There is growing interest in the capacity of mangrove ecosystems to sequester and store ‘blue carbon’. Here, we provide a synthesis of 66 dated sediment cores with previously calculated carbon accumulation rates in mangrove ecosystems to assess the effects of environmental and anthropogenic pressures. Conserved sedimentary environments were found to be within the range of the current global average for sediment accretion (approx. 2.5 mm yr –1 ) and carbon accumulation (approx. 160 g m −2 yr −1 ). Moreover, similar sediment accretion and carbon accumulation rates were found between mixed and monotypic mangrove forests, however higher mean and median values were noted from within the forest as compared to adjacent areas such as mudflats. The carbon accumulation within conserved environments was up to fourfold higher than in degraded or deforested environments but threefold lower than those impacted by domestic or aquaculture effluents (more than 900 g m −2 yr −1 ) and twofold lower than those impacted by storms and flooding (more than 500 g m −2 yr −1 ). These results suggest that depending on the type of impact, the blue carbon accumulation capacity of mangrove ecosystems may become substantially modified.

publicado na web em 16/08/2016 COMPARISONS BETWEEN REAL-TIME pCO 2 MEASUREMENTS WITH INDIRECT ESTIMATES IN TWO CONTRASTING BRAZILIAN ESTUARIES: THE EUTROPHIC GUANABARA BAY (RJ) AND THE OLIGOTROPHIC SÃO FRANCISCO RIVER ESTUARY (AL). Carbon dioxide (CO 2 ) fluxes from aquatic systems are generally derived from the gradient in the partial pressure of CO 2 (pCO 2 ) between air and surface waters. In this study, we compare real-time measurements of water pCO 2 using an equilibrator and non-dispersive infrared gas detector, with calculations based on pH and total alkalinity (TA) in two contrasting Brazilian estuaries: Guanabara Bay (Rio de Janeiro) and the São Francisco River Estuary (Alagoas). In Guanabara Bay, the measured and calculated values showed an excellent agreement (R 2 = 0.95, p < 0.0001), without significant statistical differences between the two methods. In the São Francisco River Estuary, where the entire gradient from freshwaters to seawater could be sampled, important overestimates were found for the calculated pCO 2 . The overestimation was on average 71%, and reached up to 737%. This large bias in pCO 2 calculation was verified at low pH and TA concentrations in freshwaters (pH < 7.5; TA < 700 μmol kg -1 ) possibly due to the contribution of organic alkalinity, lowering the buffer capacity of the carbonate system. As such, direct measurements of pCO 2 should be considered as a priority for CO 2 studies conducted in estuarine systems, particularly tropical systems where physical and biological processes are prone to significant spatial and temporal variability.Keywords: CO 2 ; direct measurements; spatial and temporal variability; estuaries. INTRODUÇÃOO dióxido de carbono (CO 2 ) é o principal gás do efeito estufa e tem a maior contribuição no aquecimento do sistema climático global.1 Os níveis atuais alarmantes das concentrações atmosféri-cas de CO 2 e as taxas de aumento das emissões antropogênicas ao longo das últimas décadas alertam a importância da identificação, quantificação e monitoramento das fontes e sumidouros de dióxido de carbono.2 O recente processo de acidificação dos oceanos, que também é atribuído ao aumento das concentrações de CO 2 atmosfé-rico, 3 reforça a importância dos estudos da dinâmica desse gás, tanto no oceano aberto quanto em ecossistemas costeiros. Além disso, publicações recentes relataram o aumento da acidificação costeira como resultado da hipóxia e anóxia em águas costeiras em função de estágios avançados da eutrofização, especialmente em ambientes impactados por atividades antropogênicas. [4][5][6] Os oceanos abertos são importantes sumidouros de CO 2 atmosférico com fluxos na interface água-atmosfera bem quantificados, 7 enquanto águas costeiras estão sujeitas a maiores incertezas devido à elevada heterogeneidade espacial e temporal, diferentes tipologias geomorfológicas e hidrológicas (estuários dominados por águas fluviais, dominados pelo mar, com regimes de maré, ondas e ventos diferenciados). [8][9][10] Outro aspecto a ser considerado é a menor disponibilidad...

Estuarine carbonate chemistry predicts that thermodynamic equilibration during the mixing of freshwater with seawater will generate a carbon dioxide (CO2) sink for the case of warm and poorly buffered tropical rivers. The São Francisco River estuary has historically become oligotrophic, after the construction on its watershed of a series of hydroelectric dams, where organic matter and nutrients are retained. During two cruises in late winter (Aug. 2014) and early summer (Nov. 2015), dissolved inorganic carbon (DIC) and total alkalinity (TA) increased linearly with salinity in the main estuarine channel, where the mixing time of water was half a day, and showed a close to conservative behaviour. In the main channel, water partial pressure of CO2 (pCO2) recorded at 1min frequency, followed an asymmetric bell-shaped trend versus salinity, close to the curve predicted by thermodynamic conservative mixing of freshwater DIC and TA with seawater DIC and TA. The low (0-3) salinity region was always a source of atmospheric CO2, where, despite low chlorophyll concentrations, a pCO2 diurnal change of about 60 ppmv suggested the occurrence of photosynthesis in summer . At salinities above 3, under-saturated pCO2 values (down to 225 ppmv in winter and neap tides) and invasion of atmospheric CO2 of 0.38-1.70 mmol m -1 h -1 occurred because of predominating thermodynamics during estuarine mixing. In winter and neap tides, higher river discharge, intense estuarine mixing, lower temperatures and limited tidal pumping resulted in observed pCO2 different from theoretical conservative pCO2 by less than 3ppmv at salinities >3. Conversely, in summer and spring tides, recorded pCO2 values were on average +43±35 ppmv above the conservative mixing curve, when tidal pumping, CO2 invasion and surface heating were more significant in the mixing zone, but not sufficient to offset the thermodynamic uptake of atmospheric CO2. By combining carbonate chemistry with estuarine mixing modelling and gas exchange calculations, we estimate that heating contributed to about 15% and gas exchange to about 10% of the positive pCO2 deviation from conservative mixing during summer.The remaining 75% of the deviation was maximum at ebb tides and within a salinity ranges consistent with the occurrence of tidal pumping from marches and mangrove soils. Indeed, in the mangrove channel, water were supersaturated with pCO2 values of 976±314ppmv, while in the main channel, highest positive pCO2 deviations from conservative mixing (up to +100ppmv during several hours) occurred at ebb tides. An important finding was that, in the São Francisco, the thermodynamic and biological processes compete with each other to CO2 fluxes both at low salinities where evasion and autotrophy occur, and at high salinities where invasion, heterotrophy and tidal pumping occur. Our study suggests that carbonate thermodynamics during mixing is a key process that has been overlooked in estuarine studies, although it can generate important airwater CO2 exchange and contribute significantly to...

Fossil fuels are of utmost importance to the world we live in today. However, their use can cause major impacts on the environment, especially on water resources. In this regard, algae have been intensively used as a strategy for remediation and monitoring of environmental pollution due to its efficient absorption of contaminants. In this work, samples of seaweed collected in Niterói/RJ—contaminated with kerosene and diesel—were analyzed by radiocarbon (14C) accelerator mass spectrometry (AMS) and by n-alkane quantification with gas chromatography to evaluate bioaccumulation in function of the dosage of contaminants. The biogenic content measured by radiocarbon analysis resulted in 95.6% for algae contaminated with 10 mL of kerosene and 67.6% for algae contaminated with 10 mL of diesel. The maximum intensity of n-C17 n-alkane in algae with 5 mL, 10 mL, and 15 mL of diesel was 768.2, 1878.1, and 5699.2 ng.g-1, respectively. While the maximum concentration of n-C27 in algae with 5 mL, 10 mL and 15 mL of kerosene was 3.3, 35.9, and 150.3 ng.g-1. We concluded that, for both contaminants, their incorporation into algae increases as the contamination dosage increases, making this methodology an effective technique for monitoring and remediation of urban aquatic ecosystems.

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