Study of inorganic and organic carbon in water, with emphasis on total alkalinity, in two Brazilian estuaries (MA and SP) under different tidal regimes

Author(s)

Antonio Jeferson Muniz Almeida

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto Oceanográfico (IO/DIDC)
• Defense date: 2024-08-23

Examining board members

Elisabete de Santis Braga da Graça Saraiva; José Juan Barrera Alba; Nathalie Lefèvre

• Advisor: Elisabete de Santis Braga da Graça Saraiva

Abstract

The global carbon cycle involves exchanges between air-water-sediment-biota interfaces. The air-ocean interface has been widely studied due to increasing anthropogenic emissions of atmospheric CO2, and the ocean has limited capacity to remove it from the atmosphere. The main objective of the present study was to evaluate variations in total alkalinity, and also the other members of the carbon system, and their impact on CO2 fluxes between water and atmosphere in two distinct estuarine systems, under different tidal regimes (micro and macrotides), located in the states of Maranhão and São Paulo, considering seasonality and anthropogenic pressures in the sectors of these systems. In the Raposa and Rio Paciência Estuarine System (SERP), sampling campaigns were performed in May 2022 (rainy period) and September 2022 (dry period). In the Cananéia-Iguape Estuarine-Lagunar Complex (CELCI), the campaigns took place in August 2022 (dry period) and February 2023 (rainy period). Surface water samples were sampled at 17 stations in each system, along the salinity gradient and in each of the seasonal periods. Hydrological parameters (temperature and salinity) were analyzed, following data on dissolved oxygen, pH, total alkalinity, dissolved organic carbon, chlorophyll-a, pheopigment, suspended particulate matter and suspended particulate organic material. Different parameters of the carbonate system, such as pCO2, CO2 flow and Revelle factor were calculated using the CO2Calc® software, supported by atmospheric pressure, wind speed, phosphate and silicate data. Seasonal differences considering periods of greater and lesser rainfall promote differences in the behavior of the carbon system in surface water. In general, in the SERP, the Paciência River estuary showed a greater salinity gradient and therefore the total alkalinity values varied more, while the Raposa estuary showed a greater influence of more saline waters and therefore the highest total alkalinity values. Thus, the SERP, as a whole, showed alkalinity values ranging from 1419.71 to 1813.11 µmol kg-1 in the rainy season and from 2195.23 to 2389.98 µmol kg-1 in the dry season. In this system, salinity and pH variables had a high degree of association with alkalinity. Regarding CELCI, a decreasing salinity gradient was observed from the southern region towards the northern region of the system. The highest values were observed in the Ararapira and Cananéia regions, and the lowest in the Iguape region. In general, total 12 alkalinity ranged from 467.86 to 2134.82 µmol kg-1 in the rainy season and from 729.41 to 2127.32 µmol kg-1 in the dry season. In this system, variables such as salinity, pH and the dilution process were strongly associated with alkalinity values in both periods. The distribution of variables in the carbonate system differs mainly due to the tidal regime. SERP is influenced by macro and hypertides, while CELCI is affected by microtides. This variation directly affects the emission and absorption of CO2. During the dry period, the SERP tends to emit and absorb more CO2 than the CELCI in both seasonal periods. (AU)

• FAPESP's process: 22/05823-4 - Study of the carbon system in two Brazilian estuarias (MA - SP), with emphasis on total alkalinity and differentiated hydrodynamics
• Grantee: Antonio Jeferson Muniz Almeida
• Support Opportunities: Scholarships in Brazil - Master