Guanabara bay sedimentation rates based on 210Pb dating: reviewing the existing data and adding new data

Abstract

Três testemunhos sedimentares foram coletados na Baía de Guanabara. Dois deles apresentaram perfis de concentração de 210 Pb que poderiam ser utilizados para fins de datação. Taxas de sedimentação de aproximadamente 1 cm ano -1 (cinco vezes superior aos valores de linha de base) foram observadas para os dois testemunhos, coerentes com os dados existentes na literatura relacionada à datação de sedimentos da Baía de Guanabara, empregando-se 210 Pb. A validação da datação foi realizada com base nos perfis de cobre, cromo e chumbo, no fluxo de 210 Pb e no registro histórico das principais intervenções físicas ocorridas no século passado, tais como aterro, a canalização de rios principais e a construção de vias rápidas. No final deste processo, apenas a datação de um único testemunho pôde ser adequadamente validada.Three sediment cores were taken from Guanabara Bay. Two of them yielded 210 Pb profiles that could be applied for dating purposes. Actual sedimentation rates of approximately 1 cm year -1 (five times higher than the baseline values) were observed for both sediment cores, which agree with the reviewed existing data in the literature related to Guanabara Bay sedimentation rates based on 210 Pb. Dating validation was carried out based on the chromium, copper and lead profiles, on the 210 Pb flux and on the historical record of the main physical interventions occurring in the last century, such as embankment, the channeling of main rivers and the construction of express roads. At the end of this process, only one sediment core dating could be adequately validated.

Predominance of phytoplankton-derived dissolved and particulate organic carbon in a highly eutrophic tropical coastal embayment (Guanabara Bay, Rio de Janeiro, Brazil)

“…Eutrophication in Guanabara Bay is characterized by the occurrence of very high Chl a concentrations, often reaching several hundreds of lg L -1 , high oxygen supersaturation, but moderate and variable dissolved nutrient concentration depending on the proximity of sewage sources and uptake by phytoplankton (Paranhos et al 1998;Ribeiro and Kjerfve 2002;Cotovicz et al 2015). The trophic state indexes of O'Boyle (O'Boyle et al 2013) and Trix (Vollenweider et al, 1998) ranked the bay in the category of ''eutrophic'' to ''hypertrophic'' environment (Costa Santos 2015).In addition, previous studies showed strong increases in the rates of sedimentation (Godoy et al 2012) and organic carbon burial (Carreira et al 2002) in the last 50 years. Due to the large spatial variability in the hydrological and geomorphological characteristics, and the heterogeneity of human occupation of the watershed, five sectors were defined for the treatment, computations and interpretation of the data (Fig.…”

Urban rivers as conveyors of hydrocarbons to sediments of estuarine areas: Source characterization, flow rates and mass accumulation

“…The total PAH mass deposited in the northern area of the bay, into where the CB, GM, SU, IG, and SJM rivers discharge, was estimated based on the data reported by Wagener et al (2012) for PAH concentration in surface sediments and in the sedimentation rates reported by Godoy et al (2012). The sampling points were linked to form triangles in which vertices of the average concentration from four samplings were computed.…”

Atividade De Dragagem E Circulação De Massas De Águas Oceânicas: Possíveis Influências Nas Características Físico-Químicas Na Plataforma Continental Interna Adjacente À Baía De Guanabara (Rj)

“…Sabe-se que o processo de deposição de sedimentos no fundo de estuários e baías é natural (Godoy et al, 2012). Porém, esse processo pode ser acelerado por ações antrópicas, e a taxa deposicional está associada às dinâmicas internas do oceano, como correntes e variação das marés, por exemplo, e às dinâmicas externas a ele, como variabilidade climática, precipitação e sazonalidade.…”