Ventilation of subterranean CO2 and Eddy covariance incongruities over carbonate ecosystems

[摘要] Measurements of CO₂ fluxes with Eddy Covariance (EC) systems areongoing over different ecosystems around the world, through differentmeasuring networks, in order to assess the carbon balance of theseecosystems. In carbonate ecosystems, characterized by the presence ofsubterranean pores and cavities, ventilation of the CO₂ accumulated inthese cavities and pores can act as an extra source of CO₂ exchangebetween the ecosystem and the atmosphere. In this work we analyse the effectof the subterranean heterogeneity of a carbonate ecosystem on measurementsof CO₂ fluxes by comparing measurements from two EC systems withdistinct footprints. Results showed that both EC systems agreed formeasurements of evapotranspiration and of CO₂ in periods whenrespiratory and photosynthetic processes were dominant (biological periods),with a regression slope of 0.99 and 0.97, respectively. However, in periodswhen the main source of CO₂ comes from the ventilation of subterraneanpores and cavities (abiotic periods) agreement is not good, with aregression slope of 0.6. Ground-penetrating radar measurements of thesub-surface confirmed the existence of high sub-surface heterogeneity that,combined with different footprints, lead to differences in the measurementsof the two EC systems. These results show that measurements of CO₂fluxes with Eddy covariance systems over carbonate ecosystems must be takencarefully, as they may not be representative of the ecosystem underconsideration.

[学科分类] 地球化学与岩石