Budgets of organic and inorganic carbon in a Mediterranean coastal lagoon dominated by submerged vegetation

In this article, we studied the fluxes of organic and inorganic (DIC) carbon in a coastal lagoon dominated by highly productive macrophyte meadows (Albufera des Grau, Balearic Islands). Seasonal and annual carbon budgets were performed from estimates of whole-system fluxes, and the fate of organic matter production was evaluated through a stable isotope exploration of the food web. The results showed an extremely intense cycling of DIC, with a turnover between 65 and 13 times faster than water turnover. The metabolic fluxes were the main contributors to the seasonal and annual DIC budgets, which were secondarily affected by calcite precipitation, atmospheric exchange and hydrological fluxes. The inorganic carbon dynamics was strongly determined by the seasonal cycle of the meadows. Accordingly the air-water CO2 flux shifted seasonally, and the lagoon was a sink of atmospheric CO2 during the vegetated period and a source during the period without macrophytes. The high macrophytic production played a minor role in the lagoon food web, which apparently relied on phytoplanktonic or allochthonous organic matter. A fast decomposition of macrophytic biomass appeared to be the main destiny of the annual macrophytic production, which was only secondarily buried in the sediments.