Seasonal dynamic of CO2, CH4 and N2O in the Guadalquivir estuary

Resumen

The concentration of dissolved CH4 and N2O, and the partial pressure of CO2 (pCO2) have been studied in the Guadalquivir estuary. Samples were taken in July 2017, and during March and April 2018 and 2019 in different rainy and tidal conditions. Two different types of sampling were carried out: a longitudinal transect across the river and during a tidal cycle of 24 h in the mouth of the estuary. The concentration of CH4 and N2O was obtained by using a gas chromatograph, and pCO2 was measured continuously with an infrared gas analyser. The higher values of the gases were found in the inner part of the estuary and during the low tide. These distributions of the gases are affected by the organic matter and nutrient inputs that the estuary receives, through the river itself, from lateral inputs related to salt marshes and irrigation drainage areas, and by the organic matter remineralisation processes in the sediments. Seasonal variations were observed in the Guadalquivir estuary between July 2017 (pCO2: 386.3 – 5865.6 µatm, CH4: 4.9 – 441.9 nM, N2O: 7.1 – 101.6 nM), March and April 2018 (pCO2: 376.3 – 1357.5 µatm, CH4: 5.1 – 158.0 nM, N2O: 7.6 – 71.6 nM) and March and April 2019 (pCO2: 465.1 – 2776.5 µatm, CH4: 6.3 – 73.7 nM, N2O: 4.8 – 97.0 nM). The water - atmosphere fluxes of the pCO2, CH4 and N2O are positive, so the estuary acts as a source of these gases to the atmosphere.