Carbon flux evolution throughout the microbial compartment in a brackish ecosystem of the Mediterranean Sea

The carbon flux in the aquatic environments is ruled by microbial activities that provided the main steps of both production and respiration, by means of the organic matter organication and oxidation. Sometimes such processes result in balance one each other but they often are unbalanced. Within the microbial compartment, when the production activity prevails, the organic matter undergoes to export towards higher trophic levels, or it accumulates as POC (C/N>10). If the respiratory activity prevails over the organic production, the ecosystem results unproductive. In this paper we compare the carbon fluxes, throughout the microbial compartment, of three small ponds in a brackish system of the north-eastern Sicily (Italy). The three basins (Marinello, Mergolo and Verde), located under the Cape Tindari cliff (290m), show different hydrobiological features. Microbial production (PP) and respiration (R) were monitored by 14C and ETSa methods. Moreover POC, PON, Chla and picoplankton abundance were studied, in relation to microbial activities with the aim of focusing the microbial pathways occurring in the different ponds. Results evidenced strong differences in the trophic states of the basins, ranging from oligotrophic to eutrophic conditions. Seasonal differences occurred with high productivity in Autumn, when the PP/R ratios reached the maximal values, resulting in Marinello, Mergolo and Verde ponds 7.14, 7.38, 45.44 respectively. The averages of the respiratory turnover rates ( POC/R) were 12.10, 9.46 and 13.52 ?g C d-1 l-1 respectively. In conclusion the carbon flux within each pond follows different pathways, determining the high heterogeneity and self-control capacity of the whole ecosystem.