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

Abstract

We investigate the carbon dynamics in Guanabara Bay, an eutrophic tropical coastal embayment surrounded by the megacity of Rio de Janeiro (southeast coast of Brazil). Nine sampling campaigns were conducted for dissolved, particulate and total organic carbon (DOC, POC and TOC), dissolved inorganic carbon (DIC), partial pressure of CO 2 (pCO 2 ), chlorophyll a (Chl a), pheo-pigments and ancillary parameters. Highest DOC, POC and Chl a concentrations were found in confined-shallow regions of the bay during the summer period with strong pCO 2 undersaturation, and DOC reached 82 mg L -1 , POC 152 mg L -1 , and Chl a 800 lg L -1 . Spatially and temporally, POC and DOC concentrations varied positively with total pigments, and negatively with DIC. Strong linear correlations between these parameters indicate that the production of TOC translates to an equivalent uptake in DIC, with 85% of the POC and about 50% of the DOC being of phytoplanktonic origin. Despite the shallow depths of the bay, surface waters were enriched in POC and DOC relative to bottom waters in periods of high thermohaline stratification. The seasonal accumulation of phytoplankton-derived TOC in the surface waters reached about 105 g C m -2 year -1 , representing between 8 and 40% of the net primary production. The calculated turnover time of organic carbon was 117 and 34 days during winter and summer, respectively. Our results indicate that eutrophication of coastal bays in the tropics can generate large stocks of planktonic biomass and detrital organic carbon which are permanently being produced and partially degraded and buried in sediments.

Coastal urbanization alters carbon cycling in Tokyo Bay

“…Because information on the flow of inorganic and organic carbon in urbanized coastal waters is increasingly being reported, the impacts of human activities on coastal waters are becoming clearer. However, few studies have estimated carbon cycling and budget in highly urbanized coastal waters 17 . Carbon cycling in coastal ecosystems is increasingly subject to human influences, such as land and water use changes and increased waste and pollution 18 .…”

Sources and sinks of dissolved inorganic carbon in an urban tropical coastal bay revealed by δ13C-DIC signals

“…The matrix correlation (Table S2) shows that higher values of δ 13 C-DIC are related to high levels of DO, POC, SPM, and Chl a, and low concentrations of DIC. Recent findings in Guanabara Bay showed that the DOC and POC fractions present a large phytoplankton dominance, surpassing the contribution of terrestrial sources (Cotovicz et al 2018a). Compared to other estuaries, Guanabara Bay presented the highest enrichment of 13 C-DIC in the salinity range between 20 and 30 ( Fig.…”

“…The bay is one of the most polluted coastal systems in the world that receives large inputs of untreated domestic and industrial effluents at approximately 25 m 3 s −1 (Kjerfve et al, 1997;Bidone and Lacerda, 2004). We compartmentalized the bay into five domains (sectors 1, 2, 3, 4, and 5) as described by Cotovicz et al (2015;2018a) for the treatment, computations and interpretation of the data (Fig. 1).…”

“…5b). In Guanabara Bay, this salinity interval is present in confined stratified waters of the sectors 3, 4 and 5, which are net autotrophic and phytoplankton-dominated (Rebelllo et al 1988;Cotovicz et al, 2015Cotovicz et al, , 2018a. This behavior is in contrast with most of other estuarine studies, which are mostly located in temperate regions and river-dominated ecosystems, where the effects of respiration, either in the water column or in sediments, are often much more pronounced than photosynthesis (Mook, 2001;Bouillon et al, 2003).…”

Avaliação do Índice de Estado Trófico e parâmetros de qualidade da água no reservatório da Usina Hidrelétrica de Sá Carvalho, Minas Gerais, Brasil

“…Valores elevados relacionados a essas variáveis contribuem para o crescimento excessivo de macrófitas aquáticas aderidas que podem interferir na navegação, aeração e capacidade de transporte pelo canal. Desse modo, tais indicadores possibilitam a classificação dos corpos aquáticos em diferentes graus de trofia, ou seja, permitem avaliar a qualidade da água quanto ao enriquecimento por nutrientes e seu efeito relacionado ao crescimento excessivo das algas, ou o potencial para a proliferação desses organismos fotossintetizantes (Cotovicz et al, 2017).…”