Microbial porewater data - Mobile Bay, USA

Microbial communities in subterranean estuaries (STE) mediate biogeochemical reactions of coastal groundwater discharging to the oceans; however, studies on their response to abrupt environmental changes caused by climate and land use changes are still limited. In this study, we conducted a controlled laboratory study using combined geochemical and metagenomic approaches to investigate microbial structures and their metabolic pathways under different nitrate (NO3-) inputs, saline solution, and incubation times, which were used as proxies of land use, salinization of the shallow aquifer, and climate changes. We found a highly reducing habitat and amplification of genes related to denitrification, sulfate reduction, and methanogenesis processes. Core communities consisted of Clostridia, Bacilli, Alphaproteobacteria, Gammaproteobacteria, and Desulfobaccia were observed. The qualitative degradation of terrestrial, plant-derived organic matter (i.e., tannin and lignin) was predicted to not being affected by NO3- inputs or salinity because of it being implemented by core communities and the abundance of electron donor and acceptors. However, long-term incubation allowed sufficient time for microbes to degrade less labile DOM, promoted the re-release of buried solid phase organic matter into the active carbon cycle, and increased the relative abundance of biofilm or spore-forming taxa while decreasing that of rare taxa such as methanogenic archaea. The relative proportion of less prevalent taxa were also susceptible to seasonal and endmember variability. Our results illustrate the sensitivity of microbial assemblages to environmental change and their capacity to mediate C and N cycles in coastal areas, further affecting coastal water quality and ecosystem-scale biogeochemistry.