Raw data of greenhouse gas concentrations of the Paraíba do Sul River Estuary and Mangrove Creek

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The raw data presents greenhouse gas concentrations and ancillary physico-chemical water parameters observed in the Paraíba do Sul River Estuary (PSRE), located in the northern portion of Rio de Janeiro State, forms a coastal delta discharging into the Southwestern Atlantic. Three spatial surveys were carried out in the estuary in February 2017 (Feb-17), October 2017 (Oct-17), and March 2018 (Mar-18) (Fig. 1). The dry-season surveys (Feb-17 and Oct-17) were conducted during low river discharge (288 and 178 m³ s⁻¹), whereas the wet-season survey (Mar-18) coincided with high discharge (1240 m³ s⁻¹). Each sampling campaign included both continuous and discrete measurements. Continuous, in situ monitoring of partial pressure of CO₂ (pCO₂), dissolved oxygen (DO), pH, salinity, and temperature was conducted in mangrove creeks and along the main estuarine channel, extending to the offshore river plume (for details see Cotovicz et al. 2020). (Cotovicz, L. C., Vidal, L. O., de Rezende, C. E., Bernardes, M. C., Knoppers, B. A., Sobrinho, R. L., et al. 2020. Carbon dioxide sources and sinks in the delta of the Paraíba do Sul River (Southeastern Brazil) modulated by carbonate thermodynamics, gas exchange and ecosystem metabolism during estuarine mixin. Marine Chemistry, 226(August), 103869. https://doi.org/10.1016/j.marchem.2020.103869).Surface water samples were collected at discrete stations along the survey track, at approximately three salinity units intervals across the full salinity gradient (0–35). These samples were analyzed for methane (CH₄), nitrous oxide (N₂O), chlorophyll a, and dissolved inorganic nutrients (phosphate, ammonium, nitrite, nitrate).Surveys were carried out from approximately 08:30 to 16:00. Additionally, a 24-h Eulerian time series was conducted in March 2018 in a mangrove tidal creek within the secondary channel, combining continuous measurements with discrete sampling every 1 h for the same parameters.Continuous measurements were carried out from a boat, with real-time acquisition (1-min frequency) of GPS position, pCO₂, dissolved oxygen (DO), pH, salinity, and temperature following the procedures described in Cotovicz et al., (2020).For N₂O and CH₄, water was transferred directly into 60-mL serum vials without bubble formation, poisoned with 0.1 mL of saturated HgCl₂, and sealed immediately. In the laboratory, a 10 mL He headspace was introduced into each vial, followed by vigorous shaking to promote complete equilibration between phases. After 10–12 h of equilibration, gases were analyzed by gas chromatography (GC).

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