Dynamic of greenhouse gases (CO2, CH4 and N2O) along three estuaries of the southern Iberian Atlantic basin

Laburpena

Estuaries are highly dynamic and complex coastal ecosystems, which usually act as a source of greenhouse gases to the atmosphere. In order to have a better knowledge of these systems, the partial pressure of CO2 (pCO2) and the concentration of dissolved CH4 and N2O have been studied along the salinity gradient and in relation with the tides inthree estuaries of the southern Iberian Atlantic basin: Guadalquivir, Tinto-Odiel and Guadiana. Samples were taken in July 2017 on board the B/O UCADIZ. In general, in the three systems there is an increase in the concentration of gases toward the inner part of the river, which highlights the importance of the fluvial entry of greenhouse gases into the estuary, as occurs in many other estuarine systems (Harley et al., 2015, Teodoru et al., 2015, Burgos et al., 2017). The pCO2, and the dissolved CH4 and N2O show the highest values and intervals of variation in the Guadalquivir (pCO2: 504-2940 µatm,CH4: 4.9-441.9 nM, N2O: 7.2-101.6 nM) followed by Guadiana (pCO2: 485-1401 µatm, CH4: 9.3-287.9 nM, N2O: 6.5-9.1 nM ) and Tinto and Odiel (pCO2: 513-1144 µatm, CH4: 8.0-194.3 nM, N2O: 6.0-7.3 nM). The three systems are oversaturated with CO2, CH4 and N2O, as a consequence they act as a source of these greenhouse gases to the atmosphere,reaching the maximum saturation percentages of CH4 and N2O in the Guadalquivir, 18493% and 1376% respectively and ΔpCO2 (pCO2water – pCO2atmosphere) show a maximum value of 2531 µatm in the same estuary. pCO2 and the concentrations of CH4 and N2O showed daily variations coupled to the tidal cycles in the three systems, being more evident in the Guadalquivir estuary. The highest concentrations were measured during ebb, which suggest that the systems export CO2, CH4 and N2O to the Gulf of Cádiz.