Aquatic and terrestrial environments are tightly coupled. Although aquatic environments are productive due to carbon fixation by algal populations, organic matter from forests and other terrestrial environments can also subsidize aquatic production. Florida is one of the most vegetated yet lake-rich states in the nation. Inland lakes, though small in surface area, are one of the most active sites for carbon transport on the earth and are a major component of the global scale carbon budget. Characterizing how terrigenous organic matter affects microbial communities and biogeochemical processes in lakes has significant implications for understanding global-scale nutrient cycles. We conducted a study that aimed to elucidate the impact of terrigenous organic matter on lake microbial taxa related to the carbon cycle. Water and sediment samples were collected from three Cypress swamp-connected dark colored lakes and a set of three adjacent closed (i.e. no surface inflow) clear lakes in the Ordway Swisher Biological Station (OSBS) in dry and wet seasons. We predicted that microbial communities and functions would differ between the colored and clear lakes, particularly for those microbes that are involved in primary production and methanogenesis. Microbial diversity and community compositions were determined using 16S rRNA gene-based amplicon sequencing.
Results/Conclusions
Microbial diversity, measured as observed Operational Taxonomic Units (OTUs), was significantly higher in sediment than in the water column (p<0.001). Microbial diversity in sediment was significantly higher in clear lakes than in dark-colored lakes regardless of season (p<0.001). The impact of color on water column microbial diversity was dependent on season. Clear lakes had higher diversity than dark lakes during wet season, while they had lower diversity than dark lakes during dry season. Microbial community compositions (MCC) in sediment differed significantly from those in the water column (p=0.001, ADONIS). While color significantly affected water column MCC (p=0.001, ADONIS), the impact of color on sediment MCC was relatively small. Seasons significantly affected both clear and dark-colored water column MCC (p=0.001, ADONIS), while sediment MCC was relatively consistent across seasons. Methanosaeta, an acetoclastic methanogen, was substantially more abundant in the sediment of clear lakes than dark lakes. The relative abundance of phylum cyanobacteria increased in the wet season, but to a greater degree in clear lakes than dark-colored lakes. These findings suggest that organic matter derived from forests can affect aquatic microbial community compositions and functions, which in turn have implications for both water quality management and carbon sequestration in inland lakes.