói – RJ, Brasil E-mails:[email protected]; [email protected]; [email protected]; [email protected] Recebido em: 26/01/2011 Aceito em: 17/08/2011 Abstract One hundred and fifty three superficial sediments were collected in Guanabara Bay to physical-chemistry and diatom analyses in the ambit to Monitoring Project (CENPES/PETROBRAS). A total of 146 taxa of diatoms were identified where the most frequent taxa in Guanabara Bay wereAmphora spp., Coscinodiscus spp. and Navicula yarrensis var. yarrensis. These species are potentially harmful that might harm fisheries and mariculture during blooms. The values of ecological indexes like richness and diversity followed the estuarine gradient were the higher values were found in the mouth and de low in the inner part. The multivariate analyzes permitted recognize seven diatom assemblages in the bay. The DCA analyze shows the most influence in the distribution of assemblages were the depth and pH. The diatom assemblages analyze proved to be an efficient tool in the environmental diagnosis of Guanabara Bay. Keywords: Guanabara Bay; benthic diatoms; environmental diagnosis Resumo Cento e ciquenta e três amostras de sedimento superficial da Baía de Guanabara foram coletadas durante o Projeto de Monitoramento Ambiental (CENPES/PETROBRAS). Foram identificados 146 táxons de diatomáceas onde as espécies mais abundantes foram Amphora spp., Coscinodiscus spp. e Navicula yarrensis var. yarrensis. Estas espécies identificadas são potencialmente tóxicas e podem prejudicar peixes e a maricultura durante períodos de florescência. Os índices ecológicos de riqueza e diversidade acompanharam o gradiente estuarino sendo maior na entrada da baía e baixos na região interna. As análises multivariadas permitiram reconhecer sete assembléias de diatomáceas na baía. As análises em DCA mostrou que os parâmetros ambientais mais influentes na distribuição das assembléias foram a profundidade e o pH. Os resultados obtidos mostraram que as assembléias de diatomáceas são uma importante ferramenta na caracterização ambiental da Baía de Guanabara. Palavras-chave: Baía de Guanabara; diatomáceas bentônica; diagnóstico ambiental Anuário do Instituto de Geociências - UFRJ 64 ISSN 0101-9759 e-ISSN 1982-3908 - Vol. 34 - 1 / 2011 p.64-87 Modern Diatom Distributions in Guanabara Bay Sediment and Oceanic Areas, Rio de Janeiro (Brazil) Lazaro L.M. Laut; Vanessa M. Laut; Frederico S. Silva & Alberto G. Figueiredo Jr. 1 Introduction Ecological studies on estuarine and shallow coastal water diatoms are few in number, compared The complex nature of estuaries, derived with freshwater and open ocean habitats (Sylvestre from their hydrodynamics, as well as the presence et al., 2004), and very few studies have been done of strong physicochemical gradients and intricate in tropical areas. The concern is mainly focused biological structure, imposes difficulties in on temperate estuaries (Admiraal, 1984; Sullivan, forecasting the extension of anthropogenic impacts. 2001). Multidisciplinary approaches, specific sampling strategies, as well as multiple analytical tools and Considering the studies of coastal environment a variety of models, have been used to tackle this monitoring in order to evaluate the use of bio- problem (Silva et al., 2008). indicators to assess the impact of human activities on urbanized littoral zone, this paper aims to study Monitoring nutrient levels in estuarine systems the distribution of modern diatoms on the sediment is problematic because of periodic and diffuse input from Guanabara Bay to determine estuarine gradient from non-point sources (Cattaneo & Prairie, 1995). and the impact of human activities on the quality of bay water and sediment. The micophytobenthos has been recently reviewed and was referred to as a “secret garden” (MacIntyre et al., 1996). Diatoms are considered the most important constituent of this benthic 2 Environmental Settings microalgae assemblage in estuarine and shallow coastal environments (Mc Lusky, 1989). Several Guanabara Bay is one of the largest bays on studies have revealed a highly diverse and productive the Brazilian coastline, located in Rio de Janeiro diatom assemblage within coastal and shelf sediments State. The bay, including its several islands, has (Admiraal et al., 1982; Riaux, 1983; Riaux-Gobin et an area of approximately 384 km2 and presents a al., 1998) – for instance, the chlorophyll a content coastline 131 km long and a mean water volume of per m2 of shelf bottom may exceed that of the entire 1.87 x 109 m3 (Amador, 1997; Kjerfve et al., 1997). overlying water column (Cahoon et al., 1990). The hydrographic basin extends over 4,080 km2 and includes 45 rivers, 6 of which are responsible for 85% Diatoms are widely used to monitor polluted of the runoff (100 ± 59 m3/s). The mean halfwater aquatic environments because they are sensitive volume renewal time is 11.4 days, although in some to water chemistry, especially ionic content, pH, parts of the bay it is significantly higher. Temperature dissolved organic matter and nutrients. Wide (24.2 ± 2.6°C) and salinity (29.5 ± 4.8 S) profiles geographic distribution and the well-studied ecology show a well-mixed water condition at the bay mouth, of most diatom species are cited as major advantages extending up to 15–20 km inwards. Thereafter, the in using diatoms as indicator organisms (McCormick system is moderately stratified. A sandbank located & Cains, 1994). These assumptions imply that on the ocean side of the bay mouth greatly influences diatom-based water-quality assessment tools should the inner water circulation due to current channeling have universal applicability across geographic areas (Kjerfve et al., 1997). and environments. Tides are mixed mainly semidiurnally with a Some studies have been done to understand range of 0.7 m and peak spring tidal currents reach the interactions between diatom populations on 0.5 m/s inside the bay and 1.6 m/s near the bay mudflats and various environmental factors that entrance. The central channel, with depths of 30-40 explaining their spatial and temporal distribution m and delimited by the 10 m depth isoline, transports (Admiraal, 1977; Admiraal & Peletier, 1979; the sand into the bay. The bottom topography is Adimraal et al., 1982). However, the diatom metrics influenced by tidal currents that drain through the or indexes developed in some geographic area have central channel, and by a strong sediment input. The less successful when reapplied in other areas (Pipp, increase in width after the entrance channel results 2002). This is due not only to floristic differences in a decrease of tidal current velocities, leading to among regions, but also to environmental differences the deposition of fine sands and mud. Coarse sands (Kelly et al., 1998) that modify species’ responses to predominate in the central channel and in the regions water-quality characteristics. near the bay mouth. Extensive mud deposits resulting Anuário do Instituto de Geociências - UFRJ ISSN 0101-9759 e-ISSN 1982-3908 - Vol. 34 - 1 / 2011 p. 64-87 65 Modern Diatom Distributions in Guanabara Bay Sediment and Oceanic Areas, Rio de Janeiro (Brazil) Lazaro L.M. Laut; Vanessa M. Laut; Frederico S. Silva & Alberto G. Figueiredo Jr. from the active transport of clastic material and from sieve. The sand is separated from the mud. The intensive primary production are found in the bay’s silt and clay fractions were analyzed using the northern area (JICA, 1994; Kjerfve et al., 1997). pipette method. A strong stratification of dissolved oxygen Total organic carbon (TOC) and total is observed in areas where depths are under 10 m. nitrogen (TN) were determined on precisely Surface oxygen values reach 300% oversaturation weighed (2–5 mg) sediment samples using a in the photic zone (< 5 m), while bottom (4-5 m) Carlo Erba EA 1110 elemental analyzer. Inorganic concentrations may stay below 1 ml/l (Rebello et al., carbon was removed prior to the analyses with 1990). Approximately 11 million inhabitants live in hydrochloric acid, following the method of Hedges the Greater Rio de Janeiro metropolitan area and, as & Stern (1984). Quantification was performed by a result of rapid urbanization and population growth, using calibration curves and cystine as standard. untreated sewage is discharged directly into the bay. Reference material MESS-2 (National Research Council of Canada) was used to verify accuracy. This area is the second largest industrial region Analytical precision was G1.7% for TOC and in Brazil and has over 12,000 industries operating G2.8% for TN while detection limits were along the Guanabara Bay drainage basin, and these G0.06% for TOC and G0.01% for TN. account for 25% of the organic pollution released into the bay (FEEMA, 1990). Two oil refineries process The sediment (10 ml) was processed with 7% of the national oil and approximately 2,000 10% HCl and 30% H2O2 to remove carbonates and commercial ships dock in the port of Rio de Janeiro organic matter, respectively.