Influence of reactivity on GHG fluxes to the atmosphere in a macrotidal estuary (Guadalquivir Estuary, SW Spain)

Resumen

Estuaries are systems characterized by high fluxes of greenhouse gases (GHG) to the atmosphere and play a major role in the biogeochemical cycles in the coastal zones. The distribution and water-atmosphere fluxes of the three most important GHG (CO2, CH4 and N2O) have been studied over 3 samplings between 2021 and 2022 in the Guadalquivir Estuary. These samplings consist of tidal cycles at different stations along the estuary. Samplings have been carried out under different climatic and hydrodynamic conditions. There is an important longitudinal gradient in the estuary, with low mean fluxes at the mouth of the estuary (CO2: 4.9 ± 3.4 mmol m-2 d-1; CH4: 8.6 ± 2.9 micromol m-2 d-1; N2O: -0.9 ± 1.9 micromol m-2 d-1) and high mean fluxes and variability in the inner zone (CO2: 95.8 ± 66.6 mmol m-2 d-1; CH4: 54.0 ± 65.9 micromol m-2 d-1; N2O: 42.4 ± 32.8 micromol m-2 d-1). These fluxes suggest that the estuary would act as a source of the three gases to the atmosphere. Fluxes variability are affected by several factors: temperature, salinity, water-atmosphere degassing, biogeochemical processes, benthic fluxes, and lateral inputs. Thus, the last three factors are the predominant processes influencing gas dynamics, affected by changes in temperature and rainfall regime.