Different microbial functioning in natural versus man-made mediterranean coastal lagoons in relation to season

Abstract

Coastal marsh lagoons are of high ecological relevance playing a key role in the carbon cycle but are threatened to disappear due to global change effects. Restoration practices can counteract this process. This study compares the microbial heterotrophic functioning in three “new” man-made lagoons (created in 2016) to that in three “old” lagoons (two natural plus one created in 2002) from a Mediterranean coastal marsh. The activity of a range of microbial extracellular enzymes, the functional diversity, and the dissolved organic matter (DOM) quality, together with microbial biomass and water physic-chemistry were analysed seasonally in the water column of the six lagoons during 2017. Seasonality was a key driver for the lagoons microbial functioning mainly characterized by lowest microbial activities in winter when DOM was highly aromatic after storm events and an increase in organic matter degradation capabilities from winter to summer probably due to a rise in temperature and DOM input from primary production. Significant differences among lagoons appeared when they were less connected (summer and autumn), and old lagoons showed a greater utilization of proteinaceous and polysaccharidic compounds than new lagoons probably linked to their greater algal biomass (chlorophyll content), which may be supported by their larger phosphorus content. In autumn, there was also a greater use of allochthonous plant material in the old lagoons (higher XYL, and XYL/GLU ratio) probably related to their greater development of riparian vegetation. The functional diversity was the lowest in autumn when the lagoons showed distinct functional fingerprints and the lagoon created in 2002 was grouped with the new ones and distinguished from the natural ones, suggesting that it did not achieve complete restoration. Results indicate that microbial functional parameters related to organic matter use are a relevant and sensitive tool to study lagoon restoration processes, reflecting whole ecosystem nutrient and carbon cycling