Linking bacterial and archaeal community dynamics to related hydrological, geochemical and environmental characteristics between surface water and groundwater in a karstic estuary

Subterranean estuaries (STEs) are characterized by the mixing of terrestrial fresh groundwater and seawater in coastal aquifers. Although microorganisms are important components of coastal groundwater ecosystems and play critical roles in biogeochemical transformations in STEs, limited information is available about how their community dynamics interact with hydrological, geochemical and environmental characteristics in STEs. Here, we studied bacterial and archaeal diversities and distributions with 16S rRNA-based Illumina MiSeq sequencing technology between surface water and groundwater in a karstic STE. Principal-coordinate analysis found that the bacterial and archaeal communities in the areas where algal blooms occurred were significantly separated from those in other stations without algal bloom occurrence. Canonical correspondence analysis showed that nutrients and salinity can explain the patterns of bacterial and archaeal community dynamics. The results suggest that hydrological, geochemical and environmental characteristics between surface water and groundwater likely control the bacterial and archaeal diversities and distributions in STEs. Furthermore, we found that some key species can utilize terrestrial pollutants such as nitrate and ammonia in STEs, indicating that these species (e.g., Nitrosopumilus maritimus, Limnohabitans parvus and Simplicispira limi) may be excellent candidates for in situ degradation/remediation of coastal groundwater contaminations concerned with the nitrate and ammonia. Overall, this study reveals the coupling relationship between the microbial communities and hydrochemical environments in STEs, and provides a perspective of in situ degradation/remediation for coastal groundwater quality management.